Roll over, Einstein ?
The physics world is abuzz with news that a group of European physicists plans to announce Friday that it has clocked a burst of subatomic particles known as neutrinos breaking the cosmic speed limit — the speed of light — that was set by Albert Einstein in 1905.
If true, it is a result that would change the world. But that “if” is enormous.
Even before the European physicists had presented their results — in a paper that appeared on the physics Web site arXiv.org on Thursday night and in a seminar at CERN, the European Center for Nuclear Research, on Friday — a chorus of physicists had risen up on blogs and elsewhere arguing that it was way too soon to give up on Einstein and that there was probably some experimental error. Incredible claims require incredible evidence.
“These guys have done their level best, but before throwing Einstein on the bonfire, you would like to see an independent experiment,” said John Ellis, a CERN theorist who has published work on the speeds of the ghostly particles known as neutrinos.
According to scientists familiar with the paper, the neutrinos raced from a particle accelerator at CERN outside Geneva, where they were created, to a cavern underneath Gran Sasso in Italy, a distance of about 450 miles, about 60 nanoseconds faster than it would take a light beam. That amounts to a speed greater than light by about 0.0025 percent (2.5 parts in a hundred thousand).
Even this small deviation would open up the possibility of time travel and play havoc with longstanding notions of cause and effect. Einstein himself — the author of modern physics, whose theory of relativity established the speed of light as the ultimate limit — said that if you could send a message faster than light, “You could send a telegram to the past.”
Alvaro de Rujula, a theorist at CERN, called the claim “flabbergasting.”
“If it is true, then we truly haven’t understood anything about anything,” he said, adding: “It looks too big to be true. The correct attitude is to ask oneself what went wrong.”
The group that is reporting the results is known as Opera, for Oscillation Project with Emulsion-Tracking Apparatus. Antonio Ereditato, the physicist at the University of Bern who leads the group, agreed with Dr. de Rujula and others who expressed shock. He told the BBC that Opera — after much internal discussion — had decided to put its results out there in order to get them scrutinized.
“My dream would be that another, independent experiment finds the same thing,” Dr. Ereditato told the BBC. “Then I would be relieved.”
Neutrinos are among the weirdest denizens of the weird quantum subatomic world. Once thought to be massless and to travel at the speed of light, they can sail through walls and planets like wind through a screen door. Moreover, they come in three varieties and can morph from one form to another as they travel along, an effect that the Opera experiment was designed to detect by comparing 10-microsecond pulses of protons on one end with pulses of neutrinos at the other. Dr. de Rujula pointed out, however, that it was impossible to identify which protons gave birth to which neutrino, leading to statistical uncertainties.
Dr. Ellis noted that a similar experiment was reported by a collaboration known as Minos in 2007 on neutrinos created at Fermilab in Illinois and beamed through the Earth to the Soudan Mine in Minnesota. That group found, although with less precision, that the neutrino speeds were consistent with the speed of light.
Measurements of neutrinos emitted from a supernova in the Large Magellanic Cloud in 1987, moreover, suggested that their speeds differed from light by less than one part in a billion.
John Learned, a neutrino astronomer at the University of Hawaii, said that if the results of the Opera researchers turned out to be true, it could be the first hint that neutrinos can take a shortcut through space, through extra dimensions. Joe Lykken of Fermilab said, “Special relativity only holds in flat space, so if there is a warped fifth dimension, it is possible that on other slices of it, the speed of light is different.”
But it is too soon for such mind-bending speculation. The Opera results will generate a rush of experiments aimed at confirming or repudiating it, according to Dr. Learned. “This is revolutionary and will require convincing replication,” he said.
ANOTHER REPORT from the BBC, Sep 22, 2009
By Jonathan Amos (BBC)
Puzzling results from Cern, home of the LHC, have confounded physicists – because it appears subatomic particles have exceeded the speed of light.
Neutrinos sent through the ground from Cern toward the Gran Sasso laboratory 732km away seemed to show up a tiny fraction of a second early.
The result – which threatens to upend a century of physics – will be put online for scrutiny by other scientists.
In the meantime, the group says it is being very cautious about its claims.
“We tried to find all possible explanations for this,” said report author Antonio Ereditato of the Opera collaboration.
“We wanted to find a mistake – trivial mistakes, more complicated mistakes, or nasty effects – and we didn’t,” he told BBC News.
“When you don’t find anything, then you say ‘Well, now I’m forced to go out and ask the community to scrutinise this.'”
The speed of light is the Universe’s ultimate speed limit, and much of modern physics – as laid out in part by Albert Einstein in his special theory of relativity – depends on the idea that nothing can exceed it.
Thousands of experiments have been undertaken to measure it ever more precisely, and no result has ever spotted a particle breaking the limit.
But Dr Ereditato and his colleagues have been carrying out an experiment for the last three years that seems to suggest neutrinos have done just that.
Neutrinos come in a number of types, and have recently been seen to switch spontaneously from one type to another.
The team prepares a beam of just one type, muon neutrinos, sending them from Cern to an underground laboratory at Gran Sasso in Italy to see how many show up as a different type, tau neutrinos.
In the course of doing the experiments, the researchers noticed that the particles showed up a few billionths of a second sooner than light would over the same distance.
The team measured the travel times of neutrino bunches some 15,000 times, and have reached a level of statistical significance that in scientific circles would count as a formal discovery.
But the group understands that what are known as “systematic errors” could easily make an erroneous result look like a breaking of the ultimate speed limit, and that has motivated them to publish their measurements.
“My dream would be that another, independent experiment finds the same thing – then I would be relieved,” Dr Ereditato said.
But for now, he explained, “we are not claiming things, we want just to be helped by the community in understanding our crazy result – because it is crazy”.
“And of course the consequences can be very serious.”