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Macedragon37
05-24-2011, 08:51 PM
NEW: Click the below forum to see Valve's own David Kircher's take on this conundrum.

http://forums.steampowered.com/forums/showthread.php?t=1906183

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NOTE: I apologize in advance for any sarcasm or ignorance that may be apparent in what I wrote. Sometimes I think I'm very right, but I, as well as the forum, should not that we can't be right all of the time. I hope that you find the below explanation informative, helpful, or at the very least, something interesting to think about.
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I saw the thread “Portals on moving surfaces” awhile ago, and was truly stumped. It took me quite awhile to wrap my head around the conundrum, but I think finally did it.

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http://lastopp.no/3/85598fa1714fb80014d1d7c1d04fb2fb.jpg

The question is this. If a surface with a portal on it accelerates toward and object, will it shoot out of the other portal, or not. Situation A has the cube simply plopping out of the portal. Situation B has the cube flying out of the portal.
I’ve been analyzing this situation (Maybe a bit too much).

For the sake of my sanity and mspaint, I have changed the orientation of the blue portal to just being on the ground. It is nearly the same situation, and only differs in the angle that the cube is shot out of the portal at.

PIC 1 [The Situation] http://imageshack.us/photo/my-images/40/pic1ju.png/

Firstly, let’s address the accelerating platform. The movement of the platform is in relation to the cube. The platform is accelerating down towards it. The problem faced here is that this is somehow different than the platform accelerating upwards, and the cube going flying through the stationary portal. When the frame of reference is understood, these two things are understood to be the same thing. Imagine this.

PIC 2 [Looking through the blue portal] http://imageshack.us/photo/my-images/101/pic2yt.png/

When you are standing above that blue portal, your frame of reference is the room. When you look through the blue portal, you will see a cube accelerating towards you, whether it is, or the platform with the orange portal is accelerating towards it.

Due to the frame of reference, the orange portal accelerating towards the cube is not unlike a situation where the cube would be flung through the orange portal.

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Many people have disagreed on this, but there’s something that many people are missing. Portals displace matter that go through them. Portals work by changing matter’s position in space. Take a look at this situation.

PIC 3 [The cube is seemingly accelerating and stationary at the same time] http://imageshack.us/photo/my-images/705/pic3ca.png/

Because the frame of reference is the room, the cube is accelerating (Or simply moving is more likely). Portals only have an effect on the matter that is going through them, nothing else. Once the cube goes through that orange portal and out of the blue one, it has its new position, and is most definitely moving. The portal has no affect on the parts of the cube that have already gone through it. Although this looks like simply moving of the cube, the cube is most definitely moving in respect to the room.
Why is it moving though? The orange portal. As stated before, the orange portal moving or the cube moving doesn’t really matter, and this is why.

“As an object goes through a portal, its output speed is equal to the speed that it goes in with.”

But wait, the cube isn’t moving! That’s what is the most confusing part of the situation. If you are able to ignore many other factors of the situation, and just focus on the orange portal and the cube, think about it. Despite the cube not moving in respect to the platform that it sits on, it is definitely moving in respect to the orange portal, and that’s the key.

Orientation, speed, and position of the actual portal and what is going through it are what matter. Although the cube looks not to be moving, if you were the orange portal, you would definitely think that the cube was flying towards you, and would definitely feel it fly through you.

If you are able to ignore the seemingly stationary cube, you can understand that as the cube goes through the orange portal, it’s newly displaced atoms are going at a very fast speed. There is no force which simply stops the cube from moving.

TL;DR – Understand the frame of reference. It’s B.

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This took me a hell of a lot of time to figure. I spent countless hours in the shower considering the physics of this, and how a cube could somehow get a force from nowhere.

I would really appreciate some feedback.

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I'd say it's A. You just have to imagine that it's not only the portal moving down on the cube, but the entire room on the other side of the portal as well. If you dropped an entire room on it, the cube wouldn't move, but it would appear to be accelerating upwards when observed by somebody standing inside the room.

This is where you're wrong. it's completely unlike dropping the room on the cube because portals manipulate space. Dropping a room on the cube is not like this situation because in that situation, there are no portals.

You have to understand that because the orange portal is accelerating towards the orange portal in REFERENCE to the orange portal, in both situations, the cube goes through the orange portal at a certain speed. It doesn't matter which of them looks like it's doing the moving; the speed of which the cube goes through the portal stays the same.

You have failed to take two things into account:

First, the portal ceasing to move after the cube has passed through, or from the stationary cube's frame of reference, the room then dropping away from under it.

Second, that the question is concerned with what happens at the exit portal, with the exit portal being defined as stationary. From this frame of reference, the cube shoots out.

Yes the cube would be defined as stationary in respect to the first room, (assuming portal continues its downward movement) but that's not the question, it is flung out of the exit portal, which is the answer to the question asked

Thank you. That understanding of frame of reference is necessary to understanding the same thing. I think people don't understand the example because the orange portal hits the platform and stops, rather then keep going.

I can disprove your entire theory with one quote:

If your proposed situation B was true, the portals would be creating momentum, not conserving it.

Therefore situation A is correct.

I don't think you get the situation.

THE ORANGE PORTAL IS CREATING MOMENTUM. IT IS MOVING. THAT IS ONE OF THE BIGGEST REASONS FOR CONFUSION ABOUT THIS IDEA.

What you must understand is that the orange portal moves over the cube, not like a curtain, but more like a funnel, or a vacuum.

The thing that occurs between the two portals is able to "give" the cube momentum due to the speed differences of the 2 portals. Simply because the orange portal is moving, and the blue portal is not, makes the situation difficult to understand. Because the orange portal is moving, and the cube is not, you must understand the orange portal's motion.

As far as we can tell the only thing that a portal does to an object that is speeding towards it is change it's orientation and placement. At no point can anyone use a portal to project an object using a downward motion or they would likely have used this method.

What Pythagoras says is in fact answering the question by noting that if you are in the room, e.g. the other side of the portal, and you are observing the cube coming at you the cube will remain static as it enters because as far as the cube is concerned it has not moved.

The only reason there is a discussion of it moving later is because its orientation is different after it passes through the exit portal. If the exit portal was facing straight up you would observe a cube suddenly appearing as it quickly raises into the "new room". You can think of it as looking as though it is fixed to the surface which appears to be fast approaching when you are looking through. This means the object does not actually fly off out of the exit portal as it had no momentum of its own.

The statement of "speedy thing goes in, speedy thing comes out" requires that the object itself has that velocity to begin with. It's an interesting thought to say that an object will gain the velocity of another object by benefit of a portal traveling quickly, but there just isn't any evidence in the games, let alone reality, to support it.

As far as the cube is concerned it hasn't moved?

Compeltely wrong, that's for sure. The cube goes through the portal at a very high speed, no matter what it does when it gets out. It is very much moving, and that's obvious. The cube's position in space is changed, along with it's speed, due to the orange portal overwhelming it so quickly.

That momentum isn't real. This is like saying driving past a stationary ball on the freeway and then braking next to it would send the ball rolling away..

[...]

"The momentum is already there, it's in the relative speed between portal and cube. Cube retains momentum relative to portal so shoots out of the exit portal."

NO...no it isn't. In fact, the example is very much different. In your example, the control of motion is contained in the car, therefore the ball is a the unmoving reference point. In his example (Which in part, I agree with) motion is relative to the moving portal.

Those, once again, aren't the same. You are completely forgetting that motion is also relative to the blue portal, which isn't even in this equation.

In fact, that's a terrible analogy and comparison. What are you thinking?

Key word in bold. It's all relative. However, a slowing-down car isn't an inertial reference frame any more, so conservation of momentum won't act like you expect from it's point of view.

When we talk about the blue portal and cube, they are moving at a constant speed relative to each other. It shouldn't matter if the blue portal is moving at 10 mph and the cube is at rest, or the cube is moving at 10 mph and the portal is at rest, or the portal is moving at 350 mph while the cube is moving at 340 mph in the same direction relative to the room.

I generally agree with this.

from observation in the game, gravity doesn't pass through portals, although if it did, that would make for a convincing argument on how potential energy gain is negate while being a potentially very annoying game mechanic when flinging.

the pillar would be thrust through the pitas will the cube. (if A was true and cube Had to be stationary in the other side, this would be both impossible and inconsistent)
when the portal stops moving, the pillar stops moving, leaving the cube to fly off of it, in the sane manner as Chell from an aerial faith plate

Thank you.

And of if portals could somehow transfer forces of gravity...geez. That would make for a confusing an annoying game.

Once again, portals change positions of things in space, and they conserve momentum.

So... if there's just one tiny minuscule part of the cube left in the old room when the piston stops the cube won't move, but if that tiny minuscule part does move through the portal before the piston stops the cube will shoot away?

No, not quite.

Because of portals, gravity only has an effect on, well, what it is affecting. It sounds redundant, but I'll try to explain it better. If you've got a portal on the floor and the wall, and you put your hand through the portal in the wall, your hand coming out of the floor is going to be pulled down by gravity. Because you are sticking your hand "through" the wall, it will feel as though your hand wants to fall back to your body, when in reality it's really falling due to gravity. The rest of your body however, will be pulled in the same direction that is always is.

Just because a part of the cube is right "inside" the very lip of the portal, doesn't mean much. Whatever part of it is on one side or the other will experience gravity and other forces in respect to it's position and where it's oriented. It's not as if an object has to go all the way through a portal to feel something, every part of the object feels a change in forces when it goes through the portal, bottom, top, middle, end, etc.

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The Pole Example

http://imageshack.us/f/818/pic4x.png/

This example is much more representative of the relation of the orange portal, the blue portal, and what goes through them.

Imagine that we have the same situation, but the cube sits on a pole instead. It's nearly the same situation, except there's a pole.

When the cube and the pole go through the blue portal, they come out of it at 10 m/s.

If you ignore the portals and just think about a very small platform coming through the floor of that room, it can be proven with physics that an object sitting on it would fly into the air if it suddenly stopped.

When the orange portal finally hits the floor, the pole (or small platform, whichever you would like to call it) would stop, and due to the cube's inertia, the cube would keep going.

This example is not unlike the first one, it's just that there's a pole. As stated before, objects going through a portal are affected by that portal. Objects already through the portal are unaffected by the portal, because a portal changes positions in space, and the only thing that the portal keeps changing is the pole. If a cube has a pole accelerating under it, it will accelerate and move up; this can be, and probably has been proven. The "flying up" of the cube can be proven through inertia.

As said before, it's very similar to the actual situation that is being argued. I just had to add a pole to make the situation more understandable. Although the pole is being affected throughout the example, the portals only affect it's speed in relation to the cube; nothing else.

"Dropping" The Room on The Cube Example

Picture to come (Possibly). It's difficult for me to draw.

Answer is A. Drop a tire(portal) on a marble on a standing object. The marble , due to no acceleration, will not move other than the force of the tire(portal) hitting the solid object that the marble is lying on. Your concept of a portal is so confused, The portal is simply like the tire as in what goes in it will coem out the other side keeping the same velocity.T he only reason a portal does keep the velocity is because there is velocity coming towards the portal (tire) as in throwing a marble through a tire. I have no degree in physics.


Albert Einstein "Make everything as simple as possible, but not simpler."

I've already thought about this situation, and have evidence, that it is not the same situation. There's a key difference.

The situation as described is unlike dropping a room on the cube. It's more like dropping a room on a cube that is floating in the air.

In the situation that WE are talking about, momentum comes from the difference in portals. Dropping a tir on a marble? There is no difference. Both sides of the tire are moving downwards at the same speed. Think of both sides of the tire as the portals. The sides of the tire are manipulating space, not just "falling on the marble".

And again, the situation is not similar, because you are comparing a situation in which the frame of reference is the room, to a situation where the frame of reference is the floor. When you drop the tire, you're comparing the marble to the floor. When you drop the room (In the original situation) there is NO FLOOR. It keeps falling in a sense. When you drop the room on the cube, once the cube enters the room, it is affected by gravity, just as the room is.

FusedCore
05-24-2011, 09:02 PM
This is not possible as it's the engine that would need to be fixed up to using portals on moving things.... But it may not be possible to fix it because the math that does portals is actual physics and wormhole physics and in that wormholes are fixed points in space and time that connect to each-other just like in portal 1 & 2.

PelPix
05-24-2011, 09:10 PM
I don't understand why people are implying that portals can't move. As of Portal 2, they absolutely can. I've even see a few custom maps with them. There was this one map that had a portal on a slab of concrete freehanging by a rope. Fascinating.

FusedCore
05-24-2011, 09:15 PM
I don't understand why people are implying that portals can't move. As of Portal 2, they absolutely can. I've even see a few custom maps with them. There was this one map that had a portal on a slab of concrete freehanging by a rope. Fascinating.

Those maps do not involve moving physical objects as the laser's and liquid are mirrored to look like it's actually going through the portal... Which is how the developers made it because the wormhole physics code wouldn't allow the objects to go through when the portals are moving...

_Depression
05-24-2011, 09:20 PM
This is really a case where we can theorize all we want, but we can't have any definitive experiments because we simply don't have the resources.

I enjoy this debate, and I've been lurking ever since page 2, but it just seems like it's been very circuitous.

PelPix
05-24-2011, 09:22 PM
Those maps do not involve moving physical objects as the laser's and liquid are mirrored to look like it's actually going through the portal... Which is how the developers made it because the wormhole physics code wouldn't allow the objects to go through when the portals are moving...

The map I'm remembering didn't have any liquids or lasers at all, let alone anywhere near the moving portal. I had to walk through it. It was buggy, but it did work.

CatatonicMan
05-24-2011, 09:26 PM
The map I'm remembering didn't have any liquids or lasers at all, let alone anywhere near the moving portal. I had to walk through it. It was buggy, but it did work.

In Portal 2, moving portals only work with the player and with lasers (I think). Nothing else will interact with the portal.

FusedCore
05-24-2011, 09:28 PM
The map I'm remembering didn't have any liquids or lasers at all, let alone anywhere near the moving portal. I had to walk through it. It was buggy, but it did work.

Ever watch any of the Stargate series?? Well in there you needed A fixed none moving point in space to use the Stargate(wormhole); it works exactly the same in this game except you don't need a gate device because the power(black hole) that creates the stable fixed wormhole is in the portal gun.

sdhdgasd
05-24-2011, 10:08 PM
I would really appreciate some feedback.

Here's my feedback. (http://www.youtube.com/watch?v=WrjwaqZfjIY)

FusedCore
05-24-2011, 10:14 PM
Here's my feedback. (http://www.youtube.com/watch?v=WrjwaqZfjIY)

mmmm Initiate Dialing sequence! (http://www.youtube.com/watch?v=DqUQRlmXaco)

KimuraOkagawa
05-24-2011, 10:14 PM
Ever watch any of the Stargate series?? Well in there you needed A fixed none moving point in space to use the Stargate(wormhole); it works exactly the same in this game except you don't need a gate device because the power(black hole) that creates the stable fixed wormhole is in the portal gun.

Well, if you really think about it, neither the portals nor the stargates are in absolutely fixed positions. Portals rotate relative to the planet (or whatever) the stuff they're on is attached to, so in most cases, the portals are fixed relative to each other. The stargates are moving relative to each other the whole time because of stellar drift, and the coordinate system isn't exacting, just "general region of space defined by these six constellations". So you can dial to a gate on a ship using the planet's address. Not sure what tolerance level it is, probably somewhere between "planetary geostationary orbit" and "the size of a solar system", since Earth's address never changes over the course of three series (barring intergalactic transport and timey wimey coordinates).

Likewise, momentum of object on exit of portal/stargate != absolute momentum, but momentum relative to the entrance. So on topic, portal moving toward stationary object == moving object toward stationary portal == object flings out of exit portal.

Darth Silver
05-24-2011, 10:17 PM
I think I get it. If you held your hand out directly over the portal the cube is coming through, it'd probably break a finger or two. Which means it's going fast as it comes out. Which means it'll keep going fast.

So B.

FusedCore
05-24-2011, 10:27 PM
Well, if you really think about it, neither the portals nor the stargates are in absolutely fixed positions. Portals rotate relative to the planet (or whatever) the stuff they're on is attached to, so in most cases, the portals are fixed relative to each other. The stargates are moving relative to each other the whole time because of stellar drift, and the coordinate system isn't exacting, just "general region of space defined by these six constellations". So you can dial to a gate on a ship using the planet's address. Not sure what tolerance level it is, probably somewhere between "planetary geostationary orbit" and "the size of a solar system", since Earth's address never changes over the course of three series (barring intergalactic transport and timey wimey coordinates).

Likewise, momentum of object on exit of portal/stargate != absolute momentum, but momentum relative to the entrance. So on topic, portal moving toward stationary object == moving object toward stationary portal == object flings out of exit portal.

When you dial the ship aka SG-1 and SGU(the destiny was designed with a prewarning buffer to stop the ship when an incoming gate is activated) the ships are not in motion(if they are the gate will respond with a busy signal to prevent destruction) and the DHD/Gates are calculating the momentum to compensate for instabilities but in the case of the portal tech there is no device to recalculate for instabilities while in sudden motion and the portals have to refresh every-time the object is stopped. Also during the movement the portal code switches over from the wormhole physics to the mirror code to prevent the engine from completely failing and that's one reason why you cant bring physical objects through it while in motion.

DisConnected
05-24-2011, 10:28 PM
Ever watch any of the Stargate series?? Well in there you needed A fixed none moving point in space to use the Stargate(wormhole); it works exactly the same in this game except you don't need a gate device because the power(black hole) that creates the stable fixed wormhole is in the portal gun.

Planets are constantly moving and rotating. A portal is on a planet, therefor not in a fixed location.

FusedCore
05-24-2011, 10:33 PM
Planets are constantly moving and rotating. A portal is on a planet, therefor not in a fixed location.

Planets are in a fixed point in space/time and are only using natural momentum which the DHD/Gate can compensate for...

Some people need to learn physics...

Condor_96
05-25-2011, 12:04 AM
Thank you, OP, for explaining what half the idiots in the other thread are too stupid to understand.

