C as Constant Question?

I've read several textbooks on relativity, and I haven't come across any convincing arguments as to why the constant c, should be the same everywhere and for all time. So I was wondering if the general argument goes something like this:





Assume that we are not in some special place in the universe and that the laws of physics are the same everywhere for all inertial reference frames. c as constant is part of our laws of physics.





We want to check to see if relativity should hold at some arbitrary space-time coordinate, Point.Q.





If the Principle of Relativity holds now, for all reference frames in our now (call our now, Now.A), then it is possible to find another reference frame in our now, call this one Frame.B, such that in Frame.B's now, point.Q lies on Now.B's now axis.





Since the c as constant holds for Frame.B (by assumption), it must also hold for Point.Q





Look about right?

C as Constant Question?
I've always wondered that too. If c were very slowly changing (and that begs the question of whether it is Planck's constant h and/or the permativity constant epsilon that is changing), the constant approximation would yield consistent agreement with all short-time experimental results. The question is what would be the effect on long-time experiments and could we differentiate it from c being constant for all time in some experiment. E.g., perhaps it could be a small effect which gets mixed with the Doppler effect and is hard to distinguish, for a multi-billion year old view of a quasar, say. Maybe c is constant and it is 5 billion light years away, or maybe c varies slowly and it is 4 or 6 billion light years away. Could we tell? It might not violate Hubble's law, just attribute it to more than one cause--universal expansion and fundamental "constant" shift/drift. In fact, perhaps the expansion and shift of the constants could be related. Afterall, would it be surprising if the speed of propogation in a media changed as it expanded/reduced density? Maybe the universe is like the surface of a taut, expanding balloon (but with an extra dimension). As the balloon expands, it grows tauter, and the frequency of vibrations traveling through it changes.


Now, what is the "media" is for E%26amp;M propogation in the universe? Space time? The quaint old idea of the Aether? No, not that. Michelson-Morley's experiment disuaded most of us of that idea.


Anyhow, I ramble. But I do think it is a good question you ask and not one that I've heard adequately addressed by physicists or astrophysicists.
Reply:Right C is the speed of light in all reference frames. You can also see this mathematically. Suppose you're in a rocket moving relative to earth and the rocket shoots forward a signal with speed c relative to the rocket. The speed , u,of the signal relative to the earth is


u = (u' + v)/(1+ u'v/c^2), where u' is the speed of the signal and v is the speed of the rocket.


So u = (c+v)/(1+cv/c^2) = (c+v)/(1+v/c)


=c(1+v/c)/(1+v/c) = c.


Therefore the observers in both reference frames, the earth and the rocket, see that the speed of the signal is c. This is different from the conclusion in classical physics, where the observer on earth would see the that the speed of the signal is c+v.








Later note: Maybe it's that deterministic philosophy held my many scientists, that if we know something about the universe at a particular point and time, then we somthing about it at all other points and times. But I agree with you, maybe the laws of physics break down entirely at the edge of the universe.
Reply:Uh, the value of "C" is only considered mathematically when in a "perfect" vacuum. The speed of light slows down considerably when shined from a flashlight thru a glass of water- the blue shades bend less, the red shades bend more, and the photons DO slow down. If they didn't it wouldn't refract
Reply:Responders prune and epidavros are both correct. Relativity theory was developed to explain the unexpected result of Michelson and Morley's experiment, which showed that the speed of light is constant in all reference frames. M%26amp;M had been expecting to see the speed of light influenced by the earth's motion around the sun, and were surprised to find that it isn't.
Reply:If you don't believe Albert, Try to refute him.


He said that the one Constant in the Universe is


the Velocity of Light. Nothing has "Shown Up"


yet to prove him wrong. He said nothing can travel


faster than light. Some people say that light


travels at 185,000 miles per second and other


people say 186,000 miles per second. Maybe its


185,364 miles per second. Makes no difference


to Albert. He came up with the formula that has not been seriously disputed.
Reply:see ? c? E= C+C squared=E ) the M squared=E ,now mathmatical lingo them-th=em so does mc2? relativity is symply finding similarity or rhimes ,if mc2 then e =educated and if its not the see or c then yur blind and dont see that c is not always a question but a statement telling yu to c!! so see, its not a constant question unless yu never see the point and are constantly askin
Reply:There has to be a reason why the value of "c" was chosen. The reason lies in a three-fold concept. It is the physics trilogy:





E = mc2, why mass exists





m = E/c2, the formation of mass





c2 = E/m, why a gravitational/time field exists





The last demonstrates why relativity becomes a product. There is a three page, easy to understand, writing at http://timebones.blogspot.com
Reply:The independence of c on reference frame is an experimental result. Its not something you can work out from theory - its an observation on which the theory is based.

redbud