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Is time travel possible? The view from top scientists

ARRIVING a 60-billionth of a second early after travelling hundreds of kilometres would not usually be a significant event.

But this tiny time gap is threatening to shake the foundations of physics which have stood for more than a century.

The scientific world has been stunned by an experiment which appears to show neutrinos – weakly interacting subatomic particles, which stream unnoticeably through the body every second – beat the speed of light after being beamed 732km away from the European Organization for Nuclear Research (Cern), home of the Large Hadron Collider in Switzerland, to the Gran Sasso laboratory in Italy. The results – which the team has replicated 15,000 times – have baffled researchers as it disproves Albert Einstein’s theory of special relativity, which states that nothing can travel faster than the speed of light.

If the findings of the experiment – known as Opera – are true, it could open the door to possibilities which have long been the domain of science fiction, such as time travel or extra dimensions in space. It demands a grasp of mathematics, quantum mechanics and philosophy that few can boast.

And despite three years of measurements and careful analysis, there is still a possibility that it could all turn out to be a mistake.

Among the sceptics is Professor Stephen Hawking who said: “It is premature to comment on this. Further experiments and clarifications are needed.”

To underscore just how wild the entire story is, even the scientists who carried out the experiment describe their findings as “crazy”. They’ve now released the details to the scientific world in the hope that someone will prove them wrong and no-one will have to worry about the brain-boggling implications of the findings any longer.

We asked other leading physicists to give us their opinion on what the Cern findings might mean ... if anything.

If, when you get to the end, and you find your head is hurting and you feel faint, ill and stupid, perhaps you should seek solace in the words of Muhammad Ali. He knew all about time travel. In 1974, before taking on George Foreman, he said: “I’m so fast that last night I turned off the light switch in my room and got into bed before the room was dark.” Case closed ... we think.

Alastair Heptonstall, doctor of physics from Edinburgh, now at the California Institute of Technology

“The experiment result is really pretty amazing. Physics is always pushing to understand that little bit more about the universe, and often it is the small experiments, when we think we know the answer in advance, that give the biggest results.

“The discovery of the cosmic microwave background was a similar small experiment that made a massive discovery (proof of the big bang). However, this is probably an even bigger result.

“Relativity is one of the few concepts in modern physics that has been reliably proven over and over again. The speed of light is essentially the clock that explains what time is and what causality is.

“If it is a correct measurement, there is likely to be something pretty amazing going on and it would be pure speculation as to what could cause it. There will be years of work ahead to unravel this.

“Understandably, the scientists involved are being cautious.

I’m actually quite surprised the result has got to the point where they are going public because they would have tried everything imaginable to try to discredit the measurement before they would release it.

“It’s going to be harder for outside scientists to find the flaw in their work. They themselves understand the equipment, the places where some small error could come in, and you can be sure that they will have looked at all of this.”

Prof Brian Cox, presenter of the TV series Wonders of the Universe, and particle physicist at Manchester University

“Everyone is cautious because Einstein’s theory of special relatively says nothing can travel faster than the speed of light. That’s the basis of our understanding of physics. And it protects cause and effect in the universe.

“The reason you can’t build a time machine and go flying around like Doctor Who into the past is that the speed of light is protected. It’s the universal speed limit.

“So, if you have got something travelling faster than light, it’s the most profound discovery of the past 100 years or more in physics, so it’s a very, very big deal.

“It requires a complete rewriting of our understanding of the universe. If it’s right, it’s a profoundly important discovery.

“There are theories which might suggest why, if it’s true. One of them is extra dimensions, the fact the universe might not have three dimensions but might have extra ones.

“What could be happening is that the neutrinos could be taking a shortcut through another dimension. If that’s right you are not really violating Einstein’s theory of relativity. You are just saying that his theory is valid in three dimensions, or four if you put time in there.”

Dr Charles Wang, reader in physics and lecturer in astronomy at Aberdeen University

“I have spoken to various colleagues doing research in this field and the majority view, including that of my own, is there may be elements in this experiment that would cause errors that might be underestimated.

“Science does not just rely on one set of measurements. Firm scientific knowledge has to be based on reproducible measurements. If other groups do more stringent checks and nothing wrong is found, the next step is for an independent experimental group to reproduce this result.

“If confirmed, there will be a huge impact, as relativity is one of the pillars underpinning theory of the 20th-century physics. As we enter the 21st century, there is actually an expectation of a new physics in the new century.

“In particular, the impact is that our understanding of time evolution will be revised. Travelling faster than the speed of light means you arrive at your destination before you set off. That in turn means you will be going back in time somehow.

“This has always been impossible in special relativity as you can only go forward in time, but if you break the rules of special relativity you will be allowed to go backward.