Tensor
05-25-2011, 12:09 AM
So, instead of retyping everything I said I'm going to link to what I said in the moving reference frame post. For the record the answer is A and I am nearing the finishing of my Physics degree so I do have a background in this subject.

http://forums.steampowered.com/forums/showthread.php?p=22589806#post22589806

Bhazir
05-25-2011, 12:31 AM
So, instead of retyping everything I said I'm going to link to what I said in the moving reference frame post. For the record the answer is A and I am nearing the finishing of my Physics degree so I do have a background in this subject.

http://forums.steampowered.com/forums/showthread.php?p=22589806#post22589806

So you telling us you already have portal device? Or close to building one? If not then all you know is just theory, just like the OP and none can be proven wrong. It is the same as the discussion about time travelling and how it could work.

Tensor
05-25-2011, 12:42 AM
So you telling us you already have portal device? Or close to building one? If not then all you know is just theory, just like the OP and none can be proven wrong. It is the same as the discussion about time traveling and how it could work.

Um, we have the observations made based on the game, which is the only testing we can do, otherwise why bother commenting on it. It is an amusing thought experiment, but not one outside of our abilities to understand.

Consider the cube on the floor with a portal suddenly place beneath it and the other portal placed beside it, both facing up. The cube moves through the portal because gravity pulls it down, but as it moves through it has a new gravity pulling it in another direction so it begins changing the acceleration of the cube.

Pythagoras
05-25-2011, 01:02 AM
I'd say it's A. You just have to imagine that it's not only the portal moving down on the cube, but the entire room on the other side of the portal as well. If you dropped an entire room on it, the cube wouldn't move, but it would appear to be accelerating upwards when observed by somebody standing inside the room.

Tensor
05-25-2011, 01:09 AM
I'd say it's A. You just have to imagine that it's not only the portal moving down on the cube, but the entire room on the other side of the portal as well. If you dropped an entire room on it, the cube wouldn't move, but it would appear to be accelerating upwards when observed by somebody standing inside the room.

That's actually an excellent way to put it. I agree.

Bhazir
05-25-2011, 01:13 AM
Um, we have the observations made based on the game, which is the only testing we can do, otherwise why bother commenting on it. It is an amusing thought experiment, but not one outside of our abilities to understand.

Consider the cube on the floor with a portal suddenly place beneath it and the other portal placed beside it, both facing up. The cube moves through the portal because gravity pulls it down, but as it moves through it has a new gravity pulling it in another direction so it begins changing the acceleration of the cube.

Guess you missed the point of my post, coming here and telling you have a nearly degree in physics doesn't make your theory more true. Which the time travel discussions proves as it are all intelligent people discussion but can't prove anything.

And even with your degree you should know that if you look at forces that they always looked at with a reference point. In this case if you put the room as a reference point the cube doesn't move. But if you put the reference point on the first portal the whole room moves including the cube. I guess this is something we all can agree on.

Now is the discussion goes about what reference should be used to decide how the cube comes out of the second portal? Does it get shot out into the room or does it just appear without any velocity? Gravity will be applied in both cases anyway.

Baldrickk
05-25-2011, 01:13 AM
I'd say it's A. You just have to imagine that it's not only the portal moving down on the cube, but the entire room on the other side of the portal as well. If you dropped an entire room on it, the cube wouldn't move, but it would appear to be accelerating upwards when observed by somebody standing inside the room.

You have failed to take two things into account:

First, the portal ceasing to move after the cube has passed through, or from the stationary cube's frame of reference, the room then dropping away from under it.

Second, that the question is concerned with what happens at the exit portal, with the exit portal being defined as stationary. From this frame of reference, the cube shoots out.

Yes the cube would be defined as stationary in respect to the first room, (assuming portal continues its downward movement) but that's not the question, it is flung out of the exit portal, which is the answer to the question asked

PelPix
05-25-2011, 01:13 AM
Ever watch any of the Stargate series?? Well in there you needed A fixed none moving point in space to use the Stargate(wormhole); it works exactly the same in this game except you don't need a gate device because the power(black hole) that creates the stable fixed wormhole is in the portal gun.

If you need a fixed point in space to create a stargate, then how did it ever work? Last I checked, the Earth is spinning on its axis at about 1000 miles, and orbiting around the Sun at about 67000 miles per hour.

grimrecka
05-25-2011, 01:13 AM
I can disprove your entire theory with one quote:

"Spectacular. You appear to understand how a portal affects forward momentum, or to be more precise, how it does not. Momentum, a function of mass and velocity, is conserved between portals. In layman's terms: speedy thing goes in, speedy thing comes out."

If your proposed situation B was true, the portals would be creating momentum, not conserving it.

Therefore situation A is correct.

Baldrickk
05-25-2011, 01:19 AM
I can disprove your entire theory with one quote:



If your proposed situation B was true, the portals would be creating momentum, not conserving it.

Therefore situation A is correct.

The momentum is already there, it's in the relative speed between portal and cube. Cube retains momentum relative to portal so shoots out of the exit portal. Easy.

Bhazir
05-25-2011, 01:19 AM
I can disprove your entire theory with one quote:



If your proposed situation B was true, the portals would be creating momentum, not conserving it.

Therefore situation A is correct.

And how does the cube get through the portal without any velocity? Yes the cube doesn't move relative to the room, but compared to the first portal it has velocity that is conserved in option B. But as said before we won't ever know what the correct answer is until Valve tell us how it works in the game Portal.

Tensor
05-25-2011, 01:25 AM
You have failed to take two things into account:

First, the portal ceasing to move after the cube has passed through, or from the stationary cube's frame of reference, the room then dropping away from under it.

Second, that the question is concerned with what happens at the exit portal, with the exit portal being defined as stationary. From this frame of reference, the cube shoots out.

Yes the cube would be defined as stationary in respect to the first room, (assuming portal continues its downward movement) but that's not the question, it is flung out of the exit portal, which is the answer to the question asked


As far as we can tell the only thing that a portal does to an object that is speeding towards it is change it's orientation and placement. At no point can anyone use a portal to project an object using a downward motion or they would likely have used this method.

What Pythagoras says is in fact answering the question by noting that if you are in the room, e.g. the other side of the portal, and you are observing the cube coming at you the cube will remain static as it enters because as far as the cube is concerned it has not moved.

The only reason there is a discussion of it moving later is because its orientation is different after it passes through the exit portal. If the exit portal was facing straight up you would observe a cube suddenly appearing as it quickly raises into the "new room". You can think of it as looking as though it is fixed to the surface which appears to be fast approaching when you are looking through. This means the object does not actually fly off out of the exit portal as it had no momentum of its own.

The statement of "speedy thing goes in, speedy thing comes out" requires that the object itself has that velocity to begin with. It's an interesting thought to say that an object will gain the velocity of another object by benefit of a portal traveling quickly, but there just isn't any evidence in the games, let alone reality, to support it.

Baldrickk
05-25-2011, 01:36 AM
As far as we can tell the only thing that a portal does to an object that is speeding towards it is change it's orientation and placement. At no point can anyone use a portal to project an object using a downward motion or they would likely have used this method.

What Pythagoras says is in fact answering the question by noting that if you are in the room, e.g. the other side of the portal, and you are observing the cube coming at you the cube will remain static as it enters because as far as the cube is concerned it has not moved.

The only reason there is a discussion of it moving later is because its orientation is different after it passes through the exit portal. If the exit portal was facing straight up you would observe a cube suddenly appearing as it quickly raises into the "new room". You can think of it as looking as though it is fixed to the surface which appears to be fast approaching when you are looking through. This means the object does not actually fly off out of the exit portal as it had no momentum of its own.

The statement of "speedy thing goes in, speedy thing comes out" requires that the object itself has that velocity to begin with. It's an interesting thought to say that an object will gain the velocity of another object by benefit of a portal traveling quickly, but there just isn't any evidence in the games, let alone reality, to support it.

As I've said before, cube remains static in relation to original room assuming portal maintains its movement. But that's not the question, the question is what happens on the other side, relative to the exit portal.

You could model your dropping room example with a too. With a hole in the floor, being dropped onto the cube, true. But in order to model the exit portal as having a constant velocity, static or otherwise, you would need the floor supporting the cube to fall away on impact, it doesn't follow through remember.

We could imagine the cube being fixed in space instead of on the floor, as this simplifys it a bit.

In this case, the room keeps moving at its constant speed. What happens to the cube relative to the room?
If you were standing in the room, you would see it shoot up out of the floor and hit the ceiling.

IcarusNine
05-25-2011, 02:36 AM
Actually, what will happen is that the cube will be reduced into a completely flat object on the surface of the destination portal.

The first few atoms will go through the portal and realize they have no momentum, so they shouldn't move any further. The next few atoms will go through the portal and collide with the first few atoms. They will realize, however, that they will either have to transfer momentum to those atoms to move them out of the way, or stop and transfer momentum in reverse to halt the movement (from their perspective) of the atoms behind them. Perplexed at this decision, the atoms will say "screw it" and stop colliding with eachother with the thin excuse that disruption of space has made their typical perspective on the strong nuclear force irrelevant.

The result will be a cube compressed into an atom-thick layer that has successfully avoided creating or destroying momentum, but is now only useful for grinding up and being used in the super-dense varnish of a supercolliding super-button.

Joey90
05-25-2011, 02:39 AM
Actually, what will happen is that the cube will be reduced into a completely flat object on the surface of the destination portal.

The first few atoms will go through the portal and realize they have no momentum, so they shouldn't move any further. The next few atoms will go through the portal and collide with the first few atoms. They will realize, however, that they will either have to transfer momentum to those atoms to move them out of the way, or stop and transfer momentum in reverse to halt the movement (from their perspective) of the atoms behind them. Perplexed at this decision, the atoms will say "screw it" and stop colliding with eachother with the thin excuse that disruption of space has made their typical perspective on the strong nuclear force irrelevant.

The result will be a cube compressed into an atom-thick layer that has successfully avoided creating or destroying momentum, but is now only useful for grinding up and being used in the super-dense varnish of a supercolliding super-button.
That would be what would happen, if portals didn't transfer fields through them (with the possible exception of gravity), however we know that they must do, other wise if you passed halfway through a portal then changed direction, the half that has already passed through would disconnect from your body - tasty. Which means the Strong & Weak forces at least (we have evidence that gravity doesn't pass through, but EM waves - light - passes through) must pass through the portal, and so push the atoms out of the way, meaning that the cube will come out intact, and moving upwards.

IcarusNine
05-25-2011, 02:52 AM
It's not the portals stopping the transfer of fields, it's the atoms being forced closer together but not being able to create additional momentum in order to retain their shape.

The comment about strong nuclear force was merely humorous. (We aren't closer together, we look just fine as we are!)

But while we're at it, another question... If the moving portal was traveling at sufficiently high speed, would the light travelling through it become blue-shifted as it exited the destination portal?

Baldrickk
05-25-2011, 03:17 AM
It's not the portals stopping the transfer of fields, it's the atoms being forced closer together but not being able to create additional momentum in order to retain their shape.

The comment about strong nuclear force was merely humorous. (We aren't closer together, we look just fine as we are!)

But while we're at it, another question... If the moving portal was traveling at sufficiently high speed, would the light travelling through it become blue-shifted as it exited the destination portal?

yes, I believe it would. the source (through the portal) is coming closer to you.
have to be very fast to notice though, we only notice universal redshift in part because the rest of the universe is so far away.
so, at speeds possible on earth, not any measurable difference.

Joey90
05-25-2011, 03:28 AM
It's not the portals stopping the transfer of fields, it's the atoms being forced closer together but not being able to create additional momentum in order to retain their shape.

The comment about strong nuclear force was merely humorous. (We aren't closer together, we look just fine as we are!)

But while we're at it, another question... If the moving portal was traveling at sufficiently high speed, would the light travelling through it become blue-shifted as it exited the destination portal?
The force would be provided from the platform the cube is on - as each layer of atoms goes through the portal, the ones that haven't push against them and this passes all the way down to the platform. If the cube was, say, sitting on a spring, you would see the spring compress slightly as the portal passes down over the cube (depending on how quickly it passes down).*

As for blue shift, yes, although it would probably be much easier to measure the doppler effect in sound, which takes place at a bit more manageable speed :P

*incidentally this also explains conservation of momentum if the entrance and exit portals are aligned the same way, as possibly someone was saying earlier, the earth would be (slightly) pushed down upon, exactly cancelling the upward momentum of the cube. This doesn't work if portals are not aligned the same way, although in that case it doesn't work even if they're stationary.

grimrecka
05-25-2011, 03:42 AM
I just made a map to test this theory. As much as I regret to say, the tests where inconclusive. Here's the map:

http://www.mediafire.com/?td55q6a4edud9aa

for it work you first have to type "sv_allow_mobile_portals 1" into the console

stand on the grey raised platform with blue edges and press the button to make the cube above you drop at 2000 hammer units.

Clearly the engine isn't designed to work with static objects and moving portals. You should notice that if you stand perfectly still, the cube above will stop and you won't actually travel through the portal unless your moving yourself. (whether it be jumping, strafing, ect)

Same thing happens if you place the cube on the platform: It will just get crushed unless you jiggle it.

You can counter this buy jumping and pressing the button at exactly the same time. However if you do this with you exit portal placed on the diagonal slope, the physic's glitches out and you get a massive punt vertically.

Limeaide
05-25-2011, 04:53 AM
Planets are in a fixed point in space/time and are only using natural momentum which the DHD/Gate can compensate for...

Some people need to learn physics...

Just because something is using "natural momentum" doesn't mean it is in a fixed place. You seem to have learned physics from silly science fiction.

Roeltjuh
05-25-2011, 04:55 AM
The momentum is already there, it's in the relative speed between portal and cube. Cube retains momentum relative to portal so shoots out of the exit portal. Easy. That momentum isn't real. This is like saying driving past a stationary ball on the freeway and then braking next to it would send the ball rolling away..

THE_ROFLSER
05-25-2011, 04:56 AM
This is not possible as it's the engine that would need to be fixed up to using portals on moving things.... But it may not be possible to fix it because the math that does portals is actual physics and wormhole physics and in that wormholes are fixed points in space and time that connect to each-other just like in portal 1 & 2.

Its very possible. Theres a console command that lets you put portals on moving surfaces, I.E. when you had to use a moving portal with the lazer to cut the tubes?

Baldrickk
05-25-2011, 05:15 AM
That momentum isn't real. This is like saying driving past a stationary ball on the freeway and then braking next to it would send the ball rolling away..

no, momentum is always relative. in this case its actually like saying that the ball is moving with you, so is stationary relative to you as you move, as you are counting yourself as stationary, and when you stop, (still stationary in reference to yourself) the ball accelerates. relative to the world, you would see yourself stopping. relative to yourself, you would see the world stop and the ball accelerate.

if you are running and hit a stationary wall at 10 m/s or whatever, you will hit with the same force that you would encounter if you were hit with a moving wall travelling at the same speed while you were standing stationary.

think about it. it all makes sense.

CatatonicMan
05-25-2011, 05:16 AM
That momentum isn't real. This is like saying driving past a stationary ball on the freeway and then braking next to it would send the ball rolling away..

That's not an equivalent analogy.

Roeltjuh
05-25-2011, 05:28 AM
That's not an equivalent analogy.

"The momentum is already there, it's in the relative speed between portal and cube. Cube retains momentum relative to portal so shoots out of the exit portal."

The momentum is already there, it's in the relative speed between vehicle and ball. Ball retains momentum relative to vehicle so it rolls away from the vehicle.

Seems the same to me..

I know portals aren't vehicles, but my point is that that even if something seems to have momentum from your inertial reference frame it doesn't neccesarely have momentum.

Joey90
05-25-2011, 05:34 AM
"The momentum is already there, it's in the relative speed between portal and cube. Cube retains momentum relative to portal so shoots out of the exit portal."

The momentum is already there, it's in the relative speed between vehicle and ball. Ball retains momentum relative to vehicle so it rolls away from the vehicle.

Seems the same to me..

I know portals aren't vehicles, but my point is that that even if something seems to have momentum from your inertial reference frame it doesn't neccesarely have momentum.
The vehicle is not an inertial reference frame - an inertial reference frame has no acceleration - but the vehicle does. This is the difference

StrangeQuirk
05-25-2011, 05:36 AM
"The momentum is already there, it's in the relative speed between portal and cube. Cube retains momentum relative to portal so shoots out of the exit portal."

The momentum is already there, it's in the relative speed between vehicle and ball. Ball retains momentum relative to vehicle so it rolls away from the vehicle.

Seems the same to me..

I know portals aren't vehicles, but my point is that that even if something seems to have momentum from your inertial reference frame it doesn't neccesarely have momentum.
Key word in bold. It's all relative. However, a slowing-down car isn't an inertial reference frame any more, so conservation of momentum won't act like you expect from it's point of view.

When we talk about the blue portal and cube, they are moving at a constant speed relative to each other. It shouldn't matter if the blue portal is moving at 10 mph and the cube is at rest, or the cube is moving at 10 mph and the portal is at rest, or the portal is moving at 350 mph while the cube is moving at 340 mph in the same direction relative to the room.

Whiplashr
05-25-2011, 05:40 AM
I love when people think they have the absolutely subject closing thoughts on a matter that is being hotly debated in another thread.. something so awesome and gigantic that it absolutely demands it's own thread. No way we can just continue the discussion there.. I have the answer to all of life's mysteries! I will change the world! I am making a new thread damnit!!

Now we'll just have the debate raging in two threads. Bravo sir. Bra-vo.

Roeltjuh
05-25-2011, 05:40 AM
The vehicle is not an inertial reference frame - an inertial reference frame has no acceleration - but the vehicle does. This is the difference

It's not a regular vehicle, but one that creates distortions in spacetime around it, the vehicle is surfing on this wave of spacetime. (that's one of the proposed ways of beating lightspeed). It is now an inertial reference frame that can come to a halt without becomming a non-inertial reference frame. Ball still doesn't go anywhere, though.

Baldrickk
05-25-2011, 05:40 AM
The vehicle is not an inertial reference frame - an inertial reference frame has no acceleration - but the vehicle does. This is the difference

the vehicle has no acceleration relative to itself. instead the world accelerates around it.

you can have anything as your reference point, as long as you keep all the measurements consistent. because portals bend space however, the only consistent factor is the portals themselves. you can't make a measurement relative to the room before the entry portal, and expect it to be the same with respect to the room after the item has gone through the portal.

Joey90
05-25-2011, 05:57 AM
It's not a regular vehicle, but one that creates distortions in spacetime around it, the vehicle is surfing on this wave of spacetime. (that's one of the proposed ways of beating lightspeed). It is now an inertial reference frame that can come to a halt without becomming a non-inertial reference frame. Ball still doesn't go anywhere, though.

