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Why is c invariant for all FORs? Special R took it as a postulate but it did not explain it,,,
It's a bit chicken and egg-ish. Einstien believed that c had to be constant for all observers and in exploring this turned to time dilation and length contraction. Experiment has demonstrated time dilation - more so than length contraction. However, both are necessary since the observed time dilation isn't enough by itself to keep c constant.Why is c invariant for all FORs? Special R took it as a postulate but it did not explain it,,,
That view seems backward. In the current model spacetime predates matter. And the invariance of c is only possible due to time dilation and length contraction. Eesh, anyone know a shorthand for that? How about "the phenomenon"?Before Einstein, Lorentz and others took the view that length contraction and time dilation of objects moving through an aether explained the invariance of the speed of light.
Einstein took the opposite view that the invariance of the speed of light explained length contraction and time dilation. Under that view, there is no explanation for the invariance of the speed of light, that's just a fundamental symmetry of the universe we happen to live in.
Physicists quite like explanations in terms of symmetry.
If A logically implies B and B logically implies A, then you can choose to say "A causes B" or "B causes A".And the invariance of c is only possible due to time dilation and length contraction.
It's a postulate, so it would be easy (and unhelpful) to say that it doesn't have to be explained. You choose a postulate, you apply some logic, you get some results that are valid assuming the postulate is valid, and you're done.Why is c invariant for all FORs? Special R took it as a postulate but it did not explain it,,,
Lorentz symmetry.Eesh, anyone know a shorthand for that? How about "the phenomenon"?
Thanks. Bit of a fingerful to type.Lorentz symmetry.
That's a big leap from implications to suggesting either can cause the other... How exactly do you suggest a photon might cause time dilation? Special Relativity, on the otherhand, well covers how time dilation... Lorentz symmety causes invariant c. And the experimental evidence would seem to take us beyond stating time dilation is an implication.If A logically implies B and B logically implies A, then you can choose to say "A causes B" or "B causes A".
So I could just as easily say "time dilation and length contraction are only possible due to the invariance of c."
This how the logical theory works. But in physics we always looking for a theory to explain things in a more fundamental base not just to use a chain of logical statements to reach a result!. Therefore, it is important to know how to start a good start in order to have a beautiful theory not just a logic theory. I can build up a new theory started from " the rate of heat dissipation from a hot body is directly proportional to its total surface area" but that would be a weak theory because we still have more facts to even explain that statement from a more basic logic such as the first law of thermodynamics,,, I feel that " Not all postulates can be stated in an equal Degree of Freedom"It's a postulate, so it would be easy (and unhelpful) to say that it doesn't have to be explained. You choose a postulate, you apply some logic, you get some results that are valid assuming the postulate is valid, and you're done.
SR took the invariance of the speed of light as a an assumption, though Einstein did not explain why he singled out light as a special case (Probably because electromagnetism was the only known field at the time).Why is c invariant for all FORs? Special R took it as a postulate but it did not explain it,,,
In a standford lecture on SR by Leonard Susskind, he explained it that Einstien chose to assume Maxwell was right about the speed of light being a fundamental part of the EM equations and therefore Galilean additive velocities needed to be modified.SR took the invariance of the speed of light as a an assumption, though Einstein did not explain why he singled out light as a special case (Probably because electromagnetism was the only known field at the time).
See post #3 in this thread for a better explanation:
https://www.physicsforums.com/showthread.php?t=445032
c is invariant for all Frames Of Reference because of the way the 4-dimensional universe is structured:Why is c invariant for all FORs? Special R took it as a postulate but it did not explain it,,,