PHYSICS
Superluminal Neutrinos: A Scientific Anomaly and Costly Mistake
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Image courtesy of Bruce Dorminey. Available at http://blogs-images.forbes.c brucedorminey/files/2012/04/9902017.jpeg
BY KARTIKEYA MENON
On September 22, 2011, the Oscillation Project with Emulsion-Tracking Apparatus (OPERA) collaboration at the CERN particle physics laboratory in Geneva published that it had observed neutrinos traveling faster than the speed of light (1). Using a detector situated under the Gran Sasso Mountain in Italy, OPERA observed the properties of electrically neutral fundamental particles—called neutrinos—that rarely interact with other matter and have vanishingly small mass. In the famous experiment, OPERA sent a beam of neutrinos produced at CERN through 730km of the earth’s crust, and observed that the neutrinos arrived at the detector approximately 60 nanoseconds sooner than if they had been traveling at the speed of light (2, 3). During the months it took to eventually confirm the inaccuracy of the result, the possible existence of superluminal subatomic particles sparked debate within the scientific community. Should the results prove true, they would defy Einstein’s special theory of relativity and upend our understanding of modern physics (4). One of special relativity’s primary postulates is that the speed of light is equal for all observers, meaning that no matter how fast one is moving or where one is going, the speed of light is a universal, unsurpassable constant. The theory’s predictions WINTER 2014
have been experimentally tested over the course of a century with no discrepancies since its publication in 1905 (5). If something were to travel faster than the speed of light, “basically, all of special relativity would be wrong” says Drexel University physics professor Dave Goldberg. According to Stephen Parke, a theoretical particle physicist at Fermilab in Illinois, the existence of superluminal particles implies the possibility of backwards time travel. OPERA’s spokesperson at the time, Antonio Ereditato, responded to many who questioned the results with confidence, stating that he believed strongly enough in the results to make them public. “We have checked and rechecked for anything that could have distorted our measurements but we found nothing. We now want colleagues to check them independently,” Ereditato said (6). OPERA researchers claim to have measured the 730-kilometer trip the neutrinos take between CERN and the detector to within 20 centimeters, and the time of the trip to within 10 nanoseconds (making the 60 nanosecond early arrival measurement statistically significant). OPERA’s belief in the results was also supported by some previously recorded instances of the superluminal effect, or the observation of faster-
Figure 1: Colliding muons decay into electrons, positrons and neutrinos.
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