That sounds very relativistic, and in general relativity you don't get reference frames like you do in Newtonian mechanics. If it's bending spacetime around it, then you have to be extremely careful what you're doing - you can't just make it magically stop without feeling an acceleration.

the vehicle has no acceleration relative to itself. instead the world accelerates around it.

you can have anything as your reference point, as long as you keep all the measurements consistent. because portals bend space however, the only consistent factor is the portals themselves. you can't make a measurement relative to the room before the entry portal, and expect it to be the same with respect to the room after the item has gone through the portal.
If you're in the car and it comes to a sudden stop, you feel a force relative to the car. This means it's undergoing an acceleration. if you're standing on the surface of the earth and a car comes to a sudden stop next to you, you don't feel anything.

Roeltjuh
05-25-2011, 06:00 AM
That sounds very relativistic, and in general relativity you don't get reference frames like you do in Newtonian mechanics. If it's bending spacetime around it, then you have to be extremely careful what you're doing - you can't just make it magically stop without feeling an acceleration.

Yes you can, it's not even moving.

http://www.youtube.com/watch?v=iJZXDEUOao0

You can skip to about 1.30. Notice how the world renowed Dr. Kaku says "So you have the illusion that you're moving. Actually it's space that's pushing and pulling you along."

It may be popular science, but it's still accurate.

Not quite sure what you mean by the text in bold, though.

Baldrickk
05-25-2011, 06:18 AM
That sounds very relativistic, and in general relativity you don't get reference frames like you do in Newtonian mechanics. If it's bending spacetime around it, then you have to be extremely careful what you're doing - you can't just make it magically stop without feeling an acceleration.


If you're in the car and it comes to a sudden stop, you feel a force relative to the car. This means it's undergoing an acceleration. if you're standing on the surface of the earth and a car comes to a sudden stop next to you, you don't feel anything.

its not a perfect analogy due to portals not being possible etc.
if you are in the car, like the moving ball, you are stationary relative to the car.
when the car stops. like the rest of the world, the car sees you trying to accelerate forwards, but of course as you are strapped in, it applies force to you to keep you in the same place relative to itself instead of going through the windscreen.

Matttt
05-25-2011, 06:24 AM
This did not need a second thread, egoist.

Joey90
05-25-2011, 06:25 AM
Yes you can, it's not even moving.

http://www.youtube.com/watch?v=iJZXDEUOao0

You can skip to about 1.30. Notice how the world renowed Dr. Kaku says "So you have the illusion that you're moving. Actually it's space that's pushing and pulling you along."

It may be popular science, but it's still accurate.

Not quite sure what you mean by the text in bold, though.
There's still a big issue of what exactly is happening at the side parallel to your apparent motion... Even so, I don't see how this is exactly relevant, unless you think that portals warp spacetime (in a big way) at points not on their surface? I thought it would make more sense to assume that away from the portals space & physics works exactly how we would expect.

You don't get inertial reference frames in general relativity, in special relativity you can have reference frames that are equivalent via a Lorentz transformation. In general relativity the best we can do is have a frame of 0 (or I suppose, constant) proper acceleration (http://en.wikipedia.org/wiki/Proper_acceleration)... And this can only be a local thing (inasmuch as you want a section of apparently flat spacetime, which if your thing is stretching, the whole system is not, and so you cannot compare the two parts in that frame)

Baldrickk
05-25-2011, 06:30 AM
on bending spacetime, from an outside observer's point of view, portals bend it. travelling through however, it is as if the rest of the universe has been bent.

Roeltjuh
05-25-2011, 06:35 AM
There's still a big issue of what exactly is happening at the side parallel to your apparent motion... Even so, I don't see how this is exactly relevant, unless you think that portals warp spacetime (in a big way) at points not on their surface? I thought it would make more sense to assume that away from the portals space & physics works exactly how we would expect.

You don't get inertial reference frames in general relativity, in special relativity you can have reference frames that are equivalent via a Lorentz transformation. In general relativity the best we can do is have a frame of 0 (or I suppose, constant) proper acceleration (http://en.wikipedia.org/wiki/Proper_acceleration)... And this can only be a local thing (inasmuch as you want a section of apparently flat spacetime, which if your thing is stretching, the whole system is not, and so you cannot compare the two parts in that frame)

Hmm OK thank you for explaining. I thought they were basicly the same when the scale is small.

I figured it was relevent because the only reason you guys were able to counter argument was with "the vehicle isn't an inertial reference frame, that's why it's different.". So I thought of a way to turn it into an inertial reference frame.

Dzjudz
05-25-2011, 06:59 AM
The entire problem is much more difficult than can be explained in a short post.

For example, how does gravity factor in to this problem? Does the gravity from the original cube room still have an effect on the cube through the portal?

Or imagine the cube sitting on a slim pedestal (which is fixed to the ground) and the piston portal moving around it, thrusting both the cube and the pedestal through. Once the piston portal hits the ground in the original room, does the cube suddenly shoot off the pedestal? And again, how does the cube interact with the gravity through the portal?

Joey90
05-25-2011, 07:04 AM
The entire problem is much more difficult than can be explained in a short post.

For example, how does gravity factor in to this problem? Does the gravity from the original cube room still have an effect on the cube through the portal?

Or imagine the cube sitting on a slim pedestal (which is fixed to the ground) and the piston portal moving around it, thrusting both the cube and the pedestal through. Once the piston portal hits the ground in the original room, does the cube suddenly shoot off the pedestal? And again, how does the cube interact with the gravity through the portal?
The gravity issue is a big one, the only way it can make sense, and be consistent with the in-game physics is if the gravitational field doesn't leak through portals (or you'd get strange results with non aligned portals.

The teleporter analogy would sort of fix this, but as I said before it would need to transfer the other fields through, which causes similar problems to gravity. (Imagine a massive charge below the room, then any opposite charge in the room would feel the force from that similarly to gravity.)

Macedragon37
05-25-2011, 07:05 AM
I've updated the OP with a new example; this example should make things more clear.

Baldrickk
05-25-2011, 07:15 AM
The entire problem is much more difficult than can be explained in a short post.

For example, how does gravity factor in to this problem? Does the gravity from the original cube room still have an effect on the cube through the portal?

Or imagine the cube sitting on a slim pedestal (which is fixed to the ground) and the piston portal moving around it, thrusting both the cube and the pedestal through. Once the piston portal hits the ground in the original room, does the cube suddenly shoot off the pedestal? And again, how does the cube interact with the gravity through the portal?

from observation in the game, gravity doesn't pass through portals, although if it did, that would make for a convincing argument on how potential energy gain is negate while being a potentially very annoying game mechanic when flinging.

the pillar would be thrust through the pitas will the cube. (if A was true and cube Had to be stationary in the other side, this would be both impossible and inconsistent)
when the portal stops moving, the pillar stops moving, leaving the cube to fly off of it, in the sane manner as Chell from an aerial faith plate

rowland
05-25-2011, 07:22 AM
dont have much time to think bout this stuff but i think logic is:
objects with momentum continue with it until the energy es absorbed (ex: you run until you fall down)
object without momentum stay in the same place
by this: if a portal on a surface acceletares towards the object on the ground, the object not having momentum will go through the accelerated portal and thats it (no jumping/flying out)

Baldrickk
05-25-2011, 07:24 AM
I've updated the OP with a new example; this example should make things more clear.

there is an animated .swf file linked to in the main thread. if I were at a desktop I'd find it for you.
you should probably add it to the pole illustration.

also, you mention the orange portal travelling with respect to the Orange portal. probably a typo, I'd have another read if I were you. :D

edit: file is: http://dl.dropbox.com/u/8723889/portalB.swf

Macedragon37
05-25-2011, 07:25 AM
dont have much time to think bout this stuff but i think logic is:
objects with momentum continue with it until the energy es absorbed (ex: you run until you fall down)
object without momentum stay in the same place
by this: if a portal on a surface acceletares towards the object on the ground, the object will go through the accelerated portal As an accelerated object due to the difference in speeds of the orange and blue portals.

Sorry. But no. It took me quite a long time to figure all of this out, and explain it.

I added what SHOULD be in the explanation that you just created.

Dzjudz
05-25-2011, 07:35 AM
there is an animated .swf file linked to in the main thread. if I were at a desktop I'd find it for you.
you should probably add it to the pole illustration.

also, you mention the orange portal travelling with respect to the Orange portal. probably a typo, I'd have another read if I were you. :D

edit: file is: http://dl.dropbox.com/u/8723889/portalB.swfYes that video seems fine and dandy, but consider this: what if the piston suddenly stops halfway over the cube?

rowland
05-25-2011, 07:38 AM
(referred to the first link)
also this is kindofa tricky question, if the portal does not fully cover the object, there is a posibility that the object wont go through fully, therefore the gravity will "pull" back the object until the gravity from the other side is superior 1>0.99

Baldrickk
05-25-2011, 07:45 AM
Sorry. But no. It took me quite a long time to figure all of this out, and explain it.

I added what SHOULD be in the explanation that you just created.

that makes it work

rowland
05-25-2011, 07:47 AM
Sorry. But no. It took me quite a long time to figure all of this out, and explain it.

I added what SHOULD be in the explanation that you just created.

I knew I shouldnt have read and replied to this thread...
Although your theory is most convincing, I have to see it ingame to truly believe in the theories (including mine).

Baldrickk
05-25-2011, 07:49 AM
Sorry. But no. It took me quite a long time to figure all of this out, and explain it.

I added what SHOULD be in the explanation that you just created.

Yes that video seems fine and dandy, but consider this: what if the piston suddenly stops halfway over the cube?

wait till I get home and I'll work out the equation for you.
unfortunately it may have to involve integrals unless you are willing to accept instantaneous acceleration (+/-) in order to simplify the scenario.

Baldrickk
05-25-2011, 07:54 AM
I knew I shouldnt have read and replied to this thread...
Although your theory is most convincing, I have to see it ingame to truly believe in the theories (including mine).

unfortunately, as discussed at length previously the game doesn't support it and it be too much effort for Valve to patch it in. esp. as same puzzle can be reproduced with an AFP under the portal.

ac1dtrip
05-25-2011, 07:56 AM
Answer is A. Drop a tire(portal) on a marble on a standing object. The marble , due to no acceleration, will not move other than the force of the tire(portal) hitting the solid object that the marble is lying on. Your concept of a portal is so confused, The portal is simply like the tire as in what goes in it will coem out the other side keeping the same velocity.T he only reason a portal does keep the velocity is because there is velocity coming towards the portal (tire) as in throwing a marble through a tire. I have no degree in physics.


Albert Einstein "Make everything as simple as possible, but not simpler."

Joey90
05-25-2011, 08:09 AM
Answer is A. Drop a tire(portal) on a marble on a standing object. The marble , due to no acceleration, will not move other than the force of the tire(portal) hitting the solid object that the marble is lying on. Your concept of a portal is so confused, The portal is simply like the tire as in what goes in it will coem out the other side keeping the same velocity.T he only reason a portal does keep the velocity is because there is velocity coming towards the portal (tire) as in throwing a marble through a tire. I have no degree in physics.


Albert Einstein "Make everything as simple as possible, but not simpler."
Tape a water balloon to the top of the tire and draw a little face on it, this is you. Then drop it from a good height. *splat*

I hope this isn't what you think will happen to you if you stand over the exit portal...

ac1dtrip
05-25-2011, 08:14 AM
Tape a water balloon to the top of the tire and draw a little face on it, this is you. Then drop it from a good height. *splat*

I hope this isn't what you think will happen to you if you stand over the exit portal...

Your response makes no sense. In your first example you never declare where the portal is. If I in this scenario was standing over the portal I'd continuely fall through it just like in the game at the same velocity it took me to fall through the (tire). Or you are trolling and I got trolled gg.

Joey90
05-25-2011, 08:30 AM
Your response makes no sense. In your first example you never declare where the portal is. If I in this scenario was standing over the portal I'd continuely fall through it just like in the game at the same velocity it took me to fall through the (tire). Or you are trolling and I got trolled gg.
This is the example we were talking about - portal on a panel comes down onto a cube, another portal on the floor is stationary in the room, what happens?

If it was like your example, standing near the edge of the exit portal on the floor would mean you feel a big jolt from the floor as it the panel comes down like your tire... Which doesn't happen.

Macedragon37
05-25-2011, 08:41 AM
Updated with the "Dropping" the room on the cube example.

striker720
05-25-2011, 08:48 AM
EDIT: gah, nevermind. you people managed to convince me that the answer is B. if you still want to see my original thoughts I left it in, however they have all been proven wrong. :p


I hate to disagree, seeing all the work you put into your post, but I do. Now bear with me, as this is my first post on a valve forum, and my first post on any forum in quite a while, but here's what I think.

As you said, at the start of the experiment the cube is stationary. Nothing is causing it to move. The only objects moving at the start is the wall/piston with the portal on it, and the portal on the wall/piston (let's just say it's the orange portal). What doesn't make sense (or at least to me) is how the cube gets the momentum to fling out. How could it get the momentum for this? As said, the only thing moving is the piston/wall, which doesn't even touch it, correct? How about the orange portal? Forgive me, as i'm not an expert with this kind of stuff so some of the stuff you said made next to no sense to me, but from what I did understand you seem to think this is its source of momentum (feel free to correct me if I'm wrong), however, the box doesn't really touch the portal, it just goes through it. As for what you said about seeing the box rushing toward you by looking into the portal, imagine this.

Place a portal on a wall and one on the floor. Now, take a cube, and hold it outside the hole in the wall, but don't drop it. What does it look like? Knowing gravity, it looks as if it's going to drop downwards, as if both portals were placed on a wall. However, when you DO drop the cube, it DOESN'T do this at all, it just comes back out the way it came. My point is when it comes to gravity you can't always trust what you see out of a portal. I wish I could provide some pictures in case I explained this poorly, but unfortunately I'm "artistically challenged" and the pictures would probably just confuse everyone even more.

sorry if I simplified this too much, I just wanted to make sure everyone understood what I was saying, as this entire discussion is pretty complex.


TL;DR EDITION: Speedy thing goes in, speedy thing goes out, therefore it's A.

JackDownAHill
05-25-2011, 08:52 AM
Does anyone remember the piston area from portal 1?
There is the big concrete slab with a small gap between it and the floor... You shoot a portal on the underside of the concrete slab and one on the top of it.
You then crouch to walk under it. Once you line yourself up with the portal and let go of crouch, you just stand up. No flinging or flying to be seen.

This scenario applies in this situation because you un-crouching is the same as the portal above you moving towards you.
ie. same velocity with respect to the reference frame (the portals)

therefore it is option A

/thread :D

rahel95
05-25-2011, 09:05 AM
Does anyone remember the piston area from portal 1?
There is the big concrete slab with a small gap between it and the floor... You shoot a portal on the underside of the concrete slab and one on the top of it.
You then crouch to walk under it. Once you line yourself up with the portal and let go of crouch, you just stand up. No flinging or flying to be seen.

This scenario applies in this situation because you un-crouching is the same as the portal above you moving towards you.
ie. same velocity with respect to the reference frame (the portals)

therefore it is option A

/thread :D

I said that in the old thread, someone responded to me - the problem is that the piston is not moving

zero2212
05-25-2011, 09:17 AM
well i like your post alot but
"speedy thing goes IN speedy thing goes out"
now i think it would be very wrong to say the portal is going in the cube because thats wrong
also
"portals convey momentum not create it"
rough qute
futhermore if you were standing looking into hte blue portal yes the cube would LOOK like it was speeding towards you but it wouldent be the cube is stationary
its hard to understand the cube is not mooving the space between you and the cube is
for example if you are falling from a high hight would it not look like the ground is mooving towards you
yes it would but is it?
not really you are moving twards it the grounds is not moving
it only apears to be

Otto42
05-25-2011, 09:21 AM
What doesn't make sense (or at least to me) is how the cube gets the momentum to fling out. How could it get the momentum for this? As said, the only thing moving is the piston/wall, which doesn't even touch it, correct? How about the orange portal? Forgive me, as i'm not an expert with this kind of stuff so some of the stuff you said made next to no sense to me, but from what I did understand you seem to think this is its source of momentum (feel free to correct me if I'm wrong), however, the box doesn't really touch the portal, it just goes through it.

When you say that it doesn't "touch" the portal, then you're misunderstanding the nature of how such a portal would work.

The portal isn't the ring around empty space, the portal is the whole thing itself. Remember, the portal is placed *on a wall*. So really, there's a whole portal surface on that wall that is connecting it to another portal surface, on another wall. That whole flat area is the portal. So the portal most definitely "touches" the cube.

Furthermore, the portal can exert force. It has to be able to do this, because it changes the velocity of things passing through it. Remember, velocity is speed AND direction. So since portals can clearly change your direction, then that means they can change your velocity.

Now, in the case of a set of non-moving portals, your speed will obviously remain unaffected when passing through them. But in the case where one side is moving, then your speed will be affected because the speed at which you pass through the portal is relative to the movement of the portal itself.

Consider the case where I fling a box through the air at a portal which is moving away from the box, just slightly less fast than the box's speed itself. As the box catches up to this moving portal, it starts passing through it, but very slowly. What speed should the box be moving when it comes out the other side? Same speed? Or should it just slooooowly come out instead?

Same problem, just in reverse. The relative speed of an object to the portal it's passing through determines its resulting speed on the other side.

If you prefer to think of it in terms of momentum, then here's the answer: Momentum of the total cube+portal *SYSTEM* is conserved. The cube has zero momentum (at rest). The orange portal has non-zero momentum (moving). On the other side, the blue portal has zero momentum (at rest). Therefore, the cube must have non-zero momentum (moving) when it comes out, in order to conserve the momentum of the cube+portal system as a whole.

zero2212
05-25-2011, 09:29 AM
When you say that it doesn't "touch" the portal, then you're misunderstanding the nature of how such a portal would work.

The portal isn't the ring around empty space, the portal is the whole thing itself. Remember, the portal is placed *on a wall*. So really, there's a whole portal surface on that wall that is connecting it to another portal surface, on another wall. That whole flat area is the portal. So the portal most definitely "touches" the cube.

Furthermore, the portal can exert force. It has to be able to do this, because it changes the velocity of things passing through it. Remember, velocity is speed AND direction. So since portals can clearly change your direction, then that means they can change your velocity.

Now, in the case of a set of non-moving portals, your speed will obviously remain unaffected when passing through them. But in the case where one side is moving, then your speed will be affected because the speed at which you pass through the portal is relative to the movement of the portal itself.

