Question

what happens when an unstoppable force meets an immovable object?

Answer 1

this question concerns metaphysics rather than physics

Answer 2

Any immovable object would have infinite mass leading to gravitational collapse into a black hole. Meanwhile, in the finite universe an unstoppable force could never exist because it requires infinite energy.

With this in mind, I say the reaction caused by these two phenomenon meeting would be pretty spectacular to observe ;)

Answer 3

with the equation \[E=Mc ^{2}\] mass is simply concentrated energy so an object with infinite mass has infinite energy. This would not necessarily lead to a gravitational collapse as an object with infinite mass and infinite energy is traveling at the speed of light.