Neutrinos and the speed of light? Not so fast …

Another week, another rush to proclaim Einstein was wrong. Martial Trezzini/AFP

The bartender says, “We don’t serve your kind in here”

A faster-than-light neutrino walks into a bar …

The media is champing at the bit to proclaim a discovery of faster-than-light travel by a subatomic particle, with some going as far as claiming “Einstein was wrong: relativity theory busted”.

The scientists responsible for the experiment and analysis let slip they have some preliminary data that suggests the particles travelled faster than light, but they seem to be the only ones not jumping to conclusions just yet.

The team at the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) in Italy regularly measures the detection of neutrinos emitted from another experiment at the Large Hadron Collider (LHC) in Switzerland, 730 kilometres away.

Neutrinos (electrically neutral subatomic particles) are rather indifferent to the presence of trivial things such as Earth, and zip through without so much as a passing interest (their cross-section, the probability for interaction, is extremely small). Owing to their small mass, they should do so at approximately the speed of light, c (see video below) – the speed light travels in a vacuum, known quite well to be 299,792,458 metres per second.

Using GPS timing and position data, the OPERA team claim to know the distance between the point at which neutrinos are emitted from the LHC and the point at which they are detected in Italy to a precision that allows them to predict the time the neutrinos should arrive to within ten nano-seconds (a nanosecond being a billionth of a second).

What they claim to have found, though, is neutrinos arriving 60 nano-seconds (0.00000006 seconds) early. If accurate, this would be a six standard-deviation result – enough to convince physicists that something is genuinely awry.

The scientists concerned have released the findings to the scientific community in the hope that, if something has been overlooked, it will be picked up by their peers. The peer-review process is usually quite efficient at eliminating likely sources of error, and in this case there are plenty of possibilities. But on the face of it, it seems the OPERA team has been very careful.

There’s the issue of knowing the exact positions of the source and detector to within the quoted uncertainty – keeping in mind that in the extra 60 nano-seconds the neutrinos are supposedly travelling they will cover a total of 18 metres. This means knowing those two positions – and the geodesic distance between them – to within three metres out of 730,000 metres.

AFP