Consider the case where I fling a box through the air at a portal which is moving away from the box, just slightly less fast than the box's speed itself. As the box catches up to this moving portal, it starts passing through it, but very slowly. What speed should the box be moving when it comes out the other side? Same speed? Or should it just slooooowly come out instead?

Same problem, just in reverse. The relative speed of an object to the portal it's passing through determines its resulting speed on the other side.

If you prefer to think of it in terms of momentum, then here's the answer: Momentum of the total cube+portal *SYSTEM* is conserved. The cube has zero momentum (at rest). The orange portal has non-zero momentum (moving). On the other side, the blue portal has zero momentum (at rest). Therefore, the cube must have non-zero momentum (moving) when it comes out, in order to conserve the momentum of the cube+portal system as a whole.
sorry
even if they do change your direction they have no effect on speed and since velocity is BOTH of those it dose not affect your velocity
EDIT:also about your point of the thrown cube YES but only beause the cube is mooving i throw something at it and its moving twards the yes it mooves out faster but im not throwing something at it

_Korgha_
05-25-2011, 09:32 AM
Consider an environment with no gravity (just to simplify things).

There is a cube suspended in the middle of a room with a portal moving towards it (the other portal is somewhere else in the room). Everything is stationary other than the moving portal. The only object with kinetic energy is the portal.

When the portal reaches the cube and the cube goes through the portal (the portal keeps moving), if the cube is not stationary, then it has kinetic energy, which means that the total energy of the system has increased, violating the conservation of energy.

Note: this doesn't show that the cube is definitely stationary, but it DOES show that if the cube isn't stationary when it comes out, then the conservation of energy is violated (i.e. Portals break physics).

Roeltjuh
05-25-2011, 09:32 AM
NO...no it isn't. In fact, the example is very much different. In your example, the control of motion is contained in the car, therefore the ball is a the unmoving reference point. In his example (Which in part, I agree with) motion is relative to the moving portal.

Those, once again, aren't the same. You are completely forgetting that motion is also relative to the blue portal, which isn't even in this equation.

In fact, that's a terrible analogy and comparison. What are you thinking?

What my example was meant to illustrate was more the stupidity of the B side for thinking things can fly through the roof without being touched, then to actually be a good analogy. Also, you left out everything I said after that, making me look bad. What are YOU thinking? The cube isn't moving and there are no forces pulling or pushing on it. Why would it fly off?

Just because it looks like it's moving, such as in your pole example, doesn't mean it really is moving. I'm done with this nonsense..

Otto42
05-25-2011, 09:36 AM
sorry
even if they do change your direction they have no effect on speed and since velocity is BOTH of those it dose not affect your velocity

No. Velocity is the combination of both speed and direction. Anything that changes either one is changing your velocity. Physics 101.

EDIT:also about your point of the thrown cube YES but only beause the cube is mooving i throw something at it and its moving twards the yes it mooves out faster but im not throwing something at it

That doesn't matter. It's the same basic problem. It's a matter of motion *relative to the portal*. A thing that is moving relative to the portal will have speed when it comes out the other side. It doesn't matter if you move the thing to the portal or the portal to the thing. The movement is relative to the portal, and that's where the speed difference is obtained.

Otto42
05-25-2011, 09:39 AM
Consider an environment with no gravity (just to simplify things).

There is a cube suspended in the middle of a room with a portal moving towards it (the other portal is somewhere else in the room). Everything is stationary other than the moving portal. The only object with kinetic energy is the portal.

When the portal reaches the cube and the cube goes through the portal (the portal keeps moving), if the cube is not stationary, then it has kinetic energy, which means that the total energy of the system has increased, violating the conservation of energy.

Note: this doesn't show that the cube is definitely stationary, but it DOES show that if the cube isn't stationary when it comes out, then the conservation of energy is violated (i.e. Portals break physics).

Sorry, but no. Your example is flawed because you've intentionally increased the total energy in the room when you said "the portal keeps moving".

Again, the portal is a surface, not an empty ring. The cube floating in the middle of the room touches the portal and interacts with it. So what keeps that portal moving? I assume it's on a wall or a column or expanding pillar or something? Whatever adds the force to keep that portal moving after it moves over the cube is what added the energy into the room.

No physics violations in your example.

zero2212
05-25-2011, 09:40 AM
you know what youre right
also we have to wait for valve to release the portal gun to test this
about the physics
i still belive A
because portals > physics

Otto42
05-25-2011, 09:42 AM
What my example was meant to illustrate was more the stupidity of the B side for thinking things can fly through the roof without being touched

The entire error of the A side rests on this basic misunderstanding of portals. The cube is *touched* by the portal. A portal is not a ring, it is a surface.

The cube interacts with the portal. It does touch something. It's not sitting there untouched by anything at all.

_Korgha_
05-25-2011, 09:44 AM
Sorry, but no. Your example is flawed because you've intentionally increased the total energy in the room when you said "the portal keeps moving".

Again, the portal is a surface, not an empty ring. The cube floating in the middle of the room touches the portal and interacts with it. So what keeps that portal moving? I assume it's on a wall or a column or expanding pillar or something? Whatever adds the force to keep that portal moving after it moves over the cube is what added the energy into the room.

No physics violations in your example.

Your definition of force is quite confused.

Newton's First Law:
Every body remains in a state of constant velocity unless acted upon by an external unbalanced force. This means that in the absence of a non-zero net force, the center of mass of a body either remains at rest, or moves at a constant velocity.

Therefore the portal (and whatever it's on) does not require a force to move if it already is.

Otto42
05-25-2011, 09:50 AM
Your definition of force is quite confused.
No, my definition of force is the one used by real physics.

Therefore the portal (and whatever it's on) does not require a force to move if it already is.

It requires a force to *keep moving* after it touches the cube.

If two things in your room interact, then they must necessarily trade momentum. If I bounce a cube off another cube, then there's a ricochet and they bounce around according to physical laws.

Portals are no different. It can't move across the cube and not have an effect on the subsequent movement of the portal unless something is behind it pushing it along.

If "the portal keeps moving", then it must have a force behind it to do that. Otherwise it would slow down or stop, depending on the weight of the wall behind it and its speed.

The momentum transferred to the cube (that gives it kinetic energy) would come from the slowing of the motion of the portal's surface after it interacted with the cube.

EDIT: A portal is not a "hole" in space. It's a surface that transfers matter from one point to another. It must be thus, because this transfer can affect the velocity of objects passing through it (direction is a part of velocity, after all). Things touching the portal are transferred to the other portal, and vice versa. If a portal was a true hole in space, then gravity would pass through it as well.

JackDownAHill
05-25-2011, 09:56 AM
I said that in the old thread, someone responded to me - the problem is that the piston is not moving

It doesn't matter where the momentum is coming from, as long as it is there.
You moving up at 1ms^-1 is the same as the slab moving down at 1ms^-1 (or up at -1ms^-1)

"It's all relative man" - some cool dude :cool:

(Now i had a reason why i just looked this up to further my point somehow but after finding it i cant remember what it was... :/ but here it is anyway.)

http://en.wikipedia.org/wiki/Relativity_of_simultaneity#The_train-and-platform_thought_experiment

_Korgha_
05-25-2011, 09:57 AM
No, my definition of force is the one used by real physics.



It requires a force to *keep moving* after it touches the cube.

If two things in your room interact, then they must necessarily trade momentum. If I bounce a cube off another cube, then there's a ricochet and they bounce around according to physical laws.

Portals are no different. It can't move across the cube and not have an effect on the subsequent movement of the portal unless something is behind it pushing it along.

If "the portal keeps moving", then it must have a force behind it to do that. Otherwise it would slow down or stop, depending on the weight of the wall behind it and its speed.

The momentum transferred to the cube (that gives it kinetic energy) would come from the slowing of the motion of the portal's surface after it interacted with the cube.

It would only slow down if it collided with the cube, which would cause the cube to change direction and velocity (unless the coefficient of restitution between the two was 1).

I see no evidence for your assumption that a portal is a surface, especially considering that it is possible to stand halfway through a portal with a foot on either side. No objects seem to interact with portals in the manner you've described.

Otto42
05-25-2011, 10:04 AM
It would only slow down if it collided with the cube, which would cause the cube to change direction and velocity (unless the coefficient of restitution between the two was 1).

That's correct, but it does collide with the cube. It necessarily must collide with anything passing through it.

I see no evidence for your assumption that a portal is a surface, especially considering that it is possible to stand halfway through a portal with a foot on either side. No objects seem to interact with portals in the manner you've described.

A portal is self-evidently a surface. It must rest on a surface which is behind it (a wall or floor or ceiling, and not just any but one which is both smooth and conductive enough to hold it in place). If it was a true hole in space, then it could rest in empty space.

The fact that you can stand halfway through it means nothing, since the portals are bi-directional. Anything going through one side comes out the other and vice-versa. This has the same effect.

The fact that gravity won't pass through it shows that it is selective in what passes through it. A true wormhole in spacetime would not be selective. Also notice that radio signals won't pass through it (from the radio achievements in the first game), but visible light does (light also being an electromagnetic wave).

EDIT: Also note that a portal makes a distinctive sound as something passes through it. If it was really just two connected surfaces of warped spacetime, why would it make a sound?

_Korgha_
05-25-2011, 10:10 AM
That's correct, but it does collide with the cube. It necessarily must collide with anything passing through it.



A portal is self-evidently a surface. It must rest on a surface which is behind it (a wall or floor or ceiling, and not just any but one which is both smooth and conductive enough to hold it in place). If it was a true hole in space, then it could rest in empty space.

The fact that you can stand halfway through it means nothing, since the portals are bi-directional. Anything going through one side comes out the other and vice-versa. This has the same effect.

The fact that gravity won't pass through it shows that it is selective in what passes through it. A true wormhole in spacetime would not be selective. Also notice that radio signals won't pass through it (from the radio achievements in the first game).

That's an interesting theory, but note that a true wormhole resides in an area of spacetime which is theoretically infinitely curved, meaning gravity has a negligible/nonexistant effect through it.

Now as wormholes seem to be the only method of faster-than-light travel, if it's not one of those, then it can be whatever the ♥♥♥♥ it likes (including a selective transmitter of electromagnetic radiation).

TL;DR: Portals are magic.

Otto42
05-25-2011, 10:13 AM
Portals are magic.

Granted. However, as Clarke said, "Any sufficiently advanced technology is indistinguishable from magic." :cool:

Baldrickk
05-25-2011, 10:28 AM
No, my definition of force is the one used by real physics.



It requires a force to *keep moving* after it touches the cube.

If two things in your room interact, then they must necessarily trade momentum. If I bounce a cube off another cube, then there's a ricochet and they bounce around according to physical laws.

Portals are no different. It can't move across the cube and not have an effect on the subsequent movement of the portal unless something is behind it pushing it along.

If "the portal keeps moving", then it must have a force behind it to do that. Otherwise it would slow down or stop, depending on the weight of the wall behind it and its speed.

The momentum transferred to the cube (that gives it kinetic energy) would come from the slowing of the motion of the portal's surface after it interacted with the cube.

EDIT: A portal is not a "hole" in space. It's a surface that transfers matter from one point to another. It must be thus, because this transfer can affect the velocity of objects passing through it (direction is a part of velocity, after all). Things touching the portal are transferred to the other portal, and vice versa. If a portal was a true hole in space, then gravity would pass through it as well.

'Real physics' my [3 pink hearts here]!

Force produces acceleration, no force means that velocity does not change Your post shows a clear ignorance of physics.

A car requires a force to remain moving because of friction - wind resistance and friction with the road, axles etc. Friction supplying the force required to decelerate the car.

Also a portal isn't a solid plane, in the same way that the entrance to a tunnel isn't solid. (this is of course in the case where the portals are both open) How many times have you bounced off of an open portal?

remember that in respect to the portals, the cube is moving, and stays moving at the same speed. with no change in direction.

Tensor
05-25-2011, 10:40 AM
I'm not sure where we are getting this idea that the Portal should be treated as a surface. The portals seem to act more like a window than a surface, a wormhole if must be. I can see how it would appear that the box should go flying, but everything I know is telling me that is wrong based on nothing physically influencing the cube. Now while it is true that the Velocity direction is changed, this does not mean the speed is changed.

There are two different equations for defining either part of the Velocity, one takes into account the magnitude of the velocity and another velocity and the angle between them, and the other takes into account the vector directions and uses the cross product of the two in order to determine the new direction.

So to say there is a change in the overall velocity including the speed because it changes orientation due to a portal pointing elsewhere should mean that when I go flying through a portal I should not have the same speed exiting as I do when I go through, but we know this to be false.

I know it seems that the cube should go flying because the portal is approaching quickly, but that just means a quick change in direction. Gravity does this to light all the time but does not change its velocity, it's essentially the same thing, except we have mass.

Otto42
05-25-2011, 10:41 AM
Force produces acceleration, no force means that velocity does not change Your post shows a clear ignorance of physics.
Sorry, but I am not ignorant of physics, although you seem to be.

Just to get this out of the way first, the correct answer is B. If you agree, then you're correct. If you think it's A, then you're mistaken.

That said, velocity is a vector quantity, not a scalar one. Speed is only the scalar component of the velocity vector, which includes both speed and direction.

Changing the velocity of a moving object requires a force to act upon it. You can exert force and change velocity *without* changing the speed. For example, if I'm in a spaceship moving along and I fire my rockets at right angles to my course, then my speed can remain unchanged but now I'm travelling in a new direction. This is why we measure fuel consumption in spaceships with "delta-V", which basically means a change in velocity.

Now, if we assume portals exist as given in the game, then they do change the velocity of objects which travel through them. In the case where they are non-moving portals, but in different planes, then they will alter the directional component of the velocity.

Since portals can change the velocity of objects, they must by necessity exert some force on them. That's the only way to change velocity, by exerting a force on the object.

So, since portals can exert force, then they can also change the speed of an object, given the right circumstances. This circumstance happens to be when the portal itself is moving.

Also a portal isn't a solid plane, in the same way that the entrance to a tunnel isn't solid. (this is of course in the case where the portals are both open) How many times have you bounced off of an open portal?

A portal must be a solid plane. It touches the object and transfers its component atoms (or whatever it happens to be transferring) instantly to the other portal. I assume it does this using a (magical) quantum level effect of some sort.

remember that in respect to the portals, the cube is moving, and stays moving at the same speed. with no change in direction.

True, and because of this, it gains speed when it comes out the other portal. The force pushing the portal onto the object caused a transfer of momentum from the portal (or pushing wall behind it) into the object itself, which is why the box flings out of the other portal.

Sanbantai
05-25-2011, 10:46 AM
I think a problem arises from how people perceive portals - are they similar to teleporters (marterial is transferred atom by atom in real time), or do they physically connect two separate point in the world (talking about 4th dimensional, hypothetically). If it's like a teleporter, the atoms would be physically moved, even if the box appears to be completely stationary. This situation would make the box fly upwards at some speed in the situation shown.

However, if you think about portals as as a physical connection between two points, the box would behave like it would if it was simply pushed into a hole in the wall into another room, i.e. Not move at all. The "room falling on a box" example fits here.

Otto42
05-25-2011, 10:51 AM
I'm not sure where we are getting this idea that the Portal should be treated as a surface. The portals seem to act more like a window than a surface, a wormhole if must be. I can see how it would appear that the box should go flying, but everything I know is telling me that is wrong based on nothing physically influencing the cube. Now while it is true that the Velocity direction is changed, this does not mean the speed is changed.
If it was truly a hole in space, then you'd be correct and it wouldn't move. However, if that was the case, then it would be basically a free energy device, since it's capable of exerting force and changing the directional component of velocity without energy input. You could place two portals above and below each other, and drop a bunch of water in, then stick a paddlewheel in it and voila, free energy forever.

Aperture Science surely wouldn't have gone broke if they had had such a thing.

On the other hand, if we assume that it's a surface which transfers matter from one to another, however, then there is the possibility of loss of energy from the surface itself in the transfer, thus eliminating this free energy issue. This seems more likely to me, given the other characteristics of the portals.

Gravity does this to light all the time but does not change its velocity, it's essentially the same thing, except we have mass.
Gravity does change the velocity of light, it just doesn't change the speed component. However, passing through a medium can change the speed of light.

TmanIsHere
05-25-2011, 11:01 AM
You could place two portals above and below each other, and drop a bunch of water in, then stick a paddlewheel in it and voila, free energy forever.

Aperture Science surely wouldn't have gone broke if they had had such a thing.

Let's use a paper and pencil example.
If you draw two dots on a paper and bend the paper to make two points come together, you're not exerting anything on the 2D, but you have to "bend" (exert some force on) the paper to make them come together. This requires energy, but not in the realm of 2D.

Same idea with bending space time continuum. Even if you don't see it happening in 3D, it is completely possible to "bend" the space time continuum to allow the two space to come together.

Nothing is free.

Tensor
05-25-2011, 11:05 AM
So I decided to approach this problem from a reverse angle and had the piston still moving down quickly, but the exiting portal also tied to a piston which is moving forward quickly. I found my problem lied in that we were ignoring the state of the exiting portals reference frame and by doing this I found a strange dilemma where the cube would have to adapt to the quickly moving reference frame.

I eventually became ok with this when I realized this is similar to the expansion of space in the universe as caused by the "big bang" where other galaxies are not moving away from us because they have some inherent energy transferred into them, but are made to move faster by the space itself causing it to move faster and faster away from us. How this works, I believe, is that as the cube enters the new reference frame and finds it moving, space transfers the velocity to the cube based on how much of the cube is poking through. So if the piston suddenly stops, the cube will have an amount of energy dependent on how much of the cube got through and move accordingly.

This gives us a means of showing the cube flying through space but does not interfere with the laws of physics either. If the piston continues moving then the cube will remain static with the piston as it has nowhere to go, having the same velocity as the piston and unable to travel back through the portal due to the original piston now being pressed against the ground.

Otto42
05-25-2011, 11:11 AM
Same idea with bending space time continuum. Even if you don't see it happening in 3D, it is completely possible to "bend" the space time continuum to allow the two space to come together.

How much energy do you think the Aperture Science Handheld Portal Device is capable of holding? Enough to bend the entire space time continuum? Or, perhaps, just enough to create portal surfaces which can then transfer selected kinds of matter from one point to another using the energy they gain from their surroundings?

