QUESTION: "A key factor in the commonly held view of time today, that time is an illusion, is the notion that the speed of light is absolute, a postulate of Einstein’s special theory of relativity...Setting aside any other debates about relativity theory for the moment, why would the speed of light be absolute? No other speeds are absolute, that is, all other speeds do indeed change in relation to the speed of the observer, so it’s always seemed a rather strange notion to me."
LEE SMOLIN: "Special relativity works extremely well and the postulate of the invariance or universality of the speed of light is extremely well-tested. It might be wrong in the end but it is an extremely good approximation to reality. This issue is discussed in some detail in the book. We are also working on the website, which will have on-line appendices to give more details of some topics including special relativity. Even if special relativity ultimately is transcended, it is a beautiful experience to comprehend it." https://www.independent.com/2013/04/17/time-reborn/
Mitchell J. Feigenbaum: "In this paper, not only do I show that the constant speed of light is unnecessary for the construction of the theories of relativity, but overwhelmingly more, there is no room for it in the theory." http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1234v1.pdf
Mark Buchanan: "...a photon with mass would not necessarily always travel at the same speed. Feigenbaum's work shows how, contrary to many physicists' beliefs, this need not be a problem for relativity." http://www.newscientist.com/article/mg20026801.500-why-einstein-was-wrong-about-relativity.html
Jean-Marc Levy-Leblond: "The evidence of the nonzero mass of the photon would not, as such, shake in any way the validity of the special relativity. It would, however, nullify all its derivations which are based on the invariance of the photon velocity." http://o.castera.free.fr/pdf/One_more_derivation.pdf
Sabine Hossenfelder: "If photons had a restmass, special relativity would still be as valid as it's always been. The longer answer is that the invariance of the speed of light features prominently in the popular explanations of special relativity for historic reasons, not for technical reasons. Einstein was lead to special relativity contemplating what it would be like to travel with light, and then tried to find a way to accommodate an observer's motion with the invariance of the speed of light. But the derivation of special relativity is much more general than that, and it is unnecessary to postulate that the speed of light is invariant." http://backreaction.blogspot.bg/2016/05/dear-dr-b-if-photons-have-mass-would.html
Jean-Marc Lévy-Leblond: "It could even be that future measurements highlight a tiny, but not zero, mass of the photon; the light then would no longer go at the "speed of light", or, more precisely, the speed of light, henceforth variable, would no longer be identified with the invariant speed limit. The operational procedures brought into play by the "second postulate" would become null and void ipso facto. Would the theory itself be invalidated? Fortunately, not at all." http://o.castera.free.fr/pdf/Chronogeometrie.pdf
LEE SMOLIN: "Special relativity works extremely well and the postulate of the invariance or universality of the speed of light is extremely well-tested. It might be wrong in the end but it is an extremely good approximation to reality. This issue is discussed in some detail in the book. We are also working on the website, which will have on-line appendices to give more details of some topics including special relativity. Even if special relativity ultimately is transcended, it is a beautiful experience to comprehend it." https://www.independent.com/2013/04/17/time-reborn/
Mitchell J. Feigenbaum: "In this paper, not only do I show that the constant speed of light is unnecessary for the construction of the theories of relativity, but overwhelmingly more, there is no room for it in the theory." http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1234v1.pdf
Mark Buchanan: "...a photon with mass would not necessarily always travel at the same speed. Feigenbaum's work shows how, contrary to many physicists' beliefs, this need not be a problem for relativity." http://www.newscientist.com/article/mg20026801.500-why-einstein-was-wrong-about-relativity.html
Jean-Marc Levy-Leblond: "The evidence of the nonzero mass of the photon would not, as such, shake in any way the validity of the special relativity. It would, however, nullify all its derivations which are based on the invariance of the photon velocity." http://o.castera.free.fr/pdf/One_more_derivation.pdf
Sabine Hossenfelder: "If photons had a restmass, special relativity would still be as valid as it's always been. The longer answer is that the invariance of the speed of light features prominently in the popular explanations of special relativity for historic reasons, not for technical reasons. Einstein was lead to special relativity contemplating what it would be like to travel with light, and then tried to find a way to accommodate an observer's motion with the invariance of the speed of light. But the derivation of special relativity is much more general than that, and it is unnecessary to postulate that the speed of light is invariant." http://backreaction.blogspot.bg/2016/05/dear-dr-b-if-photons-have-mass-would.html
Jean-Marc Lévy-Leblond: "It could even be that future measurements highlight a tiny, but not zero, mass of the photon; the light then would no longer go at the "speed of light", or, more precisely, the speed of light, henceforth variable, would no longer be identified with the invariant speed limit. The operational procedures brought into play by the "second postulate" would become null and void ipso facto. Would the theory itself be invalidated? Fortunately, not at all." http://o.castera.free.fr/pdf/Chronogeometrie.pdf