Why no one has measured the speed of light

[ItsNick]

Interesting video

The idea that the speed of light moves at the same speed in any direction is only a convention.

Einstein said that light’s one-way speed “is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity"

Edited October 31, 2020 by ItsNick

[commie]

2 hours ago, ItsNick said:

The idea that the speed of light moves at the same speed in any direction is only a convention.

That's a misleading statement. It's a convention in a particular context but not in most others. Therefore it's far from being only a convention.

As always with the speed of light, this is tied up with causality. This is most obvious when considering the CMB I think. If the speed of light was infinite in one direction in some kind of objective sense rather than merely from the perspective of a hypothetical photon, it would imply that the creation of the universe is happening now... but in a very different sense than is usually meant: that is, it would have happened during billions of years in the past in an expanding and then contracting circle of which your location happens to have been the center all along while it happens now in one particular direction where at an unknowable distance lies a place which is also lies in all directions around you, except in the past... a "convention", you say?

[ItsNick]

36 minutes ago, commie said:

a "convention", you say?

Yes. Because the one-way speed of light is c  (and the same as the two-way) by definition (and admitted as one by Einstein). Not because of empirical research. It's literally called the Einstein Synchronisation Convention: https://en.wikipedia.org/wiki/Einstein_synchronisation

And the speed of light doesn't necessarily have to be infinite for the two-way speed of light to differ from the one-way speed of light.

But I get your point. A difference between the two implies very odd consequences. But that's no argument against it being a convention.

[Willie]

What people in the scientific community call c is veeeeeeery narrowly defined as the speed of light in a perfect vacuum. That’s not how fast light travels in reality because reality isn’t a perfect vacuum. It’s the supposed “speed limit of the universe” because nothing, not even the photons of which light is composed, can traverse the distance from point A to point B faster than c.

[Leo Gura]

The speed of light is NOW/Infinity.

Everything is instant. Time does not exist.

Light is only given a speed relative to human cognition.

[diamondpenguin]

Lol. I can't believe I didnt think of that. It's so simple. But makes so much sense and no one thinks it's real.

[hyruga]

https://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html

Scientists measured the speed of light numerous times. 

And light travels at a slower speed through water, glass or other medium. 

We humans cannot even fully understand the Duality of light (Light as a photon/energy packet and light as a wave)

Edited November 1, 2020 by hyruga

[commie]

8 hours ago, ItsNick said:

And the speed of light doesn't necessarily have to be infinite for the two-way speed of light to differ from the one-way speed of light.

It doesn't have to but that would address issues with a finite speed of light, in QM for instance. So far as I know, that's the only argument for dropping the "convention".

8 hours ago, ItsNick said:

But I get your point. A difference between the two implies very odd consequences. But that's no argument against it being a convention.

It's an argument against it being "only a convention"... unless you redefine the word "convention", that is.

5 hours ago, Leo Gura said:

The speed of light is NOW/Infinity.

Everything is instant. Time does not exist.

That's the usual perspective (the one of a hypothetical photon) I mentioned. We were talking about something more interesting (and problematic).

Edited November 1, 2020 by commie

[ItsNick]

9 hours ago, hyruga said:

Scientists measured the speed of light numerous times.

Nobody has!   (in a vacuum)

Not directly at least. Only indirectly (the two-way speed of light).

@commie Hmmm.. Yes I did not really consider problems of a finite speed in QM. Doesn't QFT solve such problems?

14 hours ago, Leo Gura said:

Light is only given a speed relative to human cognition.

Yeah the concepts of "speed" and "time" and "space" are all relative to observers. They don't exist in any absolute sense.

[commie]

1 hour ago, ItsNick said:

Doesn't QFT solve such problems?

The math works of course but that doesn't address the more conceptual ("spooky") issues with non-local causality I was alluding to (or at least not directly). I'm far from well-read about this but I noticed a couple accessible-looking papers were published a month ago but I failed to make time for them so far...

I expect one day people will laugh at our interpretations of QM, specifically w.r.t. apparently non-local phenomena.

1 hour ago, ItsNick said:

Yeah the concepts of "speed" and "time" and "space" are all relative to observers. They don't exist in any absolute sense.

This is too often taken out of context to mean something grandiose but you're left with stuff like the CMB which is only compatible with its mainstream explanation in the context of a small set of frames.

In any case c is used in contexts not directly related to speed, time or space (most obviously to figure the energy released by nukes and such). You always have the option to go deny facts with solipsistic arguments but really, the speed of light is about as absolute as anything gets.

[ItsNick]

@commie In terms of Physics basic relativity of speed to intertial frames of reference is not very grandiose indeed (although it might be! It's subjective).

The relativity of time and space is more grandiose (Einstein's theories shocked the entire scientific community).

Beyond Physics all these concepts are all imaginary and relative to human cognition (like Leo said).

And the speed of light, or c, or speed of causality is absolute in terms of Physics. But still relative (to at least our universe) in a grander sense,

Edited November 1, 2020 by ItsNick