Easy. Prove it's not and win a Nobel for it.

Like Newtonian mechanics, our current understanding is incomplete but it's not wrong. It gets some very fundamental predictions correct when we collect data to check those predictions. Those are facts that any competing theory must also get correct.

It has already been proven not constant. An accelerating frame of reference (or even a frame of reference residing in a gravitational field) will measure c to be different velocities in different directions. The accelerating frame of reference is not any more special than any other frame of reference and can validly state that c is not constant.

 

https://newt.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm

The fine structure constant, α
So is there something that physicists can measure for which a change over time would have meaning? Yes, there is. Any quantity that doesn't have units can be measured as a ratio. For example, the fine structure constant α is a measure of the relationship between electromagnetic effects and quantum effects and it has no units.
Because it has no units, we can think of it as a ratio. Here is a simple explanation: In the Bohr-de Broglie-Sommerfeld model of the hydrogen atom, an electron 'orbits'* a proton, 'travelling' in a circle at 'speed' vH. In this picture, the fine structure constant

• α = vH/c

and takes a value close to 1/137. (There are few pure numbers in fundamental physics, so the number 137 is especially memorable for physicists.) Let's look at more basic expressions for α later. For now, let's ask:


Has the fine structure constant changed over time?
The obvious answer is: not much, or we should have noticed it. The temperature of stars (including the sun) is a strong function of α, so even a modest change would have been very observable. For instance, life has been on Earth for at least a quarter of the age of the universe, and perhaps as much as a third. This puts a limit on how much the sun's temperature could have varied over that time. (Another, much stricter limit is imposed by measurements of the reaction products of a natural atomic reactor at Oklo in Gabon that was active about two billion years ago.) So any change over this time scale must be small. But is the change exactly zero over all time?
Several years ago, my colleagues at UNSW, cosmologist John Webb and theoretical physicists Victor Flambaum and Vladimir Dzuba developed a new way of determining α from the spectra of quasar light that had passed through gas clouds on its way to earth. Quasars are very bright, so one can measure the atomic absorption spectra of very distant gas clouds. (Image courtesy John Webb.)

 

It has already been proven not constant. An accelerating frame of reference (or even a frame of reference residing in a gravitational field) will measure c to be different velocities in different directions. The accelerating frame of reference is not any more special than any other frame of reference and can validly state that c is not constant.

You are too smart to think that's what I mean with my statement to him.

• Modern relativity is based on Einstein’s two postulates. The first postulate of special relativity is the idea that the laws of physics are the same and can be stated in their simplest form in all inertial frames of reference. The second postulate of special relativity is the idea that the speed of light c is a constant, independent of the relative motion of the source.

https://courses.lumenlearning.com/physics/chapter/28-1-einsteins-postulates/

 

https://newt.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm

You know your stuff! Thanks for sharing.

 

https://newt.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm

That second link you provided:
Bohr-de Broglie-Sommerfeld model of the hydrogen atom

Fascinating reading material! Nice. Thanks.

 

@dcbingaman

"Accelerating frames of reference and or frames of reference under the influence of gravitational fields (bending of space/time) will already show that c is not a constant and will vary with the direction of c with respect to the reference body. The reference body may consider itself stationary within a gravitational field or moving. It does not matter"

You know ,

I used to "know" the speed of light was a constant,
I now know that its all relative to how its observed,

Ahh

My universe is expanding,
no pun intended,

I just about "got" Schrödinger's cat, now this ,,,
Im only 100 years behind,,,

Thank you

 

That second link you provided:
Bohr-de Broglie-Sommerfeld model of the hydrogen atom

Fascinating reading material! Nice. Thanks.

A thought over weekend
SI measurements,
a fair few seem to be hooked back to the speed of light being constant
If I have this half right, that's not a problem as to any observer, there light speed is constant ?

is that half right ?

Thanks you

 

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

Is c, the speed of light in a vacuum inertial frame, constant?
At the 1983 Conference Generale des Poids et Mesures, the following SI (Systeme International) definition of the metre was adopted:

The metre is the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.

