Dani Garavelli: Time to fire up the DeLorean?

EINSTEIN’S theory of special relativity may be beyond most of us. But everyone knows the formula E=mc2 – the equation at its heart – from O Grade physics, the Big Audio Dynamite hit of the same name or just the local pub quiz. It is a fact of life, part of our general knowledge. Or it was until last week.

Now scientists working on the Opera project at Cern – the European Centre for Nuclear Research and home of the Large Hadron Collider – have made a discovery which could up-end the theory which has underpinned physics for a century, and revolutionise our understanding of the universe.

According to Einstein, nothing travels faster than the speed of light in a vacuum. But in a series of experiments, the physicists have recorded sub-atomic particles travelling slightly faster than the 186,282 miles per second that has long been considered the cosmic speed limit.

Neutrinos sent through the ground from Geneva towards the Gran Sasso laboratory 723km away in Italy seemed to show up a tiny fraction of a second earlier than expected.

Although the physicists involved are being incredibly cautious (and have asked the international scientific community to check and recheck their results) they can find nothing which suggests their calculations are erroneous.

Indeed, while some scientists have been dismissive (University of Maryland physics department chairman Drew Baden called it “a flying carpet”, something that was too fantastic to be believable), there is a genuine air of excitement about the possibility of a discovery so profound it alters everything we know about the universe.

In particular, it has revived interest in the possibility of time travel, a phenomenon which has fascinated sci-fi devotees since HG Wells first penned the Time Machine in 1895. Since then, thousands of books, films and TV programmes have explored the concept, from Back to the Future, which saw Marty McFly put his own existence at risk by inadvertently preventing his parents from meeting, to Robert Heinlein’s short story By His Bootstraps, to numerous episodes of Doctor Who.

Einstein’s theory of a universal speed limit has been the basis for the concept of causality – that cause precedes effect. Without it, time becomes a more fluid, less linear idea. One scientist last week explained it thus: “In practical terms, a neutrino moving beyond light would translate into your toddler’s milk landing on the floor before she spilled it. Or your baby crying from his big sister’s pinch before she even touches him.”

Science has toyed with this notion for some time, in different ways. Since the 1960s, physicists have postulated the existence a hypothetical particle, known as a “tachyon” that always travels faster than light and that can therefore move backwards in time. But no tachyons have ever been detected and scientists believe, even if they exist, they would have no way of interacting with normal matter.

The prospect of faster than light time travel was given a boost ten years ago with the discovery of photons that seemed to move at a “superluminal” speed – that is, faster than light. Scientists later realised that it was only a visual effect, but held out a hope that such a phenomenon might be possible. Hopes were dashed on that front earlier this year when scientists in Hong Kong conducted experiments which showed single photons obeyed “the traffic law of the universe”.

But if confirmed, the Cern experiments breathes fresh life into the fantasy that we might one day be able to visit the past and future. “Einstein says nothing can travel faster than the speed of light – that’s the basis of our understanding of physics,” Professor Brian Cox, physicist and presenter of Wonders of the Universe told the BBC on Friday. “It protects cause and effect in the universe – it is the reason we can’t build a time machine and go flying around like Doctor Who – the speed of light is the universal speed limit.

“If you have something that is faster than the speed of light, that’s a really big deal – it’s a complete rewriting of the way the universe works.”

The emergence of time travel as a serious concept revives philosophical questions which have intrigued generations. The starting point for a plethora of books and films, the “grandfather paradox” points out that if you go back in time and kill your own grandfather before your father is born, then you won’t exist to go back in time to kill your grandfather. This is the paradox on which the Back to the Future trilogy hangs; in other stories the future is altered by much subtler events. In Ray Bradbury’s short story A Sound of Thunder the death of a butterfly causes seismic changes in the future universe.

One answer to this is that, even were time travel possible, it would prove impossible to change the course of history; the time traveller would be unable to kill his grandfather because some force of the universe, in the form of, say, a faulty gun, would intervene and block his efforts.

