Monday, October 24, 2011

Slow down there Mr. Neutrino

"Particles Faster Than the Speed of Light? Not So Fast, Some Say"


Dennis Overbye

October 24th, 2011

The New York Times

“Does E still equal MC squared?”

So asks the Irish band the Corrigan Brothers in a new song, “Einstein and the Neutrinos,” that is the latest rollicking riff on news that shocked the scientific world last month.

A group of physicists from Italy claimed they had observed the subatomic particles called neutrinos traveling faster than the speed of light. That, of course, is the cosmic speed limit declared in Albert Einstein’s theory of special relativity in 1905.

If they are right — and the jury is still out — Einstein might have some explaining to do. Among other things, a neutrino or anything else that went faster than the speed of light could go backward in time.

Physicists, who are quite sure that in fact E does still equal MC squared — whatever may come of this experiment — have expressed skepticism. But that has not stopped the ghostly neutrinos, which can sail through miles of solid lead with impunity, from achieving a sort of pop culture fame not seen since 1960, when John Updike published a poem about them in The New Yorker:

The Earth is just a silly ball

To them through which they pass

Like dustmaids down a drafty hall

Or photons through a sheet of glass.

Neutrino time-travel jokes have proliferated on the Internet. Example: “We don’t serve faster-than-light neutrinos here,” said the bartender. A neutrino walks into a bar.

Under a YouTube video of the Corrigan Brothers (who played at President Obama’s inauguration), one commenter observed: “Irish Folk & particle physics — what a combo.”

The neutrino news came from a group of physicists based at the Gran Sasso underground laboratory in Italy and doing business under the apt acronym Opera. The neutrinos, they reported on Sept. 23 in a paper and at a special symposium at CERN, the European Center for Nuclear Research, had beaten a metaphorical light beam from CERN to Gran Sasso, a distance of 457 miles, by 60 nanoseconds.

The initial response of physicists assembled at CERN and around the world was that there was probably a mistake somewhere in the experiment. Einstein’s theory is the basis of all modern physics, and has been tested a zillion times.

Technically, relativity does allow some particles, known as tachyons, to go faster than light — in fact it forbids them to slow down to light speed. The hitch is that they would have imaginary masses, whatever that means. And there is also the possibility, in some versions of string theory, of particles’ taking a shortcut through another dimension. But allowing anything to travel faster than light would open up the possibility of all kinds of problems with cause and effect and even time travel.

“It looks too big to be true,” Alvaro de Rujala, a CERN theorist, said at the time.

Or as the Corrigan Brothers put it:

Was old Albert wrong?

Oh can it be,

that fabulous theory —

relativity —

is being debunked

for the first time?

But he still might be right,

old Albert Einstein.

Physicists, in the meantime, have been flooding, the physics Internet archive, with papers debunking the Opera experiment and defending Einstein. In one paper, two professors from Boston University, Andrew G. Cohen and the Nobelist Sheldon L. Glashow, showed that if the neutrinos had been going faster than light en route to Gran Sasso, they would have lost energy at a fearsome rate by emitting other particles, causing distortions in the beam that were not seen by Opera.

Another paper — by Gian Giudice of CERN, Sergei Sibiryakov of the Institute for Nuclear Research in Moscow and Alessandro Strumia of the University of Pisa in Italy and the National Institute of Chemical Physics and Biophysics in Tallinn, Estonia — argued that according to the Standard Model, the reigning theory in particle physics, if neutrinos could violate relativity, electrons should violate it also, something that has also not been observed.

Last week, in what sounded like the coup de grâce in some circles, Ronald A. J. van Elburg, an artificial intelligence researcher at the University of Groningen in the Netherlands, suggested that the Opera group had failed to make a relativistic correction for the motions of the GPS satellites used in timing the neutrino beams. The resulting error, he said, amounted to 64 nanoseconds, almost exactly the universe-shaking discrepancy the Opera researchers were hoping to explain.

That paper got wide attention. It was mentioned on a physics blog of the magazine Technology Review, and was published by the Massachusetts Institute of Technology and other news sites around the Internet as a possible explanation of the neutrino mystery. “If it stands up, this episode will be laden with irony,” Technology Review wrote. Far from breaking Einstein’s relativity, it went on, “the faster-than-light measurement will turn out to be another confirmation of it.”

The Opera collaborators and other outside physicists now say Dr. van Elburg’s analysis is wrong and reflects confusion about how GPS systems work.

In an e-mail, Antonio Ereditato, a spokesman for Opera, said the paper did have some errors, but he declined to go into details. “You understand well that we cannot reply to anybody claiming to have an explanation of our result in terms of trivial mistakes,” he said.

Reached in Groningen, Dr. van Elburg said that an improved version of his manuscript was now under peer review.

John Learned, a neutrino physicist at the University of Hawaii, wrote in an e-mail that while the Opera results might not be right, “they are still not easily dismissed.”

“It is very unlikely to me that any distant observer will point out the error of their ways,” he continued. “If a screw-up, it is probably in the details not accessible to outsiders.”

Meanwhile, Halloween is almost here. Don’t be surprised if you have already seen Einstein in a neutrino costume.

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