I'm going to have to say they're surfaces and not holes.

(Obvious comeback: you're a hole! :D )

TmanIsHere
05-25-2011, 11:17 AM
How does someone from a 2D universe bend in 3D?

RandoM :D
05-25-2011, 11:23 AM
Why don't you just make a map and test this?.

I think that you can make it with these commands:
"sv_allow_mobile_portal_teleportation"
"sv_allow_mobile_portals"

MutantMonkey
05-25-2011, 11:24 AM
How does someone from a 2D universe bend in 3D?

It's a matter of perspective. :p


Why don't you just make a map and test this?.

I think that you can make it with these commands:
"sv_allow_mobile_portal_teleportation"
"sv_allow_mobile_portals"

It's already been shown that the engine behind Portal 2 is not capable of properly testing this question.

ac1dtrip
05-25-2011, 11:52 AM
Sorry, but I am not ignorant of physics, although you seem to be.

Just to get this out of the way first, the correct answer is B. If you agree, then you're correct. If you think it's A, then you're mistaken.

That said, velocity is a vector quantity, not a scalar one. Speed is only the scalar component of the velocity vector, which includes both speed and direction.

Changing the velocity of a moving object requires a force to act upon it. You can exert force and change velocity *without* changing the speed. For example, if I'm in a spaceship moving along and I fire my rockets at right angles to my course, then my speed can remain unchanged but now I'm travelling in a new direction. This is why we measure fuel consumption in spaceships with "delta-V", which basically means a change in velocity.

Now, if we assume portals exist as given in the game, then they do change the velocity of objects which travel through them. In the case where they are non-moving portals, but in different planes, then they will alter the directional component of the velocity.

Since portals can change the velocity of objects, they must by necessity exert some force on them. That's the only way to change velocity, by exerting a force on the object.

So, since portals can exert force, then they can also change the speed of an object, given the right circumstances. This circumstance happens to be when the portal itself is moving.



A portal must be a solid plane. It touches the object and transfers its component atoms (or whatever it happens to be transferring) instantly to the other portal. I assume it does this using a (magical) quantum level effect of some sort.



True, and because of this, it gains speed when it comes out the other portal. The force pushing the portal onto the object caused a transfer of momentum from the portal (or pushing wall behind it) into the object itself, which is why the box flings out of the other portal.



Mainly quoting this part.
Since portals can change the velocity of objects, they must by necessity exert some force on them. That's the only way to change velocity, by exerting a force on the object.


ROFL as far as the game goes portals DO NOT CHANGE VELOCITY! the velocity of the object entering the portal stays exactly the same. Object enters at x velocity through portal orange it exits through portal blue at same x velocity. What game are you playing seriously? Are you trying to create your own concept of what a portal is and how it works? If so please find another thread thanks.

Otto42
05-25-2011, 11:57 AM
ROFL as far as the game goes portals DO NOT CHANGE VELOCITY!

Yes, they do. Specifically, they can change your direction of motion. Direction of motion is part of "velocity". Change of velocity is integral to the game.

"Velocity" and "speed" are two different things. So please, go learn some basic physics before arguing things you don't understand.

Tensor
05-25-2011, 11:59 AM
Yes, they do. Specifically, they can change your direction of motion. Direction of motion is part of "velocity". Change of velocity is integral to the game.

Please, go learn some basic physics before arguing things you don't understand.

While they do change the directional component of the velocity, they do not change the speed (magnitude) of the velocity vector. So, I believe he meant to say it does not change your speed.

Otto42
05-25-2011, 12:00 PM
While they do change the directional component of the velocity, they do not change the speed (magnitude) of the velocity vector. So, I believe he meant to say it does not change your speed.

This is true, but only because the portals are non-moving. Since the portals are both at rest, their own speed components are zero and don't enter into the equations.

When you start talking about moving portals with non-zero speeds, then that doesn't hold true anymore.

And anyway, any change in velocity at all, even directional, means that the portals must be exerting a force. That was my point, portals must exert force upon things passing through them.

ac1dtrip
05-25-2011, 12:01 PM
Yes, they do. Specifically, they can change your direction of motion. Direction of motion is part of "velocity". Change of velocity is integral to the game.

"Velocity" and "speed" are two different things. So please, go learn some basic physics before arguing things you don't understand.

Show me one instance in the game which is the only place portals exist that we currently know of where the velocity is changed? Or speed for that matter. Only thing that changes your speed or velocity is gravity.

Tensor
05-25-2011, 12:02 PM
This is true, but only because the portals are non-moving. Since the portals are both at rest, their own speed components are zero and don't enter into the equations.

When you start talking about moving portals with non-zero speeds, then that doesn't hold true anymore.

I'm still of the mind to say that the portals only act as a gateway between two different reference frames and should not themselves be treated as a reference frame. That being said, I'm meeting up with some grad students to celebrate my birthday later and I'll see what they think, I may find they disagree with me.

Otto42
05-25-2011, 12:02 PM
Show me one instance in the game which is the only place portals exist that we currently know of where the velocity is changed? Or speed for that matter. Only thing that changes your speed or velocity is gravity.

Whenever your direction changes, your velocity has changed. Not your speed, but your velocity.

Velocity is not speed. These are not the same things at all.

Edit: Read. Learn. http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

ac1dtrip
05-25-2011, 12:11 PM
Whenever your direction changes, your velocity has changed. Not your speed, but your velocity.

Velocity is not speed. These are not the same things at all.

Edit: Read. Learn. http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

Congratulations on not showing me one example in the game where your 'theory' is correct.

Otto42
05-25-2011, 12:13 PM
Congratulations on not showing me one example in the game where your 'theory' is correct.

Okay. Place a portal anywhere. Place another portal at a different angle. Go through. Congratulations, you just found a place where a portal changed your velocity (and NOT your speed).

Insane_Rob
05-25-2011, 12:13 PM
Congratulations on not showing me one example in the game where your 'theory' is correct.

1. Fall in to portal on floor

2. "Fall" out of portal on wall

Direction has changed, velocity has changed, speed has remained constant.

*edit*
ninja'd

ac1dtrip
05-25-2011, 12:14 PM
1. Fall in to portal on floor

2. "Fall" out of portal on wall

Direction has changed, velocity has changed, speed has remained constant.

*edit*
ninja'd

Again as I stated before. Gravity.

Insane_Rob
05-25-2011, 12:16 PM
Again as I stated before. Gravity.

I'm confused as to what you mean, what is gravity doing in this scenario? It's causing you to accelerate downwards. The only thing that has made you change direction is the portal, not gravity.

Otto42
05-25-2011, 12:16 PM
Again as I stated before. Gravity.

Gravity didn't change your direction, the portal did. You went through in one direction, and came out in a different direction.

Look, if you're not willing to learn even the most basic physics principles and want to continue to argue and prove your own ignorance, that's fine, but you can argue with somebody else. I'm done with you.

Thingy Person
05-25-2011, 12:18 PM
Again as I stated before. Gravity.

Insane_Rob's example might entail some accumulated downward velocity as a result of gravity (which means it's not as good an example as Otto42's), but that downward velocity is turned into a horizontal one when you go through the portal.

ac1dtrip
05-25-2011, 12:20 PM
Gravity didn't change your direction, the portal did. You went through in one direction, and came out in a different direction.

Look, if you're not willing to learn even the most basic physics principles and want to continue to argue and prove your own ignorance, that's fine, but you can argue with somebody else. I'm done with you.

If the variable of gravity was taken out of this instance velocity and speed would not change. So yes gravity, NOT direction, changed your velocity and speed.

Sonicjet
05-25-2011, 12:20 PM
Is it possible that it is not the portal moving, but space it's self? say a portal is moving down the piston, could it be that the space the cube is in is moving, acceleration to the portal and the piston attached? This outlook would say that both the cube and the portal are moving, each at half the velocity of the proposed piston thus making up the full collision speed, this would mean that the cube would appear on the other side at exactly half the speed of the piston. These are portals we are talking about, space has to move with them.
Congratulations on not showing me one example in the game where your 'theory' is correct.
Velocity = Speed + Direction a portal on the floor and a second portal on the floor in one going down out the other going up.
Do it in zero G, in one going down, out the other going up. Gravity is irrelevant in this discussion.

Insane_Rob
05-25-2011, 12:21 PM
If the variable of gravity was taken out of this instance velocity and speed would not change. So yes gravity, NOT direction, changed your velocity and speed.

We are now in space, with no gravity.

Two portals are at right angles to one another.

A cube floats in to one and out the other.

It's velocity has just changed solely due to portals.

Understand?

Thingy Person
05-25-2011, 12:21 PM
If the variable of gravity was taken out of this instance velocity and speed would not change. So yes gravity, NOT direction, changed your velocity and speed.

Even in a vacuum, the direction you're moving in still changes as you go through the portal. That means the velocity has changed.

Otto42
05-25-2011, 12:23 PM
If the variable of gravity was taken out of this instance velocity and speed would not change. So yes gravity, NOT direction, changed your velocity and speed.

Speed would not change, but velocity would, because velocity is the combination of speed AND direction of motion.

Please, for the love of Chell, learn some basic physics. Read this link. It explicitly tells you why your statements are nonsense in the first couple of paragraphs.
http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

Mannam
05-25-2011, 12:23 PM
I thought Portals were just holes.

It'd be like if you slammed a hula hoop over the cube.
It wouldn't go flying out the other end.

MutantMonkey
05-25-2011, 12:26 PM
Speed would not change, but velocity would, because velocity is the combination of speed AND direction of motion.

Please, for the love of Chell, learn some basic physics. Read this link. It explicitly tells you why your statements are nonsense in the first couple of paragraphs.
http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

After repeating the same concept multiple times to the same person who constantly ignores legitimate reasoning can only be considered a Troll at which point you must light a torch, wave it at the beast menacingly and say, "BACK TO THE BRIDGES YE DIRTY BEASTY!!!" and then move on with life.

ac1dtrip
05-25-2011, 12:28 PM
Speed would not change, but velocity would, because velocity is the combination of speed AND direction of motion.

Please, for the love of Chell, learn some basic physics. Read this link. It explicitly tells you why your statements are nonsense in the first couple of paragraphs.
http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

Speed would not change, but velocity would, because velocity is the combination of speed AND direction of motion.

Please, for the love of Chell, learn some basic physics. Read this link. It explicitly tells you why your statements are nonsense in the first couple of paragraphs.
http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

Formula wise yes velocity would be changed but speed would not I will agree with that only because velocity involved the variable of direction. Since the speed would not change the portal still does not change the speed at which the object enters or leaves. So your orignal post still about the portal changing the speed is not correct.

Baldrickk
05-25-2011, 12:28 PM
I hate to disagree, seeing all the work you put into your post, but I do. Now bear with me, as this is my first post on a valve forum, and my first post on any forum in quite a while, but here's what I think.

As you said, at the start of the experiment the cube is stationary. Nothing is causing it to move. The only objects moving at the start is the wall/piston with the portal on it, and the portal on the wall/piston (let's just say it's the orange portal). What doesn't make sense (or at least to me) is how the cube gets the momentum to fling out. How could it get the momentum for this? As said, the only thing moving is the piston/wall, which doesn't even touch it, correct? How about the orange portal? Forgive me, as i'm not an expert with this kind of stuff so some of the stuff you said made next to no sense to me, but from what I did understand you seem to think this is its source of momentum (feel free to correct me if I'm wrong), however, the box doesn't really touch the portal, it just goes through it. As for what you said about seeing the box rushing toward you by looking into the portal, imagine this.

Place a portal on a wall and one on the floor. Now, take a cube, and hold it outside the hole in the wall, but don't drop it. What does it look like? Knowing gravity, it looks as if it's going to drop downwards, as if both portals were placed on a wall. However, when you DO drop the cube, it DOESN'T do this at all, it just comes back out the way it came. My point is when it comes to gravity you can't always trust what you see out of a portal. I wish I could provide some pictures in case I explained this poorly, but unfortunately I'm "artistically challenged" and the pictures would probably just confuse everyone even more.

sorry if I simplified this too much, I just wanted to make sure everyone understood what I was saying, as this entire discussion is pretty complex. :p


TL;DR EDITION: Speedy thing goes in, speedy thing comes out. But in this case, there was no speedy thing going in, so I believe the answer is A.

Thing is you have to measure everything relative to the portals, relative to the entry portal, the cube is moving - hence speedy thing.
think of it this way, you have a ring and a rod, you can move the ring over the rod or the rod through the ring, they still move pat each other at the same speed relative to each other.

Sorry, but I am not ignorant of physics, although you seem to be.

Just to get this out of the way first, the correct answer is B. If you agree, then you're correct. If you think it's A, then you're mistaken.

That said, velocity is a vector quantity, not a scalar one. Speed is only the scalar component of the velocity vector, which includes both speed and direction.

Changing the velocity of a moving object requires a force to act upon it. You can exert force and change velocity *without* changing the speed. For example, if I'm in a spaceship moving along and I fire my rockets at right angles to my course, then my speed can remain unchanged but now I'm travelling in a new direction. This is why we measure fuel consumption in spaceships with "delta-V", which basically means a change in velocity.

Now, if we assume portals exist as given in the game, then they do change the velocity of objects which travel through them. In the case where they are non-moving portals, but in different planes, then they will alter the directional component of the velocity.

Since portals can change the velocity of objects, they must by necessity exert some force on them. That's the only way to change velocity, by exerting a force on the object.

So, since portals can exert force, then they can also change the speed of an object, given the right circumstances. This circumstance happens to be when the portal itself is moving.



A portal must be a solid plane. It touches the object and transfers its component atoms (or whatever it happens to be transferring) instantly to the other portal. I assume it does this using a (magical) quantum level effect of some sort.



True, and because of this, it gains speed when it comes out the other portal. The force pushing the portal onto the object caused a transfer of momentum from the portal (or pushing wall behind it) into the object itself, which is why the box flings out of the other portal.

My ignorant of physics quote was because of your stating that an object requires energy to keep moving, whereas that is false. energy may be required to overcome an opposing force (i.e. friction) but that's just balancing forces so that there is no overall force. no force = no acceleration therefor object keeps moving.

I do agree with you that it is B, I've been saying that all along.

Yes, velocity is a vector quantity, but when passing through portal, you do not turn yourself, nor does the portal turn you, instead, you just emerge with a different direction relative to the room. relative to the portals however, you traveled in a straight line. (this is how you can see what is on the other side of a portal, as the light travels in a straight line to reach you,
sorry if I did not make that clear.
Also, there is no force exerted, due to the bending of spacetime. You probably want to wrap your head around that.

The portals do not accelerate / decelerate the cube (this is mainly the flaw that A people find with B arguments) it is just a fact that the cube is moving relative to the entry portal so it only follows that the cube is moving relative to the exit portal (at the same speed [to avoid you moaning about velocity again] as it entered)

Portals link two points in spacetime, there is no teleportation and no forces involved. Portals are formed on surfaces, as a game play mechanic, with the possible explanation that a solid structure is needed to project the portal onto it, however there is no surface there when you try to move through the portal.

I'm still of the mind to say that the portals only act as a gateway between two different reference frames and should not themselves be treated as a reference frame. That being said, I'm meeting up with some grad students to celebrate my birthday later and I'll see what they think, I may find they disagree with me.

True the entrance and exit spaces must be treated as different reference frames, but you need to have a common ground to fin some way of equating the two, this is where the portals come in, they are a common point of 'contact' between the reference frames, so in fact, you can measure everything with respect to the portal on both reference frames, and everything still holds true.

Whenever your direction changes, your velocity has changed. Not your speed, but your velocity.

Velocity is not speed. These are not the same things at all.

Edit: Read. Learn. http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm

Only in common reference frames, the portals bend spacetime, relative to the portals, the cube / player / whatever doesn't change their velocity, by extension, from each of the entry and exit reference frames, the velocity does not change, 'you see a cube coming at you through a hole in the wall, it pops out and keeps coming', it is just from an outside observer's perspective, trying to link the two seperate frames of reference together with respect to their environment, i.e. the earth, that direction of travel appears to change.

MutantMonkey
05-25-2011, 12:28 PM
I thought Portals were just holes.

It'd be like if you slammed a hula hoop over the cube.
It wouldn't go flying out the other end.

The reason that is not the case is because the "exit" of the portal is stationary. If you had a hula-hoop and had an entrance and exit attached to it, you would be correct because both portal are moving at the same speed relative to the cube meaning the relative speed at which the cube enters the hula-hoop is being negated by the backward movement of the exit portal.

Thingy Person
05-25-2011, 12:30 PM
Is it possible that it is not the portal moving, but space it's self? say a portal is moving down the piston, could it be that the space the cube is in is moving, acceleration to the portal and the piston attached? This outlook would say that both the cube and the portal are moving, each at half the velocity of the proposed piston thus making up the full collision speed, this would mean that the cube would appear on the other side at exactly half the speed of the piston. These are portals we are talking about, space has to move with them.

This depends on the reference frame. In relation to the orange portal, yes, space moves, but you could say the same about a ball that you throw into the air. In the case of the portal, it gets especially tricky since there are seemingly two spaces at either side that are actually the same space. If you presume that it's space as a whole that moves, then you have to find an explanation for a room changing its position relative to an object on the other side of a portal, while the same room is not moving if you don't look at it through the portal. For example, you can have a portal move away from a piece of cake and out of your reach if you tried to grab it through the portal, but it can still be right next to you. That's why I think it's better to just take the Portal as being the moving element.

Insane_Rob
05-25-2011, 12:31 PM
If the variable of gravity was taken out of this instance velocity and speed would not change.

Formula wise yes velocity would be changed

This is all anyone was clearing up.

DAN07
05-25-2011, 12:32 PM
You take this game way to seriously.

ac1dtrip
05-25-2011, 12:32 PM
This is all anyone was clearing up.

Thanks. I haven't opened a physics book in 20 yrs.

Otto42
05-25-2011, 12:36 PM
I thought Portals were just holes.

It'd be like if you slammed a hula hoop over the cube.
It wouldn't go flying out one end.

If you think of portals that way, then yes. However, that doesn't necessarily make sense given other aspects of them.

There's basically two ways to look at them:

1. Holes in space connecting two separate points.

2. Transmitters which transmit things from one portal to another.

The problem is the change of direction. Portals do conserve momentum, because momentum is mass times speed. The question is whether the momentum being conserved is that of only the object or that of the system of both the object and the portal itself.

