I want the sphere 2 to be hollow inside, so that the sphere 1 can proceed physics inside.

But I don't know which collider to use.

CodePudding user response：

you could create a Sphere in a 3D modelling software and invert the normals so that they face inside the sphere. in unity place the sphere with the inverted normals as a child to your hollow sphere. this will represent now the inner side of your hollow sphere. remove the meshrenderer and add a meshcollider to the sphere with the inverted normals. now you can place any object with a rigidbody component attached to it inside and it will collide with the inner side of your sphere.