Is the Speed of Light Really Slowing Down?

[jonegil]

what y'all think about that portuguese guy (joão magueijo) and his colleagues who have proposed that the speed of light has varied since the big bang (it has slowed down according to this new stream)...do you agree with this?

 

[Janus]

Even if c has varied over time, this would not make Einstein wrong. Special Relativity only requires that all observers measure the same relative speed for light regardless of their own relative motions, it doesn't matter whether that value has changed over time or not.

 

[G01]

I don't think it means that Einstein was wrong. The universal speed limit is and always was the speed of light. It's just that the speed limit has changed since then.

 

[turbo]

I don't think it means that Einstein was wrong. The universal speed limit is and always was the speed of light. It's just that the speed limit has changed since then.

Einstein said that the speed of light in a vacuum can only be considered to be constant if you can ignore the effects of gravitation imposed by the matter embedded in the space under question. This is the thought experiment model that gave rise to Special Relativity. In his 1920 book on (S and G) relativity, he said that the speed of light in a vacuum must be variable in general relativity, to allow for the refractive effects predicted by that theory.

Look at Chapter 22 here:

http://www.bartleby.com/173/

Einstein may have been disastrously wrong on this point and if so, we may have to cede the mathematicians the field and agree that somehow the Universe knows how to obey his field equations. It's going to take a pretty big effort to press that point. Penrose says that GR and QT are both going to take some pretty big hits before a theory of quantum gravity can be formulated. I think that QT will skin by and GR will take some huge hits. If there is anybody here who feels that GR would have emerged in its present form if Einstein had been aware of the flat rotation curves of spiral galaxies or the excess lensing and binding forces of clusters, I ask you if such a pragmatic man would have postulated that the discrepancy was caused by invisible, unseeable, undetectable particles that only interacted gravitationally, instead of exploring the idea that Newton's gravitational constant might be a variable and not a constant?

 

[pervect]

what y'all think about that portuguese guy (joão magueijo) and his colleagues who have proposed that the speed of light has varied since the big bang (it has slowed down according to this new stream)...do you agree with this?

I agree that Joao has proposed theories with a "variable speed of light". They also meet PF guidelines for discussion, being published in peer reviewed journals.

However, these theories have not found any experimental confirmation (at least not any reproducible experimental confirmation) that I'm aware of.

The main benefit I see of Joao's theories is that his theories has prompted us to experimentally look at the possibility of the fine structure constant varying. (I must add that I may not be giving credit to other authors - I don't know if Joao is the first person to propose such a variation or not).

In any event, the current status as far as I'm aware is that experiment does not find any reproducible evidence for such a variation (i.e. for Joao's theories). See for instance

http://prola.aps.org/abstract/PRD/v64/i10/e103505

The thing that I dislike about Joao is his attempts at self promotion. In my personal opinion, here's no reason that a theory with no experimental support should be popularized in the lay press.

 

[pervect]

Einstein said that the speed of light in a vacuum can only be considered to be constant if you can ignore the effects of gravitation imposed by the matter embedded in the space under question.

I should point out to readers who may not know any better that any local observer, using local clocks and rulers, will still measure the speed of light to be equal to 'c'. The above remarks only apply to the coordinate speed of light, something that was more popular to stress in Einstein's day than it is with the modern approach.

Ant this brings up a Pet peve: Einstein is not the only person doing physics, or even relativty. If relativity turns out to be wrong, it's not a case of "Einstein" being wrong, it's a case of Einstein, the National Bureau of standards, NIST, Clifford Will, Bradley, Airy, Michelson and Morley, Kennedy and Thorndike, Cialdea, Krisher, Champeny, Turner & Hill, DeSitter, Brecher, Alvaeger, Sadeh, Hughes-Drever, Prestage, Lamoreaux, Chupp, Phillips, Brillet and Hall, Haefle and Keating, Vessot, Alley, Bailey, Fizeau, Sagnac, Michelson and Gale, and many others being wrong too.

Furthermore, relativity has developed since Einstein's day, it's a mistake to stick one's head in the sand and ignore the more modern ways of looking at things because Einstein didn't happen to be the one who thought of looking at them that way.

 

[G01]

Ant this brings up a Pet peve: Einstein is not the only person doing physics, or even relativty. If relativity turns out to be wrong, it's not a case of "Einstein" being wrong, it's a case of Einstein, the National Bureau of standards, NIST, Clifford Will, Bradley, Airy, Michelson and Morley, Kennedy and Thorndike, Cialdea, Krisher, Champeny, Turner & Hill, DeSitter, Brecher, Alvaeger, Sadeh, Hughes-Drever, Prestage, Lamoreaux, Chupp, Phillips, Brillet and Hall, Haefle and Keating, Vessot, Alley, Bailey, Fizeau, Sagnac, Michelson and Gale, and many others being wrong too.

Good Point...

