In theory, if an unstoppable force meets an immovable object, they'd cancel each other out. Then add just one more thing and then the unstoppable force is stoppable and the immovable object is movable. This is just theory, because no such forces or objects exist. At least...not that we know of.
Actually, a physicist was talking about this. He said if you had a literal unstoppable force (also known as infinite force) and an immovable object (known as infinite mass), they would pass right through each other, neither affecting the other.
I heard that too. lol That's more of a paradox answer to the "equation" of the situation.
Likely they would just both merge together because pressing against each other with infinite and equal opposition would mean either would let down, and since they can't just ghost through each other, they would be compressed together and become a new object. An infinitely compressing one. lol
Unless they really do shove through each other molecularly but seems like that would weaken both of them, making them no longer unstoppable and immovable. lol