The Irresistible Force Paradox — Broken down
Before I go into any detail about this fascinating mystery of the scientific world, we need to establish what a paradox is in the first place. So, a paradox (also known as an antimony) is a logically self-contradictory statement that runs in contrast to your expectation. It is a statement which gives credible reasoning for one side of it yet somehow reaches the completely opposite or logically unreasonable conclusion.
Here we are looking at a paradox called the Irresistible force paradox, also known as the shield and spear paradox. Is about the outcome of the hypothetical situation when an unstoppable object is in a direct collision course with an immovable object. This paradox was first brought up in a in a 3rd century Chinese philosophical book Han Feizi. In the story it tells of a man was trying to sell him a shield and a spear. When asked how strong his spear was, he said every shield could be pierced by his spear. Then, when he was asked how strong his shield was, he said it was capable of protecting against all spear attacks. One individual then asked him what would happen if he took his spear to hit his shield; the seller was unable to provide a response. Therefore, the paradox of the irresistible force was born.
Now, when we say an immovable object, what do we really mean? Well, some people might say simply that it is an object that cannot be moved, and you would be correct in saying that, yet it is also a little more than that, think about it, when you push an object what are you changing… its acceleration, when an object changes its velocity, it cannot just go straight from one speed to another, there has to be acceleration in between, so a better way to put an immoveable object would be an Un-acceleratable object, also known as an object which cannot accelerate.
Now that is all well and good but what about an unstoppable force. Well, an unstoppable force is simply an object that we cannot stop, if we cannot stop it what can’t we do? We cannot change the velocity and if we cannot change the velocity what cannot be possible? Acceleration! The object cannot be accelerating at any moment in time making it an Un-acceleratable object.
Now that phrase sounds familiar, this is because an immovable object and an unstoppable object are the exact same thing, except from different perspectives. Another point which can help me explain this is Newtons 2nd Law, stating that acceleration = force/mass, this shows us that for an object to be un-acceleratable, an object must have a mass of ∞ as no matter how much force you apply, you will be unable to accelerate the object. But due to this fact, it is impossible for there to be an un-acceleratable object (it is impossible for an object to have infinite mass).
Obviously, if an object cannot accelerate, it does not mean that it is not moving, it means that its velocity cannot be changed, an example of this would be when an object is moving at a constant velocity, it is moving, yet it is not accelerating at the same time.
So now the question is, what happens when an unstoppable object and an immovable object collides? Obviously, there is no source of infinite energy (if there was we would be able to do a lot with it, such as make portals to other locations and break the 2nd law of thermodynamics) so we will just have to look at this as a hypothetical situation, assuming that both of the objects, besides being immovable and unstoppable, are also unbreakable, we can gather that the only possible outcome of this theoretical situation, is that the two object will just pass through each other, having no effect on one another whatsoever.
The reason why this is a paradox is due to the fact that the 2 objects cannot have a change in velocity and are also unbreakable, it is impossible for 1 object to somehow change the others movement pattern as they both would cancel each other out and therefore there is no known answer to what will happen. I understand that I gave an answer to the question in the paragraph above though this is a theoretical answer and not a proven one, hence why it is known as the irresistible force paradox.
