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Evidence of a Correction To the Speed of Light
KentuckyFC writes: In the early hours of the morning on 24 February 1987, a neutrino detector deep beneath Mont Blanc in northern Italy picked up a sudden burst of neutrinos. Three hours later, neutrino detectors at two other locations picked up a second burst. These turned out to have been produced by the collapse of the core of a star in the Large Magellanic Cloud that orbits our galaxy. And sure enough, some 4.7 hours after this, astronomers noticed the tell-tale brightening of a blue supergiant in that region, as it became a supernova, now known as SN1987a. But why the delay of 7.7 hours from the first burst of neutrinos to the arrival of the photons? Astrophysicists soon realized that since neutrinos rarely interact with ordinary matter, they can escape from the star's core immediately. By contrast, photons have to diffuse through the star, a process that would have delayed them by about 3 hours. That accounts for some of the delay but what of the rest? Now one physicist has the answer: the speed of light through space requires a correction.
As a photon travels through space, there is a finite chance that it will form an electron-positron pair. This pair exists for only a brief period of time and then goes on to recombine creating another photon which continues along the same path. This is a well-known process called vacuum polarization. The new idea is that the gravitational potential of the Milky Way must influence the electron-positron pair because they have mass. This changes the energy of the virtual electron-positron pair, which in turn produces a small change in the energy and speed of the photon. And since the analogous effect on neutrinos is negligible, light will travel more slowly than them through a gravitational potential. According to the new calculations which combine quantum electrodynamics with general relativity, the change in speed accounts more or less exactly for the mysterious time difference.
FIRST POST
(however, the apparent local time when you see this post may differ based on the apparently non-constant nature of c )
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do they correct the idealized, or do they correct the observed?
Neither. You cannot correct the speed of light, because it isn't measured, it is DEFINED as EXACTLY 299,792,458 meters per second. So it is not the speed of light that needs to be updated, but the length of the meter.
...is "more or less exactly" ?
Modest doubt is called the beacon of the wise. - William Shakespeare
You have this the wrong way around. The speed of light is not defined, it is a universal constant. It is the length of the meter that is defined based on a combination of this constant, and the international standard of time. So you are correct that if light turned out to travel slower, the length of the meter would be slightly shorter, and the speed of light would still be exactly 299792458 meter per second. This would be according to the new length of the meter though, when expressed in the old length (which is what the poster is implicitly asking for), it would most certainly be less, and could be given as such.
Of course the truth is that the speed of light is perfectly fine as it is. It's just that light isn't always exactly 'light' when it travels through space.
None of this is the issue; speed of light stays constant, as does distance measurements. What changes is the understanding of the stability of a photon of light in a vacuum and the effect of this instability on travel time while passing near a gravitational well.
So while it's a photon of light, it travels light speed. When the energy converts to kinetic energy for a breather, it is affected by the gravitational pull, in a manner significantly stronger than a neutrino is affected. When it then flops back to being a photon, it is once again traveling at the speed of light.
What intrigues me about this is that this will also have implications regarding relativity, as every time the light flips state, it is essentially anchoring itself to a location in space from which the next photon flop can take its bearing. My mind can't quite grasp the further implications of this right now, but it could really mess with observation of light from a moving point (which all points are).
The recalibration is mostly on how we project distances based on light measurements; it's now become significantly trickier, as we need to account for gravity at specific moments.
Franson's idea, as I understand it, is that during the small window between creation and annihilation, the massive particles are under the influence of gravity, which bleeds off energy. When the pair recombines, it results in a reduced velocity of the photon.
Now, as I understand it, reducing the energy of a photon would merely reduce its frequency (red-shifting), not affect its actual velocity.
However, over long distances, the total time required for a photon to travel distance X would thus be slightly more than X/c, based on the proportion of time spent as a pair of massive particles, rather than as a massless photon. From a statistical perspective, this yields an average velocity of slightly less than /c/ (the speed of light in a vaccuum).
This seems reasonable to me, at least at first.
mrsquid0 raises an issue, though: Photons in the visible light range are not sufficiently energetic to create an electron-positron pair. I do not know if the photons in question were in the visible light range or not.
NoNonAlphaCharsHere also raises an important point: the electron-positron pair *cannot* travel at the speed of light. In fact, he/she raises an even better idea than Franson; my reading of Franson's explanation is that gravity is slowing down the particles (gravity field behind the photon), but there's just as much opportunity for gravity to *speed up* the particles (gravity field in front of the photon).
Now, I don't feel like doing all the math for this one little message, so here are the things I would consider before taking this article (and the original paper) at face value: