Test sheds doubt on 'faster than light' claim


For the moment, it seems, Einstein was still correct.

Despite fevered excitement over the past six months in the scientific community as to whether or not the universe’s great ‘constant’ of the speed of light might have been broken by strange particles called neutrinos, news announced this weekend looks to have confirmed nothing still travels faster.

Scientists studying neutrinos at the OPERA (Oscillation Project with Emulsion tRacking Apparatus) project had been sending bursts of the tiny particles through the earth (using a neutrino beam supplied from CERN)  to a laboratory at Gran Sasso, 730km away underneath a mountain in Italy.

To their immense surprise, preliminary results from the experiment last  September suggested that the neutrinos – which like all things in the universe must obey the law of physics – seemed to have arrived at the target site faster than a beam of light would have done.

Had the neutrinos observed Einstein's laws, the subterranean journey could not have taken longer than the 2.4milliseconds.

However they appeared to have instead arrived at Gran Sasso 60 nanoseconds - 60 billionths of a second - earlier than light.

But a test run by a different group at the same laboratory has now clocked them travelling at precisely light speed – not faster as had been anticipated by some.

The results in September, from the OPERA group at the Gran Sasso underground laboratory in Italy, could have triggered the greatest rethink in physics and cosmology in history.

Scientists have long held that the speed of light, as predicted by Einstein in his two theories of relativity, should be the universe's absolute speed limit.

But now, the independent ICARUS measurement, using last year’s short pulsed beam from CERN, has reported that results indicate that the neutrinos DO NOT exceed the speed of light on their journey between the two laboratories.

As such, it is at odds with the initial measurement reported by OPERA last September.

"The evidence is beginning to point towards the OPERA result being an artefact of the measurement," said CERN Research Director Sergio Bertolucci.

“But it's important to be rigorous, and the Gran Sasso experiments,( BOREXINO, ICARUS, LVD and OPERA) will be making new measurements with pulsed beams from CERN in May to give us the final verdict.

“ In addition, cross-checks are underway at Gran Sasso to compare the timings of cosmic ray particles between the two experiments, OPERA and LVD.

“Whatever the result, the OPERA experiment has behaved with perfect scientific integrity in opening their measurement to broad scrutiny, and inviting independent measurements. This is how science works."

A web cast from CERN last September opened up the results to the whole scientific community for scrutiny.

The ICARUS experiment measured seven neutrinos in the beam from CERN last year. These all arrived in a time consistent with the speed of light.

"The ICARUS experiment has provided an important cross check of the anomalous result reports from OPERA last year," said Carlo Rubbia, Nobel Prize winner and spokesperson of the ICARUS experiment.

 "ICARUS measures the neutrino's velocity to be no faster than the speed of light. These are difficult and sensitive measurements to make and they underline the importance of the scientific process.”

The Icarus experiment uses 600 tonnes - 430,000 litres - of liquid argon to detect the arrival of neutrinos sent through 730km of rock from the Cern laboratory in Switzerland.

It allows an accurate reconstruction of the neutrino interactions and this technique is now recognized worldwide as the most appropriate for future large volume neutrino detectors.

"We are completely compatible with the speed of light that we learn at school," said Sandro Centro, co-spokesman for the Icarus collaboration.

"Now we are 100% sure that the speed of light is the speed of neutrinos.”

Prof Frank Close,  from Exeter College, Oxford, and a world authority on particle physics, commenting on the news, said:

“It fits in with the earlier news that OPERA had discovered that the connections of fibre optic cables could themselves introduce an uncertainty of tens of nanoseconds -  which, in my opinion, suggests that the original data had underestimated the uncertainties, such that the actual result  is (or was) consistent with travelling at light speed.”