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The need for speed

tech reviews Updated: Sep 24, 2011 23:09 IST
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Once upon a time, the only thing that traveled faster than the speed of light was gossip.

Thanks to the Internet, the whole physics world was watching on Friday when Dario Autiero, of the Institut de Physique Nucléaire de Lyon in France, in front of a roomful of physicists, put a whole new category of speed demons on the table, namely the shadowy subatomic particles known as neutrinos. He was describing a recent experiment in which neutrinos were clocked going faster than the speed of light, the cosmic speed limit set by Albert Einstein in his theory of relativity back in 1905.

According to Dr Autiero’s team, neutrinos emanating from a particle accelerator at Cern, outside Geneva, had raced to a cavern underneath Gran Sasso in Italy — a distance of 454 miles — about 60 nanoseconds faster than it would take a light beam. That amounts to a speed greater than light by about 25 parts in a million.

“We cannot explain the observed effect in terms of systematic uncertainties,” Dr Autiero told the physicists at Cern, the European organization for nuclear research. “Therefore, the measurement indicates a neutrino velocity higher than the speed of light.”

Dr Autiero said his group had spent six months trying to explain away the result, but could not do it. Given the stakes for physics, he said, it would not be proper to attempt any sort of theoretical interpretation of the results. “We present to you this discrepancy or anomaly today,” he said.

The purported effect sounds slight, but to be even slightly on the wrong side of the speed of light is forbidden in the world that Einstein described. Faster-than-light travel can also lead to the possibility of time travel, something that most physicists do not believe is possible.

Relativity has been tested over and over again for a century, and as Carl Sagan, the late Cornell astronomer, liked to say: extraordinary claims require extraordinary evidence. “This is quite a shake-up,” said Alvaro de Rujula, a theorist at Cern. “The correct attitude is to ask oneself what went wrong.”

The recent history of physics and astronomy is strewn with reports of suspicious data bumps that might be new particles or new planets and — if true — could change the way we think about the world, but then disappear with more data or critical scrutiny. Most physicists think the same will happen with this finding. The prevailing attitude was perhaps illustrated best by an XKCD cartoon, in which a character explains his intention to get rich betting against the new discovery.

Neutrinos are still a cosmic mystery. They are among the weirdest denizens of the weird quantum subatomic world. Not only are they virtually invisible and able to sail through walls and planets like wind through a screen door, but they are shape-shifters. They come in three varieties and can morph from one form to another as they travel along, an effect Dr Autiero and his colleagues were trying to observe.

Their experiment, known clunkily as Oscillation Project with Emulsion-Tracking Apparatus, or Opera, is a collaboration of 160 physicists from 11 countries, primarily Japan and Italy. It is based at the Gran Sasso laboratory, a centre for underground physics experiments that need sheltering from cosmic rays.

In the old days the process of scrutiny of a controversial measurement could have happened quietly, but the Web has changed all that. Dr Autiero’s talk at Cern and the appearance of a paper by the Opera group on the Internet Thursday night came at the end of a drumbeat of rumours and blog postings. One blog called it “Rumour of the Century.”

Some physicists, inside and outside of Cern, were critical of this process, saying the laboratory was giving too much weight to a premature result by a group that was not even part of Cern.

Nima Arkani-Hamed, a particle theorist at the Institute for Advanced Study in Princeton, said in an e-mail, “There was no need for a press release or indeed even for a scientific paper, till much more work was done. “

Rolf-Dieter Heuer, director general of Cern, said in an e-mail from Spain, “I agreed to the seminar at Cern because it is the duty of a lab like Cern to give the collaboration the possibility to ask the community for scrutiny of their findings.”

The scrutiny is surely coming.

An earlier measurement of neutrino speeds was performed by a collaboration known as Minos, for Main Injector Neutrino Oscillation Search, in 2007. Jenny Thomas of University College London, said the Minos experiment would be able to do a more precise measurement in four to six months.

“They’ve done their best,” Professor Thomas said of the Opera group. “The light’s going to shine on us now while we repeat our experiment.”