The WHY of speed of light vs. the FACT thereof

[Dale]

I've taken a couple of days to think about this. Two thoughts:

1. The fact that I have not provided a clear positive definition of reality--"Reality is..."--is a consequence of my conception of reality. I start with the notion that our knowledge is limited, that there is more to the physical universe than we have been able to measure. Given that assumption, a comprehensive definition of physical reality is probably out of reach, because one cannot define positively what one does not know. The best I can do (at this point) is a tautology: Reality is what is. I'm not happy with that; I doubt that you are.

Thanks for making that effort here. Interestingly, in all of the conversations I have had with people about defining "reality" this is only the second time that someone has actually proposed a definition, so I do appreciate having a relatively productive discussion.

I am glad that you are not happy with that definition. The big problem scientifically is that there is no clear experiment that can be used to determine "what is", particularly in the context of how you want to use the term "reality". So your definition would be a philosophical definition rather than a scientific definition. That is fine but doesn't belong on this forum. The only definition I can come up with for "reality" is religious so it doesn't belong here either which is why I avoid the term on this forum so carefully.

2. The scientific community has a tendency to blur--or at times ignore--the line between aspects of a theory which are backed up by direct measurement and those which are inferred from those measurements. In other words, scientists tend to treat their theories as completely "real", forgetting that our knowledge of reality is limited.

Sure, but that is the nature of science and inductive reasoning. We make an experiment and then we generalize the results into a theory that predicts the outcome of experiments we have not yet performed. A theory that was simply a catalog of experimental results and made no predictions would be a pretty useless theory.

It certainly is possible that if we did the Hafele-Keating experiment in airplanes painted neon pink instead of white that we would get a different result. Should we therefore hesitate to make statements about time dilation on neon pink aircraft? Well, we have a theory that accurately describes the result obtained on white aircraft (and all other results obtained to date) and according to that theory the color of the paint for the aircraft will not change the result. So we have good reason to believe that we know the result for neon-pink aircraft even though it has not been tested.

 

[AdrianZ]

Lorentz did not give wrong interpretations of the equations but you are right that Einstein said there is no need to insist on the existence of ether but you are not right when you say that his 2nd assumption is an experimental FACT. It is not and never can be. It is an assumption which doesn't matter if it is true or not. What is an experimental fact is the round trip speed of light is a constant. The 2nd postulate is that both halves of that round trip are the same which can not be measured or demonstrated to be either true or false.

It is no more possible to disprove the existence of the ether than it is to prove the existence of the ether. In fact, what Einstein's second postulate says is that you can assume that ANY inertial frame IS the one and only absolute ether frame.

what I claimed is based on the book "Introduction to Special Relativity" by Robert Resnick. if Lorentz had given a correct interpretation of the equations then the credit of the theory would've gone to him not Albert Einstein. the results of experiments like the Michelson-Morley experiment, the Fizeau experiment and many others leaded to the development of different theories like like the FitzGerald-Lorentz contraction theory, but all of those theories failed to justify later experiments. the only theory that has been proved right in all experiments so far is Einstein's special theory of relativity which is also mathematical consistent and can be simplified to Newtonian mechanics when v/c approaches zero.

about our inability of proving/disproving the existence of Aether, I think you are right. that's why I used "maybe" in my sentence. but we have many experiments against the idea of Aether, including the Michelson-Morley experiment. therefore we can't deny the possibility of an existing ether, but we can surely deny the theories developed based on the ether postulate through experiments.

 

[GregAshmore]

Thanks for making that effort here. Interestingly, in all of the conversations I have had with people about defining "reality" this is only the second time that someone has actually proposed a definition, so I do appreciate having a relatively productive discussion.

I am glad that you are not happy with that definition. The big problem scientifically is that there is no clear experiment that can be used to determine "what is", particularly in the context of how you want to use the term "reality". So your definition would be a philosophical definition rather than a scientific definition. That is fine but doesn't belong on this forum. The only definition I can come up with for "reality" is religious so it doesn't belong here either which is why I avoid the term on this forum so carefully.

Sure, but that is the nature of science and inductive reasoning. We make an experiment and then we generalize the results into a theory that predicts the outcome of experiments we have not yet performed. A theory that was simply a catalog of experimental results and made no predictions would be a pretty useless theory.

