Αρχική > επιστήμη > Physicists urge caution over apparent speed of light violation. [e.t.c., e.t.c.]

Physicists urge caution over apparent speed of light violation. [e.t.c., e.t.c.]

Scientists react with disbelief and call for repeat experiments after results suggest particles can travel faster than light.

Επιμέλεια: Νίκου Τσούλια
[Τελευταία ενημέρωση 28.9.11, 11.55 μ.μ.]
Τα ελληνικά κείμενα είναι στο τέλος του αφιερώματος.
Τα νέα εκάστοτε κείμενα προστίθενται στο τέλος των προηγουμένων, αντίστοιχων αγγλικών και ελληνικών κειμένων.

Neutrino graphic

Professor Brian Cox has said that if the Italian discovery is proved correct, it would require ‘a complete rewriting of our understanding of the universe’.

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 CoxBrian 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, and 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."


imageWhat 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 the it, if they are proved correct – and that is still a bit if. 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.


Faster than light particles found, claim scientists

Particle physicists detect neutrinos travelling faster than light, a feat forbidden by Einstein’s theory of special relativity

Subatomic Neutrino Tracks

Neutrinos, like the ones above, have been detected travelling faster than light, say particle physicists. Photograph: Dan Mccoy /Corbis

It is a concept that forms a cornerstone of our understanding of the universe and the concept of time – nothing can travel faster than the speed of light.

But now it seems that researchers working in one of the world’s largest physics laboratories, under a mountain in central Italy, have recorded particles travelling at a speed that is supposedly forbidden by Einstein’s theory of special relativity.

Scientists at the Gran Sasso facility will unveil evidence on Friday that raises the troubling possibility of a way to send information back in time, blurring the line between past and present and wreaking havoc with the fundamental principle of cause and effect.

They will announce the result at a special seminar at Cern – the European particle physics laboratory – timed to coincide with the publication of a research paper (pdf) describing the experiment.

Researchers on the Opera (Oscillation Project with Emulsion-tRacking Apparatus) experiment recorded the arrival times of ghostly subatomic particles called neutrinos sent from Cern on a 730km journey through the Earth to the Gran Sasso lab.

The trip would take a beam of light 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 sixty billionths of a second earlier, with an error margin of plus or minus 10 billionths of a second.

The measurement amounts to the neutrinos travelling faster than the speed of light by a fraction of 20 parts per million. Since the speed of light is 299,792,458 metres per second, the neutrinos were evidently travelling at 299,798,454 metres per second.

The result is so unlikely that even the research team is being cautious with its interpretation. Physicists said they would be sceptical of the finding until other laboratories confirmed the result.

Antonio Ereditato, coordinator of the Opera collaboration, told the Guardian: "We are very much astonished by this result, but a result is never a discovery until other people confirm it.

"When you get such a result you want to make sure you made no mistakes, that there are no nasty things going on you didn’t think of. We spent months and months doing checks and we have not been able to find any errors.

"If there is a problem, it must be a tough, nasty effect, because trivial things we are clever enough to rule out."

The Opera group said it hoped the physics community would scrutinise the result and help uncover any flaws in the measurement, or verify it with their own experiments.

Subir Sarkar, head of particle theory at Oxford University, said: "If this is proved to be true it would be a massive, massive event. It is something nobody was expecting.

"The constancy of the speed of light essentially underpins our understanding of space and time and causality, which is the fact that cause comes before effect."

The key point underlying causality is that the laws of physics as we know them dictate that information cannot be communicated faster than the speed of light in a vacuum, added Sarkar.

"Cause cannot come after effect and that is absolutely fundamental to our construction of the physical universe. If we do not have causality, we are buggered."

The Opera experiment detects neutrinos as they strike 150,000 "bricks" of photographic emulsion films interleaved with lead plates. The detector weighs a total of 1300 tonnes.

Despite the marginal increase on the speed of light observed by Ereditato’s team, the result is intriguing because its statistical significance, the measure by which particle physics discoveries stand and fall, is so strong.

Physicists can claim a discovery if the chances of their result being a fluke of statistics are greater than five standard deviations, or less than one in a few million. The Gran Sasso team’s result is six standard deviations.

Ereditato said the team would not claim a discovery because the result was so radical. "Whenever you touch something so fundamental, you have to be much more prudent," he said.

Alan Kostelecky, an expert in the possibility of faster-than-light processes at Indiana University, said that while physicists would await confirmation of the result, it was none the less exciting.

"It’s such a dramatic result it would be difficult to accept without others replicating it, but there will be enormous interest in this," he told the Guardian.

One theory Kostelecky and his colleagues put forward in 1985 predicted 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 said. "It might actually be the speed of neutrinos and light goes more slowly."

Neutrinos are mysterious particles. They have a minuscule mass, no electric charge, and pass through almost any material as though it was not there.

Kostelecky said that if the result was verified – a big if – it might pave the way to a grand theory that marries gravity with quantum mechanics, a puzzle that has defied physicists for nearly a century.

"If this is confirmed, this is the first evidence for a crack in the structure of physics as we know it that could provide a clue to constructing such a unified theory," Kostelecky said.

Heinrich Paes, a physicist at Dortmund University, has developed another theory that could explain the result. The neutrinos may be taking a shortcut through space-time, by travelling from Cern to Gran Sasso through extra dimensions. "That can make it look like a particle has gone faster than the speed of light when it hasn’t," he said.

But Susan Cartwright, senior lecturer in particle astrophysics at Sheffield University, said: "Neutrino experimental results are not historically all that reliable, so the words ‘don’t hold your breath’ do spring to mind when you hear very counter-intuitive results like this."

Teams at two experiments known as T2K in Japan and MINOS near Chicago in the US will now attempt to replicate the finding. The MINOS experiment saw hints of neutrinos moving at faster than the speed of light in 2007 but has yet to confirm them.

• This article was amended on 23 September 2011 to clarify the relevance of the speed of light to causality.


Neutrino stories move faster than the speed of science

Journalists reporting that neutrinos can travel faster than the speed of light have jumped the gun and done a disservice to science

Martin Robbins Friday 23 September 2011, guardian.co.uk

XKCD on Neutrinos XKCD on Neutrinos (http://xkcd.com/955/)

A little before six last night, Reuters tweeted a report stating that Italian scientists had detected tiny particles called ‘neutrinos’ moving faster than the speed of light (paper). If true, they have witnessed a phenomenon that, according to established theory, should be impossible.

If. Within hours of Reuters’ tweet, a chorus of physicists had expressed their reservations, culminating this morning in Professor Jim Al-Khalili bravely threatening to eat his boxer shorts live on television if the findings are correct. Science; red in tooth, claw and underpants.