Another proposition is that there are an infinite number of alternate universes, created every time we take a decision which might change the course of events. Under this theory, a time traveller could kill his grandfather in one universe but continue to exist in a number of parallel universes.

Then there is Stephen Hawking’s Chronology Protection Conjecture, which posits that the laws of physics make time travel impossible on anything but a submicroscopic scale, thus preventing time paradoxes.

Over the years, science fiction writers have found many ingenious ways around the universal speed limit. One way is simply to postulate that in the future there’s a whole new theory of fundamental physics subsumes Einstein’s theory of relativity in the same way as Einstein’s subsumed Newton’s.

News that this might actually prove to be the case opens up a whole new range of possibilities for them. Ironically, Ken MacLeod, author of The Star Fraction and The Stone Canal, had just handed in the final proof correction of his latest book Intrusion – a book which assumes tachyons are still hypothetical at the point in the future when the book is set – when he heard the news from Cern.

“In a sense, time travel is already allowed by current physics, but in very peculiar circumstances which we have no real basis for assuming can ever actually come to pass; for example ideas like wormholes. There is even a schema for time warps, but they involve unbelievably physically difficult things like gigantic rotating cylinders,” says MacLeod.

“I don’t think this changes the possibilities for time travel. In the HG Wells build-a-time-machine sense, it is probably physically impossible. However if these results are correct, no matter how tiny the difference it is, if it’s possible for some particles to travel even a tiny fraction faster than the speed of light, it radically affects the basis of the theory of relativity and thereby the whole basics of physics as it’s understood.”

Such a discovery would up-end the principles on which quantum mechanics are based and would revolutionise computing – imagine if an information-carrying particle could travel faster than the speed of light.

The journey from Cern to Gran Sasso should take a beam of light around 2.4 milliseconds to complete, but, after running the experiment for three years and timing the arrival of 15,000 neutrinos, scientists discovered that the particles arrived at Gran Sasso 60-billionths of a second earlier, with an error margin of plus or minus ten-billionths of a second.

Having tried and failed to find any fault in the equipment or methodology which would undermine them, the scientists are throwing them over to the wider scientific community for a second opinion.

“We want just to be helped by the community in understanding our crazy result – because it is crazy,” Antonio Ereditato, co-ordinator of the Opera project, said. In particular, they are likely to be subjected to further experiments at Fermilab in Chicago and T2K in Japan.

“I have read the paper and they’ve done a thorough job and have seen an effect which is very significant in experimental terms,” says Professor Tony Doyle, of Glasgow University’s School of Physics and Astrology, who has worked on the Large Hadron Collider.

“The startling thing is they’ve made a very precise measurement of these neutrinos over a fixed distance, using GPS systems, and they’ve found they arrive effectively about 20 metres ahead of when the light would arrive. It’s the most outstanding result you could imagine in the past 100 years in scientific terms, if it turns out to be true,” he says.

But Dave Goldberg, an astrophysicist at Philadelphia’s Drexel University, believes if faster-than-light neutrinos did exist, it is likely they would have been observed in nature before now. He points out that in 1987, detectors on Earth identified neutrinos and photon light particles from an exploding star, with both types of particles reaching Earth at almost exactly the same moment. According to Goldberg’s calculations, if neutrinos travel faster than light by the amount the Opera team claims, then neutrinos from that supernova should have been detected in 1984 – three years before the photons.

If the Cern results are eventually confirmed, the next stage will be to work out how it is possible for the neutrinos to travel so fast. Some scientists have already suggested they could be taking shortcuts through a new, hidden dimension of space.

“Special relativity only holds in flat space, so if there is a warped fifth dimension, it is possible that on other slices of it, the speed of light is different,” Joe Lykken, of Fermilab, has said.

Professor Cox says this would allow Einstein’s theory to retain some credibility. “If some theory like that is right then we are not violating Einstein’s theory of relativity – we are saying it is valid in three dimensions, or four if you put time in there, but not in others,” he explained.

Even in a world where technology is advancing at break-neck speed, absorbing the implications of the Cern experiments could take some time - however you define it.