The Speed Of Light Might Be Wrong
What do you all think?

The speed of light depends on the permittivity and the permeability of the matter through which light travels. Maxwell's equation in regard to the speed of light shows that. The speed of light is affected by gravity; black holes are proof of that. Light also slows down when going through glass or water. Diamonds slow it down even more. Who can tell what the permeability or permittivity is somewhere far in outer space. My guess is that the speed of light in free space has been measured as accurately as it can be done.
Molecool, When you say wrong, by how much do you think it is?
The headline is misleading, it is not really "wrong". The issue here is twofold :
1. The value of c is a purely local measurement
2. The vacuum has a nontrivial quantum structure
The consequences of (2) are negligible on small scales ( i.e. locally ), however, thus far no one has considered what kind of impact quantum effects such as pair production have on the large scale propagation of light. This is a surprising oversight, since now that someone has brought it to our attention it appears to be staring us squarely in the face But I do agree with exchemist in that we should wait for this to go through peerreview first before getting too excited or anxious about it. Also, contrary to what a few popsci articles I have seen seem to be claiming, this is not going to "break" all of our existing models on astrophysics and cosmology and send us back to the drawing board with tails between our legs. However, if this turns out to be a real effect, it will necessitate adjustments on some of our models, but the basic principles of cosmology still stand firm.
In terms of magnitude, this effect would add approximately 1 hour to the propagation time of light for every 37,000 light years of distance.
This isn't my field but I imagine a lot will turn on the incidence of pairproduction events while light is in transit. I thought I had read somewhere that the probability of pair production is related to frequency and (in the context in which I was then reading) would only be significant for gamma rays. But I suppose over intergalactic distances and times of flight, even lower frequency light may undergo this process from time to time.
You can trust neutrinos to go at the speed of light, but not necessarily photons over a vast expanse of space as photons can be interrupted in the vacuum forming electrons and positrons which then annihilate and form another photon, the whole process only taking a 'squillionth' of a second. I think that is what is being implied.
Just a little terminological remark here, this is not really pair production in a sense, this is either called vacuum polarization or photon selfenergy. Important distinction is that in this case fermions are both virtual therefore doesn´t exist at all.
edit: OK, Motl showed that this article is BS, shame on me for not seeing this :D
Last edited by Gere; July 2nd, 2014 at 04:41 PM.
Luboš Motl has a rather poor opinion of this paper and is typically blunt about it:
The Reference Frame: Franson's "breakthrough" concerning the speed of light
Would the person that understands string theory please step forward.. Bang.. that's fixed, next...
I find it concerning that how willing to use the word 'wrong' is the media..
When a adjustment due to gravity fields is all this is about.. or am I wrong again.
It's a little like the use of the word lie's.. Some times a shortage of testing experiment can lead to a error of conclusion.. fare.
Luboš Motl is from my university Oh god hes a legend
Any "journal" that CHARGES (1950$) for publishing is a scam. Any "paper" published in such a "journal" is not worth the paper it is printed on.
Yet, I have not detected any signs of NJP being a scam. It is not indexed as predatory openaccess journal, it has a legitimate Wikipedia article and it is indexed in scientific databases. Is the publication fee the sole reason to assume it is a scam or do you have other reasons?
So exactly what does it matter if there is a very small error in the measured speed?
Are you sure?
"SFU has been rated as Canada's best comprehensive university (in 1993, 1996, 1997, 1998, 2000, 2008, 2009, 2010, 2011 and 2012) in the annual rankings of Canadian universities in Maclean's magazine since 1991. The Higher Education Strategy Associates ranked Simon Fraser University 6th nationally in Science and Engineering and 10th nationally in Social Sciences and Humanities.[17] Research Infosource, Canada's leading provider of research intelligence evaluation, named SFU the top comprehensive university in Canada for "publication effectiveness" in 2006. Similar to most Canadian universities, SFU is a public university, with more than half of funding coming from taxpayers and the remaining from tuition fees. SFU was ranked 8th among all Canadian universities by Academic Ranking of World Universities  2012, and Webometrics Ranking of World Universities,[18] which ranks universities on their presence on the Internet, ranks Simon Fraser University 5th in Canada, 67th in North America and 83rd in the world."
Simon Fraser University  Wikipedia, the free encyclopedia
Simon Fraser is a real university located in Vancouver, British Columbia, Canada. To suggest it is a low grade diploma mill is simply ridiculous.
