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Charge of the Light Brigade

BU physicists rebut claim that neutrinos move faster than light

| From BU Today | By Rich Barlow

Physicists at the Gran Sasso National Laboratory in Italy claim they observed particles that move faster than light. Photo by Randal Schwartz

It’s not exactly Romney vs. Cain, but the Einstein vs. speedy neutrinos debate has captured the world of particle physics like a presidential debate rivets New Hampshire. In September, Italian physicists reported that they had evidence that neutrinos—electrically neutral, subatomic particles—have the ability to travel faster than light, a feat deemed impossible by Einstein’s theory of relativity. (For one thing, the New York Times reports, it would mean neutrinos could time-travel to the past.)

Einstein can rest in peace, however, if BU physicists Andrew Cohen and Sheldon Glashow are right. In response to the Italians’ claim, the pair published a paper arguing that if neutrinos had traveled faster than light, they would have shed other particles, and thereby energy, to the point that it would have distorted their beam in ways that were not observed by the Italians. In their coverage of the highly charged issue, the Times and the journal Nature both cited the BU physicists’ paper.

Cohen is a College of Arts & Sciences physics professor; Glashow is the Arthur G. B. Metcalf Professor of Mathematics and Science and winner of a 1979 Nobel Prize in Physics. Their predicted loss of energy by neutrinos is based on “the known properties of neutrinos…as measured in prior experiments, plus a few assumptions, such as conventional conservation of energy and momentum,” says Cohen. “Given these assumptions, it is a straightforward exercise to calculate the rate of electron-positron emission that we describe in our paper.”

He and Glashow published their paper on arXiv, an electronic print service for scientific articles owned by Cornell. Among their acknowledgements, the authors credit “impromptu conversations” with students in the Kilachand Honors College.

Another research collaboration, called ICARUS (Imaging Cosmic and Rare Underground Signals), based at the same Italian lab as the Einstein challengers, fueled the BU prediction by reporting that the neutrinos did not show the energy loss suggested by the BU pair, although those researchers did not measure the neutrinos’ actual speed.

The observations that set off the debate come from a research group with an equally highbrow acronym, OPERA (Oscillation Project with Emulsion-Tracking Apparatus). Those scientists claim that their neutrinos raced from Geneva’s CERN physics lab to the Gran Sasso National Laboratory in Italy, 457 miles away, outrunning a “metaphorical” light beam by 60 nanoseconds, according to the N.Y. Times.

The inscrutability of the argument moved the normally staid and sedate newspaper to print one of many neutrino jokes making their way around the Internet: “We don’t serve faster-than-light neutrinos here,” said the bartender. A neutrino walks into a bar.

Whatever they think of the joke, Cohen and Glashow don’t think much of the likelihood that OPERA’s neutrinos moved as quickly as is claimed.

“The question is surely not settled,” says Cohen. “OPERA is repeating their experiment with some modifications that should help clarify the interpretation of the result.” He says he expects to see the results of the do-over, as well as of similar research elsewhere, within the next six months.

Or perhaps, if things really can go faster than the speed of light, in the last six months.

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