Paul Davies 2003: "Was Einstein wrong? The idea of a variable speed of light, championed by an angry young scientist, could one day topple Einstein's theory of relativity. Einstein's famous equation E=mc^2 is the only scientific formula known to just about everyone. The "c" here stands for the speed of light. It is one of the most fundamental of the basic constants of physics. Or is it? In recent years a few maverick scientists have claimed that the speed of light might not be constant at all. Shock, horror! Does this mean the next Great Revolution in Science is just around the corner?" http://www.prospectmagazine.co.uk/magazine/waseinsteinwrong/
It was just hype in 2003 - the "mavericks" were selling their books - but the suggested dramatic consequences if the speed of light is variable, not constant as Einstein postulated in 1905, are by no means an overestimation. They are even an underestimation, judging from the words of the "angry young scientist" himself - the "next Great Revolution in Science" will be preceded by a sweeping catastrophe:
"The speaker Joao Magueijo, is a Reader in Theoretical Physics at Imperial College, London and author of Faster Than the Speed of Light: The Story of a Scientific Speculation. He opened by explaining how Einstein's theory of relativity is the foundation of every other theory in modern physics and that the assumption that the speed of light is constant is the foundation of that theory. Thus a constant speed of light is embedded in all of modern physics and to propose a varying speed of light (VSL) is worse than swearing! It is like proposing a language without vowels." http://www.thegreatdebate.org.uk/VSLRevPrnt.html
"But the researchers said they spent a lot of time working on a theory that wouldn't destabilise our understanding of physics. "The whole of physics is predicated on the constancy of the speed of light," Joao Magueijo told Motherboard. "So we had to find ways to change the speed of light without wrecking the whole thing too much." http://www.telegraph.co.uk/technology/2016/12/06/speed-light-discovered/
Is Einstein's 1905 constant-speed-of-light postulate false? Here is the original formulation:
Albert Einstein, ON THE ELECTRODYNAMICS OF MOVING BODIES, 1905: "...light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body." http://www.fourmilab.ch/etexts/einstein/specrel/www/
If interpreted correctly, the Doppler effect directly refutes the postulated independence from "the state of motion of the emitting body". Here is an incorrect interpretation - the postulate is saved by the false ad hoc assumption "The distance between successive pulses is now smaller than when both sender and receiver were at rest":
Albert Einstein Institute: "We will start with a very simple set-up, which you can see in the following animation. On the right-hand side, drawn in green, there is a sender that emits pulses in regular succession. On the left-hand side there is a receiver, drawn in blue. The pulses themselves are drawn in red, and they all travel at the same speed from right to left. Everytime the sender emits a new pulse, a yellow indicator light flashes once. Likewise, a flashing light indicates when a pulse has reached the receiver:
Next, let us look at a slightly different situation, where the source is moving towards the detector. We assume that the motion of the sender does not influence the speed at which the pulses travel, and that the pulses are sent with the same frequency as before. Still, as we can see in the following animation, the motion influences the pulse pattern:
The distance between successive pulses is now smaller than when both sender and receiver were at rest. Consequently, the pulses arrive at the receiver in quicker succession. If we compare the rates at which the indicator lights at the receiver and at the sender are flashing, we find that the indicator light at the receiver is flashing faster." [END OF QUOTATION] http://www.einstein-online.info/spotlights/doppler
Einsteinians make the following assumption above, which is essentially identical to Einstein's 1905 constant-speed-of-light postulate:
Assumption 1: "The motion of the sender does not influence the speed at which the pulses travel."
Assumption 1 goes hand in hand with another assumption:
Assumption 2: "The distance between successive pulses is now smaller than when both sender and receiver were at rest."
Assumption 2 is false - the pulses do not bunch up when the source (sender) is moving. If they did, by measuring the (variable) distance between the pulses, an observer in the frame of the source would know whether he is moving or at rest, which contradicts the principle of relativity.
Since Assumption 2 is false, Assumption 1 is false as well. If the speed of the moving source is v, the speed of the light relative to the receiver is c'=c+v, in violation of Einstein's relativity.
That the speed of light is variable, c'=c+v, not constant, c'=c, was proved by the Michelson-Morley experiment in 1887:
Wikipedia: "Emission theory, also called emitter theory or ballistic theory of light, was a competing theory for the special theory of relativity, explaining the results of the Michelson–Morley experiment of 1887. [...] The name most often associated with emission theory is Isaac Newton. In his corpuscular theory Newton visualized light "corpuscles" being thrown off from hot bodies at a nominal speed of c with respect to the emitting object, and obeying the usual laws of Newtonian mechanics, and we then expect light to be moving towards us with a speed that is offset by the speed of the distant emitter (c ± v)." https://en.wikipedia.org/wiki/Emission_theory
The analysis of the above information unavoidably leads to the following conclusion:
In 1887 the Michelson-Morley experiment UNEQUIVOCALLY confirmed the variable speed of light posited by Newton's emission theory of light and refuted the constant (independent of the speed of the light source) speed of light posited by the ether theory and later adopted by Einstein as his 1905 second postulate.
Banesh Hoffmann says essentially the same:
Banesh Hoffmann, Relativity and Its Roots, p.92: "Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether. If it was so obvious, though, why did he need to state it as a principle? Because, having taken from the idea of light waves in the ether the one aspect that he needed, he declared early in his paper, to quote his own words, that "the introduction of a 'luminiferous ether' will prove to be superfluous." https://www.amazon.com/Relativity-Its-Roots-Banesh-Hoffmann/dp/0486406768
Here is the short truth about the Michelson-Morley experiment:
John Norton: "The Michelson-Morley experiment is fully compatible with an emission theory of light that CONTRADICTS THE LIGHT POSTULATE." http://philsci-archive.pitt.edu/1743/2/Norton.pdf