Evidence of a Correction To the Speed of Light 347
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.
Re:So, what's the correction? (Score:5, Informative)
It is the average speed of the light over very large distances that needs a correction, to account for the portions of travel where the light, well, is not light. The photons still move at 2.99x10^8m/s. It's the electrons and positrons that move slower.
Re:So, what's the correction? (Score:5, Informative)
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.
Re:Is there a 'less nerdy version'? (Score:5, Informative)
photons and neutrinos both travel at approximately the same speed in vacuum - "the speed of light"
However, when it comes to going through a non-vacuum, like a star, neutrinos have a straight shot because they don't interact with anything and the photons have to run through a pinball game (or a pachinko game, if you've seen those) until they actually get out. Best estimates of the time difference to date are about 3 hours.
Because of that, they would expect to see the light about 3 hours after seeing the neutrino burst, but in this case it looks like it was 7+ hours instead.
This guy (if I'm understanding it right) is saying that even "in a vacuum" light does enough zig-zagging to add a few hours to the transit time of a 163000 lightyear trip.
Re:Which means (Score:3, Informative)
I think you are confusing neutrinos, which have been known for a while, with tachyons, which are speculative and haven't been detected. Neutrinos don't move faster than light.
Re:Even that Sounds Wrong (Score:1, Informative)
photons don't take 4000 years to exit the core of our sun. photons get absorbed and emitted by mass in the sun, and there's some time between those two events. It's not "the same photon" that takes 4000 years. It's the energy in that photon. It's one of the stupidest things we say in college classes. The point is that the sun is very dense, but we fail miserably at getting that point across with the "photon" example. It's not even a stimulated emission, it's just energy.