Backwards Flow of Time

[phasma_phasmatis]

I just figured out that if you make the time step negative and that makes the simulation run in reverse.

Is this old news?

[Darvince]

Enlighten me.

[Joshimitsu91]

Never noticed that before! Lol.

[ChemicalBR0]

cool.
I was wondering if you could run time backwards.

[Dan Dixon]

This is a untested feature that results from not checking on the sign added to the time step textbox.

I'm not sure if anyone else has pointed this out.

[Lazareth]

Nice! I was curious about a way to "turn back time" such that you could replay certain periods of time in the simulation.

I'm planning to use this great piece of work for a roleplay campaign (IN SPACE!) that I will be GM'ing with my friends.

However, I'm curious about the exact implementation of the physics by you, Dan, since you say the negative timestep is an untested feature and not something you intended. Is the simulation time symmetric? I realize it must be calculating 'in reverse' and not actually playing back, so simulation inaccuracies would of course be magnified by 'playing over' the same period of time multiply times, but I'm more worried about sudden changes in physics than simulation accuracy

[Dan Dixon]

I realize it must be calculating 'in reverse' and not actually playing back, so simulation inaccuracies would of course be magnified by 'playing over' the same period of time multiply times...

Correct. For the best results. Save the simulation and reload it to prevent the magnification of inaccuracies.

... but I'm more worried about sudden changes in physics than simulation accuracy

It's doing the same math, but with a negative sign in front of the time step. There shouldn't be any sudden change or issue with accuracy that wouldn't happen with a positive time either.