More, er, detailed critiques have come from Czech physicist Luboš Motl, particle physicist Ben Still, and Phil "Bad Astronomer" Plait, with New Scientist publishing a suitably sceptical article this morning. Twitter’s reaction was, inevitably, a humorous hashtag, #mundaneneutrinoexplanations:

@alinasnd: Neutrinos going faster than light? Nope. Chuck Testa! #mundaneneutrinoexplanations

@blakestacey: Calculations done by visiting Americans who still don’t get the metric system. #mundaneneutrinoexplanations

@rushyo: Finally! Proof that the Windows progress bar should not be used in a scientific context #mundaneneutrinoexplanations

Why so much scepticism? Carl Sagan once said that "extraordinary claims require extraordinary evidence." If your experiment seems to break the laws of physics, then the prior probability of the result is so tiny that you’re more likely to have made a mistake than a new discovery, and you’re going to have to work hard to convince people otherwise. The claims being made here are certainly in that category. As Nature put it:

"If neutrinos are travelling faster than light speed, then one of the most fundamental assumptions of science — that the rules of physics are the same for all observers — would be invalidated. "

Extraordinary claims indeed, but while they could be true there’s little substance behind them so far. The evidence is a single, tentative finding, contradicted by other observations of neutrinos which have failed to see the same effect. The work has yet to be properly published or peer reviewed, let alone scrutinized or replicated by the scientific community. At the time the Reuters report appeared, the researchers hadn’t even uploaded their draft paper to Arxiv, the pre-print repository. We don’t know if the claim is true or not, but we know that if it is, it needs more substantial evidence behind it.

This can’t yet be presented as ‘fact’ then, but that’s exactly what Reuters chose to do with their headline, "Particles found to break speed of light". Nature News posted a similar headline, "Particles break light-speed limit" and declared "Neutrino results challenge cornerstone of modern physics." Sure, the article went on to explain that other researchers were cautious about the result, but I’m not sure that’s good enough. Often the impression left by a headline sticks. On Twitter, the headline is often all that’s tweeted, and all that many people see.

The contrast between mainstream media coverage and commentary on blogs has been fascinating. The news broke in the evening, and it’s only this morning that the best science journalists – people like Hannah Devlin at The Times (£), Tom Chivers at The Telegraph and Lisa Grossman at New Scientist – have been on the case (there are a exceptions of course, our Ian Sample did a good job last night, and the BBC’s Jason Palmer had a brilliant piece up as I was eating my dinner).

Coverage on the quality science blogs wasn’t necessarily better, but it did seem to be more timely and more critical – a number of good physics bloggers had blogged or tweeted their opinions by yesterday evening, many of them working physicists themselves, and they were keen to put the reports into proper perspective; emphasizing the preliminary nature of the findings, the scope for error and the need for caution.

Isn’t this all a bit unseemly though? Watching the claims and counter-claims rippling through cyberspace reminded me of the ‘ArsenicGate’ debacle last December, in which research supposedly relating to extra-terrestrial life was overhyped by NASA’s press machine and the wider media, resulting in a backlash of criticism directed at both the agency and the researchers.

The difference is that in that case at least a peer-reviewed paper had been published. Here we’ve been subjected to science-by-press-release, in the manner of Susan Greenfield. Those defending this will say that the researchers are simply trying to solicit robust feedback from the scientific community, but the last time I checked Reuters was a news agency, not a scientific journal or a conference of peers.

That’s not to say that scientists shouldn’t discuss preliminary results in public, or that the media should only report on finished works of research. In fact I believe the opposite – the media should do much more to provide an overview of science in progress, and drop their fixation on individual papers as somehow representing ‘truth’ in science rather than a starting point for debate. The online discussion that has sprung up around this research is fascinating, joke hashtags aside, and both science and the public discourse are richer for it.

The problem isn’t that the research is in the public domain, it’s the undignified manner in which it got there, dumped onto the world stage in a sprawling heap, like Mr Bean under the spotlight in the famous title sequence. What isn’t clear at the moment is whether Reuters dug up the story themselves, or whether the researchers of their institutions fed the information to the news organization (if I get a response on this I’ll let you know. Note: Ananyo has posted a helpful explanation in the comments).

Either way, the end result is unhelpful. A tentative finding has been portrayed in headlines as a statement of scientific fact, and as a result the excitement and uncertainty of science has been crushed into the tedious ‘he said, she said’ paradigm favoured by journalists who at times seem allergic to the phrase "we just don’t know."

These claims could be right or wrong, and if they’re wrong they could still be extremely useful and interesting regardless. That nuance is part of what makes science so interesting, and losing it robs the public of context, understanding, and ultimately the truth; that something odd happened and we’re not sure why yet.

Anyway, enough moaning from me. Here are some more #mundaneneutrinoexplanations:

@crispian_jago: Clearly bad news neutrinos

@enniscath: Maybe light is just slowing down? It’s pretty old; maybe it’s lost a yard or two of pace?

@bobohara: The calculations were done with Excel

@physicsdavid: Speed of light is only a limit in the reality-based community

@AnneMurdaugh: Forgot it is still daylight saving time.

@drskyskull: Cheating neutrinos jumped the starting gun: physics ref failed to notice.

@physicsdavid: Due to austerity measures the speed of light has been reduced

@notmattbellamy: Bipolar atoms stabilized on serotonin-uptake inhibitors yield high-functioning neutrinos.

@blakestacey: #CERN physicists let undergrads near the experiment

@sciencecomedian: Confused neutrino with one sent later

@sjuriz: All Melmacians turned on their hair-dryers at the same time.

@stradling: Fermilab saboteurs playing with CERN team’s minds

@pvwheatley: Light had bad clutch work during red shift.

@sciencecomedian: Study published by Wakefield et al


From the archive, 19 April 1955: Einstein as a man

Originally published in the Manchester Guardian on 19 April 1955

We much regret to announce the death at Princeton, New Jersey, yesterday of Dr Albert Einstein. He was 76. Dr Einstein had entered hospital on Friday for treatment of arterio-sclerosis.

Even a layman can tell what made Albert Einstein famous as a scientist. But what was the secret of his truly amazing fame as a man? It was something quite simple and human, a genuine personal affection by many thousands for someone they never knew. They may have heard he was a great man, but they seem to know he was a good man. Anything from him apparently could be taken on trust.

In the years before the war we used to go for an hour’s walk together every day of the week, and even in the quiet by-lanes of Princeton passers-by would grin and greet him with a "Good afternoon" – there was no fawning or intrusion, but one could see that people really were glad and did feel better for having had a glimpse of him.

He was physically a lazy man, apart from his short walks, but he loved to sail a small boat; when I once asked him what made him take to sailing, he said: "Because it is the only sport which demands no physical effort!"

There was the evident simplicity of the man – glaring in a way in his unconcern for appearance. Not only did he not wear a hat, but he could not stand collar and tie or socks. One day when I called to accompany him to a lecture by a foreign visitor he astonished me by appearing in a starched collar. "Oh, you are getting vain!" He grinned and said laughingly "Höchste Zeit!" ("It is about time, too!").

Time and again he abandoned the retiring, undemanding life of his choice to join colleagues in a fight for some general issue or other. And of course he was utterly uncompromising when it was a matter of scientific truth – uncompromising above all with himself. I used to tease him with the suggestion he had chosen me as walking companion because I had no mathematics at all and so he was safe from prying questions, but in fact now and then he did used to tell me about what he was doing – and how clear it all seemed when he spoke!

When a telegram arrived from the Israeli Ambassador in Washington asking to be received on the following day – we knew what it meant, as there had been a rumour that Mr Einstein would be offered the Presidency of Israel. Mr Einstein was greatly moved but insisted on telephoning himself to the Ambassador at once, for his main and urgent thought was how to spare the Ambassador the embarrassment of his inevitable refusal.


The laws of physics. Or are they more like guidelines?

Is fundamental physics too theory-led?

