[Suggestion] Being able to go back in time

[kao16]

Hi, im new to the forum although i've had universe sandbox for about 2 years. I've always wondered if it is possible to implement a feature to not only stop the simulation but also go back in time through it

For example in the supernova simulation i would love to stop and go back to the time it actually explodes. I think it would be a very interesting feature for users that want to buy the game too.
Would you like to see it in the future?

[SyzygyΣE]

It's simply impossible to simulate the universe in reverse through conventional methods. That's just the way physics works. This has been suggested before, but a dev has stated here that it is currently not something they are actively working on.

[emarksmi]

I was thinking bout this as well, until I thought about what I was really asking for.  Essentially, you are running the simulation backwards which means reversing every velocity, spin rate, etc.  The result wouldn't really be backing up in time at all but a new simulation starting from an arbitrary point.  The more I thought about it, the more pointless it became.

[Jar]

Essentially, you are running the simulation backwards which means reversing every velocity, spin rate, etc.  The result wouldn't really be backing up in time at all but a new simulation starting from an arbitrary point.  The more I thought about it, the more pointless it became.

We actually just added a feature that will do exactly as you described, reversing the velocities, rotations, and time. It will likely be in our next update. It may not be what most people will expect with a "Reverse Time" feature, in that it will indeed be a "new simulation" as SyzygyΣE suggested, and things like collisions won't be reversed. But we still think it's an interesting experimental tool, and it does work well for simulations of timed events, like the eclipse.

[emarksmi]

But we still think it's an interesting experimental tool, and it does work well for simulations of timed events, like the eclipse.

Excellent!  I can think of other places where it might be useful to be able to reverse the simulation and see what happens (running a 3 body problem backwards, for example).

[unisandplayr1]

I don't think people really want a "reverse time" feature.  They want to go back and re-watch the same forward event as much as they like.

This means it should be MUCH EASIER than trying to bend the laws of physics and computational computer science.

I propose a feature that simply takes Snapshots in time and space.  A stateful representation of this snapshot doesn't need to a very large file... as it is merely a text file (XML?) of all objects and their properties (position, velocity, etc). 

The "rewind" feature merely reloads the snapshot.  And no need for the complex physics of running a simulation in reverse time (not even by reversing spin and velocity).

In practice, this can be much better than manually saving simulations, as this feature can a few options configurable by the user:

• auto-snapshot ever X units of time
• keep X snapshots and auto-delete previous

This allows users to auto-pause on collision and then load a snapshot to re-watch.

[Austritistanian]

Essentially, you are running the simulation backwards which means reversing every velocity, spin rate, etc.  The result wouldn't really be backing up in time at all but a new simulation starting from an arbitrary point.  The more I thought about it, the more pointless it became.

We actually just added a feature that will do exactly as you described, reversing the velocities, rotations, and time. It will likely be in our next update. It may not be what most people will expect with a "Reverse Time" feature, in that it will indeed be a "new simulation" as SyzygyΣE suggested, and things like collisions won't be reversed. But we still think it's an interesting experimental tool, and it does work well for simulations of timed events, like the eclipse.

That's all cool, but what about impact events, explosions, supernovas, and stellar evolution? For those things to work you would have to reverse the physics completely. How are you going to implement that?

[tkulogo]

I don't think people really want a "reverse time" feature.  They want to go back and re-watch the same forward event as much as they like.

This means it should be MUCH EASIER than trying to bend the laws of physics and computational computer science.

I propose a feature that simply takes Snapshots in time and space.  A stateful representation of this snapshot doesn't need to a very large file... as it is merely a text file (XML?) of all objects and their properties (position, velocity, etc). 

The "rewind" feature merely reloads the snapshot.  And no need for the complex physics of running a simulation in reverse time (not even by reversing spin and velocity).

In practice, this can be much better than manually saving simulations, as this feature can a few options configurable by the user:

• auto-snapshot ever X units of time
• keep X snapshots and auto-delete previous

This allows users to auto-pause on collision and then load a snapshot to re-watch.

This is so true. So often, something happens that is remarkable and you didn't really catch it. Maybe and autosave that would save once a minute and automatically delete most of them so you'd have a selection of save points to jump back to. As long as it could be turned off, it wouldn't be a performance hit.