Independent Concurrent Physics Simulations

Hi,

I'm looking for a way to run simple physics simulations for the main game thread (~50fps) while also running simple simulations in the background at much higher frame rates of about x100 speed (or as fast as possible), or to run many independent instances concurrently at faster speeds. By simple, I mean basic translation 2D physics with circles and rectangles that are rarely colliding for about 20 or so objects.

I imagine that the ideal solution would be involving multiple independent instances of Unity's inbuilt Box2D physics engine running on separate threads. But as far as I know, Unity only does one internal physics update per game loop, so I assume this will inherently prevent me from using multiple independent instances.

At the moment I'm leaning towards either writing my own basic physics (prefer not since it will be a lot of work to optimise) or to download Box2D separately and see if I can make it work. But I thought I'd see if there are any elegant solutions involving Unity's inbuilt systems or otherwise first.