Jon Butterworth Sunday 4 September 2011,  guardian.co.uk

black hole bidisha thought for the day

In a black hole, the three giant theories of physics – quantum mechanics, gravitation and thermodynamics – come into apparent conflict.
Photograph: EPA

The comments on "Life and Physics" vary wildly, but one recurring theme amongst some commenters is a perception that fundamental physics is too theory-led, that we are obsessed with proving beautiful, reductionist theories and really we should just explore. And that we spend too much time arguing about untestable things.

This is not a criticism to be lightly dismissed, and some of the time, for some physicists, it is almost certainly a fair one. However, I would like to make three counter points.

Thought experiments

In my piece about black holes and fuzzballs, some objected, correctly, that what goes on inside black holes is pretty much inaccessible to experimental test. So why even discuss it? For me, the interest in the discussion is the conflict, in what amounts to an "extreme thought experiment", between three amazingly successful theories, or "laws of physics" if you prefer. Quantum mechanics, gravitation and thermodynamics have their laws, and their underlying picture of the universe. They have credibility by virtue of each being able to describe a vast range of phenomena, ranging from steam engines through planets to the central processing unit in your computer. In a black hole, these laws come into apparent conflict. The territories of three giants overlap. By thinking through the contradictions which arise, we can find gaps in the theories, develop new understanding, and in the end hopefully derive observable predictions which would test such understanding. It is a hugely worthwhile exercise, unless you are utterly uninterested in understanding how things work or in benefiting from such understanding.

Electroweak symmetry breaking

To some it appears the Large Hadron Collider is a disproportionate investment of time, money and expertise in chasing some theorists’ dream. I disagree, of course. While the Higgs is the headline, the LHC is genuinely exploring new territory for whatever might be there. The energy frontier (or if you like, the short distance frontier – we study nature at smaller distance scales than anywhere else) remains a frontier of knowledge, whether Peter Higgs says it is or not. Plus, we have very good reason, from experiment alone, to think this part of the frontier is special. Look at this plot:

DIS cross sections electron-proton scattering: Credit DESY, ZEUS and H1 experiments.

What is shows is essentially the probability of an electron bouncing off a proton, with the energy of the bounce increasing as you go from left to right. The blue points show the times when it bounces because of its electric charge – the electromagnetic force. The red points are the times when it bounces by swapping a W boson – the weak force. You can see that at low energies (toward the left) the electromagnetic bounce is much more likely. But at high energies (on the right) the weak force is just as likely to be responsible as the electromagnetic. There is a symmetry between the two forces which is restored at this energy*. These are data. Measured. No theory. (The curves are theory, but ignore them.)

The LHC, for the first time in the history of science, allows us to explore properly above that energy, into the region where the symmetry holds. Our theory says the Higgs breaks the symmetry. But even without that theory, you might think exploring physics above this fundamentally important energy scale is an exciting thing to do, and might tell us how these forces work, and why they are sometimes the same and sometimes different.


Finally, the LHC data have so far led to a bonfire of theories. While big ideas like supersymmetry or extra dimensions have not been disproved (yet), many many options for them have been closed off.

It is true many of us have our favourite theories, but in the end the data decide, and as an experimentalist I am seriously enjoying making myriad bright ideas face the music. We have waited a long time, theorising and guessing. Now, at last, we are able to look at some more of the answers.

* The scale on the horizontal axis is actually the distance in metres (very small). But where the curves meet is the equivalent of about 100 GeV in energy.


My favourite particle: the neutrino

I started writing about neutrinos because I love them. They are quite magical really; the Universe is completely swarming with them (they are the second most abundant particle after photons) but we know practically nothing about them. And what we do know is really weird. Guest post by Lily Asquith

Lily Asquith Saturday 2 April 2011, guardian.co.uk

I wrote down "My favourite particle: the neutrino" to fit in with the other particle articles. But it isn’t my favourite particle. I toyed with "Not my favourite particle: the neutrino" but that just felt disrespectful. Then I decided it doesn’t matter what I write at the top of the page. Why do I need this post to fall into line with the others? I suppose it’s because I want symmetry. I want that warm, comfortable-yet-exciting feeling you get when starting to read the next book in a trilogy.

The neutrino was postulated (imagined-up) for a similar reason: the desire for symmetry.

A hundred years (ish) ago there was lots of great experimental science going on. There was no clear idea what atoms were, but there was an understanding that they weren’t solid balls. Ernest Rutherford and others had established, through experiments, that there was a nucleus in the center of an atom and had postulated that electrons were ‘in orbit’ around this nucleus. He came up with this description based purely on his experimental results: there was no theory at the time that predicted this.

I feel quite nostalgic for this sort of experiment-driven theory. In the era of the LHC it is not the done thing to come up with a new theory to describe what we see experimentally. In general, our results have to fit some theory that has already been proposed. When they don’t (they don’t) we tune the theoretical predictions to match our data, like twiddling a load of knobs (most of these theory predictors, which we call Monte Carlo, have twenty or thirty knobs) until we get some agreement. I am moaning about this, but really we don’t have a choice.

Anyway, back to the good old days.

Something called Beta decay had been observed. They had a name for it before they knew it for what it was. It was a nice bit of real-world, useful, observational science. It was noticed that some atoms would emit radiation without any provocation to do so.

This is what we call radioactivity. Active radiation. Nothing to do with the radio, other than that radio also works via radiation. Radio is carried by electromagnetic radiation (my first love – the photon). What radiation is is the loss of energy by something. That energy invariably travels somewhere else in some form or other. But the thing with radioactivity is it is not deliberate. It just happens "naturally".

When first discovered it triggered a whole host of money-making schemes, similar to modern-day homeopathy I suppose, except homeopaths make their millions out of plain water and packaging, whereas back in the day the quacks were raking it in by selling people radioactive face-cream. The scientists rebelled, lots of people got cancer and the business end closed. I laughed at these adverts and showed my mates, and then I felt really sad because I thought about people in the future (okay, the present) laughing at my friends for buying 0% proof hogswart.

Anyway (again), the science continued, and we realized that what was happening was that part of the atom, in fact part of the nucleus, was ‘decaying’.

It was established that the radiation being emitted was electrons, because the measurement of the emitted particles’ charge and mass was exactly the same as for electrons. The electrons weren’t being thrown ‘out of orbit’, they were being emitted from the nucleus. This is interesting, because the atomic nucleus only contains protons (with a charge of +1) and neutrons (with a charge of zero). To get a negatively charged particle out of this we thought that the neutron must decay into a proton and an electron: zero charge= +1 and -1. Great. This fitted nicely with the experimental measurement of the atom before and after it went through Beta decay.

Beta decay spectrum from http://www.cobra-experiment.org/

But this is where things stopped being comfortable. This picture predicts precisely the energy that the emitted radiation (the electron) must have. Depending on what kind of atom is doing the decay, we should be able to predict exactly how much energy the electron has.When they measured the energy carried by these emitted electrons, they found that the electrons could have any energy. This was a huge problem because conservation of energy was (and is) the closest we get to feeling comfortable with any knowledge in particle physics. It always works. We don’t have to appeal to the fact that the theory is beautiful and elegant, we just do cold, hard experiments. And warm, soft ones. Any kind of one. We always get the same answer: energy is conserved. Always. But not in radioactivity.

 carbon14 decay from http://education.jlab.org/glossary/betadecay.html

Wolfgang Pauli wasn’t having any of it. There must be something else emitted, something that the instruments were not detecting. Pauli described the properties that this invisible particle must have; It is neutral (no charge), it has a small (or zero) mass and it has spin half like the electron. If the new particle was emitted along with the electron, then the electron could have any energy, because the total energy emitted could still add up to be the exact value predicted by the theory. The new particle would have to be a ghost, traveling through matter without interacting at all. Then we could explain why it was not detected.

