Is the speed of light truly constant in all reference frames?

[ataraxic89]

From the POV of light it shouldn't be moving at all as the closer you get to c the shorter the distance in the axis of direction. As light is at c there is no distance. But then there is no axis of direction either. And light neither moved nor took any "time" to move or not move because time has "stopped" at c. So it is now a particle-wave that seems to be a point outside of time, aka zero dimensional.

If I recall light is also a force carrier of EM with no mass (though it does have momentum) and as such when it hits something it ceases to exist and imparts the energy in its momentum to the thing, perhaps nudging an electron up a level.

I guess I am just confused. How is light both not moving, teleporting (distance over no time), and taking time to get somewhere? Does this mean that at c the universe itself is zero dimensional? Perhaps what we experience as dimensions is merely interference with quantum fields but really it is all in the same "place". My brain hurts.

 

[PeterDonis]

From the POV of light it shouldn't be moving at all

There isn't a well-defined "POV of light" in the sense you mean. Please see the forum FAQ on this:

https://www.physicsforums.com/showthread.php?t=511170

If I recall light is also a force carrier of EM with no mass (though it does have momentum) and as such when it hits something it ceases to exist and imparts the energy in its momentum to the thing, perhaps nudging an electron up a level.

This is correct, yes.

Does this mean that at c the universe itself is zero dimensional?

No. It means that "at c" is not a valid "point of view" in the sense you mean.

 

[Naty1]

My brain hurts.

not surprising...it takes some time to think about what is physical and what isn't.

Just the 'idea' of massless particles seems a bit crazy...so we need to develop some different perspectives...

Many years ago people worried about falling off the edge of the [flat] earth...and some must have wondered why the oceans didn't spill over...and the sea level go down...

Now we know the Earth is about spherical, we have a different issue: If people in, say, Canada are standing 'upright', how can people in India, say, on the opposite side of the sphere think they are also standing 'upright'...why doesn't blood rush to their heads??... So such perspectives have to be abandoned because they don't fit.

 

[jalsck]

I asked a similar question here https://www.physicsforums.com/showthread.php?t=677194. I think it is an interesting question, but I'm no physicist. We observe light traveling at c not matter our frame of reference. Is this fact telling us something in addition to SR and GR about the universe? It feels like there is some concept slapping me in the face saying "hey look at me", but I just can't see it. I've taken the advice of more learned people on this forum and started working through the Lorentz transformation. At the moment I'm wondering if there is any physics that explains why light is observed to travel at c or is it just accepted as being the case. By that I mean, we know the properties of light based on our observations, but what would be the universe according to light? It's not possible to transform to light's perspective using the Lorentz transformation, that makes perfect sense. I think that fact tells us something about the universe according to light. I've got zillions of questions, but need to refrain from pestering people that have already done the study. When I'm on top of SR and GR I'll pester them ;)

 

[ghwellsjr]

I asked a similar question here https://www.physicsforums.com/showthread.php?t=677194. I think it is an interesting question, but I'm no physicist. We observe light traveling at c not matter our frame of reference. Is this fact telling us something in addition to SR and GR about the universe? It feels like there is some concept slapping me in the face saying "hey look at me", but I just can't see it. I've taken the advice of more learned people on this forum and started working through the Lorentz transformation. At the moment I'm wondering if there is any physics that explains why light is observed to travel at c or is it just accepted as being the case. By that I mean, we know the properties of light based on our observations, but what would be the universe according to light? It's not possible to transform to light's perspective using the Lorentz transformation, that makes perfect sense. I think that fact tells us something about the universe according to light. I've got zillions of questions, but need to refrain from pestering people that have already done the study. When I'm on top of SR and GR I'll pester them ;)

No, we don't observe light traveling at c. We can't observe light traveling. Instead, we define light to be traveling at c in all directions in any Inertial Reference Frame (IRF).

 

[jalsck]

No, we don't observe light traveling at c. We can't observe light traveling. Instead, we define light to be traveling at c in all directions in any Inertial Reference Frame (IRF).

Thanks for pointing that out George. If I had said that we measure light to be traveling at c in any IRF would that have been correct?

James

 

[ghwellsjr]

Thanks for pointing that out George. If I had said that we measure light to be traveling at c in any IRF would that have been correct?

James

No, it's the same problem. Part of the definition of an IRF is that light travels at c. We use that definition to establish the meaning of coordinate time throughout the IRF, in other words, to synchronize our imaginary clocks throughout the IRF. If we then turn around and "measure" how fast light travels by using the coordinate times on these imaginary clocks, we cannot help but get an answer of c.

If we use real clocks, we have to first synchronize them by using the transit time of light, or something equivalent, and then if we make a measurement, we will get c. Do you call that a measurement of how fast light travels? There is no way around this "problem". Look up the wikipedia article on the One-Way Speed of Light. You might find "physicsforums.com/showthread.php?t=656924" of interest or this one.