Scientists around the world reacted with shock yesterday to results from an Italian laboratory that seemed to show certain subatomic particles can travel faster than light. If true, the finding breaks one of the most fundamental laws of physics and raises bizarre possibilities including time travel and shortcuts via hidden extra dimensions.
Scientists at the Opera (Oscillation Project with Emulsion-tRacking Apparatus) experiment in Gran Sasso, Italy, found that neutrinos sent through the Earth to its detectors from Cern, 450 miles (730km) away in Geneva, arrived earlier than they should have. The journey would take a beam of light around 2.4 milliseconds to complete, but after running the Opera experiment for three years and timing the arrival of 15,000 neutrinos, the scientists have calculated the particles arrived at Gran Sasso 60 billionths of a second earlier, with an error margin of plus or minus 10 billionths of a second. The speed of light in a vacuum is 299,792,458 metres per second, so the neutrinos were apparently travelling at 299,798,454 metres per second.
A cornerstone of modern physics is the idea that nothing can travel faster than light does in a vacuum. At the turn of the 20th century Albert Einstein encapsulated this idea in his theory of special relativity, which proposes that the laws of physics are the same for all observers and led to the famous equation E=mc2, indicating that mass and energy are equivalent.
Brian Cox, a professor of particle physics at the University of Manchester, urged caution. "If you've got something travelling faster than light, then it's the most profound discovery of the last 100 years or more in physics. It's a very, very big deal," he said on BBC 6 Music on Friday. "It requires a complete rewriting of our understanding of the universe."
Professor Jim Al-Khalili at the University of Surrey said it was most likely that something was skewing the results. "If the neutrinos have broken the speed of light, it would overturn a keystone theory from the last century of physics. That's possible, but it's far more likely that there is an error in the data. So let me put my money where my mouth is: if the Cern experiment proves to be correct and neutrinos have broken the speed of light, I will eat my boxer shorts on live TV."
Opera co-ordinator Antonio Ereditato said his team was "recovering from the shock" of the discovery and would leave the physics community to explain the result. "We made a measurement and we believe our measurement is sound," he said. "Now it is up to the community to scrutinise it. We are not in a hurry. We are saying, tell us what we did wrong, redo the measurement if you can." He added: "There will be all sorts of science fiction writers who will give their own opinions on what this means, but we don't want to enter that game."
If the measurements are shown to be correct, physicists will have to modify their understanding of special relativity. There are several theories that could help explain the results.
Heinrich Paes at Dortmund University and colleagues believe it might be possible for neutrinos to move through hidden extra dimensions of space and effectively take shortcuts through space-time.
"The extra dimension is warped in a way that particles moving through it can travel faster than particles that go through the known three dimensions of space. It's like a shortcut through this extra dimension. So it looks like particles are going faster than light, but actually they don't."
Another potential explanation for the observation was given by Alan Kostelecky at Indiana University. He proposed in 1985 that an energy field that lies unseen in the vacuum could allow neutrinos to move faster through space than photons, the particles that make up light.
"This is a field that sits in the vacuum and as a result, things travelling in the vacuum will have unconventional properties," he said. "It may very well be that neutrinos travel faster than light does in that medium. It is not at all unreasonable that that would be the case."
Professor Dave Wark, leader of the UK group on the T2K neutrino experiment in Japan, cautioned that scientists would "require a very high standard of proof and confirmation from other neutrino experiments around the world".
Susan Cartwright, senior lecturer in particle astrophysics at Sheffield University, said there were many potential sources of error in the Opera experiment. "The sort of thing you might worry about is have they correctly accounted for the time delay of actually reading out the signals? Whatever you are using as a timing signal, that has to travel down the cables to your computer and when you are talking about nanoseconds, you have to know exactly how quickly the current travels, and it is not instantaneous."
Cartwright works on T2K, which sends neutrinos over a 295km distance. "We could certainly check this, but MINOS [the neutrino experiment at Fermilab in the US] are in a better position because we are still doing repairs after the earthquake that struck Japan."
