Physics Engine Randomness

For some reason there is a bit of randomness in every simulation. But that's not as bad as the fact that there is a very big difference between the way it simulates before and after saving. I have no idea why this happens. I'm using version 0.05 for windows.


Active Member
The randomness is because Unity's (the game engine) physics engine isn't deterministic. There was a lengthy discussion about this on the old forum, but unfortunately I don't think that's still accessible. I never noticed a big difference after saving though. Could you maybe provide some instructions on replicating this ?


Staff member
In addition, there is some randomness built into the game.
Anyways, not a bug

EDIT: didn't see "after save" + new post with pictures.
If I remember correctly, bombs create a random torque, can't remember if it has some random values in the force too.
I've added the "after save" picture to show that the block doesn't fly as much as it did before that. It just stops at the first checkpoint.


Staff member
A video or gif probably would be better for this.
How peculiar.

Hmm. I tried exactly the same stunt with a half wood block instead of the middle block, and it didn't do the same thing; it flew the same distance after I saved. But when i made a thing to weigh the starting block, it weighs the same both before and after saving. Perhaps there's some sort of physics-related script that runs whenever a block is placed, but it doesn't affect the starting block at the beginning because it is never really "placed", but the script also gets run for each part when the machine is saved or loaded?
My guess is the save file's location is less precise than the editor's, so some block positions move slightly on being loaded.
Either that or it's another bug in the save system, either failing to read locations or failing to write them accurately.
Ooh Very helpful information guys! I love it... Hopefully though this will all help to resolve the issue! :) (will add to the compilation thread now)