I was wondering if anyone had the source code for rigidBody. I was hoping to modify the behavior of the physics engine, but am new to Unity, so I have no idea how to do so. I was hoping I would be able to simply find the source for the rigidBody component and modify that, but if there is a better way, I would like to know.
there isnt.
You can get the source code to the Unity engine but you need to buy a license, which can be quite pricey.
So basically what I said 
If you are looking to modify the behaviour, youre just going to have to do so through understanding the physics engine and how to work around it.
What ‘special’ things are you trying to do?
Well I searched this up on google because I wanna know how rigidbody works and I want to know how to do slope detection because it’s pretty confusing