The CERN research institute near Geneva said measurements over three years had shown neutrinos pumped to a receiver in Gran Sasso, Italy, had arrived an average of 60 nanoseconds sooner than light would have done -- a tiny difference that could nonetheless undermine Albert Einstein's 1905 special theory of relativity
"Extraordinary claims require extraordinary evidence, and this is an extraordinary claim," eminent cosmologist and astrophysicist Martin Rees told Reuters.
"It is premature to comment on this," Professor Stephen Hawking, the world's most well-known physicist, told Reuters. "Further experiments and clarifications are needed."
Professor Jenny Thomas, who works on neutrinos at CERN's friendly rival Fermilab near Chicago in the United States, commented: "The impact of this measurement, were it to be correct, would be huge."
CERN's own research director Sergio Bertolucci said if the findings were confirmed -- and at least two separate laboratories are likely to start work on this in the near future -- "it might change our view of physics".
The high level of caution is normal in science where anything that could be a breakthrough discovery, especially overturning well-established thinking, is in principle always checked and rechecked by other researchers.
In a comment issued by CERN, the world's leading laboratory for particle research on the edge of Geneva, Bertolucci underscored this principle.
"When an experiment finds an apparently unbelievable result and can find no artefact of the measurement to account for it, it is normal to invite broader scrutiny....it is good scientific practice," he said.
The measurements were posted on the scientific website http://arxiv.org/abs/1109.4897 overnight.
The discovery would open up intriguing theoretical possibilities.
"Light speed is a cosmic speed limit and it exists in order to protect the law of cause and effect," said Professor Forshaw.
"If something travels faster than the cosmic speed limit, then it becomes possible to send information into the past - in other words, time travel into the past would become possible. That does not mean we'll be building time-machines anytime soon though - there is quite a gulf between a time-travelling neutrino to a time-travelling human."