Scientists 'break' speed of light but what does this actually means?
It was slightly alarming to wake up yesterday to discover that everything you thought you understood about time and space could be wrong.
But how many of us who read about the experiment in Switzerland involving impossibly fast particles called neutrinos knew what on earth these scientists had done – or what it meant? To find out, I called Jeff Forshaw, a professor of particle physics at the University of Manchester.
So, Jeff, why is this such a big deal?
If it were true, then it overturns Einstein's special theory of relativity, and in an interesting way. In Einstein's theory the speed of light is special. It is a cosmic speed limit. If something goes faster than the speed of light, then you've got the possibility of time travel.
What have these scientists done?
It's very simple. They've fired a beam of particles called neutrinos from a gun in Geneva which have smashed into an underground brick wall in Gran Sasso, 730km away. They've measured how far it is. They've measured how long it's taken, and it would appear to have travelled faster than the speed of light. They fire it out of a high-intensity proton source that produces a beam of neutrinos and smashes into a ton of bricks made out of photographic emulsion. It's very very hard to stop neutrinos. If you want to detect one you have to stop it. Make it interact with something.
How have they managed to fire it, catch it 730kms away, and measure its speed so accurately?
These are the things that they'll be nervous about. By my calculation, the neutrino would win the race by 18 metres, and a time of 60 nanoseconds. So they must know the distance between Cern and Gran Sasso to much better than 18 metres, and they must measure the time to much better then 60 nanoseconds.
I don't know exactly how they've done that. Of course there hasn't been an actual race. You would have to bore a hole all the way for the light beam to travel through. The neutrinos however can travel through the rock.
What exactly is this thing that's gone faster than the speed of light?
Neutrinos. They are tiny, very light particles that are produced very abundantly in the centre of the sun, although these ones weren't. They have a very tiny mass. The Nobel Prize for physics a few years ago was given to the person who proved their mass wasn't zero. It is much lighter even than the electron. They are a necessary by-product of the process which generates energy in the sun.
So why didn't Einstein know about these neutrinos?
In Einstein's time, in the early 20th century, understanding of elementary particles was rudimentary.
So what would he make of all this?
I don't think he'd be so arrogant as to think his ideas were set in stone. We do have a problem with relativity theory and gravity, for example. Everything's not done-and-dusted in theoretical physics, though you'd have been hard-pressed to find anybody who thought this experiment would have disproved it all.
So why can't something go faster than the speed of light?
Because it would violate the laws of cause and effect. Something could go back in time and witness the moment of its own creation.
But these neutrinos have only gone a little bit faster than the speed of light. Wouldn't you have to go a lot faster to do that?
No, not strictly, no. It would take a long time to get there, because you're only going that little bit faster. You might well die of old age before you did. But the idea is that, as soon as you start travelling faster than the speed of light, you are moving through time.
The idea that you could get into a rocket and go back in time is a long way off: it is merely the theoretical possibility that there is something that can move faster than it. We don't really have any option but to accept that this is not possible. It's sewn in to the theory of the universe. If special relativity is true and something can travel faster than the speed of light, then you can go back in time.
Does it make time travel possible?
Well it makes it possible for those neutrinos. They are the most elusive particles in the universe. The fact that there is something in space time that has this feature is enough to upset the theory.
Are there any practical implications?
Well not now, but if it is true, then the law of cause and effect is no longer sacrosanct. If you insist that cause and effect must be true, then Einstein's theory of space and time is wrong. The idea that anything can go back and violate the law of cause and effect is so repugnant to scientists that they would have to ditch Einstein's theory and find something else that makes it sacrosanct again.
Einstein completely overturned Newton's ideas. This discovery, if true, would be to Einstein's theory of relativity what Einstein's theory was to Newton.
Do you think the scientists have got this right?
I don't know. I honestly don't know. When I listen to science stories, when really interesting things come up, they get out in to the media. I bet these scientists would have liked to have been able to sit on it until they'd got independent verification. Lots of things like this happen and don't turn out to be true. There are many more false alarms than truths.
They've got to know this distance to an absurd accuracy. Measure the neutrinos' speed to a ridiculous accuracy.
Even if you've got a brilliant team working really hard, which I'm sure they have, you still can't know. If the experiment turns out not to be true it'll be interesting to see what they did wrong.
People will be sceptical until it has been independently verified, which you can only do by using some completely different piece of apparatus, a completely different experiment, to get the same result.
So could someone actually go and kill their grandmother?
Well, the theoretical physicist Freeman Dyson said a very good argument against the possibility of time travel is that we've never met any time travellers. If someone in the future had done it, someone would have come back.
Back to the drawing-board: How top physicists see it
Dr David Whitehouse
Author and astronomer
If this is true it will be a revolution. It rewrites the whole basement rules of physics and opens the door to time machines and faster-than-light travel, things that weren't possible under Einstein. Science does not respect feelings or emotions, and there are scientists who have spent their whole lives studying Einstein, who may have to come to terms with the fact that he was wrong.
Professor Andy Parker
Professor of High Energy Physics, Cambridge University
In science we are always looking for things that go against the rules we have set, so in that sense I am very happy to get something we don't expect, but you would normally have an alternative hypothesis for it to fit into and in this case there doesn't seem to be one.
That is not to say it is wrong, but it is why it is so startling.
Professor Dan Tovey
Professor of Particle Physics, University of Sheffield
It is difficult to think of results in physics in recent years that could claim to be of such fundamental significance. The implications could be very exciting, but my suspicion – and I assume that of much of the scientific community – is that they have missed something and that is causing the effect. To have acceptance of something like this could take a very long time – to refute it could take very little time indeed!
Dr Lucie Green
Research Fellow working at UCL's Mullard Space Science Laboratory
I like the way it exposes how science is carried out and the fact that experimentation is difficult. I am not sure it is going to be such a massive game changer. I hope that isn't what is going to happen, because if we have to start again it would be really difficult!
Interviews by Chris Stevenson