“Of course, that doesn’t mean a Doctor Who will happen any time soon, but it will give a theoretical basis for that and would mean some breakthrough in time travel may start to occur for elementary particles.”

Prof Franz Muheim, head of the Institute for Particle and Nuclear Physics, Edinburgh University

“If confirmed, this would be extraordinary. However, for extraordinary claims, you need extraordinary proof, so we are not yet there.

“The paper has just been submitted and it will be peer-reviewed. I have read it and they are good and careful physicists and there are no obvious things which are wrong, but because it is so extraordinary, it will need one or two other experiments to either confirm or disprove it. It violates causality – basically, Einstein’s theory says nothing can go faster than the speed of light.

“I don’t think the speed of light limit is gone, if the experiment is to hold up. There are models which could accommodate this, in sci-fi called wormholes. In particle physics these are extra-dimensions. Naively speaking, if there is a dimension in which the neutrinos can go into in Geneva and come out of in Gran Sasso a bit earlier, that could be an explanation. However, this is speculation.

“My institute has research groups on Atlas and LHCb, experiments currently taking data at the Large Hadron Collider (LHC). One way this links to the neutrino experiment are these extra-dimensions because they could produce effects which could be measured at the LHC experiments. If this (neutrino experiment) stands, it would be on the level of discovering radioactivity. It would question all our understanding. But we are not there yet and, to be fair to Opera, they haven’t claimed they have discovered superluminal (speed faster than the speed of light). They just said these guys arrived 60 nanoseconds too early.”

Prof Michael Seymour, particle physicist, Manchester University

“I have looked through the paper and they have done a very thorough job themselves of trying to look for potential problems. We still have to see if anyone else can find something they did wrong but, if true, it is certainly an extremely exciting and unexpected result.

“In terms of the way we think about the world, it has deep implications because Einstein’s theory of relativity has been the building block of everything we have done in the past 100 years, and our whole understanding of the way the world works at a fundamental particle level. If it is true, it is the first clear evidence of something beyond that. I wouldn’t say it means his theory of relativity is wrong, but it means we have found something that has to be added to that theory. It is not complete. It doesn’t describe everything we have found in the world.

“At a very fundamental level, this changes the way we think about particle physics and the sub-atomic world. What sort of implications that has is very hard to say, because we actually don’t have a theory that is able to describe this faster-than-light travel in detail. It will certainly give theorists a lot to think about.

“In recent years what has excited me the most is the discovery that most of the universe we live in is dark matter and dark energy. The bit we are concerned with in our everyday life is only a tiny fraction, 4%, of the universe. Most of what the universe is made of is still completely mysterious to us.”

Prof Geoffrey Hall, physicist at Imperial College London

“I think the experimenters have done a very good job, that is clear, they’ve made a big effort. Obviously to judge these things immediately is very difficult because there are a lot of complicated and really impressive measurements and techniques used to do this. But, to be honest, the most likely thing is that there is some error.

“They are not claiming this is the result. They are claiming they want to understand better what this discrepancy is. So I believe that to get into speculating is a bit early, but I understand why people would be interested in doing so.

“We were fortunate enough to see a supernova detected in 1987 and so they detected the neutrinos from that ... There was no indication of such a thing happening with the neutrinos of that energy travelling over an immense distance. There are at least circumstantial grounds for being suspicious that this is an experimental error – not a mistake, but the difficulty of doing such a measurement as accurately as they need to get this result.

“It is difficult when you have got something which is a foundation to say what would happen if you change the foundation, because you rely on it for almost everything. It is a small effect, but it is not excluded that such things are giving us some deeper insight into nature.”

Prof Tony Doyle, research group leader of the particle physics experiment group at Glasgow University

“It looks all very credible. These are all renowned scientists who have been collecting data for the past few years and not actually looking for this effect, so I think it is baffling for them as well.

“The fundamental tenets of physics have stood since Einstein came up with the special theory of relativity in 1905 and said speed of light is constant and everything we have measured has shown as a constant.

“There are always get-out clauses. These particles are very weakly interacting. And they appear to travel faster than the speed of light. Which is very strange and weird, something we couldn’t really have expected to happen.

“But it doesn’t means that everything to do with the constancy of the speed of light is completely turned on its head. It means we have to consider there is room in some new theory for some particles which can travel at a different speed, faster than the speed of light. And these at face value apparently can.

“This is the biggest thing to have happened in the past 100 years. To now see that perhaps a different way of viewing the speed of light as a fundamental constant opens up all sorts of possibilities.

“But I wouldn’t immediately jump on my time-travelling mobile. You have to get control of these neutrinos and start measuring their properties.”

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