A large number of experiments have shown that both superluminal motion (not necessarily of light) and subluminal motion of light in a vacuum are possible. However the scientific community is unable to react adequately because Einsteinians bombard it with idiotic and confusing explanations, often involving "group velocity" and "phase velocity". Experimentalists are forced to include such explanations in their articles - otherwise there would be no publication. Sometimes "group velocity" and "phase velocity" turn out to be insufficiently confusing and Einsteinians resort to the ultimate weapon - the speed of something called "information" (as if Einstein had based his 1905 second postulate on the speed of information, not on the speed of light). This speed, although not defined in physics, can solve any problem of the Einstein cult:

Robert W. Boyd, Daniel J. Gauthier, Controlling the Velocity of Light Pulses: "So why do laboratory results of fast light not necessitate the superluminal transfer of information? It is believed that the explanation lies in the distinction between Vg [group velocity] and the information velocity. The group velocity can take on any value. However, the information velocity can never exceed c and, according to many models, is always equal to c." http://science.sciencemag.org/content/326/5956/1074.full

LIGO fakers: "The fact that the speed of gravitational waves is equal to the speed of electromagnetic waves is simply because they both travel at the speed of information." https://discovermagazine.com/the-sciences/why-does-gravity-travel-at-the-speed-of-light

If it were not for the confusing environment created by the Einstein cult, both superluminal motion (not necessarily of light) and subluminal motion of light in a vacuum would be regarded as commonplace. Just a few examples (note idiotic explanations as to why the effect does not topple Einstein's relativity):

"For generations, physicists believed there is nothing faster than light moving through a vacuum -- a speed of 186,000 miles per second. But in an experiment in Princeton, N.J., physicists sent a pulse of laser light through cesium vapor so quickly that it left the chamber before it had even finished entering. The pulse traveled 310 times the distance it would have covered if the chamber had contained a vacuum. Researchers say it is the most convincing demonstration yet that the speed of light -- supposedly an ironclad rule of nature -- can be pushed beyond known boundaries, at least under certain laboratory circumstances. [...] The results of the work by Wang, Alexander Kuzmich and Arthur Dogariu were published in Thursday's issue of the journal Nature." http://www.cbsnews.com/news/faster-than-the-speed-of-light/

"Physicists manage to SLOW DOWN LIGHT INSIDE VACUUM...This finding shows unambiguously that the propagation of light can be slowed below the commonly accepted figure...even when travelling in air or vacuum" http://rt.com/news/225879-light-speed-slow-photons/

"Glasgow researchers slow the speed of light" https://www.dailymotion.com/video/x2ffsym

"Light hits near infinite speed in silver-coated glass. A nano-sized bar of glass encased in silver allows visible light to pass through at near infinite speed. The technique may spur advances in optical computing. [...] In a vacuum the refractive index is 1, and the speed of light cannot break Einstein's universal limit of 300,000 kilometres per second. Normal materials have positive indexes, and they transmit at the speed of light in a vacuum divided by their refractive index. Ordinary glass, for instance, has an index of about 1.5, so light moves through it at about 200,000 kilometres per second. The new material contains a nano-scale structure that guides light waves through the metal-coated glass. It is the first with a refractive index below 0.1, which means that light passes through it at almost infinite speed, says Albert Polman at the FOM Institute AMOLF in Amsterdam, the Netherlands. But the speed of light has not, technically, been broken. The wave is moving quickly, but its "group velocity" the speed at which information is travelling is near zero." http://www.newscientist.com/article/dn23050-light-hits-near-infinite-speed-in-silvercoated-glass.html

"Speed of light broken with basic lab kit. Electric signals can be transmitted at least four times faster than the speed of light using only basic equipment that would be found in virtually any college science department. Scientists have sent light signals at faster-than-light speeds over the distances of a few metres for the last two decades - but only with the aid of complicated, expensive equipment. Now physicists at Middle Tennessee State University have broken that speed limit over distances of nearly 120 metres, using off-the-shelf equipment costing just $500. [...] While the peak moves faster than light speed, the total energy of the pulse does not. This means Einstein's relativity is preserved, so do not expect super-fast starships or time machines anytime soon." https://www.newscientist.com/article/dn2796-speed-of-light-broken-with-basic-lab-kit/