It does have a funding arrangement for graduate students to publish in open access journals.
The journals must be ones listed in the Directory of Open Access Journals
Directory of Open Access Journals
Directory of Open Access Journals
But back to the serious question.
What does a small difference in the measured speed of light at interstellar distances through space really make?
We already know that space is not a perfect vacuum and the theoretical speed of light is only through a perfect vacuum.
I believe some evidence to possibly prove this is inaccurate. Since gravity waves are similar to light waves from what I have been reading. Wouldn't this break the laws of energy? Because if a n object takes 5newtons of force to move against gravity in space on return it would have less energy on return but instead of 7 hours it would be in newtons.
If you catch what I'm saying that would be the destruction of energy which is impossible. The only way is if light and gravity waves are affected exactly the same on the way out
Actually, there are some major differences, most notably that gravitational radiation is quadrupole in nature ( EM is dipole ), and in that the polarisation states of the two are different ( 45 degrees v 90 degrees ). The notion of "energymomentum carried by a gravitational wave" is also problematic, since energy is not localisable in GR  one has to average out over several wavelengths to make this a meaningful concept, unlike in the case of EM.
I have read over the paper. Although I have not verified the details of the mathematical calculations, barring algebraic or numeric errors the QED parts make sense. I am not knowledgeable enough to review the General Relativity he uses. Basically he puts the GR in as a potential energy in the QED Lagrangian, which is surely an approximation and which I cannot judge the reasonableness of. If that idea is reasonable, then he has a very interesting idea. Basically he is saying that there is in Relativity a speed of "ideal" light, the speed light would have if it had no interactions of any kind. Then there is the actual speed of light which he gets analogously to the way the effective speed of light in dielectrics is obtained. The physics behind the smaller speed is that the photon can very briefly turn into an electronpositron pair, which might behave somewhat differently than the photon that gave rise to them. This could indeed be very, very wrong, but it isn't nonsense and the size of the effect he calculates is reasonable. I am very anxious to get the opinion of a General Relativist about the technique.
I haven't yet heard any professional ideas that definitively that refute this idea, and actually nothing that indicates that the writer had actually read the paper carefully. That lack does not mean, of course, that the paper isn't wrong, but I haven't yet seen a persuasive rebuttal.
I should perhaps mention that I am a retired particle theorist but have done no recent calculations in the field.
I would love to be able to make more technical comments on this, but my problem is that I am sitting on the opposite end of the bench  I am fairly well versed in GR, but my knowledge about QFTs is extremely limited. What we need is someone who is equally comfortable in both realms. Personally I think the paper does make sense, and I can't immediately spot any major objections either.
Pair production from photons is empirical fact, so the answer to that part is yes.
As for gravitational waves, the answer would have to be no  gravity waves and electromagnetic waves are not really similar other than in the trivial sense that both obey wave equations. Other than that, there are major differences between the two.
Take a look at this sentence: "According to general relativity [38, 39], the speed of light c as measured in a global reference frame is given by..."
also in Figure 2 (a): " Any effect that this process may have on the velocity of light is removed using renormalization techniques to give the observed value of c0. " this doesn´t seem right.
Also change in energy of photon would lead to change in wavelenght, he ignores that and this leads to his change in speed of light. Also he calculated this thing for one such process but in reality these processes are happening repeatedly, that would lead to extremely fast loss of photon energy.
I think the major problem though is that speed of light is defined by measurement of the very same photons which undergo such loop processes.
I agree that the first of your quotations raises some concern. Your comment that he seems to have kept the wavelength of the photon constant rather than using it to compensate for the change of energy looks very cogent. This looks to be a significant problem.
On your second point, I assume he is using standard techniques here. The problem is that diagram (a) gives an infinite result. His result would still be interesting if the difference between (a) and (b) would be finite, as the infinity would be absorbed into value of c in the Lagrangian. If the rest of the work makes sense a check that this renormalization works properly should be checked formally, and it would be by somebody even if he didn't. Also, both parts of Figure 2 would conserve energy in normal QFT since no new free particles are created by the diagram.
On your third point, one effect of his argument, if valid, would seem to be the replacement of the "speed of light" in Special Relativity by a "maximum possible speed" not directly attached to the photon. This is another place where justification would be needed.
Clearly Franson's paper would be only a beginning, if (and only if) it makes sense at all. The wavelength business seems to me to be a point that is very damaging. It makes me worry about whether his method of putting gravitational effect into QFT for the photon is indeed justified.
