The universal constancy of c

[eiapeteides]

Einstein does not define the units for distance (m) and time (s) independently of the speed of light c. Special relativity defines a time interval as distance divided by c and distance as time interval multiplied by c:

 

c = 300.000.000 m/s

s = 300.000.000 m/c

m = cs/300.000.000

 

If, in the equations above, we substitute s or m with their respective definitions we obtain:

 

c = 300.000.000m/300.000.000m/c <=> c=c

 

The statement c=c is surely always true independently of the actual value of c. This is a classical example of a circular argument. If the units of measurement are defined by nothing more then the postulate of the universal constancy of c then it shouldn’t come as a surprise that measurements utilizing those units can’t but confirm the universal constancy of c.

 

It appears as if in special relativity units of measurement have no physical meaning. They seem to be pure mathematical scaling factors which are set for each reference frame in such a way, that the universal constancy of c is maintained.

 

Is relativity still a theory of nature or is it just a theory of mathematics?

Is there a difference between mathematical and physical?

 

The complete argument can be found on my blog http://hellenicflame.blogspot.com

[CPL.Luke]

actually the units of time and distance are defined in relation to the velocity of an object, and the speed of light.

 

by stating that the speed of light c is constant in all reference frames you can derive the lorentz transformations of distance and time. these transformations do like you said require that the speed of light = c in all reference frames, however if this weren't the case than we would see that the transformations did not produce meaningful results.

 

for instance under relativity a ruler traveling at very high speeds relative to an observer will appear to be much shorter than an identical ruler at rest with respect to an observer. This is a testable prediction, because the prediction has been confirmed in experiment we know tha the speed of light c is constant.

[timo]

Let´s start with a minimalisitc reply:

 

If the units of measurement are defined by nothing more then the postulate of the universal constancy of c then it shouldn’t come as a surprise that measurements utilizing those units can’t but confirm the universal constancy of c.

You should ask yourself whether it was the chicken or the egg that came first.

 

 

Is relativity still a theory of nature or is it just a theory of mathematics?

Is there a difference between mathematical and physical?

Physics is a natural science meaning it should reflect the behaviour of nature. If a mathematical model properly reflects the behaviour of nature, then it´s egligible to be called a physical model (and therefore a theory of nature).

[eiapeteides]

for instance under relativity a ruler traveling at very high speeds relative to an observer will appear to be much shorter than an identical ruler at rest with respect to an observer. This is a testable prediction, because the prediction has been confirmed in experiment

 

So if I understand you correctly you are saying that all observers measure c=300.000.000 m/s but the "meter-stick" gets shorter depending on the observers velocity?

 

How is c constant if all observers measure velocity in m/s but use different meter sticks?

 

And has this contraction of "meter-sticks" been ever observed?

 

I've got a masters degree in aerospace and worked 7 years for esa. I' am not an expert but quite familiar with the mathematics of special relativity. But I honestly can't see how it makes sense.

[swansont]

Einstein does not define the units for distance (m) and time (s) independently of the speed of light c. Special relativity defines a time interval as distance divided by c and distance as time interval multiplied by c:

 

I don't think SR defines time interval or distance. The constancy of c was a postulate, and inferred from E&M, which requires a constant c in all inertial frames to work. Since E&M works, it seems a reasonable thing to investigate for kinematics. The behavior of SR is a result of the postulate. Since the behavior has been confirmed, many times over, the postulate is confirmed.

[Farsight]

eiapeteides, here's how it makes sense:

 

http://www.scienceforums.net/forum/showthread.php?t=24050

[Royston]

eiapeteides, here's how it makes sense:

 

It's probably not a good idea to cite threads raised in speculations for questions raised in the 'physics' forum.

[Klaynos]

eiapeteides, here's how it makes sense:

 

http://www.scienceforums.net/forum/showthread.php?t=24050

 

Disregard this.

 

SR effects have been detected many many times...

[Farsight]

Huh? I don't challenge Special Relativity, nor do I dispute experimental confirmation of time dilation. I hold the same view as Einstein.

[Klaynos]

Huh? I don't challenge Special Relativity, nor do I dispute experimental confirmation of time dilation. I hold the same view as Einstein.

 

I wasn't saying you where, my SR comment was directed at a question asked earlier about experimental evidence of changing meter sticks. But your posts are speculation and therefore imo should not be linked to here. Hence my first comment.

[eiapeteides]

experimental evidence of changing meter sticks

 

Do you have a link to any resources about the experimental confimation of length contraction? I don't dispute your statement but I came up empty when I googled it up.

[Klaynos]

https://www.worldscientific.com/physics/3180.html

 

and:

 

http://www.google.com/scholar?q=experimental+evidence+%22lorentz+transformation%22+length+contraction&btnG=Search&hl=en&lr=

[eiapeteides]

Thanks for the links! But none of them provides any experimental evidence of length contraction. There were some proposals for experimental verification though. So far i do not see any evidence!

[swansont]

The experiments have been to confirm time dilation rather than length contraction, since it's a lot easier to measure.

[Farsight]

How about the Michelson Morley Experiment?

[swansont]

How about the Michelson Morley Experiment?

 

How is that an independent measurement of length contraction?

[Farsight]

Fitzgerald proposed length contraction as an explanation for the null result.

 

http://en.wikipedia.org/wiki/George_Fitzgerald

 

I don't know if you'd class that as independent, but eiapeteides was asking for experimental evidence and that's the best I could come up with.

[fredrik]

This is and old thread (before my time here) but I happened to see it now. Like has been said already the constancy of the speed of light is a postulate of SR. Formally there are just a few postulates in SR that formally can be treated as axioms, and SR can be derived from it.

 

The nature of the postualte of the "constancy of the speed of light" in deriving SR logically has (logically) nothing to do with electromagnetism or specific units. It might as well be written as

 

There exists a signal, whos speed of propagation is the same relative to any intertial observers.

 

This is enough. You do now have to worry about the physical nature of this signal or what units to use. It has to do with information signalling between observers.

 

One may still ask an interesting question as a teaser: Is it possible to give another answer to why is there a signal whos speed of propagation is constant to all, than that it better be accepted since it has proven consistent so far?

 

I personally hint ther there may be an alternative, abstracted way of arguing that there exists such a signal, but it remains speculative. It would have to do with the perceptoion of spacetime. And I have a feeling that it eventually boils down to information encoding and it can be argued from principles of information encoding, and the relation may be beacuse both room and time are related from first principles.

 

The units however is just some arbitrary standard and is not magical.

 

/Fredrik