"Researchers at the University of Ottawa observed that twisted light in a vacuum travels slower than the universal physical constant established as the speed of light by Einstein's theory of relativity. [...] In The Optical Society's journal for high impact research, Optica, the researchers report that twisted light pulses in a vacuum travel up to 0.1 percent slower than the speed of light, which is 299,792,458 meters per second. [...] If it's possible to slow the speed of light by altering its structure, it may also be possible to speed up light. The researchers are now planning to use FROG to measure other types of structured light that their calculations have predicted may travel around 1 femtosecond faster than the speed of light in a vacuum." http://phys.org/news/2016-03-optical-slower.html

"Light Pulses That Travel Faster Than Light Created [...] The technique developed at NIST is called four-wave mixing, and it works by altering some parts of each individual light pulse. This makes the light move forward faster than it normally would when traveling through a vacuum. [...] The physicists explain that the new research does not violate Albert Einstein's theory on general relativity - which states that the speed of light in a vacuum is the fastest achievable in the Universe. They say that a sort of loophole exists in this theory. By careful tuning of the light source and advanced calculations, it is possible to nudge portions of the light pulses so that they arrive at their destination ahead or behind the main pulse. [...] With four-wave mixing, the NIST investigators produced laser pulses that arrived at their destination a full 50 nanoseconds faster than photons traveling through a vacuum." http://news.softpedia.com/news/Light-Pulses-That-Travel-Faster-than-Light-Created-267499.shtml

"Light hits near infinite speed in silver-coated glass. A nano-sized bar of glass encased in silver allows visible light to pass through at near infinite speed. The technique may spur advances in optical computing. [...] In a vacuum the refractive index is 1, and the speed of light cannot break Einstein's universal limit of 300,000 kilometres per second. Normal materials have positive indexes, and they transmit at the speed of light in a vacuum divided by their refractive index. Ordinary glass, for instance, has an index of about 1.5, so light moves through it at about 200,000 kilometres per second. The new material contains a nano-scale structure that guides light waves through the metal-coated glass. It is the first with a refractive index below 0.1, which means that light passes through it at almost infinite speed, says Albert Polman at the FOM Institute AMOLF in Amsterdam, the Netherlands. But the speed of light has not, technically, been broken. The wave is moving quickly, but its "group velocity" the speed at which information is travelling is near zero." http://www.newscientist.com/article/dn23050-light-hits-near-infinite-speed-in-silvercoated-glass.html

See more here: https://twitter.com/pentcho_valev

Pentcho Valev

"Spatially structured photons that travel in free space slower than the speed of light" Science 20 Feb 2015: Vol. 347, Issue 6224, pp. 857-860 http://science.sciencemag.org/content/347/6224/857

"Although the maximum speed of light is a cosmological constant - made famous by Einstein's Special Theory of Relativity and E=mc^2 - it can, in fact, be slowed down: that's what optics do." http://www.gmanetwork.com/news/story/417655/scitech/science/exclusive-this-pinay-physicist-can-slow-down-light-without-touching-it

"The speed of light is a limit, not a constant - that's what researchers in Glasgow, Scotland, say. A group of them just proved that light can be slowed down, permanently." http://www.upi.com/Science_News/2015/01/23/Scientists-slow-down-light-particles/1191422035480

It would be too dangerous just to say "The speed of light is not a constant" - the godfathers of the Einstein cult would punish you severely. So experimentalists judiciously say "The speed of light is a limit, not a constant" and the punishment is not very cruel. The discovery is sentenced to oblivion, and that's all.

More here: https://twitter.com/pentcho_valev

Pentcho Valev