Of course this was not a comfortable place to be, but it was slightly less uncomfortable than violating the law of conservation of energy.

Pauli was aware of his responsibility, famously saying "I have done a terrible thing. I have postulated a particle that cannot be detected".

Wolfgang PauliWolfgang Pauli: he knew his stuff.

Is it okay to make a prediction that we cannot test? Science is about trying to describe the way the world works; our understanding should be based on what we observe and our theories should be testable. This is why some experimentalists laugh at string theory. I for one am happy to ignore it until someone comes up with a way for us to test its validity. Okay, some of the reason I ignore it is because it is hard, but I would be much more inclined to make the effort if I thought it was any use.

Thankfully, the little neutral ones, neutrinos, can be detected. It is just very, very difficult to do. This is because they simply do not interact with the particles that make up matter. Neutrinos can fly past an atom as if it were not there. They are neutral, so they are not affected by electromagnetic fields. The only thing in nature they have anything to do with is the weak nuclear force, so they tend to just whizz through the universe, through planets and through us, leaving no trace.

We do detect the odd one. The first was 25 years after Pauli’s prediction, by Cowan and Reines. Back in 1987 we saw a whopping 24 of them in just a few seconds, thanks to a supernova going off in the vicinity. But generally they are a bugger to catch.

So what do we know about neutrinos now? Almost nothing, but the little bit we do know is very interesting indeed. The standard model of particle physics (the theory that we are most happy with when putting together all the little bits of knowledge we have gathered from thousands of experiments over a hundred years) tells us that neutrinos have no mass, like photons. We now know that this is not the case. Neutrinos do have mass. We know that the three kinds of neutrinos must all have different masses, so at least two of them cannot be zero. I feel like nobody really talks about this. Perhaps I hang out with the wrong kind of physicists. Neutrino experiments have shown the standard model to be deeply flawed, yet we still persist in calling it "the standard model".

I have finished writing this now without actually saying a single thing about why I love the neutrino. I haven’t mentioned that they are able to change flavour (neutrino oscillations) or that they could be their own antiparticle (are they Majorana or Dirac particles?) or that they can help us understand dark matter, or that the fate of the universe is in their hands.

Each one of these things is completely deserving of its own post, written by someone who knows their onions and is able to write something that is not 90% digression.


The hunt for neutrinos in the Antarctic

The IceCube project has constructed a giant detector in the Antarctic ice to find subatomic particles. It could reveal where cosmic rays come from – and their cause. We meet the scientists at the south pole

ice cube lab antarctica

The IceCube laboratory at the Amundsen-Scott South Pole Station, Antarctica. Photograph: http://www.icecube.wisc.edu

Spencer Klein is holding a thick glass ball the size of a watermelon and it is stuffed with electronics. For 10 minutes or so, he turns it over in his hands and talks through what it does, how it works and the brutal environment it can withstand. This last point turns out to be key. Over the past half-decade, more than 5,000 of these objects have been shipped to the south pole, strung together like beads, and buried deep in the Antarctic ice sheet.

Klein is a physicist at the Lawrence Berkeley National Laboratory that sits high on the hills overlooking the University of California’s Berkeley campus and beyond to San Francisco Bay. The glass ball in his hands is a "digital optical module" (DOM), an exquisitely sensitive light detector that lies at the heart of what must be one of the most ambitious projects in the history of science. By freezing these modules into the ground around the US Amundsen-Scott south pole station, on the high plain of Antarctica, Klein and his colleagues have turned a cubic kilometre of pristine polar ice into an enormous cosmic observatory.

The $272m (£170m) IceCube instrument is not your typical telescope. Instead of collecting light from the stars, planets or other celestial objects, IceCube looks for ghostly particles called neutrinos that hurtle across space with high-energy cosmic rays. If all goes to plan, the observatory will reveal where these mysterious rays come from, and how they get to be so energetic. But that is just the start. Neutrino observatories such as IceCube will ultimately give astronomers fresh eyes with which to study the universe.

The frigid conditions at the south pole meant construction teams could only work on IceCube between November and February each year when ski-equipped planes can safely make the 1,800-mile round trip to the research station. The DOMs are designed to run on precious little power, a measly 5W each, but even so, it takes 10 planeloads of fuel to run IceCube for a single year.

ice cube telescope DOM
The final digital optical module (DOM) is prepared for the telescope.

The final piece of the observatory was put in place a week before Christmas when engineers used a hot-water drill to melt the last of 86 holes in the ice. The holes reach a depth of 2.5km (1.5 miles) and down each is lowered a string of 60 DOMs that are locked in place when the water in the hole refreezes. The pressure is so great at these depths that air bubbles are squeezed out of the ice, leaving it almost perfectly transparent.

Physicists on the IceCube project are now completing a series of checks on the latest additions to their bizarre instrument to see if the equipment survived the ordeal of being installed. Assuming it has – and only a couple of DOMs have failed in the project’s history – the instrument will soon swing into action and its search for cosmic rays will begin in earnest. "Our best calculations show that we need an instrument this size to have a good chance of seeing these cosmic ray sources," says Klein. "Now we’re done, we have it."

An Austrian-born scientist called Victor Hess discovered cosmic rays 100 years ago. In a series of hot-air balloon flights, Hess measured the radiation around him at altitudes up to and beyond five kilometres. As he rose up through the atmosphere, radiation levels initially fell, but then rose steeply until they were double that at sea level. Hess reasoned that radiation must somehow reach Earth from outer space.

Cosmic rays are now known to be highly energetic particles that originate in outer space and bombard our planet from all directions. Most are made up of charged particles, such as metal ions, but these are of little use to space scientists hoping to discover the origins of high-energy cosmic rays. Charged particles are deflected by magnetic fields as they race across space, making it hard, or impossible, to retrace their route and locate their cosmic birthplace.

Neutrinos are different. Produced alongside cosmic rays in outer space, neutrinos are uncharged and pass through normal matter almost entirely unhindered. Instead of being pushed and pulled around as they head towards Earth, neutrinos move in a straight line, giving scientists a good chance of tracing them directly back to their origins.

The most energetic cosmic rays seen in nature pack far more punch than any particle accelerator has ever achieved on Earth. "Some carry the same amount of energy as a well-hit tennis ball," says Klein. "To put that in context, if you wanted to build an accelerator that energetic, with the same technology they use at the Large Hadron Collider [at Cern, in Switzerland], you would need a ring of magnets the size of Earth’s orbit around the Sun."

Scientists have some ideas about what cosmic events might produce these extraordinarily energetic cosmic rays. They could be driven by shockwaves emanating from exploding stars, or be propelled from supermassive black holes that sit at the centres of galaxies, gobbling up stars and other objects in the vicinity. In one scenario, cosmic rays stream out when a black hole collides with a neutron star.

"The biggest puzzle about cosmic rays is that they are the highest-energy particles we can see in the universe and yet we don’t know what makes them. We have ideas, but it remains one of the outstanding mysteries of physics. What we want to find out is, how is nature doing this?" says Subir Sarkar, an astroparticle physicist at Oxford University and leader of the British team that works on IceCube.

