What if the most fundamental concept in physics didn’t exist, or at least not as we think it does?
Begin with a simple case from everyday experience. You’re sitting motionless on a couch in your living room. It’s quiet. You’re still. But are you moving?
Experience says no, you’re not going anywhere. You’re resting.
Now consider Earth’s rotation. The planet is spinning about 1,000 miles per hour at the equator. That means your body is arcing through space, even as you feel completely still.
But that’s not all. Earth is orbiting the Sun at roughly 67,000 miles per hour, so your position is changing even far more rapidly than we can even imagine.
But the Sun is moving too, as our solar system sweeps around the galaxy at over 450,000 miles per hour. And the galaxy? It too is hurtling through space, relative to other galaxies, estimated at an astounding 1.3 million miles per hour.
So are you moving or not?
It seems as if you’re moving relative to almost everything in the universe, except perhaps your couch. We can conclude, as Einstein did, that each of those motions is relative.
But now imagine the strangeness for an observer from afar, in the seemingly nowhere of deep space. If this observer could make out the details of your path, he would not see you traveling in a straight line. Your path would appear as a strange swirling, whirling, and almost inexplicable motion of all these other motions combined. So would that be your real motion?
Well, there’s the catch. What makes his measurement of your motion any more real? Are any of those measurements more real than the others? What defines “real” motion at all? Relativity tells us none of them is the “real” one. Each is just a different “frame of reference.”
A frame of reference is the physical perspective measurements are made from. We can think of it like a coordinate system attached to an observer or object. When you’re sitting on a train, your frame of reference moves with the train, making other passengers appear stationary while trees outside appear to move.
And even stranger, do you have objectively defined motion?
The Disintegration of Motion
This leads to something even more fundamental. As we consider your motion through the universe, we realize there is nothing to set one frame of reference over another, nothing that defines how you truly are moving. You cannot answer the question “Am I really moving?” without also asking “Relative to what?” So according to two different frames of reference, you could be moving and not moving at the same time. The strangeness comes from the fact that both are equally real and true in reality, not just as a mental model.
This may create a subtle crisis, not because we’re unsure how to calculate things, but because the very concept of motion begins to disintegrate.
If we strip away all frames of reference, motion evaporates. Nothing is still and nothing is moving. There are no points to compare, no coordinate grid to assign. No direction exists. Only the object itself, alone.
“Motion,” it turns out, is not a property an object has. Let that truly sink in for a moment. We are not saying it isn’t real, because motion is very real. After all, when an object accelerates, that can be felt in any frame of reference. However, we are saying that motion doesn’t exist as a property of matter. Instead, it is only a statement about how one body or system’s state changes in relation to another.
And here is the real insight: If we remove all other objects, anything else to relate to, then motion itself dissolves. Again, let that sink in. If you have no other objects, then there is no motion.
Oh, but surely the object is still moving in space, but we just can’t tell. No, this would be to make motion a property of an object or pretend that there is some invisible grid that is there in space, but we just can’t see it.
Let’s take this thought experiment further. What happens when we apply it not to a human on a couch, but to the most elementary physical situation possible?
What happens when we imagine a universe with only one particle and ask what motion means then?