And no.. its answer is not “42”..
Let’s jump right into it, shall we? What would happen if an unstoppable force struck an immovable object? Well, first, let’s break down the objects themselves. We’ll throw in some physics, because everyone loves physics, and then try to Mythbuster’s this one.
An unstoppable force is usually in reference to an object that is either moving at such a rate, nothing in the Universe will ever stop it. These exist right now.. kind of.. Photons of light are unstoppable. They pass through each other when they would otherwise collide if they had mass, and because they have no mass, they’re omit from certain pesky things like Gravity to a certain degree. Black holes for instance, are so gravity intense, light can’t even escape. So, to backtrack on what I said earlier, even light is not an unstoppable force. Since a massless object is not unstoppable, then an unstoppable force must have mass, right? You can only have mass or not, there is no in between. Well, to have mass and momentum, then you have energy. Basic physics are E=MC². However, to have something massive doesn’t mean it’s unstoppable. To be unstoppable, you need to have so much mass and momentum that even the constant force of gravity isn’t enough to slow you down.
Since Gravity itself is constant and is everywhere, then to be unstoppable you need to have infinite mass. To have infinite mass, you need to have infinite energy. Since you’re currently alive, that means you have some energy, therefore an object like that can’t exist because it doesn’t have the infinite amounts of requirements.
Unfortunately, the same is true for an immovable object. To be immovable, you need to be so heavy that no matter the object striking your surface, even something of equal mass and volume, you would not budge even a single beard second. Yes that’s an actual measurement of length.. see?
To take the Mythbuster’s approach to this problem, let’s say they somehow existed in our Universe. What would happen? Would total destruction happen of the entire Universe? Something with infinite energy and mass colliding with something else that’s also infinite energy and infinite mass? Assuming you don’t over-think this and see that you can’t have two things that share infinite resources of the same resource, then we can proceed.
To put it blunt, nothing would happen. Chances are, these two objects would pass right through each other much like photons of light do right now. You can’t have infinite energy and infinite mass, and if you could, you leave nothing left for the opposing object. There is no plausible way that this could exist, in any form. An object with a defined mass or energy level, no matter the amount (note: defined means it’s not infinite), will eventually slow down and stop.
It may take longer than the Universe would exist, but if we take that out of the equation, it would happen.. eventually..