Why is the Speed of Light Constant?

[DaveC426913]

That is quite the bold statement! However, it is not factual. The fact is, the more accurate you make the scale, the less likely it is you will ever get it to balance! ... I am convinced that physicists, by convention assign that value only to hide the fact that we cannot yet measure it.

Empirical observation is only one method of scientific analysis. There are ways of showing something to be true that go beyond empirical observation. Thus is the nature of our universe as mathematically quantifiable.

For example, we can demonstrate - without the ability to observe or measure it - that an electron is a fundamental particle, with no substructure. The reasoning is that, as per HUP, any smaller particles will have a proportionately larger momentum of uncertainty. The upshot of this is that the substructural components of the electron would be larger and more massive than the electron itself.

Another famous one is the hypothesis of hidden variables affecting entangled particles at a distance. Read up on Bell's hidden variables theorem, which demonstrates, astonishingly, that there can't be hidden properties that we don't know about.

This is just a couple of simple examples. I'm simply trying to point out to you that empirical measurement is only one of many tools.

 

[Varnick]

That is quite the bold statement! However, it is not factual.

I disagree with both of these points. Firstly, I can't see how the statement is "Bold" when it has been a part of established standard model physics for over 40 years. As to your second point, Neutrinos are described as electrically neutral by the standard model, which is backed up by large amount of experimental data. If your principle of "Nothing can be 0" were true, then leptons would take part in strong interactions, which is not the case. Your idea that we only measure things to a certain level, and that they do have a charge but it's just really small is, simply, false. Please see

http://en.wikipedia.org/wiki/Standard_model
http://en.wikipedia.org/wiki/Neutrino

 

[DrGreg]

what i wanted to imply...doesn't it sound a bit weird that we are generating mass out of nothing...I mean...There should be something around which to form the remaining mass...something which can act as a base... also...if the mass comes out of nothing...then how are we going to exactly predict its position or velocity...(since it won't be moving anymore with the velocity of light)so we are not able to predict either position or velocity of this newly generated mass...Please clear this doubt..

Well, as I said before, most physicists nowadays don't use the concept of relativistic mass at all; they call it "energy" instead via the equation E = m_{rel}c^2, and so they write instead

E^2 = m_{inv}^2c^4 + p^2c^2​

and they say a photon has energy but no mass (meaning "invariant mass").

So, your comment above would translate as "we are generating energy out of nothing" -- except that it's not out of nothing, all the energy that goes into a photon (or any other particle) will have come from somewhere else. The total energy of all particles in a "closed" system (not interacting with anything outside) is always constant.

Note also that in quantum theory you cannot exactly predict the position or velocity of anything, you can only calculate a probability.

 

[schroder]

I disagree with both of these points. Firstly, I can't see how the statement is "Bold" when it has been a part of established standard model physics for over 40 years. As to your second point, Neutrinos are described as electrically neutral by the standard model, which is backed up by large amount of experimental data. If your principle of "Nothing can be 0" were true, then leptons would take part in strong interactions, which is not the case. Your idea that we only measure things to a certain level, and that they do have a charge but it's just really small is, simply, false. Please see

http://en.wikipedia.org/wiki/Standard_model
http://en.wikipedia.org/wiki/Neutrino

So your argument is based upon the “Authority” of Wikipedia and the Standard Model?
Great advances in science are not made by defending the status quo and not daring to rock the boat. If Newton and Einstein did science in this way, where would we be now? Still in the 17th century, I reckon. All I am proposing here is that we should not accept zero values because it makes our equations “come out right” and reinforce our existing theories. Good science is not done by people with closed minds. I have not claimed a non-zero value but I do accept the possibility of such for the mass of a photon and there is no empirical evidence that refutes that possibility. Instead of simply accepting zero mass, I would much rather see what minimum value of mass a photon can possesses without completely undermining physics as we know it and also what minimum value might account for the finite velocity of light. A zero value, in my estimation, should result in an infinite velocity of light, which we know is nonsense. What else can cause light to have a velocity less than infinity if not some amount of mass? And don’t you think the mathematics is ugly when we use one equation for objects that are traveling at less than c, and another for light? If you placed light in a box in such a way that it did not change the momentum of the box, only increased the energy of the box, what effect would that have on the mass of the light box? These are questions that even Wikipedia cannot answer!