Professor Jenny Thomas of University College London, a spokesperson for the MINOS neutrino experiment, said if the discovery was proved correct, it "would overturn everything we thought we understood about relativity and the speed of light".
Ereditato said the Opera team was going through a mix of feelings. "There is excitement, adrenaline, because you feel you have hit something hot. Another feeling is exhaustion. A third feeling is let's look again and again and think of other checks we have not yet done."
What has been discovered?
A fundamental subatomic particle, the neutrino, seems to be capable of travelling faster than the speed of light.
Where on the scale of amazing/ surprising is this finding?
If the Gran Sasso results are correct, scientists would have reason to believe that Einstein's of special relativity is wrong. This is troubling, as the theory has been tested countless times in experiments and never disproved.
The trip would 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, the scientists discovered that the particles arrived at Gran Sasso 60 billionths of a second earlier, with an error margin of plus or minus 10 billionths of a second.
Since the speed of light in a vaccum is 299,792,458 metres per second, the neutrinos were apparently travelling at 299,798,454 metres per second.
What are neutrinos?
Neutrinos are electrically neutral particles that have a tiny (but non-zero) mass. They interact very weakly with normal matter, making them almost impossible to detect. Tens of billions of neutrinos pass through your fingertip every second. They are created in certain types of radioactive decay, during collisions between atoms and cosmic rays and during nuclear reactions such as those that occur at the heart of the Sun.
Are there any theories that might explain the result?
If the result is proved correct – and that is still a big if – you have to go into some relatively uncharted areas of theoretical physics to start explaining it. One idea is that the neutrinos are able to access some new, hidden dimension of space, which means they can take shortcuts. Joe Lykken of Fermilab told the New York Times: "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."
Alan Kostelecky, an expert in the possibility of faster-than-light processes at Indiana University, put forward an idea in 1985 predicting that neutrinos could travel faster than the speed of light by interacting with an unknown field that lurks in the vacuum. "With this kind of background, it is not necessarily the case that the limiting speed in nature is the speed of light," he told the Guardian. "It might actually be the speed of neutrinos, and light goes more slowly."
Does this mean that time travel is possible?
Don't hold your breath – we won't be routinely jumping into the past in DeLoreans any time soon. If particles could travel faster than light, special relativity suggests travelling backwards through time is a possibility, but how anyone harnesses that to do anything useful is beyond the reach of any technology or material we have today.
Building in part on my talk at the time conference, Scott Aaronson has a blog post about entropy and complexity that you should go read right now. It’s similar to one I’ve been contemplating myself, but more clever and original.
Back yet? Scott did foolishly at the end of the post mention the faster-than-light neutrino business. Which of course led to questions, in response to one of which he commented thusly:
Closed timelike curves seem to me to be a different order of strangeness from anything thus far discovered in physics—like maybe 1000 times stranger than relativity, QM, virtual particles, and black holes put together. And I don’t understand how one could have tachyonic neutrinos without getting CTCs as well—would anyone who accepts that possibility be kind enough to explain it to me?
The problem Scott is alluding to is that, in relativity, it’s the speed-of-light barrier that prevents particles (or anything) from zipping around and meeting themselves in the past — a closed loop in spacetime. On a diagram in which time stretches vertically and space horizontally, the possible paths of light from any event define light cones, and physical particles have to stay inside these light cones. “Spacelike” trajectories that leave the light cones simply aren’t allowed in the conventional way of doing things.
What you don’t see in this spacetime diagram is a slice representing “the universe at one fixed time,” because that kind of thing is completely observer-dependent in relativity. In particular, if you could move on a spacelike trajectory, there would be observers who would insist that you are traveling backwards in time. Once you can go faster than light, in other words, you can go back in time and meet yourself in the past. This is Scott’s reason for skepticism about the faster-than-light neutrinos: if you open that door even just a crack, all hell breaks loose.