If you look at them as holes in space, then the box won't move, because nothing acted upon it. The problem with this approach is that it leads to free energy, basically. If you can change an objects position without any energy expenditure whatsoever, then you can work that into a way to create free energy.

If you look at them as transmitters of some form, then the portal is a surface acting upon the object, which means that it is acting on the whole system. Momentum of the system itself would be conserved in this case, and the portal would expend some amount of energy from somewhere to move the object to the other portal. In such a case, the energy of the portal's own motion would make the box jump in the air when it exited the other portal. This method doesn't lead to a free energy case, because energy had to be expended to make the movement from one to the other happen.

The first case defies the laws of physics if you limit it to three dimensions. If you assume that it's pulling energy out of another dimension (due to the bending of spacetime in some way), then it's not really "free" energy anymore and that's all right. Of course, in this case, it would be "free enough" to make practical use of.

The second case defies no physical laws we know of, except for the whole "magic" quantum teleportation bit, which is hazy and undefined at best. It's feasible given what we do know about how the universe works.

Mannam
05-25-2011, 12:39 PM
The reason that is not the case is because the "exit" of the portal is stationary. If you had a hula-hoop and had an entrance and exit attached to it, you would be correct because both portal are moving at the same speed relative to the cube meaning the relative speed at which the cube enters the hula-hoop is being negated by the backward movement of the exit portal.

Alright, yeah, that explanation alongside the pole experiment totally makes sense.

Thanks.

Gordon Nukem
05-25-2011, 12:45 PM
I made these animations to personally help myself visualize these situations a little bit better. Some of you might find them useful I guess.

Situation A (http://www.swfcabin.com/open/1306350076) | Situation B (http://www.swfcabin.com/open/1306350058) | Halfway through (http://www.swfcabin.com/open/1306350017)

Edit: For some reason swfcabin takes forever to load. Just bare with it.

Dzjudz
05-25-2011, 01:53 PM
The Pole Example

http://imageshack.us/f/818/pic4x.png/

This example is much more representative of the relation of the orange portal, the blue portal, and what goes through them.

Imagine that we have the same situation, but the cube sits on a pole instead. It's nearly the same situation, except there's a pole.

When the cube and the pole go through the blue portal, they come out of it at 10 m/s.

If you ignore the portals and just think about a very small platform coming through the floor of that room, it can be proven with physics that an object sitting on it would fly into the air if it suddenly stopped.

When the orange portal finally hits the floor, the pole (or small platform, whichever you would like to call it) would stop, and due to the cube's inertia, the cube would keep going.

This example is not unlike the first one, it's just that there's a pole. As stated before, objects going through a portal are affected by that portal. Objects already through the portal are unaffected by the portal, because a portal changes positions in space, and the only thing that the portal keeps changing is the pole. If a cube has a pole accelerating under it, it will accelerate and move up; this can be, and probably has been proven. The "flying up" of the cube can be proven through inertia.

As said before, it's very similar to the actual situation that is being argued. I just had to add a pole to make the situation more understandable. Although the pole is being affected throughout the example, the portals only affect it's speed in relation to the cube; nothing else.This example presupposes that gravity fields do not permeate through portals. What if the portal stops halfway down the cube? The top half somehow has 10m/s momentum upwards but the bottom half is stationary.

Macedragon37
05-25-2011, 01:57 PM
This example presupposes that gravity fields do not permeate through portals. What if the portal stops halfway down the cube? The top half somehow has 10m/s momentum upwards but the bottom half is stationary.

Teehee. You might want to read what you just typed. ;)

Of course gravity fields don't go through portals. If they did, the second you shot 2 portals, everything would be out of wack.

And about the "read what you just typed" thing, you just said that the top half of the cube is 10 m/s. If the portal stops moving, the cube stops moving in relation to the blue portal.

MutantMonkey
05-25-2011, 02:21 PM
This example presupposes that gravity fields do not permeate through portals. What if the portal stops halfway down the cube? The top half somehow has 10m/s momentum upwards but the bottom half is stationary.

What would happen is the momentum the exiting portion of the cube would pull on the portion that hasn't made it through. Depending on how much force that actually is, the cube would either pull itself through or remain where it was.

Now, the above scenario assumes that the transition in portals is clean. When I was discussing this with a physics friend, we started talking about the possibility of their being a tine gap between the portals where particles are separated and then put back together, in which case the results could be gruesome. Anything from the exposed portion being ripped from the rest of the "body" or just an absolute disintegration of the object going through.

Dzjudz
05-25-2011, 02:21 PM
Teehee. You might want to read what you just typed. ;)

Of course gravity fields don't go through portals. If they did, the second you shot 2 portals, everything would be out of wack.

And about the "read what you just typed" thing, you just said that the top half of the cube is 10 m/s. If the portal stops moving, the cube stops moving in relation to the blue portal.So... if there's just one tiny minuscule part of the cube left in the old room when the piston stops the cube won't move, but if that tiny minuscule part does move through the portal before the piston stops the cube will shoot away?

Dzjudz
05-25-2011, 02:24 PM
What would happen is the momentum the exiting portion of the cube would pull on the portion that hasn't made it through. Depending on how much force that actually is, the cube would either pull itself through or remain where it was.

Now, the above scenario assumes that the transition in portals is clean. When I was discussing this with a physics friend, we started talking about the possibility of their being a tine gap between the portals where particles are separated and then put back together, in which case the results could be gruesome. Anything from the exposed portion being ripped from the rest of the "body" or just an absolute disintegration of the object going through.So you're saying that depending on the deceleration of the piston the cube will stay still, make a slight hop but not go through, or go through altogether?

Apollo33
05-25-2011, 02:33 PM
The portals can't be "sucking" as you say or objects would come out with more momentum than they had when they entered. You're also creating energy out of nowhere. In your theory, a portal falling over a stationary cube would shoot it out with some momentum. Then what happens if a portal falls over a huge stack of cubes? Do you say it will shoot every cube out with that same momentum? Unless the portal has some external power source, this doesn't make sense... And even then you would be suggesting that an unimpeded portal literally couldn't pass over a really massive object unless it had enough energy to do so.

IcarusNine
05-25-2011, 02:36 PM
This example presupposes that gravity fields do not permeate through portals. What if the portal stops halfway down the cube? The top half somehow has 10m/s momentum upwards but the bottom half is stationary.
If you slap someone, their head will gain sideways momentum, but the rest of their body isn't going to notice until their neck decides it has enough tensile strength to keep their head attached.

An object is composed of smaller parts, each with its own momentum.

MutantMonkey
05-25-2011, 02:36 PM
So you're saying that depending on the deceleration of the piston the cube will stay still, make a slight hop but not go through, or go through altogether?

No that is not what I said. Please read it again.

Dzjudz
05-25-2011, 02:36 PM
A more interesting problem:

3 Cube Tower (http://imageshack.us/m/806/9549/abcl.png)

What happens to Cube A, Cube B and Cube C respectively?

MutantMonkey
05-25-2011, 02:39 PM
A more interesting problem:

3 Cube Tower (http://imageshack.us/m/806/9549/abcl.png)

What happens to Cube A, Cube B and Cube C respectively?

A flies.

B moves. How much is dependent on the amount of force the portion of the cube that is through the portal applies to the rest of the cube.

C does nothing.

Dzjudz
05-25-2011, 02:44 PM
No that is not what I said. Please read it again.It is though. You are saying that if the deceleration is abrupt it shoots through but if it is gradual then the cube will stay still.

MutantMonkey
05-25-2011, 02:48 PM
It is though. You are saying that if the deceleration is abrupt it shoots through but if it is gradual then the cube will stay still.

Ah, gotcha. Yes it would remain there.

Dzjudz
05-25-2011, 02:48 PM
Extreme deceleration would mean tearing the object in half then :).

MutantMonkey
05-25-2011, 02:53 PM
Extreme deceleration would mean tearing the object in half then :).

Could, not would. It depends on the amount of force it takes to rip that object in half vs the amount of force it would take for that object to pull itself through vs. the amount of force that object can inherently withstand before fracturing/ripping. If we are still talking to the cube, the amount of force to rip it in half is probably quite a bit more than the force required for the cube just to pull itself through.

Pheonix Wright
05-25-2011, 03:02 PM
It's A. the object comes out with the same velocity the object had going in. If I move a door frame at 60mph and you jump through the middle of it your not gonna be going 60mph....

Macedragon37
05-25-2011, 03:19 PM
It's A. the object comes out with the same velocity the object had going in. If I move a door frame at 60mph and you jump through the middle of it your not gonna be going 60mph....

I'm sorry, but I have to disagree. Portals have the ability to change the force and direction of things that go through them. Pretend that you're the orange portal. If you accelerate towards the cube, or the cube accelerates towards you, it doesn't really matter. The cube will go through you at the same speed in both situations.

Also, the door frame analogy is somewhat flawed, considering that if you only thought about a door frame and nothing else, you'd go through the door, and the door would then keep accelerating away from you. If you keep the frame of reference as the door, to the door, you're moving.

Dzjudz
05-25-2011, 03:30 PM
You're not just moving the door, you are moving the entire reality behind it with it. After you go through the door, not only will the door be moving away from you at 60mph, you will be moving through your new surroundings at 60mph.

wits
05-25-2011, 04:12 PM
A more interesting problem:

3 Cube Tower (http://imageshack.us/m/806/9549/abcl.png)

What happens to Cube A, Cube B and Cube C respectively?

Actually, you can only stack 2 cubes, anymore will make them all fall. Seems to be something in the code.

Pheonix Wright
05-25-2011, 04:27 PM
I'm sorry, but I have to disagree. Portals have the ability to change the force and direction of things that go through them. Pretend that you're the orange portal. If you accelerate towards the cube, or the cube accelerates towards you, it doesn't really matter. The cube will go through you at the same speed in both situations.

Also, the door frame analogy is somewhat flawed, considering that if you only thought about a door frame and nothing else, you'd go through the door, and the door would then keep accelerating away from you. If you keep the frame of reference as the door, to the door, you're moving.

they keep the same momentum and direction they only change position in space otherwise you'd be going in and out with different momentum's in game...

Dzjudz
05-25-2011, 04:32 PM
they keep the same momentum and direction they only change position in space otherwise you'd be going in and out with different momentum's in game...In-game you don't go through moving portals.

Pheonix Wright
05-25-2011, 04:33 PM
You're not just moving the door, you are moving the entire reality behind it with it. After you go through the door, not only will the door be moving away from you at 60mph, you will be moving through your new surroundings at 60mph.

portals reposition only what goes through them not the fabric of reality:rolleyes: if what you said was true you would see rooms break and look like they were drawn by MC Escher whenever you opened up a portal anywhere...

Pheonix Wright
05-25-2011, 04:36 PM
In-game you don't go through moving portals.

that doesn't change what I just said...it still applies:rolleyes:

Dzjudz
05-25-2011, 04:43 PM
Instead of the door example you should think of it more like a train.

Imagine the doorway being on the front of a train. That train moves toward you with 60mph. You jump through the door. Now you are moving 60mph through the train, going rapidly from the front of the train to the back.

The same goes with a portal. Let's say you have one portal on a door, and the other portal on a wall inside a room. Now you stick that portal on the front of that same train that moves toward you with 60mph. You will see the room coming at you with 60mph. Jumping through the portal will now shoot you from the wall portal with 60mph going to the opposite wall in the room.

wads
05-25-2011, 05:07 PM
i haven't read this entire thread, but the solution seems obvious if you think about it right. I'm surprised to see there is so much disagreement.

given the nature of the portals, one only needs to consider two properties:

let #1 be the relative velocity of the moving portal and the cube

let #2 be the relative velocity of the two portals

for #1=0, you have the trivial case, where nothing happens.

for #1=| 0, you have two choices,

in the case of #2=0, you will have the cube 'plop' out. this corresponds with dropping the room on the cube. (assuming both portals is in the room)

for #2 =| 0, you have the general case as described by the original problem, the velocity of the cube after it exits the portal is a simply matter of vector addition. therefore the cube will shoot out if the moving portal is going fast enough. you simply add #1 to #2. for a stationary exit portal(relative to the cube), the cube exit velocity is just the original relative velocity.

this problem has nothing to do with acceleration whatsoever. gravity only comes into play if you wanted to calculate the trajectory of the cube AFTER it leaves the exit portal.

edit: i have a degree in physics, working on phd.

edit2: the issue with an object being half and half through the portal, as well as the moving portal stopping after the box is through is solved by assuming the interface between the 2 portals is infinitely thin(a valid assumption), and that the object in question be a point mass.

in other words, at the instant in time when the point mass is in contact with the moving portal, it is in two places at once. then there is no issue.

of course, that's not a valid assumption irl, but we're talking about portals here.

edit3: after thinking about this further, i admit that this problem isnt at obvious as simple or obvious as i first thought.

from reading a few of the arguments about forces and transfers of momentum( or the lack thereof) i can see a major point of confusion.

people are applying real physical principles of physics to analyze the problem. however the problem requires an unphysical postulate. the surface that connect the two portals needs to be treated essentially as a discontinuity in space. therefore mass is not traveling between the portals, instead mass is 'magically' destroyed then recreated at the other end, and given the same momentum it had previously. if you look at the problem in that way you will see that the issues people bring up about momentum or force can be eliminated.

Apollo33
05-25-2011, 06:00 PM
/thread ... this guy has a b.s. in physics

except what we're discussing is physically impossible, and that's why no one will ever agree. a room with one or both portals moving can't be simultaneously one solid (physically consistent) room and also warping space all around in different directions.

edit:
therefore mass is not traveling between the portals, instead mass is 'magically' destroyed then recreated at the other end, and given the same momentum it had previously. if you look at the problem in that way you will see that the issues people bring up about momentum or force can be eliminated.
so now you've changed to saying a cube at rest will plop out regardless of the speed of the moving portal that goes over it?

wads
05-25-2011, 06:21 PM
/thread ... this guy has a b.s. in physics

except what we're discussing is physically impossible, and that's why no one will ever agree. a room with one or both portals moving can't be simultaneously one solid (physically consistent) room and also warping space all around in different directions.

edit:

so now you've changed to saying a cube at rest will plop out regardless of the speed of the moving portal that goes over it?

no. it will keep the same velocity it had before entering the portal. and like all velocities, it's a relative velocity.

basically what i mean to say with that last edit is the fact that portals and the object need not touch to exchange energies.

MeStinkBAD
05-25-2011, 06:47 PM
Ummm... you people should stop focusing on the portals. Focus on the cube. From it's perspective, everything else is moving and it's stationary. This is key for solving this odd "what-if" question you've asked.

MutantMonkey
05-25-2011, 06:49 PM
Ummm... you people should stop focusing on the portals. Focus on the cube. From it's perspective, everything else is moving and it's stationary. This is key for solving this odd "what-if" question you've asked.

You can look at it from the perspective of the fly on the wall, the result would still be the same.

MeStinkBAD
05-25-2011, 06:58 PM
You can look at it from the perspective of the fly on the wall, the result would still be the same.

But no one can agree on the result right now lol.

Apollo33
05-25-2011, 07:12 PM
no. it will keep the same velocity it had before entering the portal. and like all velocities, it's a relative velocity.

basically what i mean to say with that last edit is the fact that portals and the object need not touch to exchange energies.
So you saw there's an issue with conservation of energy/momentum, and your answer is to just assume that the portal has an infinite store of energy to transfer to every object it goes over?

Here's what doesn't make sense to me: it requires a fixed amount of energy to move a portal up and down over objects that are sitting on the ground under it. You're saying that if we put a ping-pong ball under the portal, and the portal comes down over it at 10m/s, the ball is injected with whatever energy is needed to move at 10m/s out of the other portal. But then if you sit a 15lb bowling ball under the portal, the portal comes down and the ball gets a huge amount of energy to fly up in the air at 10m/s. And somehow the portal is determining the mass of the objects and pulling energy out of the ether to give them a velocity.

This does make sense if you're assuming that the room behind the moving portal is actually moving with it at 10m/s... but if it's all the same room and you see that the room is NOT moving, it doesn't make sense.

So what makes sense to me is to think of the portals as "point teleporters" that simply teleport the object to the other portal with whatever energy/momentum it had when the portal hit it. If the object has no momentum, then regardless of the speed of the portal/teleporter, when the portal hits the object (or its center of mass) it's teleported to the other portal and has no momentum there.

Meallme0
05-25-2011, 07:16 PM
So, what, if I place a cube on the ground, then move a door frame through it extremely fast, will the cube rocket out the other side?

Macedragon37
05-25-2011, 07:43 PM
they keep the same momentum and direction they only change position in space otherwise you'd be going in and out with different momentum's in game...

I don't think that you understand the significance of the situation that is being presented. The point of the situation, the one that has cused this whole debate, is reliant on the fact that a portal is moving, instead of the thing going through it.

When, in the game, do you go through a portal flying towards you? Never. You don't go in and out with different momentums in the game, because in the game, the portals are pretty much never moving with respect to one another.

Macedragon37
05-25-2011, 07:48 PM
So, what, if I place a cube on the ground, then move a door frame through it extremely fast, will the cube rocket out the other side?

No, because you said "the ground". This is a change in reference point.

Unless of course you didn't mean that, then I will respond carefully. Yes, it would look like the cube was rocketing away from you. Because, no matter what's moving, the door frame or the cube, either way the distance between them will quickly grow. If those are the objects that you're examining, then yes, the cube would look like it was rocketing away from the door, whether the door's doing the moving, or the cube is.

Macedragon37
05-25-2011, 07:52 PM
portals reposition only what goes through them not the fabric of reality:rolleyes: if what you said was true you would see rooms break and look like they were drawn by MC Escher whenever you opened up a portal anywhere...

Heh, yeah, he's right. You're not "moving reality", the portals only change what goes through them.

wads
05-26-2011, 03:04 AM
So you saw there's an issue with conservation of energy/momentum, and your answer is to just assume that the portal has an infinite store of energy to transfer to every object it goes over?

Here's what doesn't make sense to me: it requires a fixed amount of energy to move a portal up and down over objects that are sitting on the ground under it. You're saying that if we put a ping-pong ball under the portal, and the portal comes down over it at 10m/s, the ball is injected with whatever energy is needed to move at 10m/s out of the other portal. But then if you sit a 15lb bowling ball under the portal, the portal comes down and the ball gets a huge amount of energy to fly up in the air at 10m/s. And somehow the portal is determining the mass of the objects and pulling energy out of the ether to give them a velocity.

