The headlines scream “CERN scientists ‘break the speed of light’” and “Scientists upend Einstein’s theory of relativity in Swiss experiment“. It’s a big enough surprise that other headlines immediately respond with “Scientists query faster-than-light claim” and “Faster-than-light travel discovered? Slow down, folks“. Indeed, the best, most balanced coverage I’ve been able to find thus far is the Washington Post’s “Particles faster than light: Revolution or mistake?“.
While I’m not a professional physicist, I think that it’s pretty obvious how this is most likely to turn out and I’m pretty surprised that the most likely scenario hasn’t received more attention. One of three things *must* be true. Either neutrinos do travel slightly faster than light or the CERN experimental results are incorrect *OR* our consensus value for the speed of light is incorrect. Yet, only the first two scenarios are receiving any press.
Within the original CERN paper “Measurement of the neutrino velocity with the OPERA detector in the CNGS beam“, the critical point is that the relative difference of the neutrino velocity and the consensus speed of light is (2.48 ± 0.58) x 10-5.
Small as this is percentage-wise, we can be absolutely sure that neutrinos aren’t normally that much faster because it would mean that we should have seen the neutrinos from Supernova 1987A almost four years earlier than they (and the light) was observed. The odds that the CERN neutrinos were somehow different from the S1987A neutrinos and thus had a higher speed are very improbable. With other, more likely possibilities available, it is safe to discard (for now) the thought of faster-than-light neutrinos.
The second possibility — that the CERN results are inaccurate by such a small percentage due to a heretofore unrecognized source of error — is certainly far more probable than the first hypothesis (faster-than-light neutrinos). Yet, these are the best-of-the-best physicists, other scientists have been scrutinizing their methodology without result, and these are not the first experiments showing these results. The fact that it is still even being considered that these results *might* have a higher probability of being correct than Einstein’s theory shows much about the perceived reliability of their work.
Which leaves the third possibility — that our consensus value for the speed of light is incorrect by a small percentage. How likely is that?
First, it must be remembered that the speed of light is NOT a constant. It varies with the medium of transmission. The speed that theoretically can not be surpassed is the speed of light in a vacuum. Scientists can and have slowed the speed of light to as little as 38 miles/hour (equal to a fast bicyclist) by creating such exotic substances as a Bose-Einstein condensate of sodium to transmit it through.
Similarly, gravity also affects the speed of light. Einstein himself said “the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity . . . hold only so long as we are able to disregard the influences of gravitational fields”. And, indeed, in 1964, Irwin Shapiro showed that the time delay of a radar signal bounced off of Venus just before it passed behind the sun was about 200 microseconds longer than it should have been if the sun weren’t present just as predicted by Einstein’s formula c’ = c ( 1 + V / c2). Not to mention that this experiment has been repeated numerous times with increasing accuracy by the MIT Haystack and others.
Neutrinos are affected by ordinary matter much less than electromagnetic radiation is. Indeed, the neutrinos in the CERN experiment traveled through the earth’s crust for a reasonable portion of their flight. It seems more than plausible that the CERN neutrinos were simply traveling at the speed of light in a vacuum without gravity and that our consensus previous measurements of the speed of light (*all* necessarily taken without a perfect vacuum and in the unavoidable presence of gravity) are off by the small percentage suggested by the CERN experiments.
Determining the exact source and cause of the error in our current consensus speed of light may well open up vistas nearly as exciting as a “true” faster-than-light particle and/or shed more light upon phenomena ranging from dark matter and dark energy to the Pioneer anomaly. This is science at it’s best and most exciting. If only more people could appreciate the real depth and glory rather than mere appearance of a CERN vs. Einstein heavyweight fight.