But rest easy! It doesn’t necessarily follow. Theorists are more than ingenious enough to come up with ways to allow particles to move faster than light without letting them travel along closed curves through spacetime. One minor technical note: if some particle moves faster than light, it’s not “closed timelike curves” that we should be worried about, it’s “closed spacelike curves on which physical particles move.”
But we shouldn’t necessarily even worry about that. The usual argument that faster than light implies the ability to travel on a closed loop assumes Lorentz invariance; but if we discover a true FTL particle, your first guess should be that Lorentz invariance is broken. (Not your only possible guess, but a reasonable one.) Consider, for example, the existence of a heretofore unobserved fluid pervading the universe with a well-defined rest frame, that neutrinos interact with but photons do not. Or a vector field with similar properties. There are various ways we could imagine some background that actually picks out a preferred frame of reference, violating Lorentz invariance spontaneously.
If that’s true, the argument that FTL implies closed loops through spacetime no longer works. Even if neutrinos are able to sneak outside light cones, there may nevertheless be “neutrino cones” to which they are still confined. These neutrino cones could be a little bit broader than ordinary light cones, but they could still define a fixed notion of “going forward in time” that even neutrinos couldn’t violate.
There’s a nice (although technical) discussion of this in a short paper by Robert Geroch. Read Section 2 for the math, Section 3 for the words. From the discussion:
In short, the causal cones of special relativity, from this perspective, have no special place over and above the cones of any other system. This is democracy of causal cones with a vengeance. This, of course, is not the traditional view. That view — that the special relativity causal cones have a preferred role in physics — arises, I suspect, from the fact that a number of other systems — electromagnetism, the spin-s ﬁelds, etc — employ precisely those same cones as their own. And, indeed, it may be the case that the physical world is organized around such a commonality of cones. On the other hand, it is entirely possible that there exist any number of other systems — not yet observed (or maybe they have been!) — that employ quite diﬀerent sets of causal cones. And the cones of these “other systems” could very well lie outside the null cones of special relativity, i.e., these systems could very well manifest superluminal signals. None of this would contradict our fundamental ideas about how physics is structured: An initial-value formulation, causal cones governing signals, etc.
The odds are still long against the OPERA result being right at face value. But even if it’s right, it doesn’t immediately imply that neutrinos are time-travelers.
FNN COMMENTARY: A more plausible answer is that time is a duality between large scale paired motions. In other words, we live in a DUAL TIME UNIVERSE and that there is zero chance that light is the standard of motion in our Universe. So that Einstein's Special Relativity speed limits have been proven incorrect. Also, Einstien's General Relativity attempts to utilize a 96% missing mass to account for such extreme galactic motions, Both General Relativity and Special Relativity are wrong and have held science back in understanding how the Graviton Cycle is the cause for forward time mass formational processes in the arms of galaxies. All existing conditions placed on our observation of the data, such as the notion that Universe was created by a Big Bang have caused a failure to understand the true nature of motion in our Universe. Most likely, DTU paired motions on large scales generate a tremendous flux torsion fields that generate polarity reversals within the cores of Proton's and AGN Cores of Galaxies. It is this flux exchange from our Antimatter partner that streams into the ecliptic as the Graviton Cycle that terminates with Graviton Capture in cores of Proton's, terminating forward time causing Antimatter induction as a polarity reversal releases HFTL (HIGHER FREQUENCY THAN LIGHT) Antigraviton's back towards reverse time in extreme motions away from mass forming gravity well at upwards to 20 billion times the speed of light. The Graviton Cycle drives not only all atomic motion but the formational process of mass itself. The discovery that Neutrino's operate FTL is just the beginning of a huge crack in the data that will force all existing theories to be re-evaluated. I can't wait to see what Fermi Labs comes up with from the claim that they have discovered a new force of Nature. We are talking about a super symmetry, CPT is conserved between large scale paired motions between matter and antimatter, and because matter dominates forward time while antimatter dominates reverse time there are ZERO violations only misinterpretations of the data---as usual from the Zeitgeist mind sets of current theoretical physics.