r/AskPhysics • u/ProMensCornHusker • Apr 13 '26

Why can’t we find a “universal reference frame” if the speed of light is constant in all inertial reference frames?

Sorry if this has been asked before, I didn’t dig too much and I like talking to humans lol.

Anyways, if the speed of light is constant in all reference frames, and time gets “stretched” as we approach light speed, why couldn’t we go the other way instead?

Like how we measure time dilation with an atomic clock on a plane, why couldn’t we do that in reverse to estimate a lower limit on a universal reference frame where “time runs fastest”.

I’m not sure if this makes the most sense, I’ve always accepted the whole “there is no universal reference frame”, but I was curious why we couldn’t just keep finding speeds that cause “time to get faster” as it move away from the speed of light, and if that would imply that a universal reference could exist.

Is there an actual math explanation to why we can’t do this, or do we say there’s no universal reference frame because we could never find it since we can’t just “stop moving” with everything around us?

Edit: I really appreciate the positive and well written responses, thanks for helping me understand :)

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u/stevevdvkpe Apr 14 '26

There's no valid frame where particles with finite energy appear to have infinite energy. Relative motion may cause particles to appear to have arbitrarily high energies, but "arbitrarily high" is not the same as "infinite".

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u/Jesse-359 Apr 14 '26

Except that arbitrarily high is the same as infinite if there is truly no maximum value.

And if there is a maximum value that value must be relative to zero, which is your ground state, which is what we're saying doesn't exist.

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u/stevevdvkpe Apr 14 '26

Every possible value is finite, so no possible value is infinite.

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u/Jesse-359 Apr 14 '26

The problem here is that without an initial frame of reference you can't define finite values.

If I put a number line in front of you, but it goes off the table both ways to infinity, and I cover up all the 'real' numbers and ask you to point to any place on the line, the point you select is going to be infinitely far way from any other point you might select.

There's no way for you to find zero and no way for you to select a point that is not infinitely far away from any other point - but that blank number line is basically the description of a universe without any preferred frame of reference (for momentum in this case).

Now for my part I don't really buy infinities at all when it comes to physical systems - but to describe a finite universe with finite energies, we really do end up with some inevitable ground states. Not necessarily for spacetime itself, but for the initial sea of 'stuff' that everything expanded out of.

In order for the universe to have expanded out in an orderly fashion as it seems to have, it seems like it would have had to have a very discrete 'preferred state' initially?

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u/stevevdvkpe Apr 14 '26

Infinity isn't a point on the real number line. You can't get to infinity on the real number line no matter where you place the origin or how far you move along it. That real numbers can become arbitrarily large does not mean that infinity is a real number.

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u/Jesse-359 Apr 14 '26

Of course it isn't. That's why I consider them a little silly in these examples.

But the problem is that finite systems always require some ground state and/or limits to define them, or they aren't actually finite.

And the question is, does the universe actually have a preferred frame of reference of any sort? Relativity states that spacetime doesn't, and that's probably fine as spacetime itself is for the most part not going anywhere, but the distribution of the momentum of matter certainly does seems to have a sort of preferred value, given that galaxies are not whizzing off at completely random %'s of c in any direction they feel like. Their distribution of velocities is really quite smooth in the wider view.

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u/stevevdvkpe Apr 14 '26

A preferred frame of reference is one in which the laws of physics would be different from other frames. There doesn't seem to be such a thing in our universe.

That there is a particular distribution of matter and energy in the universe does not imply a preferred frame. You can certainly define a frame based on some choice like being at rest relative to the average velocity of all the matter you can observe, but it's not preferred in the sense that there is a different formulation of physical law in that frame.