IceCube is not the first neutrino observatory to be built by scientists, but it is by far the largest. In 1987, three neutrino detectors, constructed in caverns in Japan, America and the Caucasus, became the first to spot a few handfuls of neutrinos that sprayed out of a supernova called 1987A, which exploded in the Large Magellanic Cloud, a neighbouring galaxy to ours. In Siberia, a Russian-German team has lowered cables carrying 192 light sensors into the clear depths of Lake Baikal, turning 10 megatonnes of water into a neutrino detector. Another neutrino observatory, Antares (Astronomy with a Neutrino Telescope and Abyss Environmental Research), was built off the coast of Toulon in France in Mediterranean waters 2.5km deep. Antares complements IceCube as a northern hemisphere-based observatory.

Even with an instrument the size of IceCube, scientists expect to see only a few hundred neutrinos a day. The elusive particles reveal themselves on the rare occasions that they collide with the nuclei of oxygen atoms in the ice. When this happens, a neutrino produces a particle called a muon, a heavy relative of the electron. These muons travel faster than the speed of light in ice and release a shockwave of faint, blue light that is picked up by IceCube’s light sensors.

In a lab on the surface, signals from DOMs throughout the IceCube observatory are combined and analysed to work out the direction and energy of neutrinos that left their tracks. The scientists will look for muons that move upwards through the ice, as these are produced by neutrinos that passed through the Earth before reaching the detector. Far more downwards-moving muons are produced by charged particles in the atmosphere above the detector, but these don’t point back to the sources of cosmic rays. "We essentially use the Earth as a giant filter to absorb all the particle junk that is made locally," says Sarkar.

Over time, the IceCube observatory will build up a "neutrino map" of the sky and with luck find hotspots in the heavens where high-energy cosmic rays appear to come from. By comparing this map with those already made by optical, infra-red, radio and x-ray telescopes, scientists may finally learn where, and even how, cosmic rays are made.

Recently, the IceCube team signed an agreement with the Nasa scientists who operate the Swift satellite that scours space for gamma ray bursts, the most violent events in the universe. Whenever Swift spots one, Nasa tells the IceCube scientists so they can immediately check that part of the sky for neutrinos.

Klein says about 90% of the urge to understand cosmic rays is intellectual, but unravelling the natural processes that propel particles around in space could be used to transform technology on the ground. "If we can learn how cosmic rays are produced, we might learn something useful for building accelerators on Earth," he says.

One region of space that is a likely source of cosmic rays is a galaxy 10 million light years away called Centaurus A. There is little to see through an optical telescope because the galaxy is obscured by dust, but infrared images from Nasa’s Spitzer space telescope cut through the haze to show a spiral galaxy falling into a black hole at the centre of Centaurus A. When Nasa’s Chandra space telescope took x-ray images of Centaurus A, it saw huge jets erupting from the centre of the galaxy.

"Centaurus A looks different at every wavelength we’ve tried. The question is, what will it look like through a neutrino observatory?" says Sarkar. With neutrinos, scientists may finally be able to look deep into the heart of a galaxy and see what Sarkar calls the "central engine" that churns out cosmic rays.

Even as IceCube goes into action, scientists have begun work on prototype neutrino observatories that are larger still. The Arianna neutrino observatory will turn 100 cubic kilometres of the Ross ice shelf in Antarctica into a colossal neutrino detector.

Francis Halzen, IceCube’s lead scientist at the University of Wisconsin-Madison, turns to Marcel Proust when asked how neutrino observatories such as IceCube might give us new insights into the workings of the cosmos: "The real voyage of discovery consists not in seeking new landscapes but in having new eyes."

As the short summer and its 24-hour days of sunlight come to an end at the south pole, work on IceCube has turned to upgrading computer systems and packing up the hot-water drill for long-term storage. Now the scientists face a waiting game: it is time to see if the Antarctic ice can catch their elusive quarry.

Neutrino graphic 

Explainer: the subatomic world

Inside the atom

Schoolchildren learn that we are made of atoms, which consist of a dense nucleus made of protons and neutrons, composed of quarks, surrounded by a cloud of electrons. But more exotic particles make up our universe too.

Less familiar particles

Neutrinos are like electrons but electrically neutral. Created as a result of certain types of radioactive decay or reactions such as those that take place in stars, they are very light and travel close to the speed of light and pass through ordinary matter almost undisturbed. There are three types, or "flavours", of neutrino: electron neutrinos, muon neutrinos and tau neutrinos. Each type also has a corresponding antiparticle, called an antineutrino.

The basic ingredients of matter

Electrons and neutrinos are classified as leptons, which don’t feel the strong or nuclear force. Together with another family of particles called quarks (themselves divided into six "flavours"), which do feel the strong force, leptons are known as fermions. These are the particles we associate with matter.

Fundamental forces

All elementary particles are either fermions or bosons (depending on their "spin"). The latter are particles we associate with fundamental forces. There are gauge bosons – gluons, W and Z bosons and photons – and two hypothetical bosons: gravitons and the Higgs boson. It is hoped that experiments at the Large Hadron Collider at Cern in Switzerland will find Higgs bosons.


Higgs boson signals fade at Large Hadron Collider

Cern scientist says he sees ‘no striking evidence of anything that could resemble a discovery’ in hunt for Higgs boson

Ian Sample, guardian.co.uk, Monday 22 August 2011

Large Hadron Collider

Screens show data from a collision at the Large Hadron Collider.
Photograph: Denis Balibouse/Reuters

Ripples of excitement swept through the physics community last month when Cern scientists reported what looked like glimpses of the long-sought Higgs boson. But the hopes have been dashed as it was revealed that the tantalising hints had all but faded away.

Researchers at the Large Hadron Collider (LHC) near Geneva noticed intriguing signals in their data in July that they thought might be caused by the elusive sub-atomic particle. But the latest analyses, based on nearly twice as much data, saw those signals weaken considerably. The news was broken at the Lepton-Photon conference in Mumbai.

"We see no striking evidence of anything that could resemble a discovery," Guido Tonelli, spokesman for the Compact Muon Solenoid (CMS) detector group at Cern, told the Guardian.

One of the main objectives of the collider is to discover what gives mass to elementary particles, something many physicists credit to the Higgs boson. The LHC has two large, multipurpose detectors, Atlas and CMS, and last month both teams independently reported signals that suggested the Higgs boson might weigh between 120 and 140GeV (gigaelectronvolts), the units of mass used in particle physics. One GeV is roughly equivalent to the mass of a proton, a subatomic particle found in atomic nuclei.

But in Mumbai both teams said the signals had faded, although it was too early to completely rule out a Higgs particle in that mass range. In particle colliders, it is common for signals to come and go because of statistical blips or fluctuations.

"We might be very close to a depressing moment in which we conclude those fluctuations were statistical jokes, but there is also the possibility of seeing them grow with more data. The exciting part is that after 20 years of preparation and work, I would say this will be decided by Christmas," Tonelli said.

Results so far suggest that if the most simple version of the Higgs boson is real (some theories call for multiple Higgs particles), it must have a mass between 114GeV and 145GeV.

Particle physicists rank their confidence in new results on a scale in which a "three sigma" signal counts as an "observation", and a more robust five sigma signal claims a concrete discovery.

