“The weight of evidence for an extraordinary claim must be proportional to its strangeness.” These words of Pierre-Simon Laplace, the 18th century French mathematician and astronomer, apply to an Italian research team's recent claim that it has found that fundamental particles called neutrinos break the light barrier. This strange and extraordinary result was naturally received with scepticism in the world of science. That nothing can move faster than light was immortalised in 1905 by Albert Einstein's Special Relativity, a theory that has been tested countless times in diverse physics experiments involving high energy particles. Indeed the many experiments at Cern, the European centre for particle physics in Geneva, from where neutrinos are shot through the earth to be detected by this underground Italian experiment called Opera at Gran Sasso, 732 km away, are themselves different tests of Einstein's theory. Opera found that the neutrinos, which are about a million times lighter than electrons, arrived about 60 nanoseconds earlier than the time light would have taken. This corresponds to neutrinos travelling at a speed of 1.0000247 times 299,792,458 m/s — the speed of light. To measure neutrino speed with such great precision is an achievement; and Opera has measured the speeds of 15,233 neutrinos with checks and counter-checks. So if this were true, it would shake the very foundations of physics done over the last century; there is nothing in known physics of a causal four-dimensional universe that can explain it. Last week Opera reconfirmed the original finding by measuring the time of flight of each of 20 well-separated extremely short duration neutrino pulses. The burden of the critiques of Opera's measurements has been that there could be some unsuspected minute systematic errors, particularly in the exact timing of departure and arrival of neutrinos.
Soon after the first announcement, Nobel Laureate Sheldon Glashow and Andrew Cohen argued convincingly, on the basis of simple physics, why the experiment must be wrong. They said if neutrinos had travelled faster than light, they would have lost energy during their travel through radiation in a manner akin to the sonic boom when an object breaks the sound barrier. Another Italian experiment, Icarus, quickly seized on this observation and measured the energies of the arriving neutrinos. Using the same source of neutrinos from Cern, it found that there was no unusual loss of energy in the detected neutrinos. Announced just two days ago, this would seem a refutation of the faster-than-light finding. But since the Opera scientists did not quite agree with the Glashow-Cohen argument, they are unlikely to be impressed by the Icarus results. Meanwhile, other neutrino experiments have geared up to see if the extraordinary evidence to match the strange result exists. What one is witnessing is yet another instance of the method of science at work.