Einstein said that the speed of light in a vacuum can only be considered to be constant if you can ignore the effects of gravitation imposed by the matter embedded in the space under question. This is the thought experiment model that gave rise to Special Relativity. In his 1920 book on (S and G) relativity, he said that the speed of light in a vacuum must be variable in general relativity, to allow for the refractive effects predicted by that theory.

I see. This is interesting stuff. I'm going to look into it.

 

[rbj]

what y'all think about that portuguese guy (joão magueijo) and his colleagues who have proposed that the speed of light has varied since the big bang (it has slowed down according to this new stream)...do you agree with this?

i agree with John Barrow http://en.wikipedia.org/wiki/Planck_units#Planck_units_and_the_invariant_scaling_of_nature and Michael Duff ( http://www.arxiv.org/abs/hep-th/0208093 and http://xxx.lanl.gov/abs/physics/0110060 ) and, i think, John Baez (can't find the link here) about it.

 

[jonegil]

Michael Duff is related to string theory...the other two idk

 

[rewebster]

'Is Einstein wrong?' is, to me, the same as asking, 'Is Newton wrong?'.

I don't know if Newton expressed any self-doubts, but even Einstein was humble enough to do so.

 

[pmb_phy]

what y'all think about that portuguese guy (joão magueijo) and his colleagues who have proposed that the speed of light has varied since the big bang (it has slowed down according to this new stream)...do you agree with this?

Einstein's speed of light postulate states that the speed of light is invariant. Einstein never said it was a constant in time, although he might have assumed it.

Pete

 

[rbj]

Michael Duff is related to string theory...the other two idk

John Barrow writes books. one book (where the quote in the Wikipedia article is taken) is called The Constants of Nature; from Alpha to Omega, the numbers that encode the deepest secrets of the universe. John Baez, besides being a cousin of the more well known singer Joan Baez, is a pretty well known physicist and prof at U.C. Riverside. all of these guys have biographies on the web, including at Wikipedia.

Duff doesn't use a spit of string theory to take issue with the VSL claims. it's much more fundamental than that. it's essentially that whatever Magueijo or Davis or Davies claim, the speed of light (or whatever ostensibly instantaneous action) is always 1 Planck length per Planck time and when we measure or perceive anything, any physical quantity, we are measuring a dimensionless quantity, like counting tick marks on a ruler. all we really know are the dimensionless quantities and those are the only quantities that matter, in the final analysis.

if you say, "see here, the number of meter sticks that light travels in a second has changed." (assuming we have reverted back to the pre-1960 definition of the meter), then i would say that either or both the number of Planck lengths per meter stick has changed and/or the number of Planck times per clock tick has changed. and it's those two dimensionless numbers that are the salient values. it all boils down to dimensionless parameters, and c nor G nor \hbar nor \epsilon_0 are dimensionless numbers, so i can choose my units of length, time, mass, and charge so that those four constants can come out to be anything (real and positive) that i want. and nature does not give a rat's ass what system of units i choose to use.

it's not that the variation in dimensionful constants is wrong, it's not even wrong. the variation of dimensionful constants is not operationally meaningful. you may think that you have measured or perceived a change in some dimensionful parameter, but what really has changed is some dimensionless ratio of like dimensioned quantities. it's these dimensionless values that are perceivable and meaningful.

 

[Voltage]

Einstein said that the speed of light in a vacuum can only be considered to be constant if you can ignore the effects of gravitation imposed by the matter embedded in the space under question. This is the thought experiment model that gave rise to Special Relativity. In his 1920 book on (S and G) relativity, he said that the speed of light in a vacuum must be variable in general relativity, to allow for the refractive effects predicted by that theory. Look at Chapter 22 here...

For the record, turbo means this:

"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its result hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)..."

 

[G01]

'Is Einstein wrong?' is, to me, the same as asking, 'Is Newton wrong?'.

I don't know if Newton expressed any self-doubts, but even Einstein was humble enough to do so.

History does tell us that eventually every theory is going to be replaced by one which is more "correct" in the sense that it covers more phenomena and more situations. I don't think this means the original theory was wrong, it just means that there is a range of validity to the theory.

 

[rewebster]

History does tell us that eventually every theory is going to be replaced by one which is more "correct" in the sense that it covers more phenomena and more situations. I don't think this means the original theory was wrong, it just means that there is a range of validity to the theory.

Sort of...

Some (the main idea) are (may be)/were entirely wrong, and the newer one may just use 'some' of the info of the 'old' one---

 

[jonegil]

Popper expresses this very well on his books...a theory must be falsified...there are no "True and Permanent" theories...look at the example of earth...geocentric model...

 

[rewebster]

I think there are some facets of some theories that will remain as permanent and will have some validity (adjusted for specific variables/new info).

 

[jonegil]

I think there are some facets of some theories that will remain as permanent and will have some validity (adjusted for specific variables/new info).