A five sigma signal means the chance of the result being a statistical fluke is less than one in three million. Since July, the Higgs-like signals seen by the CMS group have fallen from around 2.8 to 2.3 sigma. Those seen by the Atlas group have dropped from around 2.8 to less than two.

"We need to be patient. We need to take data and analyse them and understand them," said Fabiola Gianotti, head of the Atlas detector group. "At the same time, we are super-excited, because we are very close. We are months away from really solving one of the major mysteries in fundamental physics. It’s so close I feel I can touch it with my hand."

She added: "If the Higgs boson is not there, then a completely new scenario opens up: there must be something else that plays the role of the Higgs boson."


After Report on Speed, a Rush of Scrutiny

CERN, via Associated Press

The world was watching as scientists announced that neutrinos from the CERN laboratory had raced to an Italian site faster than it would take a light beam.

By DENNIS OVERBYE, The New York Times, September 23, 2011
  • One upon a time, the only thing that traveled faster than the speed of light was gossip.

Dario Autiero, of the Institut de Physique Nucléaire de Lyon, on Friday explained his team’s findings on neutrinos.

Thanks to the Internet, the whole physics world was watching on Friday when Dario Autiero, of the Institut de Physique Nucléaire de Lyon in France, in front of a palpably skeptical roomful of physicists, put a whole new category of speed demons on the table, namely the shadowy subatomic particles known as neutrinos. He was describing a recent experiment in which neutrinos were clocked going faster than the speed of light, the cosmic speed limit set by Albert Einstein in his theory of relativity back in 1905.

According to Dr. Autiero’s team, neutrinos emanating from a particle accelerator at CERN, outside Geneva, had raced to a cavern underneath Gran Sasso in Italy — a distance of 454 miles — about 60 nanoseconds faster than it would take a light beam. That amounts to a speed greater than light by about 25 parts in a million.

“We cannot explain the observed effect in terms of systematic uncertainties,” Dr. Autiero told the physicists at CERN, the European organization for nuclear research. “Therefore, the measurement indicates a neutrino velocity higher than the speed of light.”

Dr. Autiero said his group had spent six months trying to explain away the result, but could not do it. Given the stakes for physics, he said, it would not be proper to attempt any sort of theoretical interpretation of the results. “We present to you this discrepancy or anomaly today,” he said.

The purported effect sounds slight, but to be even slightly on the wrong side of the speed of light is forbidden in the world that Einstein described. Faster-than-light travel can also lead to the possibility of time travel, something that most physicists do not believe is possible.

Relativity has been tested over and over again for a century, and as Carl Sagan, the late Cornell astronomer, liked to say: extraordinary claims require extraordinary evidence. “This is quite a shake-up,” said Alvaro de Rujula, a theorist at CERN. “The correct attitude is to ask oneself what went wrong.”

And the assembled CERN physicists were only too happy to oblige, diving in, after Samuel C. C. Ting, an M.I.T. Nobelist in the audience, offered his congratulations for work “very carefully done.” They asked detailed questions about, among other things, how the scientists had measured the distance from CERN to Gran Sasso to what is claimed to be an accuracy of 20 centimeters, extending GPS measurements underground. Had they, for example taken into account the location of the Moon and tidal bulges in the Earth’s crust?

The recent history of physics and astronomy is strewn with reports of suspicious data bumps that might be new particles or new planets and — if true — could change the way we think about the world, but then disappear with more data or critical scrutiny. Most physicists think the same will happen with this finding. The prevailing attitude was perhaps illustrated best by an XKCD cartoon, in which a character explains his intention to get rich betting against the new discovery.

Neutrinos are still a cosmic mystery. They are among the weirdest denizens of the weird quantum subatomic world. Not only are they virtually invisible and able to sail through walls and planets like wind through a screen door, but they are shape-shifters. They come in three varieties and can morph from one form to another as they travel along, an effect Dr. Autiero and his colleagues were trying to observe.

Their experiment, known clunkily as Oscillation Project with Emulsion-Tracking Apparatus, or Opera, is a collaboration of 160 physicists from 11 countries, primarily Japan and Italy. It is based at the Gran Sasso laboratory, a center for underground physics experiments that need sheltering from cosmic rays.

The action begins in a tank of hydrogen gas inside a building at CERN. Atoms in puffs of gas from the tank get stripped of their electrons, becoming naked protons, and then get sent on a Coney Island-style speed ride through a series of particle accelerators, eventually winding up in the main ring of the Large Hadron Collider — the mother of all particle accelerators.

For the Opera experiment, some of the protons are siphoned off at an intermediate energy and slammed in pulses 10 microseconds long into a graphite target, where they produce a pulse of lesser particles called mesons. The mesons in turn decay into neutrinos, which then disappear into the Earth in the direction of Gran Sasso. There, the arriving neutrinos run into an assemblage of lead bricks and photographic emulsion.

In theory, during the trip, which takes a few milliseconds, some of the neutrinos should shape-shift from a variety known as muon neutrinos to tau neutrinos. The goal of the Opera experiments was to study this transformation: In three years, the researchers have recorded some 16,000 neutrinos in their detector, but only one tau neutrino.

Measuring the speed of the neutrinos was only a side ambition, explained Antonio Ereditato of the University of Bern, the head of the Opera collaboration. “Now it is becoming a main issue,” he said, adding, “we would like to see some tau neutrinos,” to appreciative laughter from the audience.

In the old days, when scientists sent around copies of journal articles and wrote letters to one another, the process of scrutiny of a controversial measurement could have happened quietly, but the Web has changed all that. Dr. Autiero’s talk at CERN and the appearance of a paper by the Opera group on the Internet Thursday night came at the end of a drumbeat of rumors and blog postings. One blog called it “Rumour of the Century.”

Some physicists, inside and outside of CERN, were critical of this process, saying the laboratory was giving too much weight to a premature result by a group that was not even part of CERN.

Nima Arkani-Hamed, a particle theorist at the Institute for Advanced Study in Princeton, said in an e-mail, “There was no need for a press release or indeed even for a scientific paper, till much more work was done. They claim that they wanted the community to scrutinize their result — well, they could have accomplished that by going around and giving talks about it.”

Rolf-Dieter Heuer, director general of CERN, said in an e-mail from Spain, “I agreed to the seminar at CERN because it is the duty of a lab like CERN to give the collaboration the possibility to ask the community for scrutiny of their findings.”

The scrutiny is surely coming.

An earlier measurement of neutrino speeds was performed by a collaboration known as Minos, for Main Injector Neutrino Oscillation Search, in 2007. Jenny Thomas of University College London, said the Minos experiment would be able to do a more precise measurement in four to six months.

“They’ve done their best,” Professor Thomas said of the Opera group. “The light’s going to shine on us now while we repeat our experiment.”


Tiny Neutrinos May Have Broken Cosmic Speed Limit

By DENNIS OVERBYE, The New York Times, September 22, 2011

  • Roll over, Einstein?

The physics world is abuzz with news that a group of European physicists plans to announce Friday that it has clocked a burst of subatomic particles known as neutrinos breaking the cosmic speed limit — the speed of light — that was set by Albert Einstein in 1905.

If true, it is a result that would change the world. But that “if” is enormous.

