Changes

Much of modern theoretical physics, including all of relativity, involves a fundamental "speed of light", denoted '''c'''.  Relativity has its origins in the behavior of light in various experiments, notably the [[Michelson-Morley experiment]].  So the behavior of light is used as the definition of '''c''' in various formulas, such as [[E=mc²]], [[E^2=(mc^2)^2+(pc)^2]], and [[Maxwell's Equations]].  This also fits in perfectly with the notion that a photon, being massless, must have speed '''c''' in all frames of reference.  And it fits in with the notion that particles of exceedingly small rest mass, but reasonable energy, will travel at nearly the speed of light.

Much of modern theoretical physics, including all of relativity, involves a fundamental "speed of light", denoted '''c'''.  Relativity has its origins in the behavior of light in various experiments, notably the [[Michelson-Morley experiment]].  So the behavior of light is used as the definition of '''c''' in various formulas, such as [[E=mc²]], [[E^2=(mc^2)^2+(pc)^2]], and [[Maxwell's Equations]].  This also fits in perfectly with the notion that a photon, being massless, must have speed '''c''' in all frames of reference.  And it fits in with the notion that particles of exceedingly small rest mass, but reasonable energy, will travel at nearly the speed of light.

The electron neutrino is believed to have a mass of 0.25 Ev, or .44x10^-36 kg, and hence travel at very nearly the speed of light for reasonable energies.  An announcement from the OPERA/Gran Sasso experiment in 2011<ref>http://www.nature.com/news/2011/111020/full/news.2011.605.html</ref> seemed to indicate that neutrinos were observed traveling faster than light.  (This finding was later found to be flawed).  Assuming the neutrinos had energy of about .27x10^-8 joules, their speed would have been slower than '''c''' by a factor of 1 in 10²², which would come out to .25x10^-24 seconds over the 730 kilometer test.  That time difference would be many orders of magnitude too small to observe.

The electron neutrino is believed to have a mass of 0.25 Ev, or .44x10⁻³⁶ kg, and hence travel at very nearly the speed of light for reasonable energies.  An announcement from the OPERA/Gran Sasso experiment in 2011<ref>http://www.nature.com/news/2011/111020/full/news.2011.605.html</ref> seemed to indicate that neutrinos were observed traveling faster than light.  (This finding was later found to be flawed).  Assuming the neutrinos had energy of about .27x10⁻⁸ joules, their speed would have been slower than '''c''' by a factor of 1 in 10²², which would come out to .25x10⁻²⁴ seconds over the 730 kilometer test.  That time difference would be many orders of magnitude too small to observe.

But 20^th century theories of Quantum Electrodynamics indicate that photons interact with the "vacuum polarization" of the vacuum through which they are traveling.<ref>http://www.extremetech.com/extreme/184879-einsteinian-error-the-25-year-old-supernova-that-could-change-the-speed-of-light-forever</ref>  Photons can spontaneously split into electron-positron pairs, which interact with each other gravitationally before recombining.  This causes light to travel about 1 part in 300 million slower than '''c'''.  Since neutrinos don't interact with the electromagnetic force, they are not subject to the vacuum polarization effect, and travel only 1 part in 10²² slower than '''c''', which is faster than photons.

But 20^th century theories of Quantum Electrodynamics indicate that photons interact with the "vacuum polarization" of the vacuum through which they are traveling.<ref>http://www.extremetech.com/extreme/184879-einsteinian-error-the-25-year-old-supernova-that-could-change-the-speed-of-light-forever</ref>  Photons can spontaneously split into electron-positron pairs, which interact with each other gravitationally before recombining.  This causes light to travel about 1 part in 300 million slower than '''c'''.  Since neutrinos don't interact with the electromagnetic force, they are not subject to the vacuum polarization effect, and travel only 1 part in 10²² slower than '''c''', which is faster than photons.

Now there have been a few careful investigations of whether the [[fine structure constant]], &alpha;, could have changed slightly.  These involve examination of spectra from very distant stars, and examination of the isotopic mix of the fission products from the Oklo event.  But these results are speculative and far from convincing.

Now there have been a few careful investigations of whether the [[fine structure constant]], &alpha;, could have changed slightly.  These involve examination of spectra from very distant stars, and examination of the isotopic mix of the fission products from the Oklo event.  But these results are speculative and far from convincing.

Some Fundamentalists and Creationists posit a serious decline in the speed of light over the eons, but these are typically in the context of a view of the universe that is radically different from the accepted view.  For example, some suggest that the Earth was in some kind of "time dilation field", sometimes gravitationally caused, for some period of time.  These theories are rarely found outside of Fundamentalist web sites<ref>https://creation.com/speed-of-light-slowing-down-after-all</ref>.

Some Fundamentalists and Creationists posit a serious decline in the speed of light over the eons, but these are typically in the context of a view of the universe that is radically different from the accepted view.  For example, some suggest that the Earth was in some kind of "time dilation field", sometimes gravitationally caused, for some period of time.  These theories are rarely found outside of Fundamentalist web sites.<ref>https://creation.com/speed-of-light-slowing-down-after-all</ref>

Theories of serious decline in the speed of light are often called [[C decay]].  One of the proponents of this, [[Barry Setterfield]], suggests the use of different time scales, an "atomic" scale and a "gravitational" one, to get the effect.  He published graphs showing the consequent C decay, with the curves conveniently converging to the modern value, always just in time to  stay within the ever-increasing precision of measurements, and then extrapolated backward over many orders of magnitude.  Interestingly, his redefinition of the time scale meant abandoning the "Young Earth" theory and accepting an age of the universe close to the scientifically accepted value of about 13 billion years.

Theories of serious decline in the speed of light are often called [[C decay]].  One of the proponents of this, [[Barry Setterfield]], suggests the use of different time scales, an "atomic" scale and a "gravitational" one, to get the effect.  He published graphs showing the consequent C decay, with the curves conveniently converging to the modern value, always just in time to  stay within the ever-increasing precision of measurements, and then extrapolated backward over many orders of magnitude.  Interestingly, his redefinition of the time scale meant abandoning the "Young Earth" theory and accepting an age of the universe close to the scientifically accepted value of about 13 billion years.