An experiment showing it is possible to travel faster than the speed of light, and so confound a fundamental principle of theoretical physics, has passed its first serious test of validity.
Scientists have excluded one of the sources of error that could have led them to make a mistake when they announced in September that a beam of sub-atomic particles had travelled a fraction of a second faster than light.
They repeated the first experiment, in which they had fired pulses of neutrons from the Cern underground laboratory near Geneva through solid rock to subterranean particle detectors at the Gran Sasso National Laboratory in Italy about 750km (466 miles) away.
This time the length of the neutron pulses was shortened to eliminate one possible source of error.
Instead of the pulses lasting 10.5 millionths of a second, as in the original experiment, they were made about 3,000 times shorter, at just 3 billionths of a second.
This enabled experimenters to eliminate the possibility that they were getting confused over the start and end of each pulse – critical with measurements involving minute fractions of a second.
Like the earlier experiment, the test found the neutrons arrived at the Italian site some 60 billionths of a second faster than if they were travelling at light speed – some 186,282 miles per second and supposedly the maximum velocity at which anything can move.
Travelling faster than light is considered impossible under the current laws of physics. Breaking the universal constant would overturn Albert Einstein's special theory of relativity, which has held sway over theoretical physics for more than a century.
"A measurement so delicate and carrying a profound implication on physics requires an extraordinary level of scrutiny," said Professor Fernando Ferroni, president of the Italian Institute for Nuclear Physics and a spokesman for the international Opera consortium, which carried out the test.
"The positive outcome of the test makes us more confident of its result, although a final word can only be said by analogous measurements performed elsewhere in the world. One of the eventual systematic errors is now out of the way, but the search is not over."
Physicists now await a repeat of the experiment by other researchers at the Minos group at Fermilab in Batavia, Illinois, before they tear up their textbooks – or eat their boxer shorts, as Prof Jim Al-Khalili at Surrey University vowed to do if the experiment proved correct.
"I am not yet ready to get out my knife and fork," he said. "The results have only dealt with some possible errors. There are still a number of other possible errors and uncertainties that they are working on ruling out.
"Ideally, the experiment would have to be done somewhere else entirely to try to verify the controversial result that these tiny particles really are going faster than light in case there is still a systemic problem with this particular experiment at Cern."
The speed of light, in metres per second – a universal constant in the laws of physics
Distance travelled (in km), by neutrinos in Cern experiment
Billionths of a second – how much faster than light the neutrinos travelledReuse content