Even before the European physicists had presented their results — in a paper that appeared on the physics Web site arXiv.org on Thursday night and in a seminar at CERN, the European Center for Nuclear Research, on Friday — a chorus of physicists had risen up on blogs and elsewhere arguing that it was way too soon to give up on Einstein and that there was probably some experimental error. Incredible claims require incredible evidence.

“These guys have done their level best, but before throwing Einstein on the bonfire, you would like to see an independent experiment,” said John Ellis, a CERN theorist who has published work on the speeds of the ghostly particles known as neutrinos.

According to scientists familiar with the paper, the neutrinos raced from a particle accelerator at CERN outside Geneva, where they were created, to a cavern underneath Gran Sasso in Italy, a distance of about 450 miles, about 60 nanoseconds faster than it would take a light beam. That amounts to a speed greater than light by about 0.0025 percent (2.5 parts in a hundred thousand).

Even this small deviation would open up the possibility of time travel and play havoc with longstanding notions of cause and effect. Einstein himself — the author of modern physics, whose theory of relativity established the speed of light as the ultimate limit — said that if you could send a message faster than light, “You could send a telegram to the past.”

Alvaro de Rujula, a theorist at CERN, called the claim “flabbergasting.”

“If it is true, then we truly haven’t understood anything about anything,” he said, adding: “It looks too big to be true. The correct attitude is to ask oneself what went wrong.”

The group that is reporting the results is known as Opera, for Oscillation Project with Emulsion-Tracking Apparatus. Antonio Ereditato, the physicist at the University of Bern who leads the group, agreed with Dr. de Rujula and others who expressed shock. He told the BBC that Opera — after much internal discussion — had decided to put its results out there in order to get them scrutinized.

“My dream would be that another, independent experiment finds the same thing,” Dr. Ereditato told the BBC. “Then I would be relieved.”

Neutrinos are among the weirdest denizens of the weird quantum subatomic world. Once thought to be massless and to travel at the speed of light, they can sail through walls and planets like wind through a screen door. Moreover, they come in three varieties and can morph from one form to another as they travel along, an effect that the Opera experiment was designed to detect by comparing 10-microsecond pulses of protons on one end with pulses of neutrinos at the other. Dr. de Rujula pointed out, however, that it was impossible to identify which protons gave birth to which neutrino, leading to statistical uncertainties.

Dr. Ellis noted that a similar experiment was reported by a collaboration known as Minos in 2007 on neutrinos created at Fermilab in Illinois and beamed through the Earth to the Soudan Mine in Minnesota. That group found, although with less precision, that the neutrino speeds were consistent with the speed of light.

Measurements of neutrinos emitted from a supernova in the Large Magellanic Cloud in 1987, moreover, suggested that their speeds differed from light by less than one part in a billion.

John Learned, a neutrino astronomer at the University of Hawaii, said that if the results of the Opera researchers turned out to be true, it could be the first hint that neutrinos can take a shortcut through space, through extra dimensions. Joe Lykken of Fermilab said, “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.”

But it is too soon for such mind-bending speculation. The Opera results will generate a rush of experiments aimed at confirming or repudiating it, according to Dr. Learned. “This is revolutionary and will require convincing replication,” he said.


Was Einstein Wrong? A Faster-Than-Light Neutrino Could Be Saying Yes

By Michael D. Lemonick Friday, Sept. 23, 2011, TIME

Physicists have a stock phrase they trot out whenever someone claims to have made an astounding new discovery about the universe. "Important," they say, "if true."

It’s a tactful way of saying "Don’t bet on it," and they’ve been saying it a lot over the past day or so. The reason: a team of European scientists has reportedly clocked a flock of subatomic particles called neutrinos moving at just a shade over the speed of light. According to Albert Einstein’s special theory of relativity, that can’t be, since light, which cruises along at about 186,000 miles per second (299,000 km/sec.), is the only thing that can go that fast.

If the Europeans are right, Einstein was not just wrong but almost clueless. The implications could be huge. Particles that move faster than light are essentially moving backwards in time, which could make the phrase cause and effect obsolete.

"Think of it as being shot before the trigger is pulled," wrote University of Rochester astrophysicist Adam Frank on his NPR blog. Or, as Czech physicist Lubos Motl put it on his blog, "You could kill your grandfather before he had his first sex with your grandmother, thus rendering your own existence needed for the homicide inconsistent with the result of the homicide."

The evidence for this complete upending of modern physics and cosmic decorum comes from an experiment involving two top-notch physics installations. The first is CERN, the European Center for Particle Physics, near Geneva, where a particle accelerator created the swarm of neutrinos in the first place. These bits of matter are bizarre no matter how you look at them: they’re so elusive that one of them could pass through a chunk of lead a trillion miles thick without a bump.

It’s no surprise, then, that the swarm created at CERN could fly out of the accelerator, zip right through the Alps and appear in the Gran Sasso Observatory, located in a tunnel deep beneath Italy’s Apennine Mountains. Most of the neutrinos kept on going, but just a few, by pure chance, were intercepted by one of the observatory’s neutrino detectors. And when the two labs synchronized their watches, it appeared that the particles had made the 450-mi. (724 km) journey 0.0025% faster than a beam of light would have (if light could travel through mountains, that is).

That splinter of a second isn’t much, but it’s enough to overturn a century of firmly established physics, rewrite the textbooks and throw the faculties at major universities around the world into a collective tizzy. In short, it’s really important.

If true.

No one is tearing up the Einsteinian rule book just yet. As physicists well know, astonishing results like this often turn out to be wrong, especially when they haven’t been double-checked. Sometimes that means the group announcing the big news has done shoddy work, like the Utah chemists who announced to great fanfare back in 1989 that they’d achieved controlled nuclear fusion on a tabletop — the cold-fusion kerfuffle — trumping the physicists who’d been struggling for years to do the same thing with billion-dollar machines. Sometimes it just means the researchers have overinterpreted what they’re seeing, as when NASA scientists said they’d found evidence of life in a rock from Mars.

And sometimes, the researchers have gone about things the right way, carefully checking their equipment and their calculations to make sure they aren’t being fooled by some mundane, potentially embarrassing glitch. The Grand Sasso scientists have done just that kind of due diligence here, and you know what? They still can’t find any evidence that they’ve missed anything.

But that doesn’t mean they haven’t. It’s always possible that their instruments are misbehaving in too subtle a way for anyone to detect at this point. Given the stakes if the equipment is right — if neutrinos really can move faster than light — nobody’s buying the shocking result until another set of researchers, using another set of instruments, gets the same answer. Indeed, that’s exactly what Antonio Ereditato, of the University of Bern, leader of the Gran Sasso end of the experiment, is hoping for. He told the BBC: "My dream would be that another, independent experiment finds the same thing. Then I would be relieved." This very willingness to be double-checked — and proved wrong — gives the scientists greater credibility, even if the jury is still out on their findings.

A second opinion may be coming soon. A group at the Fermilab accelerator complex, near Chicago, says it’s preparing to do just the follow-up round of studies Ereditato welcomes. As it happens, Fermilab physicists made their own faster-than-light neutrinos claim back in 2007. It too would have been important if true, but on closer analysis, the evidence went away. The Fermilab scientists immediately accepted the verdict that time, just as the Europeans undoubtedly will if this new "discovery" goes up in smoke, as physicists everywhere are betting it will.

