Steam Users' Forums [UPDATED: The "Pole" Example] RE: Portals on moving surfaces [My solution]]
 Register FAQ Search Today's Posts Mark Forums Read

05-24-2011, 08:51 PM   #1
Macedragon37

Join Date: Jul 2010
Reputation: 52
Posts: 586
RE: Portals on moving surfaces [My solution + Feedback and examples]

NEW: Click the below forum to see Valve's own David Kircher's take on this conundrum.

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

----------------------------------------------------------------------------------------------------------------------------------------------------
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.
----------------------------------------------------------------------------------------------------------------------------------------------------

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.

---

http://lastopp.no/3/85598fa1714fb800...c1d04fb2fb.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.

---

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.

---

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.

---

Quote:
 Originally Posted by Pythagoras 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.

Quote:
 Originally Posted by Baldrickk 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.

Quote:
 Originally Posted by grimrecka 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.

Quote:
 Originally Posted by Tensor 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.

Quote:
 Originally Posted by Roeltjuh 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?

Quote:
 Originally Posted by StrangeQuirk 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.

Quote:
 Originally Posted by Baldrickk 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.

Quote:
 Originally Posted by Dzjudz 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.

---

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.

Quote:
 Originally Posted by ac1dtrip 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."

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.

Last edited by Macedragon37: 05-26-2011 at 06:57 PM.

 05-24-2011, 09:02 PM #2 FusedCore   Banned Join Date: Jun 2010 Reputation: 346 Posts: 2,310 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.
 05-24-2011, 09:10 PM #3 PelPix   Join Date: Jan 2010 Reputation: 4 Posts: 14 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.
05-24-2011, 09:15 PM   #4
FusedCore

Banned
Join Date: Jun 2010
Reputation: 346
Posts: 2,310
Quote:
 Originally Posted by PelPix 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...

Last edited by FusedCore: 05-24-2011 at 09:21 PM.

 05-24-2011, 09:20 PM #5 _Depression   Join Date: Apr 2011 Reputation: 67 Posts: 510 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.
05-24-2011, 09:22 PM   #6
PelPix

Join Date: Jan 2010
Reputation: 4
Posts: 14
Quote:
 Originally Posted by FusedCore 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.

05-24-2011, 09:26 PM   #7
CatatonicMan

Join Date: Jun 2008
Reputation: 794
Posts: 8,813
Quote:
 Originally Posted by PelPix 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.

05-24-2011, 09:28 PM   #8
FusedCore

Banned
Join Date: Jun 2010
Reputation: 346
Posts: 2,310
Quote:
 Originally Posted by PelPix 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.

05-24-2011, 10:08 PM   #9
sdhdgasd

Banned
Join Date: May 2010
Reputation: 18
Posts: 114
Quote:
 Originally Posted by Macedragon37 I would really appreciate some feedback.
Here's my feedback.

05-24-2011, 10:14 PM   #10
FusedCore

Banned
Join Date: Jun 2010
Reputation: 346
Posts: 2,310
Quote:
 Originally Posted by sdhdgasd Here's my feedback.
mmmm Initiate Dialing sequence!

05-24-2011, 10:14 PM   #11
KimuraOkagawa

Join Date: Dec 2010
Reputation: 41
Posts: 465
Quote:
 Originally Posted by FusedCore 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.

 05-24-2011, 10:17 PM #12 Darth Silver   Guest Posts: n/a 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.
05-24-2011, 10:27 PM   #13
FusedCore

Banned
Join Date: Jun 2010
Reputation: 346
Posts: 2,310
Quote:
 Originally Posted by KimuraOkagawa 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.

Last edited by FusedCore: 05-24-2011 at 10:30 PM.

05-24-2011, 10:28 PM   #14
DisConnected

Join Date: Jun 2009
Reputation: 196
Posts: 861
Quote:
 Originally Posted by FusedCore 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.

05-24-2011, 10:33 PM   #15
FusedCore

Banned
Join Date: Jun 2010
Reputation: 346
Posts: 2,310
Quote:
 Originally Posted by DisConnected 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...

Last edited by FusedCore: 05-24-2011 at 10:53 PM.

 Steam Users' Forums [UPDATED: The "Pole" Example] RE: Portals on moving surfaces [My solution]]

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is Off HTML code is Off Forum Rules

All times are GMT -7. The time now is 05:55 AM.