This does make sense if you're assuming that the room behind the moving portal is actually moving with it at 10m/s... but if it's all the same room and you see that the room is NOT moving, it doesn't make sense.

So what makes sense to me is to think of the portals as "point teleporters" that simply teleport the object to the other portal with whatever energy/momentum it had when the portal hit it. If the object has no momentum, then regardless of the speed of the portal/teleporter, when the portal hits the object (or its center of mass) it's teleported to the other portal and has no momentum there.

this whole argument is basically equivilent to arguing about how a lightsaber works, or not warp drives work. you cant use real life physics to explain it. the best explanation is one where you make unphysical assumptions.

also, many people are forgetting that the relative motion between the portals is just as important as the motion between the object.

in the game the two portals are always in the same frame of reference. this is not the case when only 1 of the portals is moving. as i've said in my first post.

bottom line, the object will move how the programmers of the game programmed it to move. there is no real physical law to predict how it will move.

Dzjudz
05-26-2011, 04:08 AM
Ummm... you people should stop focusing on the portals. Focus on the cube. From it's perspective, everything else is moving and it's stationary. This is key for solving this odd "what-if" question you've asked.From the cube's point of view: you are first stationary in a room with a piston coming at you very fast, through the portal on the piston, you see a room moving very fast towards you as well. When the piston passes you, you are suddenly inside a new room, but you are moving very quickly through it. Whether the piston now stops or not, this does not stop you from continuing to move very fast through the room. This is because once you through the portal, the relative motion of the portals stops having an effect on you.

In the new room, the point of view of the cube is pretty much that of a person standing on top of a moving car, pretending that he is stationary and the world is moving around him instead. The car suddenly stopping won't stop him from still moving forward through the world.

Tensor
05-26-2011, 04:40 AM
I'm still of the mind to say that the portals only act as a gateway between two different reference frames and should not themselves be treated as a reference frame. That being said, I'm meeting up with some grad students to celebrate my birthday later and I'll see what they think, I may find they disagree with me.

I discussed it with the grad students and they actually made a believer out of me so I am now changing my stance. I guess my problem originally was how it was being discussed but they have since convinced me that the cube will go flying out of the second portal when the piston comes down on it.

ac1dtrip
05-26-2011, 06:24 AM
Holy tripple hijacked thread batman.

MutantMonkey
05-26-2011, 06:30 AM
I discussed it with the grad students and they actually made a believer out of me so I am now changing my stance. I guess my problem originally was how it was being discussed but they have since convinced me that the cube will go flying out of the second portal when the piston comes down on it.

I'm curious what they told you that made you a believer because a lot of the concepts they would have told you about have been mentioned numerous times in this and the other thread.

Maggus
05-26-2011, 07:22 AM
so thats it?
we (B voters) are right? B seems so be correct?

after 5 seconds of thinking about the picture when i first saw it, my conclusion was B because of the portal reference. Some days later someone confirms the same idea with this tread that i was having too (of course better explained).

now Tensor talked to some students and now he changed his mind and confirms this?

Baldrickk
05-26-2011, 07:22 AM
I'm curious what they told you that made you a believer because a lot of the concepts they would have told you about have been mentioned numerous times in this and the other thread.

I wouldn't worry too much about what, its probably someone sitting sown with you and explaining it and being able to reiterate or approach something you don't understand from a different direction that helps.

if on the other hand there was something that they told you that really shifted your views, then please share.

MutantMonkey
05-26-2011, 07:24 AM
so thats it?
we (B voters) are right? B seems so be correct?

after 5 seconds of thinking about the picture when i first saw it, my conclusion was B because of the portal reference. Some days later someone confirms the same idea with this tread that i was having too (of course better explained).

now Tensor talked to some students and now he changed his mind and confirms this?

It's B. No doubt about it.

Maggus
05-26-2011, 07:26 AM
win!!!
(sry i had to do this :D)

Baldrickk
05-26-2011, 07:58 AM
it has to be B. I mean, even if you don't look at the physics and read posts, A people seem to still have problems with what would happen in every case.
B people seem to have an answer for everything that is thrown at them.
I think that's the main cause of the 5 mins of A people being the only ones posting and saying "ok A is impossible but we don't agree with B either, so we'll just say both are impossible"
whereas B people are yet to have a flaw in their reasoning being pointed out.

*there have been cases where b people have said silly things and these have been called out and fixed or re-explained correctly by someone else.

Freeze-18
05-26-2011, 04:46 PM
Ok, really? Do you need a whole new thread to say your opinion is B? Jesus.

http://lastopp.no/3/57a9c3c9dd642f027ed2168daba59511.png

Situation B seems unlikely to me. That's all. Not going to make a new thread to show the world either.

But I'm willing to change stances. I just don't understand why the cube would be "sucked up" into the portal here.

I understand the momentum transferring that's implied here, but the portal doesn't actually 'hit' the object so I don't see how that would work.

maddios
05-26-2011, 05:02 PM
Thread is tl;dr.

Why is it B? A box that is not moving enters the portal and suddenly it gains momentum?

StarCraft
05-26-2011, 05:06 PM
Ok, really? Do you need a whole new thread to say your opinion is B? Jesus.

I think it's A, anyway. Here's why...

http://lastopp.no/3/57a9c3c9dd642f027ed2168daba59511.png

Situation B seems incredibly unlikely to me.

I understand the momentum transferring that's implied here, but the portal doesn't actually 'hit' the object so I don't see how that would work.



exactly, why anyone would think it's b is beyond me. unless portals all of a sudden have / can create movable / potential energy, which in portal they do not. if your talking about real life physics, you don't know that since portals are not real.

another example: http://www.youtube.com/watch?v=B6wntWQ3zn4#t=5m00s

I don't see how it could be B, at least not in the game Portal.

_Depression
05-26-2011, 05:06 PM
Read: http://forums.steampowered.com/forums/showthread.php?t=1906183

maddios
05-26-2011, 05:10 PM
Read: http://forums.steampowered.com/forums/showthread.php?t=1906183

That doesn't answer my question. He says the cube part of the cube gains momentum as soon as that part exits the blue portal. Again, since when do portals affect momentum in any way?

_Depression
05-26-2011, 05:20 PM
That doesn't answer my question. He says the cube part of the cube gains momentum as soon as that part exits the blue portal. Again, since when do portals affect momentum in any way?

The portals aren't affecting momentum. Let me see if I can extrapolate a little:

"...as [the cube] emerges from the blue side, it must have speed equal to that of the moving orange portal." Portals don't affect an objects momentum, but an object does enter through a portal at some velocity "x" that must transfer exactly to the exit portal. That's why the cube has momentum, because "[t]he momentum of the blue side would be "created" as discrete portions of the cube's mass teleported and were instantaneously at speed."

At the end of his email, Kircher states that "It [momentum] must necessarily result from whatever energy goes into warping space such that a portal can not only exist, but move."

CatatonicMan
05-26-2011, 05:30 PM
That doesn't answer my question. He says the cube part of the cube gains momentum as soon as that part exits the blue portal. Again, since when do portals affect momentum in any way?

Portals preserve momentum, but only with respect to each other.

With respect to the room, portals not parallel to each other change momentum (though not speed). If a portal is moving, it can change speed as well.

Dzjudz
05-26-2011, 05:30 PM
exactly, why anyone would think it's b is beyond me. unless portals all of a sudden have / can create movable / potential energy, which in portal they do not. if your talking about real life physics, you don't know that since portals are not real.

another example: http://www.youtube.com/watch?v=B6wntWQ3zn4#t=5m00s

I don't see how it could be B, at least not in the game Portal.It is because you fail to realise the difference between these two situations:
- two stationary portals and you moving through them (the video you linked).
- one of the portals moving toward you.

Let's take that video you linked. Let's say the piston you are standing on moves up at a rate of 5 m/s. You agree that this results in you shooting out the other portal at 5 m/s right?

Now consider the following change: instead of that blue portal above you being stationary, it is also on a piston, but moving down toward you at 5 m/s. This would result in you shooting out the other portal at 10 m/s, not 5 m/s.

You can think of it like this: how fast am I moving through the portal? Let's say you are 2 meters tall. In the first cast of only you moving upwards at 5 m/s, you would move through the portal in 0.4 seconds. However, in the second case the blue portal is also moving down toward you at 5 m/s. This means you are going through the portal twice as fast, you will be through in 0.2 seconds. This also means that your exit speed must be twice as fast as the first case.

StarCraft
05-26-2011, 05:58 PM
It is because you fail to realise the difference between these two situations:
- two stationary portals and you moving through them (the video you linked).
- one of the portals moving toward you.

Let's take that video you linked. Let's say the piston you are standing on moves up at a rate of 5 m/s. You agree that this results in you shooting out the other portal at 5 m/s right?

Now consider the following change: instead of that blue portal above you being stationary, it is also on a piston, but moving down toward you at 5 m/s. This would result in you shooting out the other portal at 10 m/s, not 5 m/s.

You can think of it like this: how fast am I moving through the portal? Let's say you are 2 meters tall. In the first cast of only you moving upwards at 5 m/s, you would move through the portal in 0.4 seconds. However, in the second case the blue portal is also moving down toward you at 5 m/s. This means you are going through the portal twice as fast, you will be through in 0.2 seconds. This also means that your exit speed must be twice as fast as the first case.

If portals have an affect in momentum, then I guess your right. I just believed that portals transfered you to the other side, regardless of which the speed of the portal was approaching you at. you would just go through the portal quicker, without any change in speed and momentum if you where stationary. thanks.

_Depression
05-26-2011, 06:12 PM
If portals have an affect in momentum, then I guess your right. I just believed that portals transfered you to the other side, regardless of which the speed of the portal was approaching you at. you would just get there quicker (go through the portal quicker), without any change in speed and momentum if you where stationary. thanks.

It doesn't affect momentum, though, that's the point. Think of it this way:

Think of an object as made up of 10 layers of 1-inch-tall blocks stacked vertically. As the top block goes "through" the orange portal, that block comes out of the blue portal - and with every block that comes through, that first block has to move one inch farther out of the portal to accomodate the rest of it that is coming through. That block now has a velocity, and therefore momentum, because the blocks beneath it are in a sense pushing it farther out of the portal.

It's not really the portal that's giving an object momentum, it's the object giving itself momentum.

Macedragon37
05-26-2011, 06:57 PM
Updated with the link to David Kirchers email thread.

http://forums.steampowered.com/forums/showthread.php?t=1906183

_Depression
05-26-2011, 08:27 PM
Gotta love Dave

rafman400
05-26-2011, 08:33 PM
I vote for situation A

OJ191
05-26-2011, 10:02 PM
Portals do not affect momentum of objects travelling through them in any way. They are like a hole in a wall. If you throw a cube through that hole, it will retain all of it's momentum. If you slam a mashy spike plate with a hole in the middle down onto a cube, the cube will not move, but it will pass through the hole. Now imagine if you could put the other end of the hole ANYWHERE YOU WANT yet it has NO effect on how it acts until the cube is out the other side.

Slam a mashy spike plate (spikes removed) with a portal on it, onto a cube, and the cube will dribble out the other end. It would stay put, except when the plate hits the ground there is no longer any room for the cube on that side of the portal, it passes through. But all movement is done by the portal not by the cube, there is NO momentum imparted because there is no physical contact to transfer momentum.

EDIT: If portals could affect momentum then there would be no "speedy thing goes in, speedy thing comes out". You would either be accelerated or decelerated depending on how it worked. But you wouldn't keep the same speed.

CasualT2
05-27-2011, 12:29 AM
I'd say B. Simply because A wouldn't make sense.

I'll let others do the explaining.

Baldrickk
05-27-2011, 01:09 AM
Thread is tl;dr.

Why is it B? A box that is not moving enters the portal and suddenly it gains momentum?
Look at the .gif in OP of original thread. Do you agree with the cube moving as it exits the portal? I.e. growing from the floor.
Now, a cube has mass, and if it is moving as in the .gif, an image that people agree on, then it also has momentum.
Oh look, there's your momentum.
Unfortunately the explanation for it being there is a somewhat more complex version of: The portal is a folding of spacetime, that when one end is moved in relation to the other, changes the relative point of contact between two points, while changing the point of contact. This results in one part of the world moving in relation to the other, while from an outside observer's point of view, due to an observer not being in the same frame of reference of the portals, the world remains constant and unchanging.
In short, the universe moves while staying still.

exactly, why anyone would think it's b is beyond me. unless portals all of a sudden have / can create movable / potential energy, which in portal they do not. if your talking about real life physics, you don't know that since portals are not real.

another example: http://www.youtube.com/watch?v=B6wntWQ3zn4#t=5m00s

I don't see how it could be B, at least not in the game Portal.

I'll quote myself here, as it's been agreed that portals don't conserve energy:
I place a portal on the ceiling and another beneath your feet. Enjoy your free potential

It doesn't affect momentum, though, that's the point. Think of it this way:

Think of an object as made up of 10 layers of 1-inch-tall blocks stacked vertically. As the top block goes "through" the orange portal, that block comes out of the blue portal - and with every block that comes through, that first block has to move one inch farther out of the portal to accomodate the rest of it that is coming through. That block now has a velocity, and therefore momentum, because the blocks beneath it are in a sense pushing it farther out of the portal.

It's not really the portal that's giving an object momentum, it's the object giving itself momentum.

That is another way of thinking about it, thanks. In the end though, I don't think it matters exactly how it works, as long as we know the outcome.
It's like gravity; we know it exists and can model it very precisely. We don't however know how it works (yes we understand distorting spacetime, but why does that happen?) We can make guesses, the latest being the Higgs Boson, but we don't know why it happens, not yet at least. We can however see its effects, kinda like portals.

Portals do not affect momentum of objects travelling through them in any way. They are like a hole in a wall. If you throw a cube through that hole, it will retain all of it's momentum. If you slam a mashy spike plate with a hole in the middle down onto a cube, the cube will not move, but it will pass through the hole. Now imagine if you could put the other end of the hole ANYWHERE YOU WANT yet it has NO effect on how it acts until the cube is out the other side.

Slam a mashy spike plate (spikes removed) with a portal on it, onto a cube, and the cube will dribble out the other end. It would stay put, except when the plate hits the ground there is no longer any room for the cube on that side of the portal, it passes through. But all movement is done by the portal not by the cube, there is NO momentum imparted because there is no physical contact to transfer momentum.

EDIT: If portals could affect momentum then there would be no "speedy thing goes in, speedy thing comes out". You would either be accelerated or decelerated depending on how it worked. But you wouldn't keep the same speed.

Ok, working backwards for the hello of it. You are mixing up velocity and speed, velocity is a function of speed and direction. Direction can change, this requires acceleration, without a change in speed. As momentum is a function of velocity and mass, the momentum would change with velocity but not (necessarily) with speed.

You are stating that no matter what speed you enter a portal, you come out at a constant slow speed. (have you even played the game?) Most puzzles would be impossible were that the case.

Portals are not just holes, they are holes linking two points. While you did kinda get this, you then said that something passing through is not affected by the other side until it has passed through.
Here's a thought experiment. Put a portal on a wall. Put another between 2 walls with say, 5cm gap, I.e. not enough to squeeze your body into.
By your reckoning, you can pass through the portal all the way, without hitting the wall, only coming into contact with it after you have finished passing through. If course you are halfway through said wall at this time.

Hilarity ensues. From me at least, I don't quite know what state you'd be in.

OJ191
05-27-2011, 01:22 AM
Look at the .gif in OP of original thread. Do you agree with the cube moving as it exits the portal? I.e. growing from the floor.
Now, a cube has mass, and if it is moving as in the .gif, an image that people agree on, then it also has momentum.
Oh look, there's your momentum.
Unfortunately the explanation for it being there is a somewhat more complex version of: The portal is a folding of spacetime, that when one end is moved in relation to the other, changes the relative point of contact between two points, while changing the point of contact. This results in one part of the world moving in relation to the other, while from an outside observer's point of view, due to an observer not being in the same frame of reference of the portals, the world remains constant and unchanging.
In short, the universe moves while staying still.



I'll quote myself here, as it's been agreed that portals don't conserve energy:




That is another way of thinking about it, thanks. In the end though, I don't think it matters exactly how it works, as long as we know the outcome.
It's like gravity; we know it exists and can model it very precisely. We don't however know how it works (yes we understand distorting spacetime, but why does that happen?) We can make guesses, the latest being the Higgs Boson, but we don't know why it happens, not yet at least. We can however see its effects, kinda like portals.



Ok, working backwards for the hello of it. You are mixing up velocity and speed, velocity is a function of speed and direction. Direction can change, this requires acceleration, without a change in speed. As momentum is a function of velocity and mass, the momentum would change with velocity but not (necessarily) with speed.

You are stating that no matter what speed you enter a portal, you come out at a constant slow speed. (have you even played the game?) Most puzzles would be impossible were that the case.

Portals are not just holes, they are holes linking two points. While you did kinda get this, you then said that something passing through is not affected by the other side until it has passed through.
Here's a thought experiment. Put a portal on a wall. Put another between 2 walls with say, 5cm gap, I.e. not enough to squeeze your body into.
By your reckoning, you can pass through the portal all the way, without hitting the wall, only coming into contact with it after you have finished passing through. If course you are halfway through said wall at this time.

Hilarity ensues. From me at least, I don't quite know what state you'd be in.

No, not that you would always come out at a slow speed. I'm saying if YOU leap through a hole (portal) you will come out at that same speed. If someone pushes a hole over your head, you aren't moving through space while still going through the hole. Now this gets a bit more complex when a portal is being shoved over your head, but the theory should remain the same.

Baldrickk
05-27-2011, 01:27 AM
No, not that you would always come out at a slow speed. I'm saying if YOU leap through a hole (portal) you will come out at that same speed. If someone pushes a hole over your head, you aren't moving through space while still going through the hole. Now this gets a bit more complex when a portal is being shoved over your head, but the theory should remain the same.

Ok, I might have misread you a bit there. However, your head emerges from the hole at the speed it entered it.

If the hole comes at you quickly, you go through faster.

If the exit is elsewhere and stationary, you come out of it at the same speed, but because it isn't moving around you, you have to be the one moving at speed.

OJ191
05-27-2011, 01:44 AM
I know what you're getting at, it hurts my head trying to think about it lol.

Baldrickk
05-27-2011, 01:46 AM
I know what you're getting at, it hurts my head trying to think about it lol.

