Caution on faster-than-light claim

PUBLISHED : Sunday, 02 October, 2011, 12:00am
UPDATED : Sunday, 02 October, 2011, 12:00am


The quest for neutrinos (subatomic particles) raised more questions about physics than it answered last week, but local physicists say the latest finding will not interfere with groundbreaking research at Daya Bay, north of Hong Kong.

Last week scientists at Cern (European Organisation for Nuclear Research) said they had found neutrinos moving faster than light - which is impossible according to Einstein's theory of relativity.

The claim must be taken with a pinch of salt, said Dr Chu Ming-chung of Chinese University's physics department. It would take a lot of time to confirm Cern's anomaly and whether or not it was proven correct, the Daya Bay Reactor Neutrino Experiment would not be affected.

The Daya Bay project is a Sino-US collaboration aimed at helping scientists study the basic properties of neutrinos and the great mystery of why matter predominates over antimatter in the universe. Chu, a key investigator in the experiment, said: 'It will take much more scrutiny into the systematic uncertainties of the [Cern] experiment. So I would say let's be careful and wait for more people to do more studies before believing in the faster-than-light result.

'If it's confirmed, it would indeed be very surprising. It would rank as the most important discovery of recent years.'

Even if it proves to be true, it will not affect the neutrino experiment at Daya Bay - at least not the scientists' original goal of measuring a property of neutrinos called theta-one-three. That measurement would only count the number of neutrinos, regardless of their speed, Chu said.

If neutrinos can travel faster than the speed of light, then basic laws of physics might have to be rewritten, he said. If particles can travel faster than light, the theory of special relativity suggests travelling backwards through time would be possible. But how anyone could actually do that is beyond the reach of any technology or material available today.

Physicists have suggested a hypothetical subatomic particle, the tachyon, that can travel faster than light and move backwards in time. But they think that tachyons, if they exist, cannot interact with normal matter.

Chu said: 'I myself have always thought that neutrinos will teach us a lot about physics. Neutrinos have always been strange within the standard model of particle physics, and understanding them is one of the most important tasks we face today.'

'Most people know that the equation E=mc2 - which was published 106 years ago as of last Tuesday - tells us that mass and energy can be converted to each other. But the equation also tells us that, as a particle speeds up [gaining in energy], its mass increases and becomes more difficult to accelerate. Einstein's theory then tells us that it takes an infinite amount of energy to accelerate a particle to the speed of light. So it is impossible in practice to get a particle that initially has less speed than light to get up to that speed. However, it does not say anything about whether particles can exist that have always had a speed faster than that of light.'

That is why Cern's claim last week is theoretically possible, he said.

Professor John Leung, of The University of Hong Kong's physics department, said: '[The Cern result] is extremely surprising news to me ... if the result were ultimately confirmed, certainly it would be one of the most important discoveries of the century. Scientists would be forced to return to their blackboards, and time travel would no longer be a fiction.'

Professor Jason Pun Chun-shing, of the same department, said the world of physics was facing a 'no-loss' situation. 'If the results are proven to be correct, then it would indeed be one of the most remarkable discoveries in science. But if not, we are still going to learn so much more about this field of science because of all the theoretical and experimental effects inspired by this result.'

Breaking the speed limit

The Opera (Oscillation Project with Emulsion-tRacking Apparatus) experiment recorded the time it took subatomic particles called neutrinos to travel 730km through the earth.


Geneva, Switzerland

Global positioning system synchronises clocks at two locations

Neutrinos are generated at Cern's Super Proton Synchrotron accelerator

Muon neutrino

Neutrinos travel through detector at Cern that records exact time they leave using GPS system

Tau neutrino

Neutrinos are transformed during their journey from muon neutrinos to tau neutrinos in a process called oscillation

LNGS lab

Neutrinos arrive at Gran Sasso after 2.4 milliseconds - they hit photographic film and lead sheets on arrival

The target at Gran Sasso

The neutrinos' target is 150,000 bricks made of photographic film and lead.

Speed of light

299,792,458 metres per second

Speed of neutrinos

299,798,454 metres per second (60 billionths of a second quicker)

Source: Cern