Scientists from all over the world are examining the results of an experiment that seems to disprove one of the cornerstones of modern physics.
Experts at the European Organisation for Nuclear Research (Cern) in Switzerland believe they have clocked particles called neutrinos travelling faster than the speed of light.
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.
According to Einstein, the speed of light, 186,282 miles per second (299,792km per second) is a "cosmic constant" and nothing in the universe can travel faster, because physical objects have a mass, whereas light does not.
Cern says a neutrino beam fired from a particle accelerator near Geneva to a lab 454 miles (730km) away in Italy arrived 60 nanoseconds faster than the speed of light.
The claim has been met with a range of responses from scientists, with some expressing amazement while others dismissed it as a mistake.
"The feeling that most people have is this can't be right, this can't be real," said James Gillies, a spokesman for Cern.
He said the readings have so astounded researchers that they are asking others to independently verify the measurements before claiming an actual discovery.
"They are inviting the broader physics community to look at what they have done and really scrutinise it in great detail," he said.
Dr David Whitehouse, a space scientist and author, said that if the experiment is proved to be true then it would be a revelation on a par with Einstein's own theories.
"It is an earthquake, a revolution in physics," he said.
"As soon as you are arrogant enough to think you understand the universe, the universe comes along and shows you are not right."
Dr Whitehouse said the findings technically meant that time travel might be possible.
"Everything is now open - because time, speed and the speed of light are all linked."
However, one physicist based in Melbourne, Australia, concluded that the startling claim was simply the result of an error.
Dr John P Costella said the group at Cern had made an "embarrassing gaffe" by miscalculating the experiment's statistical uncertainty.
"One must conclude that (the team) has simply made a mistake, albeit a highly embarrassing one which has gathered international media coverage," he said.
University of Maryland physics department chairman Drew Baden called it "a flying carpet", something that was too fantastic to be believable.
Scientists at the competing Fermilab in Chicago have promised to try to replicate the results.
"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.
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