This defines the speed of light in vacuum to be exactly 299,792,458 m/s. Unfortunately it doesn't mention anything about inertial frames, but you can consider a measurement in an inertial frame to be implied.

But this is not the end of the matter. The SI is based on very practical considerations. Definitions are adopted according to the most accurately known measurement techniques of the day, and are constantly revised. At the moment you can measure macroscopic distances most accurately by sending out laser light pulses and timing how long they take to travel using a very accurate atomic clock. (The best atomic clocks are accurate to about one part in 1013.) It therefore makes sense to define the metre unit in such a way as to minimise errors in such a measurement.

The SI definition makes certain assumptions about the laws of physics. For example, it assumes that the particle of light, the photon, is massless. If the photon had a small rest mass, the SI definition of the metre would become meaningless because the speed of light would change as a function of its wavelength. The SI Committee could not just define it to be constant; instead, they would have to fix the definition of the metre by stating which colour of light was being used. Experiments have shown that the mass of the photon must be very small if it is not zero (see the FAQ entry What is the mass of the photon?). Any such possible photon rest mass is certainly too small to have any practical significance for the definition of the metre in the foreseeable future, but it cannot be shown to be exactly zero—even though currently accepted theories indicate that it is. If the mass weren't zero, the speed of light would not be constant; but from a theoretical point of view we would then take c to be the upper limit of the speed of light in vacuum so that we can continue to ask whether c is constant.

The SI definition also assumes that measurements taken in different inertial frames will give the same results for light's speed. This is actually a postulate of special relativity, discussed below.

Yes, apparent superluminal speed being observed is pretty common in the universe.
https://iopscience.iop.org/article/10.1086/307499/pdf
https://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/Superluminal/superluminal.html

 

A thought over weekend

SI measurements,

a fair few seem to be hooked back to the speed of light being constant

If I have this half right, that's not a problem as to any observer, there light speed is constant ?



is that half right ?


Thanks you

I wouldn't speculate too much about it. As far as what is currently known the speed of light is indeed constant for all NON-ACCELERATED reference frames.

In the real world of course there may be slight aberrations in the actual speed recorded simply because there are accelerations happening all around us. Not only are we orbiting the Sun in a constantly accelerating-decelerating fashion (as implied by Kepler's laws) but according to Einstein's General Theory of Relativity even the Earth itself creates a gravitational field which effectively constitutes an acceleration. In this neck of the cosmos at least, a non-accelerated reference frame is kind of an elusive beast!

 

https://phys.org/news/2022-02-einstein-relativity-theory-strict-based.html

Einstein's relativity theory passes strict test based on LHAASO observation

Einstein's theory of relativity, the cornerstone of modern physics, requires that physical laws have Lorentz symmetry. In the more than 100 years since Einstein proposed his theory of relativity, the validity of Lorentz symmetry has undergone numerous experimental tests.

However, there is an irreconcilable contradiction between general relativity, which describes gravity, and quantum mechanics, which describes the laws of the microscopic world. In order to unify general relativity and quantum mechanics, theoretical physicists have made unremitting efforts and have developed theories such as string theory and loop quantum gravity theory. These theories predict that Lorentz symmetry is likely to be broken at very high energies, which means relativity may need to be modified at high energies.

LHAASO is a large-scale cosmic ray experiment in China. During the process of construction in 2021, the world's highest energy gamma ray event was recorded by LHAASO, with its energy up to 1.4 PeV (1 PeV = 1015 electron volts). At the same time as setting a world record, it also provided a valuable opportunity for exploring the basic laws of physics, such as Lorentz symmetry.

Lorentz symmetry breaking may cause high-energy photons to become unstable, rapidly decaying into an electron-positron pair or into three photons. "In other words, the high-energy photons automatically disappear on their journey to Earth if Lorentz symmetry is broken, which implies the energy spectrum we measured should be truncated at a particular energy," said Prof. Bi.

The data from LHAASO show that the current gamma ray spectrum continues to high energies above PeV, and no "mysterious" disappearance of any high-energy gamma ray events has been found. This result shows that Lorentz symmetry is still maintained when approaching the Planck energy scale.

 

http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel