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The idea of the speed of light being as fast as something can go is pretty well accepted. I'm wondering if the top speed might be (very slightly) higher? Lemme explain.

I was reading about particle acceleration, and how accelerating a particle to the speed of light would require infinite energy.

According to a quick Google search, the LHC is getting particles up to 0.999999991 c. For someone such as myself, I might as well consider that the speed of light. I mean, it's so close, right?

So what if in a similar vein, the speed of light is very, very close to the absolute top speed? Is that possible?

If the speed of light in a vacuum was something like 0.9999999999999999999999999999999999 to the absolute top speed in the universe, would we ever know the difference? (this number is just an example to show how the speed of light could be imperceptibly close to the absolute top speed, and yet still not be the fastest speed possible).

Michael Gazonda
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We would know the difference. Here are two possible ways we could tell:

One is that Maxwell's equations tell us exactly how fast light has to go, always. It doesn't matter how you're moving, theory predicts that every beam of light will always be moving at the same speed relative to you. There is only one speed for which that property can hold true, and that's the ultimate speed limit. So if light moves at a speed that's always the same, it must be moving at the ultimate speed limit.

Another way we could tell is that any particles that don't have mass must always travel at the exact same speed as all other particles that don't have mass, and that speed has to be as fast as anything could possibly go- the ultimate speed limit. If light had mass, then lower energy photons (like radio waves) would move slower than higher energy photons (like x-rays), and we would be able to measure that. We can't measure any such difference, which means that light travels at the same speed no matter what energy it has, therefore it must be massless and traveling at the ultimate speed limit.

Ergo, yes, the speed of light and the top speed through space must be equivalent. Top speed cannot be even a teensy bit higher.

There is, however, a loophole- space itself can move faster than light. As a result of that fact and the expansion of the universe, the farthest away galaxies that we can see are actually moving away from us faster than the speed of light, because the space that they occupy is expanding away from the space that we occupy. So the speed of light is not quite "the top speed inside the universe", for appropriate definitions of "speed" and "inside the universe".

Logan R. Kearsley
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