It certainly is possible that if we did the Hafele-Keating experiment in airplanes painted neon pink instead of white that we would get a different result. Should we therefore hesitate to make statements about time dilation on neon pink aircraft? Well, we have a theory that accurately describes the result obtained on white aircraft (and all other results obtained to date) and according to that theory the color of the paint for the aircraft will not change the result. So we have good reason to believe that we know the result for neon-pink aircraft even though it has not been tested.

Granted that a theory which makes no predictions is of little value. However, the claims of scientists should be scientific--falsifiable in principle. I chose the example of infinite charge on the electron because even the claimants know that the claim is not falsifiable. The adherents to that part of the theory believe something to be real which cannot be measured.

Early on, I found such claims to be an impediment to acceptance of the theory. I felt that the whole body of work--which seems half crazy to the newbie anyway--was of the same character as those unscientific claims.

I'm headed back into Taylor-Wheeler. It's time for me to learn how to work with the theory, not just read about it.

 

[Dale]

the claims of scientists should be scientific--falsifiable in principle.

I agree completely.

I'm headed back into Taylor-Wheeler. It's time for me to learn how to work with the theory, not just read about it.

Always a good choice. Please let us know if you get stuck at some point.

 

[phyti]

Since the speed of light c, can be derived from the permittivity and permeability constants of the vacuum, why can't the constant c result from the properties of space?
GR models gravity as the effect of mass deforming space, and quantum theory deals with vacuum fluctuations.
Space is something by virtue of its properties.

 

[Buckethead]

... It is not and never can be. It is an assumption which doesn't matter if it is true or not. What is an experimental fact is the round trip speed of light is a constant. The 2nd postulate is that both halves of that round trip are the same which can not be measured or demonstrated to be either true or false.

It is no more possible to disprove the existence of the ether than it is to prove the existence of the ether. In fact, what Einstein's second postulate says is that you can assume that ANY inertial frame IS the one and only absolute ether frame.

This is one of the most interesting, succinct and profound comments I have read on this forum. If it could be stated more concisely I would create a huge banner in 1000 pt text and hang it on the wall in my office. Nice job!

 

[grav-universe]

This is one of the most interesting, succinct and profound comments I have read on this forum. If it could be stated more concisely I would create a huge banner in 1000 pt text and hang it on the wall in my office. Nice job!

Yes, I also agree that was very well put indeed.

 

[ghwellsjr]

what I claimed is based on the book "Introduction to Special Relativity" by Robert Resnick. if Lorentz had given a correct interpretation of the equations then the credit of the theory would've gone to him not Albert Einstein. the results of experiments like the Michelson-Morley experiment, the Fizeau experiment and many others leaded to the development of different theories like like the FitzGerald-Lorentz contraction theory, but all of those theories failed to justify later experiments. the only theory that has been proved right in all experiments so far is Einstein's special theory of relativity which is also mathematical consistent and can be simplified to Newtonian mechanics when v/c approaches zero.

about our inability of proving/disproving the existence of Aether, I think you are right. that's why I used "maybe" in my sentence. but we have many experiments against the idea of Aether, including the Michelson-Morley experiment. therefore we can't deny the possibility of an existing ether, but we can surely deny the theories developed based on the ether postulate through experiments.

I don't suppose you could provide exact quotes from your book that make statements such as "Lorentz gave a wrong interpretation of his equations" or "experiments have proven SR correct and other theories incorrect" or "we can deny ether based on experiments"? Please?

I like what you said in your first post about Lorentz believing in æther while Einstein said there was no need to insist on the existence of æther. In other words, Lorentz felt the need to always pick a reference frame in which he was never at rest with respect to the æther so that MMX would experience length contraction and time dilation (because there was little chance that he could be at rest in the absolute æther frame) while Einstein said its OK to always assume that MMX is at rest in the absolute æther frame and everyone else that is moving are the ones that are experiencing length contraction and time dilation. It's that difference that made Einstein stand out from all the others and why he deserves all the credit for Special Relativity.

But you should acknowledge that if Special Relativity is an accurate description of reality, and that it affirms every inertial reference frame as being exactly like an absolute æther rest frame, then it certainly cannot be used to deny that an absolute æther rest frame could exist (but known only to Mother Nature).

