Deakin Communicating Science 2016

EES 200/101

Physics gone wild, Immovable object vs Unstoppable force?

One of physics’ most pondered yet confusing questions: What happens when an immovable object meets and unstoppable force? Or if you really want to get technical, what the hell is up with the irresistible force paradox?

Superman had this question put forward to him by the Ultrasphinx, with the provision of the right answer ensuring the life of Lois Lane. Superman answered by simply stating: “They surrender” which was accepted by The Ultrasphinx and Lois was allowed to live.

Unfortunately, physics isn’t always that simple. Firstly, we need to define what actually constitutes an immovable object. Given that the principle of relativity means that nothing can ever really be immovable. So let’s limit this to a simple definition of “if something is not in a state of motion, you cannot put it into a state of motion, by applying a force to it.” Essentially this object would have to have an infinite mass, so that no matter how great of a force you applied, the acceleration would be zero (shout out to my main man Newton for that second law of motion, F=ma).


The Ultrasphinx doing his thing. Source: DC Comics

Again, technically speaking, all forces are unstoppable as they are consistently reacting with the world around them, including light. As light hits us, the photons cause a slight change in our momentum that we can do nothing about unless we avoid light altogether or decide to become transparent. But let’s not define force in the traditional sense like electromagnetism or gravity, instead let’s simply say that it is “an object whose velocity cannot be changed”.

So understanding that if velocity can’t be changed, this automatically means that the acceleration has to be equal to zero. But that puts us in a conundrum, because this would mean that if an immovable object and both an unstoppable force have accelerations that equal zero, then by and large they are exactly the same thing, just seen from different reference points…. yep. Mind blown.

In reality this is not possible because according to E=mc^2 , infinite mass would require infinite energy and for this to be possible, forget Kim Kardashian because we wouldn’t be talking about breaking the internet, it’d more likely be breaking physics and by extension the whole entire universe (most likely via a massive black hole that would contain the entire universe inside of it).

So theoretically, ignoring gravity, if these two unacceleratable and infinitely massive objects were moving towards each other and were to collide, they would simply have to pass through one another with no effect on each other at all. This is due to the fact that by definition, their velocity cannot be change.

Yes physics, you win again.


  2. DC Comics
  3. Kaczor, Christopher (2009). This Rock, 20(3).



Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s


This entry was posted on May 15, 2016 by in Burwood - Friday 11am and tagged , .

Deakin Authors

%d bloggers like this: