Saturday, October 15, 2011

Superluminal Neutrinos? Not So Fast!

A recent report that neutrinos might have exceeded the speed of light over a test course was touted as a possible exception to Einstein's rules of relativity, and led to a hope notion that the basic rules might need revision.  This is a pretty high bar to jump, and physicists from all over started thinking about and examining the study to check it's results:

Nature itself provided such a study when a star went supernova, and released a burst of neutrinos that were detected on earth three hours before the burst of light.  Superluminal?  No:
One of the earliest objections to the faster-than-light interpretation came from an astrophysical observation. In 1987, a powerful supernova showered Earth with light and neutrinos. While neutrino detectors observed neutrinos arriving about three hours before the light, this was due to the lightweight particles getting a head start. Neutrinos, which hardly interact with matter, escaped the exploding stellar core with relative ease while photons, absorbed and re-emitted by the various elements, took longer to flee. If the effect from OPERA were as large as observed, scientists have calculated that the neutrinos should have arrived more than four years in advance of the light.
Other scientists objected that even if the neutrinos started faster than light, known processes would have slowed them down to the speed of light:
According to the Standard Model, neutrinos at sufficiently high energies should produce a virtual electron-positron pair through a process known at Cohen-Glashow emission. As explained in a paper by Nobel laureate Sheldon Glashow and his colleagues, these emanations would have sapped energy from the faster-than-light neutrinos, causing them to slow down.
Moreover, if electron neutrinos are allowed to exceed the speed of light, electrons should also be allowed to exceed the speed of light:
But if electron neutrinos moved at the speed suggested by the OPERA experiment, then electrons should also travel faster than the speed of light by at least one part in 1,000,000,000, or one billionth. Experiments have established theoretical limits that electrons remain subliminal at a precision down to more than 5 part in a thousand trillion, effectively ruling this scenario out.
But the real kicker came when someone thought just a little harder, and came up with what is likely the reason for the discrepency:
The OPERA team used GPS satellites to accurately measure the 730-km distance between their detector and the CERN beam where the neutrinos were produced. Yet, according to special relativity, calculations will be slightly different when two observers are moving relative to one another.

Since the satellites were zipping around the Earth, the positions of the neutrino source and the detector changed. According to the paper, the movement would account for a 64 nanoseconds discrepancy, nearly exactly what the OPERA team observes.
The claim basically amount to an assertion that the original authors failed a college level physics class final exam question.  There is a much longer and more detailed description of how this works here.

This is the way science is supposed to work. 

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