I'm not surprised, I've done quite a but of thinking with portals since the first game. It's probably the only reason I'm not comatose!

TmanIsHere
05-27-2011, 05:55 AM
While I applaud Macedragon for his contact with David Kircher, he's (David is) making it a B because it's "convenient" to make it a B. If they nitpicked every single detail, they would come to a conclusion that neither A nor B make sense.

We all know with a stationary portal, it acts just like it was a hole in space. Do you know what Rube Goldberg machine is? The way David is explaining is a Rube Goldberg machine except he's trying to make things work in real time without getting theoretical.

Let me explain that in order to follow the B theory explained by David, following needs to be true:

Measure mass and velocity and teleport them instantaneously. This is ALL material involved including the photons.(Wow, that's a lot of data to transfer)

Teleport them in at the same mass and velocity that they came in the portal. (Wow, hard enough to teleport something still, now we can teleport launch object at the same speed? Really?)

So everytime you shoot something on a wall, this magical device gets attached to the wall. And mind you, it has near-0 thickness. (Another something we don't even have explanation for!)

If it was just a device (and not something that connects two points, why do the portal disappear once you create a new one?

This same device was able to shoot from you portal gun and get beamed into the moon almost instantaneously? So they created a device that can launch at the speed of light?

If you can explain everything up there realistically, I applaud you. You could be the next Einstein. I think it's a lot easier to wrap it up with "what looks like a hole, and acts like a hole, is a hole." So in the duration, I would like to think it's a hole in the space time continuum. In other words, it still stands that it could be either A or B or neither A nor B... or as David explained it,

Again, entirely fictional and just my opinion.

This whole example is, in fact, Schrödinger's cat.

Macedragon37
05-27-2011, 06:51 AM
While I applaud Macedragon for his contact with David Kircher, he's (David is) making it a B because it's "convenient" to make it a B. If they nitpicked every single detail, they would come to a conclusion that neither A nor B make sense.

Well thank you. And yes, I can concede that this is situation is very much fictional, and probably too difficult to explain if you really wanted to somehow make it theoretical (Which you probably can't, because portal guns don't exist).

We all know with a stationary portal, it acts just like it was a hole in space. Do you know what Rube Goldberg machine is? The way David is explaining is a Rube Goldberg machine except he's trying to make things work in real time without getting theoretical.

The real time explanation helped me personally.

Let me explain that in order to follow the B theory explained by David, following needs to be true:

Measure mass and velocity and teleport them instantaneously. This is ALL material involved including the photons.(Wow, that's a lot of data to transfer)

Portals must require a lot of energy I guess.

Teleport them in at the same mass and velocity that they came in the portal. (Wow, hard enough to teleport something still, now we can teleport launch object at the same speed? Really?)

So everytime you shoot something on a wall, this magical device gets attached to the wall. And mind you, it has near-0 thickness. (Another something we don't even have explanation for!)

Yes, I've considered that as well. How does that even work?

If it was just a device (and not something that connects two points, why do the portal disappear once you create a new one?

Woah. Okay, you're going into a whole nother discussion...

This same device was able to shoot from you portal gun and get beamed into the moon almost instantaneously? So they created a device that can launch at the speed of light?

Well I assume that it's light that is being shot.

If you can explain everything up there realistically, I applaud you. You could be the next Einstein. I think it's a lot easier to wrap it up with "what looks like a hole, and acts like a hole, is a hole." So in the duration, I would like to think it's a hole in the space time continuum. In other words, it still stands that it could be either A or B or neither A nor B... or as David explained it,

I don't think it can all be explained realistically. Oh well.

This whole example is, in fact, Schrödinger's cat.

That's one of my favorite paradoxes. :D

Well, you have caused me to now consider a bunch more paradoxes, conundrums, and discussions, so thank you.

MutantMonkey
05-27-2011, 06:56 AM
Well, you have caused me to now consider a bunch more paradoxes, conundrums, and discussions, so thank you.

Not really. I don't think anyone at this point has argued that portal guns can become a reality.

The debate is centered around the possibility of a portal gun existing in real life and how it would interact with what it would come in contact with based around a frame-set that Portal/Portal 2 has given us.

If you want to distract from the thought experiment by questioning the development and functionality of the portal gun and the portal it creates, that is fine, but it has nothing to do with what we are talking about.

Macedragon37
05-27-2011, 07:10 AM
Not really. I don't think anyone at this point has argued that portal guns can become a reality.

The debate is centered around the possibility of a portal gun existing in real life and how it would interact with what it would come in contact with based around a frame-set that Portal/Portal 2 has given us.

If you want to distract from the thought experiment by questioning the development and functionality of the portal gun and the portal it creates, that is fine, but it has nothing to do with what we are talking about.

I'm...sorry?

Like I said, those are whole other discussions, I wasn't trying to "distract" from the current discussion. So here's what I have to say.

---

Are we done? David Kircher, the man who helps make the physics of the portal games, has come up with his own solution. I pretty much agree with it. Maybe I could ask you if you agree with it. Do you?

It makes sense that such a motion of the cube should not happen all at once, and instead should happen over the time that the orange portal is interacting with the cube. So it's definitely not the old A (The cube doesn't move at all), and it isn't really the other A (It'll plop out no matter what speed). It's more of A variant of B and A.

So the solution: The cube will move through the orange portal in a proportion to the amount of the cube that goes through the portal, and the speed that it goes through the portal. Confirmedly, it would be less than the orange portal platform's initial speed, but it would still be substantial.

I'll leave "Is it possible to even make a portal gun?" in a different thread.

I quoted you but that comment was more directed at the guy you quoted.

Oh, haha, sorry about that.

MutantMonkey
05-27-2011, 07:14 AM
I'm...sorry?

Like I said, those are whole other discussions, I wasn't trying to "distract" from the current discussion. So here's what I have to say.

---

Are we done? David Kircher, the man who helps make the physics of the portal games, has come up with his own solution. I pretty much agree with it. Maybe I could ask you if you agree with it. Do you?

It makes sense that such a motion of the cube should not happen all at once, and instead should happen over the time that the orange portal is interacting with the cube. So it's definitely not the old A (The cube doesn't move at all), and it isn't really the other A (It'll plop out no matter what speed). It's more of A variant of B and A.

So the solution: The cube will move through the orange portal in a proportion to the amount of the cube that goes through the portal, and the speed that it goes through the portal. Confirmedly, it would be less than the orange portal platform's initial speed, but it would still be substantial.

I'll leave "Is it possible to even make a portal gun?" in a different thread.

I quoted you but that comment was more directed at the guy you quoted.

Baldrickk
05-27-2011, 07:19 AM
I'm...sorry?

Like I said, those are whole other discussions, I wasn't trying to "distract" from the current discussion. So here's what I have to say.

---

Are we done? David Kircher, the man who helps make the physics of the portal games, has come up with his own solution. I pretty much agree with it. Maybe I could ask you if you agree with it. Do you?

It makes sense that such a motion of the cube should not happen all at once, and instead should happen over the time that the orange portal is interacting with the cube. So it's definitely not the old A (The cube doesn't move at all), and it isn't really the other A (It'll plop out no matter what speed). It's more of A variant of B and A.

So the solution: The cube will move through the orange portal in a proportion to the amount of the cube that goes through the portal, and the speed that it goes through the portal. Confirmedly, it would be less than the orange portal platform's initial speed, but it would still be substantial.

I'll leave "Is it possible to even make a portal gun?" in a different thread.

I agree with it, it's what I've been trying to say the whole time :p
I have to admit though that he went a little further into it than I have because I wanted to follow the kiss principle as much as possible, hence my posts mostly being as generic as possible and making assumptions to simplify the scenario ad much as possible, however much that has helped it not.

If someone doesn't agree at this point, I think you'll have to come up with a convincing argument soon or forever hold your peace.

TmanIsHere
05-27-2011, 07:49 AM
Not really. I don't think anyone at this point has argued that portal guns can become a reality.

The debate is centered around the possibility of a portal gun existing in real life and how it would interact with what it would come in contact with based around a frame-set that Portal/Portal 2 has given us.

If you want to distract from the thought experiment by questioning the development and functionality of the portal gun and the portal it creates, that is fine, but it has nothing to do with what we are talking about.

Congratulations. Ok, you agree with David Kircher. Yet, we're arguing about something that has not been programmed into Portal/Portal 2. If anything, David Kircher couldn't have said it any better

Again, entirely fictional and just my opinion.

Bravo. Do you want a cookie?

MutantMonkey
05-27-2011, 08:26 AM
Congratulations. Ok, you agree with David Kircher. Yet, we're arguing about something that has not been programmed into Portal/Portal 2. If anything, David Kircher couldn't have said it any better



Bravo. Do you want a cookie?

I don't understand the snarky tone of your post, or rather the necessity of it.

I am simply saying that some people are trying to have a discussion on how portals would impact the objects they come in contact with based somewhat on the framework that the Portal games have provided and that trying to question the reality of the actual portals and portal gun add no value to the discussion thusly they are distractions.

It's unfortunate that you find that offensive and somewhat puzzling at the same time. If you don't want to participate with the discussion, you dont have to, but could you also be kind enough to leave the distractions at the door? If not, you should be prepared to be reminded that the comments have no bearing on the debate at hand.

TmanIsHere
05-27-2011, 08:34 AM
I don't understand the snarky tone of your post, or rather the necessity of it.

I am simply saying that some people are trying to have a discussion on how portals would impact the objects they come in contact with based somewhat on the framework that the Portal games have provided and that trying to question the reality of the actual portals and portal gun add no value to the discussion thusly they are distractions.

It's unfortunate that you find that offensive and somewhat puzzling at the same time. If you don't want to participate with the discussion, you dont have to, but could you also be kind enough to leave the distractions at the door? If not, you should be prepared to be reminded that the comments have no bearing on the debate at hand.

I've already discussed this in the other thread. If you care to read through hundred some pages of my view, you'd understand my point.

MutantMonkey
05-27-2011, 08:40 AM
I've already discussed this in the other thread. If you care to read through hundred some pages of my view, you'd understand my point.

I'm not interested in hunting down your posts that seemingly justify derailing an on going discussion. I'm more interested in the discussion and the points of view about the experiment that people are bringing forward.

If there is to be a discussion about the creation of such portals and the devices that would create them, that is a separate discussion for another thread.

TmanIsHere
05-27-2011, 09:11 AM
First, I'd like to apologize for sounding snarky. I get frustrated when I have to do the same thing over and over again. Having said that, this discussion thread is no different than the one posted before. The only difference is that we brought in David Kircher to the discussion, who I assume, has big influence on how the Portal universe works.

I challenge you to understand A's perspective first before you disclaim it. I say this because it holds as much validity as a scenario that you believe to be is right.

I'm not interested in hunting down your posts that seemingly justify derailing an on going discussion. I'm more interested in the discussion and the points of view about the experiment that people are bringing forward.

If there is to be a discussion about the creation of such portals and the devices that would create them, that is a separate discussion for another thread.

GuruFunk
05-27-2011, 09:18 AM
I'd say, instead, imagine the piston was your arm and you're holding the cube. If the answer was B, you'd physically feel both your arm and the cube being pulled by some force which would accelerate the cube upward. If that were the case, where would that force come from? Like other's have said, this is merely a case of illusion and perception. It would seem like the cube would be launched up because that's what would normally occur if the initial piston with the cube was moving, but in this case, it isn't. It is simply physics playing tricks on the mind because that's how we normally see things.

TmanIsHere
05-27-2011, 09:44 AM
I'd say, instead, imagine the piston was your arm and you're holding the cube. If the answer was B, you'd physically feel both your arm and the cube being pulled by some force which would accelerate the cube upward. If that were the case, where would that force come from? Like other's have said, this is merely a case of illusion and perception. It would seem like the cube would be launched up because that's what would normally occur if the initial piston with the cube was moving, but in this case, it isn't. It is simply physics playing tricks on the mind because that's how we normally see things.

If this is the case B without bend in space time, as soon as something emerges from portal, the speed changes from 0 to however fast the portal is descending. So, imagine you're at a rest and your head pops over the portal. If the portal was coming down at 100mph, I would imagine you'd get decapitated.

I sure as heck don't want that kind of portal.

P.S. Ooops. I retract what I said.

The momentum of the blue side would be "created" as discrete portions of the cube's mass teleported and were instantaneously at speed.

TmanIsHere
05-27-2011, 10:11 AM
If the momentum was "created", he's either implying that the mass or speed is created from out of nowhere. This defies physics because we know that matter can't be created nor destroyed and I have no idea how you could make speed without some physical force.

MutantMonkey
05-27-2011, 10:11 AM
First, I'd like to apologize for sounding snarky. I get frustrated when I have to do the same thing over and over again. Having said that, this discussion thread is no different than the one posted before. The only difference is that we brought in David Kircher to the discussion, who I assume, has big influence on how the Portal universe works.

I challenge you to understand A's perspective first before you disclaim it. I say this because it holds as much validity as a scenario that you believe to be is right.

You dont have to challenge me as A was the side I was initially on during the early stages of the last big thread.

What changed my mind was seeing arguments and scenarios that gave credence to B. With those arguments, I went to my best friend who majored in physics at NC State. After discussing it with him, it became very clear that B was the most correct choice.

Having personally been on both sides of the argument, I get why some people think it may be A, but with proper explanation and understanding of basic principles and laws, it is clearly B or some derivation of B.

Macedragon37
05-27-2011, 04:05 PM
You dont have to challenge me as A was the side I was initially on during the early stages of the last big thread.

What changed my mind was seeing arguments and scenarios that gave credence to B. With those arguments, I went to my best friend who majored in physics at NC State. After discussing it with him, it became very clear that B was the most correct choice.

Having personally been on both sides of the argument, I get why some people think it may be A, but with proper explanation and understanding of basic principles and laws, it is clearly B or some derivation of B.

Well I'm glad that a seemingly pointless "physics" debate was also very important to someone other than me. I really enjoy thinking about these kinds of things.

_Depression
05-27-2011, 08:38 PM
If the momentum was "created", he's either implying that the mass or speed is created from out of nowhere. This defies physics because we know that matter can't be created nor destroyed and I have no idea how you could make speed without some physical force.

Kircher said in his email that the momentum is "created" by the transferring of the object from one portal to another. I like this explanation, so:

Imagine you have a stack of cubes on the platform that the portal is moving down toward. Now, as each cube comes up out of the other portal, it has to "push" the ones that came out before it to make room. That's where the momentum comes from.

CatatonicMan
05-27-2011, 11:08 PM
Kircher said in his email that the momentum is "created" by the transferring of the object from one portal to another. I like this explanation, so:

Imagine you have a stack of cubes on the platform that the portal is moving down toward. Now, as each cube comes up out of the other portal, it has to "push" the ones that came out before it to make room. That's where the momentum comes from.

While it makes a decent conceptual picture, the cubes don't actually exert any extra force on each other when passing through the portal.

TmanIsHere
05-28-2011, 07:21 AM
The momentum of the blue side would be "created" as discrete portions of the cube's mass teleported and were instantaneously at speed.

That quote was from David Kircher himself. I don't think it's possible to transfer speed without external force or transfer of momentum acting on it. Basically, it'll have to destroy momentum and recreate momentum on the other side. That never made any sense in a physical world. It makes as much sense as warping space time.

discrider
05-28-2011, 08:17 AM
I'd say, instead, imagine the piston was your arm and you're holding the cube. If the answer was B, you'd physically feel both your arm and the cube being pulled by some force which would accelerate the cube upward. If that were the case, where would that force come from? Like other's have said, this is merely a case of illusion and perception. It would seem like the cube would be launched up because that's what would normally occur if the initial piston with the cube was moving, but in this case, it isn't. It is simply physics playing tricks on the mind because that's how we normally see things.

If you were holding the cube, you'd feel nothing as the portal moved over your arm, bar a sharp increase in the wind chill factor.

David's explanation was wrong in this respect. The cube never feels itself being pulled by the moving bit at the boundary, since the moving portal maintains the spacing between all of the cube's particles, there are no internal forces between these particles to indicate an acceleration, and from the cube's point of view there never is an acceleration. They simply move from a stationary room into a moving one because a panel moved over them, and experience no acceleration whatsoever.

The cube and your arm are never accelerated. You just suddenly gain velocity without feeling anything (to the outside observer).

Timeroot
10-06-2011, 10:28 PM
I don't see what everyone's arguing about. Take Einstein's and Maxwell's field equations for transmission of electric and gravitational forces (all we really need if we're using classical mechanics here). Then just introduce a new boundary condition to connect the portals. For all relevant fields f, it will be something like lim(x->Portal A on non-wall side)[f(x)]=lim(x->Portal B on non-wall side)[f(x)]. Then, define something about what happens on the wall-based side. (Something simple like reflecting waves back, or absorbing them simply, should work fine.)

Then, you've got some laws of physics you can do whatever you want with. Including things like, for instance, having two portals collide, or a portalled wall smash down on an object, but pause halfway across the object (which otherwise makes interesting problems with cutting off the momentum for no reason from the perspective of the other side).

A lot of questions will be answered, note, with unusual air currents that occur, I think. For instance, if you push a portalled wall through air, that air will push on the air on the other side, and generate a current of wind.

Okay mods you can lock this thread now I think.

(P.S. MUCH SARCASM IS HAD ABOVE)

Condor_96
10-06-2011, 10:43 PM
I don't see what everyone's arguing about. Take Einstein's and Maxwell's field equations for transmission of electric and gravitational forces (all we really need if we're using classical mechanics here). Then just introduce a new boundary condition to connect the portals. For all relevant fields f, it will be something like lim(x->Portal A on non-wall side)[f(x)]=lim(x->Portal B on non-wall side)[f(x)]. Then, define something about what happens on the wall-based side. (Something simple like reflecting waves back, or absorbing them simply, should work fine.)

Then, you've got some laws of physics you can do whatever you want with. Including things like, for instance, having two portals collide, or a portalled wall smash down on an object, but pause halfway across the object (which otherwise makes interesting problems with cutting off the momentum for no reason from the perspective of the other side).

A lot of questions will be answered, note, with unusual air currents that occur, I think. For instance, if you push a portalled wall through air, that air will push on the air on the other side, and generate a current of wind.

Okay mods you can lock this thread now I think.

(P.S. MUCH SARCASM IS HAD ABOVE)

Did you REALLY need to necromance this thread? Really?


And yes, necromance is a word. Look it up.