 

[Fredrik]

A zero value, in my estimation, should result in an infinite velocity of light, which we know is nonsense.

Your estimation is wrong. When we take Minkowski space to be the mathematical model of spacetime and take the postulates of quantum mechanics seriously, a mass of zero implies that the speed is =1, not infinity. We could of course reject SR or QM, but then the question is, what would we replace them with? I assume you have an answer to that, since you were able to estimate the speed of massless particles to be infinite.

If you placed light in a box in such a way that it did not change the momentum of the box, only increased the energy of the box, what effect would that have on the mass of the light box? These are questions that even Wikipedia cannot answer!

The mass would increase by the amount E/c², where E is the energy. I would be surprised if that answer isn't somewhere in Wikipedia.

 

[Varnick]

So your argument is based upon the “Authority” of Wikipedia and the Standard Model?
Great advances in science are not made by defending the status quo and not daring to rock the boat. If Newton and Einstein did science in this way, where would we be now? Still in the 17th century, I reckon. All I am proposing here is that we should not accept zero values because it makes our equations “come out right” and reinforce our existing theories. Good science is not done by people with closed minds. I have not claimed a non-zero value but I do accept the possibility of such for the mass of a photon and there is no empirical evidence that refutes that possibility. Instead of simply accepting zero mass, I would much rather see what minimum value of mass a photon can possesses without completely undermining physics as we know it and also what minimum value might account for the finite velocity of light. A zero value, in my estimation, should result in an infinite velocity of light, which we know is nonsense. What else can cause light to have a velocity less than infinity if not some amount of mass? And don’t you think the mathematics is ugly when we use one equation for objects that are traveling at less than c, and another for light? If you placed light in a box in such a way that it did not change the momentum of the box, only increased the energy of the box, what effect would that have on the mass of the light box? These are questions that even Wikipedia cannot answer!

So first my statement is bold, now it is the status quo? How intriguing. Of course we should look to improve on theories, I know that there are flaws in the standard model, but unless you can propose a better theory with charged neutrinos, I think we must agree that neutrinos are, for now, electrically neutral.

V

 

[DaveC426913]

Great advances in science are not made by defending the status quo and not daring to rock the boat. If Newton and Einstein did science in this way, where would we be now?

Oh jeez. Here we go... The ol' "let's break all the rules" gambit.

If you were to "do science" the way Newton and Einstein did, you would have brushed up on the science and done your research rather than make wild, fanciful armchair speculations about things you've never studied.

Sounds like food for the Lock ness monster...

 

[Varnick]

Thank-you, DaveC426913, for some sense finally. This last page or so of discussion is because of my wild and spurious claim that a photon had no mass. If I knew such unsupported ideas weren't welcome here, I would not have posted. </frustrated sarcasm>

V

 

[George Jones]

I have not claimed a non-zero value but I do accept the possibility of such for the mass of a photon and there is no empirical evidence that refutes that possibility. Instead of simply accepting zero mass, I would much rather see what minimum value of mass a photon can possesses without completely undermining physics as we know it

Any non-zero rest mass for photon would destroy gauge invariance of electrodynamics, which, in turn, would probably mean that quantum electrodynamics would not be renormalizable. Renormalizable QED is, over a wide range of experiments, the most accurately verified theory of physics.

Also, while we do not have direct empirical that the rest mass of a photon is exactly zero, very small experimental upper bounds on the rest mass of the photon exist.

[EDIT]
http://www.ncbi.nlm.nih.gov/pubmed/12633416

puts an experimental upper bound of about 10^{-54} kg.
[/EDIT]

With this, I'm putting this thread to bed.