Last edited by mvb; July 8th, 2014 at 08:37 AM.
So instead of renormalizing charge he renormalized speed of light? Could you elaborate? I am not overly familiar with renormalization group. My understanding is this:
we want to find full Feynman propagator for photon. Using simple Dyson equation we can "upgrade" unperturbed propagator
to full propagator
where is one particle irreducible diagram.
Since this can work as internal line between two fermion lines then in some basic Feynman graph one gets a factor of (electrical charge) from both vertexes at the ends of propagator. Therefore internal photon propagator can be written like this
where is renormalization parameter. We can "easily" calculate that irreducible diagram and get to divergent integral, then use dimensional regularization, split it to finite contribution and divergent term and that divergence is then hidden in renormalized charge and/or renormalized field. This results in modifying lagrangian with corresponding counterterms. That is my understanding.
I don´t know how to renormalize speed of light using this standard technique. Perhaps you could explain some more. My take on renormalization is very naive and simplistic so any deeper knowledge would be appreciated.
I haven't figured out if he actually did any renormalization or not, and it isn't normally necessary to renormalize velocities, at least explicitly. I am worried that he may simply have assumed E = h f is valid and used that relation to get the speed of light. If so, I need to see a justification for putting a potential energy for the photon into E = h f. I now think that this may be the weak point of the paper.
However, in any event I would like to know rigorously that virtual pairproduction does or does not effect properties that depend on a particle's moving at the speed of light. I haven't seen it done, and I suspect that no one thinks about the possibility. After all, this process is much like the progress of a photon through a dielectric, which in fact does affect the effective speed of the light. Moreover, neutrinos can move faster than "effective photons" in a dielectric.
He doesn´t do any renormalization in his paper. He actually says that in standard renormalization procedure the effect of selfenergy on speed of light is removed. Figure 2 (a): "...Any effect that this process may haveon the velocity of light is removed using renormalization techniques to give the observed value of c0.... " This doesn´t seem right to me.
What he is saying is that the infinite parts of the renormalization are not changed, and the additional terms are finite. I read past that originally, and I don't especially like it now that you have pointed it out. Skimming section 3 again I see that he really hasn't checked the finiteness of the process, and he assumes E=h f to get the speed. So, as you are pointing out, he hasn't really proved anything.
So I think where we are is that he has a rough calculation with the intriguing result that he roughly matches the delay time between arrival of the photons and the neutrinos from the supernova of 1987, and no proof that his calculation is likely to be correct. I hope (I think) that someone will try to do the calculation better. It has been 50 years more or less since I worked through a real renormalization calculation, and I don't really want to dig out the old books and try it again, especially since a negative result would likely get no attention whatsoever.
Not necessarily. There is a nonzero probability for this to happen spontaneously in vacuum. That's the main idea behind the paper.
The two main differences are :What are the main differences between them?
1. Gravitational waves are quadrupole in nature, whereas EM radiation is dipole
2. The polarisation modes for gravitational waves are offset by 45 degrees, whereas the EM ones are 90 degrees
No, gravitational waves are periodic oscillations in the metric of spacetime, whereas EM radiation are excitations of the electromagnetic field.are gravitational waves EMR anyway?
I am not sure how you define "regular gravity". Under normal circumstances gravity is static, in the sense that the coefficients of the metric don't depend on time. Gravitational waves on the other hand are described by a timedependent metric.and why are they different from regular gravity?
Last edited by Markus Hanke; July 10th, 2014 at 01:20 AM.
Excellent, and clear as usual, Marcus, thanks a lot. You are a great tutor!
I just ran into another piece of data that is relevant to the Franson paper, because it provides another possible mechanism for later arrival of photons relative to neutrinos from supernova 1987a. In a note about recent scientific results it was reported that evidence had recently been found for the passage of photons from an astronomical object through an ionized plasma, with a resulting change in the frequency of the photons. The plasma acts like a dielectric for the photons going through; this means that the effective speed of the light will be lowered while it is passing through the plasma. It wouldn't take much of this to produce the time difference between the neutrinos that are believed to have come from the supernova and the light seen in ordinary telescopes. This means that there is a possible conventional explanation for the neutrinos arriving first, preventing a proof that the photons were delayed by virtual pair production.
I still think that the idea is fascinating, but I don't see how it will be quickly made plausible that the idea is correct.
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