 

[yossell]

Having a definition of a word certainly is a precondition if you want to make meaningful statements using the word. If I were to try to discuss my opinion about "the distinction between farglmoger and our measurement of farglmoger" wouldn't you consider it necessary for me to define "farglmoger"?

If you can't define "real" then stop using the word. Otherwise you are literally writing nonsense.

Unless one allows circular definitions - which wouldn't help - I don't see how one can insist that all terms must be definable. Eventually, a chain of definitions must come to an end.

I don't know how to define away the logical constants `and', `or', `there is', `for all', nor the mathematical notion `set'.

 

[Dale]

Unless one allows circular definitions - which wouldn't help - I don't see how one can insist that all terms must be definable. Eventually, a chain of definitions must come to an end.

Sure, but I am not looking for a chain of definitions and would even be OK with a rather circular definition of reality as long as it were something that could be measured or otherwise determined experimentally. My objection isn't about constructing a minimal axiomatization of the word "reality" but rather constructing an operational definition that would be relevant to a scientific discussion instead of a philosophical or religious discussion.

 

[AdrianZ]

I don't suppose you could provide exact quotes from your book that make statements such as "Lorentz gave a wrong interpretation of his equations" or "experiments have proven SR correct and other theories incorrect" or "we can deny ether based on experiments"? Please?

I like what you said in your first post about Lorentz believing in æther while Einstein said there was no need to insist on the existence of æther. In other words, Lorentz felt the need to always pick a reference frame in which he was never at rest with respect to the æther so that MMX would experience length contraction and time dilation (because there was little chance that he could be at rest in the absolute æther frame) while Einstein said its OK to always assume that MMX is at rest in the absolute æther frame and everyone else that is moving are the ones that are experiencing length contraction and time dilation. It's that difference that made Einstein stand out from all the others and why he deserves all the credit for Special Relativity.

But you should acknowledge that if Special Relativity is an accurate description of reality, and that it affirms every inertial reference frame as being exactly like an absolute æther rest frame, then it certainly cannot be used to deny that an absolute æther rest frame could exist (but known only to Mother Nature).

according to the book I mentioned, Lorentz talked about length-contraction, not time dilation. if you claim Lorentz had come up with a consistent theory explaining time dilation and invariant light speed please provide resources verifying your claim.

I didn't say the existence of Aether can be denied, I said if we pose a theory based on the idea of Aether, we can do experiments to check the predictions of the theory and if it fails, the theory will be rejected. That's what we have done so far. what I meant was "all other theories based on the Idea of Aether before the SR had been rejected through experiments and Einstein's special theory of relativity was the only theory that successfully solved the contradictions between Maxwell's equations and Newtonian mechanics".

 

[Domenico Mico]

I appreciate the responses, although some are beyond my ken - IANAP. However, their net net still seems to be (1) it is because it is, and (2) that's the way the math requires it. For some reason, I don't have the same problem with time being flexible (two seemingly incongruent sides of the same coin?). It's all amusing as heck.

Hi, JoeShiner,
One more answer for you. This is how I see it. Once upon a time there was a monopole which, as Faraday wanted, generated an electric field which in turn generated a magnetic field which in turn etc... etc...
It appears that both of them at the starting line were full of energy and behaved like a bull at the gates with the end result that one second later, just before the end, we find them again, but this time they both are breathless. At the end of the run there it is: the surviving magnetic component is so tired that is unable to generate a further electric field and puts the final touch at the speed of light. The story ends, I think, with a somewhat undulating magnetic component joining, in its extremely weak conditions, his predecessors for the make-up of our expanding universe.

 

[harrylin]

what I claimed is based on the book "Introduction to Special Relativity" by Robert Resnick. if Lorentz had given a correct interpretation of the equations then the credit of the theory would've gone to him not Albert Einstein. the results of experiments like the Michelson-Morley experiment, the Fizeau experiment and many others leaded to the development of different theories like like the FitzGerald-Lorentz contraction theory, but all of those theories failed to justify later experiments. the only theory that has been proved right in all experiments so far is Einstein's special theory of relativity which is also mathematical consistent and can be simplified to Newtonian mechanics when v/c approaches zero.

about our inability of proving/disproving the existence of Aether, I think you are right. that's why I used "maybe" in my sentence. but we have many experiments against the idea of Aether, including the Michelson-Morley experiment. therefore we can't deny the possibility of an existing ether, but we can surely deny the theories developed based on the ether postulate through experiments.