Yes, the progress of science is based on that but it is like an asymptote..it will never reach the prefection

 

[rewebster]

I guess that depends on your ideas of 'perfection' and the application that the specific facet is being used to calculate was is needed.

e.g.--And some think that Einstein is the one holding the dice.

 

[Ruian]

a theory is based on a postulates... that postulate probably be wrong or right... But we have to consider a theory to be true for a moment... and yes it might be replaced by another theory which is true or more true or more technically explained...

 

[triggernum5]

If the speed of light was to vary, what would be the speed of propagation of the change itself? And if there were to be a finite speed of propagation from a particular point, what could be the effects?
(I guess the context I'm visualizing is analagous to gravitational propagation, because unless c varies uniformly with time since the big bang, there could be no universal simultanaity, which in this scenario would be necessary for relativity to hold-up without corrections.. Would it not?

 

[ssiminga]

this might sound stupid, but if it were true that the speed of light can vary over time, can this possibly mean that there is some extremely slow inertial frame that moves at the "speed of propogation"

 

[J.F.]

what y'all think about that portuguese guy (joão magueijo) and his colleagues who have proposed that the speed of light has varied since the big bang (it has slowed down according to this new stream)...do you agree with this?

Fock-Lorentz transformations
and time-varying speed of light
http://arxiv.org/PS_cache/gr-qc/pdf/9905/9905046v1.pdf

For bodies not being points SR is wrong.

 

[Antenna Guy]

For bodies not being points SR is wrong.

I've wondered whether two bodies of mass coming into contact might constitute a [non-transformable] discontinuity in a Lorentz manifold.

Although I'm not smart enough to say if that may, or may not constitute a problem for GR...

Regards,

Bill

 

[J.F.]

I've wondered whether two bodies of mass coming into contact might constitute a [non-transformable] discontinuity in a Lorentz manifold.

Although I'm not smart enough to say if that may, or may not constitute a problem for GR...Regards,Bill

When Einstein formulated his special relativity, he developed his dynamics for point particles. Of course, many valiant efforts have been made to extend his relativity to rigid bodies, but this subject is forgotten in history.

http://www.math.rutgers.edu/~shtelen/Research/GillZachary97.pdf

 

[Antenna Guy]

When Einstein formulated his special relativity, he developed his dynamics for point particles. Of course, many valiant efforts have been made to extend his relativity to rigid bodies, but this subject is forgotten in history.

http://www.math.rutgers.edu/~shtelen/Research/GillZachary97.pdf

Interesting - The last time I posted an interpretation suggestive of a 4-space vector with an imaginary time component, I had my post deleted and got a slap on the wrist...

Thanks for the link - I'll have to do some digging on Poincare.

Regards,

Bill

 

[Alfi]

Interesting thread.

reminds of Leibniz and his nocturnal doubling thoughts.

It makes it experimentally difficult to measure a change with equipment that changes.

 

[belliott4488]

It looks like this is an old thread that just got a new lease on life, so I'll throw out what I believe is a relevant question: is the expansion of the universe equivalent to the speed of light getting smaller?

I asked this question of the professor teaching my GR course long ago, and he answered "Yes," although I don't think I've seen anyone assert that point since then. It makes me wonder if he was just shutting me up and the answer should have been, "No."

The reason for asking it is that I was wondering what it meant for space-time to expand, i.e. relative to what? If space is expanding, then our measuring rods all expand along with it, so we shouldn't notice any difference when we measure distances (the equivalent statement can be made about our clocks). The only thing that would indicate that distances had indeed grown would be that it would now take light longer to get from one point to another, but to us that could look either like the distance had grown or like light had slowed down.

Are the two truly equivalent, or is there some other standard relative to which we can say that the universe (or space-time in general) expands?

 

[dst]

It looks like this is an old thread that just got a new lease on life, so I'll throw out what I believe is a relevant question: is the expansion of the universe equivalent to the speed of light getting smaller?

I asked this question of the professor teaching my GR course long ago, and he answered "Yes," although I don't think I've seen anyone assert that point since then. It makes me wonder if he was just shutting me up and the answer should have been, "No."

The reason for asking it is that I was wondering what it meant for space-time to expand, i.e. relative to what? If space is expanding, then our measuring rods all expand along with it, so we shouldn't notice any difference when we measure distances (the equivalent statement can be made about our clocks). The only thing that would indicate that distances had indeed grown would be that it would now take light longer to get from one point to another, but to us that could look either like the distance had grown or like light had slowed down.

Are the two truly equivalent, or is there some other standard relative to which we can say that the universe (or space-time in general) expands?

Wouldn't that mean that dimensionless constants based on c would also change?

 

[belliott4488]

Wouldn't that mean that dimensionless constants based on c would also change?

Like the fine structure constant? I guess so ... would that be wrong?