View Full Version : Inaccurate solar system simulation?

12-30-2011, 04:30 PM
So the solar system simulation, when left run for 100k years, has the Sun moving away from her place and all planets as well, also they stop rotating around the sun.

What is happening there? Seems like a bug in the simulation to me? I mean, I never heard of such an end of the world scenario. It seems like the influence of the universe expansion is set very much too high.

EDIT: Trying it again with the other accuracy option, after 50 years Mars loses its orbit and then things get worse. After only 4000 years the solar system is more or less destroyed.

Dan Dixon
12-30-2011, 04:48 PM
This happens because you're running the simulation with a time step that's too high. As you increase the time step you decrease the accuracy of the simulation, and inversely making the time step smaller will increase the accuracy of the simulation.

Does that help and make sense?

Here's a more technical answer:

12-30-2011, 04:50 PM
That should be better documented then. So no easy going through the years. :-)

Playing around with that seems to get funny effects. Setting the time step of the Earth-Moon simulation to roughly 10 hours makes a nice visual effect for me. ;-)


Dan Dixon
12-30-2011, 07:22 PM
That should be better documented then.

Agreed. I just wrote about this in another thread:

"This is a fundamental issue with any gravity simulator where the larger the time step the less accurate the simulation. Universe Sandbox does not currently simulate the expansion of the universe. We want to make this issue more understandable and intuitive in a future version. My fault that this issue is confusing."

12-31-2011, 12:55 AM
I was just messing around with the time section in our solar system while watching the Voyager craft to see how far they had gone by todays measurements and was suprised to see Venus flying off at one point in the future, so i increased it further, and by 2187 Earth was no longer in orbit!

Dan Dixon
12-31-2011, 06:18 AM
You decreased the accuracy so much that everything flew apart.

You can make Earth fly away faster by turning up the time step even more.