Actually that is very inaccurate, as it's quite the opposite (but it's not your fault). Different book writers credited Einstein and Lorentz differently. And this is what Einstein admitted in 1907, discussing what then became known as the Lorentz-Einstein theory:

"We [...] assume that the clocks can be adjusted in such a way that
the propagation velocity of every light ray in vacuum - measured by
means of these clocks - becomes everywhere equal to a universal
constant c, provided that the coordinate system is not accelerated.
[..this] "principle of the constancy of the velocity of light," is at
least for a coordinate system in a certain state of motion [..] made
plausible by the confirmation through experiment of the Lorentz theory
[1895], which is based on the assumption of an ether that is
absolutely at rest".
- http://www.soso.ch/wissen/hist/SRT/E-1907.pdf

I will elaborate on that clarification by Einstein in a direct reply to the OP, as it is very helpful to understand the "WHY".

 

[harrylin]

I have puzzled over a couple of things relating to the speed of light as a constant to all observers. I fully recognize that it has been demonstrated to be so, and that those demonstrations have been confirmed by facts such as the existence and workability of GPS; however, these go much more to the FACT THAT the speed of light is a constant. I also recognize that, mathematically speaking (and I'm no math whiz), it MUST be a constant, since "somethin's got to give"; however, these do not satisfy my need to understand WHY the speed of light is a constant; or, put another way, HOW CAN IT BE that the speed is constant? I mean, everything else "gives" - the cars on the highway going toward one another or passing one another... and the trains, the planes, etc., but not light. HOW is it happening? Is light scrunching up or stretching out somehow as it needs to (but not as to speed [?!]), to the various and relevant observers?

As an aside - With reference to various experiments that have been conducted involving gravitational effects on time using atomic clocks aboard airplanes, if a quantum entanglement experiment was conducted involving photons that are "on" two different airplanes at two different gravitational states (and tied to atomic clocks, of course), what would be the result?

BTW, I am not a physicist and perhaps have no business at all sticking my nose in, but if some of you more well versed in these matters than I might take pity on me (and provide a bit of forgiveness of my ignorance, and benefit of the doubt, I'd be most appreciative). Thank you!

Hi Joe, several people have in part answered your question but if I did not overlook it, they forgot to mention clock synchronization.

First of all, in GPS the speed of your GPS receiver relative to a GPS radio signal is NOT constant, but exactly like you expect from cars and airplanes etc (in modern jargon, the closing velocity is c-v). In GPS, the Earth is a single system in which clocks everywhere are synchronized in agreement with each other.

What you probably can picture is Lorentz's model to explain light propagation. In that model, light is a wave in a medium and its speed is independent of the speed of the source. Moving objects in that medium slightly deform and clocks slightly slow down, but those are small effects that are not the main issue for replying your question that seems to focus on the one-way speed of light.

To measure the one-way speed, we have a light ray that propagates from one clock in the lab to another clock.

Funny enough, you can find any speed you like, depending on how you synchronize your clocks. In relativity, if you set up an independent measurement system then you typically use light or radio waves to synchronize your clocks; when you measure the same speed both ways, then you have synchronized your clocks!

Probably you can imagine that in a moving system, light takes longer in the forward direction than in the backward direction; and that by adjusting the clocks, you can make the measured speed equal in both directions. That speed would be very slightly less than c if the lab did not very slightly contract; those two effects exactly cancel.

With that explanation, light is not scrunching up or stretching out somehow, but objects are slightly affected; and the main explanation to your question is that clocks of independent systems are synchronized in such a way that the measured speed is again c.

I hope that this explains to you or some others "how it can be" that the speed that is measured in systems that move relative to each other, is constant.

Einstein clarified it as follows:

"We [...] assume that the clocks can be adjusted in such a way that
the propagation velocity of every light ray in vacuum - measured by
means of these clocks - becomes everywhere equal to a universal
constant c [..]
[this] "principle of the constancy of the velocity of light," is [..] made
plausible by the confirmation through experiment of the Lorentz theory
[1895], which is based on the assumption of an ether that is
absolutely at rest".
- http://www.soso.ch/wissen/hist/SRT/E-1907.pdf

And from my rather limited knowledge of quantum entanglement, the results should be independent of gravitational potential.