We’re all familiar with the laws of our universe and how they affect our daily life. Things fall if you drop them, it takes energy to move things, etc. What we don’t often think about is that the laws of our universe do not have to be the way that they are. In fact, we may live in a multiverse where infinitely many other rules of physics might exist. This post will focus on the first law of motion in our universe and how it could be different in other universes, as well as the sometimes bizarre effects of those different laws.
The first law of motion states that objects will move at a constant velocity unless acted upon by an outside force. This means that our universe offers zero resistance to velocity. If something starts moving in empty space then it will move in that same direction at the same speed forever.
Now, it does not have to be that way. A universe could exist that had a gradual* resistance to velocity. In that case, something moving in empty space would gradually slow down and come to a stop. This is familiar to us on Earth, and is actually the way people thought our universe worked for much of human history.
There could also be a universe with an immediate* resistance to velocity. This would be very weird to us because objects, no matter how fast they were moving, would stop immediately when you stopped applying a force to them. This would mean that any motion would require enormous amounts of energy, and depending on the other properties of that universe, it could end up becoming completely frozen. Maybe that one wouldn’t be such a great place to live.
Returning to our universe, acceleration is very different from velocity. The first law of motion implies an immediate resistance to acceleration. No matter how high an object’s rate of acceleration, if you stop applying a force, then that acceleration will instantly cease and the object will just move with a constant velocity. This is why a ball that you’re spinning on a rope above your head will fly away in a straight line when you let it go. Once there is no force to keep it turning (accelerating), it just continues at a constant velocity (speed and direction).
Again, it does not have to be that way. There could be only a gradual resistance to acceleration, where the rate would gradually slow before an object came to rest at a constant velocity. This would mean that the ball released from above your head would continue turning for a while before it straightened out. Baseball pitchers would appreciate the ability to throw the ball faster and with much greater amounts of curve in this universe (although hitters wouldn’t like it so much).
There could also be a universe with zero resistance to acceleration. This would mean that once something began accelerating, it would accelerate at that same rate forever. In that strange universe, the ball released from above your head would continue spinning forever, and if you threw the ball it would eventually approach the speed of light.
So, changing just one physical law can have large effects and different areas of the multiverse could exhibit some very strange types of motion. I think I would like to see some of those. Perhaps we will simulate some of them one day, or invent video games where people could play with different physical laws. Or perhaps we’re already in one of those simulations, and people from a different universe are observing the effects of our laws right now.
*The description of certain terms will serve as their definition in the context of this post.
EconUnleashed 