Scientists at the world's largest physics lab think they may have proved Albert Einstein's theory of relativity wrong - by breaking the speed of light.
Experts at the European Organisation for Nuclear Research (CERN)http://public.web.cern.ch/public/ in Switzerland believe they have clocked neutrinos travelling fast enough to shatter the central pillar of physics.
But they cannot quite believe it themselves, they say, because according to Einstein's famous 1905 equation, E=mc2, it is simply impossible.
"The feeling that most people have is this can't be right, this can't be real," said James Gillies, a spokesman for CERN.
Mr Gillies said the readings have so astounded researchers that they are asking others to independently verify the measurements before claiming an actual discovery.
It's a shock. It's going to cause us problems, no doubt about that - if it's true.
Fermilab head theoretician Stephen Parke
They are inviting the broader physics community to look at what they have done and really scrutinise it in great detail," he said.
Ideally they want someone elsewhere in the world to repeat the measurements, he said.
Scientists at the competing Fermilab in Chicago have promised to start such work immediately.
"It is a shock," said Fermilab head theoretician Stephen Parke, who was not part of the research in Geneva.
"It is going to cause us problems, no doubt about that - if it is true."
The Chicago team had similar faster-than-light results in 2007, but those came with a giant margin of error that undercut its scientific significance.
Others were sceptical about CERN's claim that the neutrinos - one of the strangest known particles in physics - were observed smashing past the cosmic speed barrier of 186,282 miles per second (299,792km per second).
University of Maryland physics department chairman Drew Baden called it "a flying carpet", something that was too fantastic to be believable.
CERN says a neutrino beam fired from a particle accelerator near Geneva to a lab 454 miles (730km) away in Italy travelled 60 nanoseconds faster than the speed of light.
Scientists calculated the margin of error at just 10 nanoseconds, making the difference statistically significant.
But given the enormous implications of the find, they still spent months checking and rechecking their results to make sure there were no flaws in the experiment.
"We have not found any instrumental effect that could explain the result of the measurement," said Antonio Ereditato, a physicist at the University of Bern, Switzerland, who was involved in the experiment, known as Opera.
The CERN researchers are now looking to the United States and Japan to confirm the results.