People in need of a quick boost to their personal depth often quote famous paradoxes and follow it with a quizzical stare. It annoys me. One of the more common ones is the following: “What happens when an unstoppable force meets an immovable object?” It’s a favourite because it gives the impression that not only does the speaker often plumb the depths of philosophy, but physics as well.

The question is an old one, a brief glimpse at the wikipedia article quotes an ancient chinese fable, which is the basis for their word for paradox. Above article also offers a few solutions, including ones that invalidate the question semantically and physically, as well as quoting a book Iain Banks, which seeks to solve it using newton’s law of conservation of energy, which states that upon contact of the two entities, they both lose their titiluar properties.
These answers are all very interesting, but all seem to delve into the realm of a hypothetical reality which is too similar to our own. We assume that these two things will “try their best” to obey the laws of physics that they inherently break. I’d like to look at the question from a purely logical, assume nothing point of view.

Questions of semantics inevitably arise when discussing things in this manner, and this is especially true here, where there are many variations of the wording of the paradox. I am happy to discuss these if you think that my choice of wording, etc. influences the flow of my argument.
The Argument is as follows:

We know that an unstoppable force exists. This is defined as a force which cannot stop or be stopped.

We know that an immovable object exists. This is defined as an object which cannot move or be moved.

We know that the unstoppable force moves in such a way that it collides with the immovable object.

The question then is: What happens when this collision occurs.
There are three possible outcomes that do not cause our earlier assertions to become false.

1. The unstoppable force passes through the immovable object. This is I think is the most sound as it appears to best preserve the assumptions of the question.

2. 1 of the entities is destroyed or ceases to exist. This relies on the idea that ceasing to exist does not constitute stopping or moving.

3. Both objects are destroyed or cease to exist. This is a little nicer to our internal visualisation as we two occurrences of infinity ought to have equal effects on one another.

These three results maintain all the assumptions put forward by the question.


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