Or maybe it won’t: the history of science may be littered with claims that were ultimately proved false, but some outrageous ideas turn out to be true in the end. Take dark matter, the mysterious, invisible stuff that outweighs the visible stars and galaxies by a factor of 10 to 1. When it was first proposed in the 1930s, nobody believed it. When it reappeared in the 1960s, everyone laughed. Now it’s firmly accepted as a fundamental part of the universe.

That kind of thing just might happen again. "Based on past experience, these results are probably wrong," writes Adam Frank at NPR.org, "but it sure would be a wild ride if they prove correct."


Have Scientists Found a Faster-than-Light Particle?


CERN’s Large Hadron Collider particle accelerator in Geneva

(GENEVA) — A startling find at one of the world’s foremost laboratories that a subatomic particle seemed to move faster than the speed of light has scientists around the world rethinking Albert Einstein and one of the foundations of physics.

Now they are planning to put the finding — and by extension Einstein — to further high-speed tests to see if a revolutionary shift in explaining the workings of the universe is needed — or if the European scientists made a mistake. (See pictures of CERN.)

Researchers at CERN, the European Organization for Nuclear Research, who announced the discovery Thursday are still somewhat surprised themselves and planned to detail their findings on Friday.

If these results are confirmed, they won’t change at all the way we live or the way the universe behaves. After all, these particles have presumably been speed demons for billions of years. But the finding will fundamentally change our understanding of how the world works, physicists said.

Only two labs elsewhere in the world can try to replicate the results. One is Fermilab outside Chicago and the other is a Japanese lab put on hold by the tsunami and earthquake. Fermilab officials met Thursday about verifying the European study and said their particle beam is already up and running. The only trouble is that the measuring systems aren’t nearly as precise as the Europeans’ and won’t be upgraded for a while, said Fermilab scientist Rob Plunkett.

"This thing is so important many of the normal scientific rivalries fall by the wayside," said Plunkett, a spokesman for the Fermilab team’s experiments. "Everybody is going to be looking at every piece of information."

Plunkett said he is keeping an open mind on whether Einstein’s theories need an update, but he added: "It’s dangerous to lay odds against Einstein. Einstein has been tested repeatedly over and over again."

Going faster than light is something that is just not supposed to happen according to Einstein’s 1905 special theory of relativity — the one made famous by the equation E equals mc2. Light’s 186,282 miles per second (299,792 kilometers per second) has long been considered the cosmic speed limit. And breaking it is a big deal, not something you shrug off like a traffic ticket.

"We’d be thrilled if it’s right because we love something that shakes the foundation of what we believe," said famed Columbia University physicist Brian Greene. "That’s what we live for."

The claim is being greeted with skepticism inside and outside the European lab.

"The feeling that most people have is this can’t be right, this can’t be real," said James Gillies, a spokesman for CERN, which provided the particle accelerator to send neutrinos on their breakneck 454-mile trip underground from Geneva to Italy. France’s National Institute for Nuclear and Particle Physics Research collaborated with Italy’s Ran Sass National Laboratory for the experiment, which has no connection to the Large Harden Collider located at CERN.

Gillies told The Associated Press that the readings have so astounded researchers that "they are inviting the broader physics community to look at what they’ve done and really scrutinize it in great detail."

That will be necessary, because Einstein’s special relativity theory underlies "pretty much everything in modern physics," said John Ellis, a theoretical physicist at CERN who was not involved in the experiment. "It has worked perfectly up until now." And part of that theory is that nothing is faster than the speed of light.

CERN reported that a neutrino beam fired from a particle accelerator near Geneva to a lab 454 miles (730 kilometers) away in Italy traveled 60 nanoseconds faster than the speed of light. Scientists calculated the margin of error at just 10 nanoseconds, making the difference statistically significant.

Given the enormous implications of the find, they spent months checking and rechecking their results to make sure there were no flaws in the experiment.

A team at Fermilab had similar faster-than-light results in 2007. But that experiment had such a large margin of error that it undercut its scientific significance.

If anything is going to throw a cosmic twist into Einstein’s theories, it’s not surprising that it’s the strange particles known as neutrinos. These are odd slivers of an atom that have confounded physicists for about 80 years.

The neutrino has almost no mass, it comes in three different "flavors," may have its own antiparticle and even has been seen shifting from one flavor to another while shooting out from the sun, said physicist Phillip Schewe, communications director at the Joint Quantum Institute in Maryland.

Fermilab team spokeswoman Jenny Thomas, a physics professor at the University College of London, said there must be a "more mundane explanation" for the European findings. She said Fermilab’s experience showed how hard it is to measure accurately the distance, time and angles required for such a claim.

Nevertheless, the Fermilab team, which shoots neutrinos from Chicago to Minnesota, will go back to work immediately to try to verify or knock down the new findings, Thomas said.

Drew Baden, chairman of the physics department at the University of Maryland, said it is far more likely that there are measurement errors or some kind of fluke. Tracking neutrinos is very difficult, he said.

"This is ridiculous what they’re putting out," Baden said, calling it the equivalent of claiming that a flying carpet is invented only to find out later that there was an error in the experiment somewhere. "Until this is verified by another group, it’s flying carpets. It’s cool, but…"

So if the neutrinos are pulling this fast one on Einstein, how can it happen?

Stephen Parke, who is head theoretician at the Fermilab said there could be a cosmic shortcut through another dimension — physics theory is full of unseen dimensions — that allows the neutrinos to beat the speed of light.

Indiana University theoretical physicist Alan Kostelecky, theorizes that there are situations when the background is different in the universe, not perfectly symmetrical as Einstein says. Those changes in background may change both the speed of light and the speed of neutrinos.

But that doesn’t mean Einstein’s theory is ready for the trash heap, he said.

"I don’t think you’re going to ever kill Einstein’s theory. You can’t. It works," Kostelecky said. Just there are times when an additional explanation is needed, he said.

If the European findings are correct, "this would change the idea of how the universe is put together," Columbia’s Greene said. But he added: "I would bet just about everything I hold dear that this won’t hold up to scrutiny."


Particles Found to Travel Faster than Speed of Light

Neutrino results challenge a cornerstone of Albert Einstein​’s special theory of relativity, which itself forms the foundation of modern physics.

By Geoff Brumfiel and Nature magazine | Scientific American, September 22, 2011

Image: CERN

An Italian experiment has unveiled evidence that fundamental particles known as neutrinos can travel faster than light. Other researchers are cautious about the result, but if it stands further scrutiny, the finding would overturn the most fundamental rule of modern physics—that nothing travels faster than 299,792,458 meters per second.

The experiment is called OPERA (Oscillation Project with Emulsion-tRacking Apparatus), and lies 1,400 meters underground in the Gran Sasso National Laboratory in Italy. It is designed to study a beam of neutrinos coming from CERN, Europe’s premier high-energy physics laboratory located 730 kilometers away near Geneva, Switzerland. Neutrinos are fundamental particles that are electrically neutral, rarely interact with other matter, and have a vanishingly small mass. But they are all around us—the sun produces so many neutrinos as a by-product of nuclear reactions that many billions pass through your eye every second. [Click here to read more about CERN’s Large Hadron Collider]

The 1,800-tonne OPERA detector is a complex array of electronics and photographic emulsion plates, but the new result is simple—the neutrinos are arriving 60 nanoseconds faster than the speed of light allows. "We are shocked," says Antonio Ereditato, a physicist at the University of Bern in Switzerland and OPERA’s spokesman.

Breaking the law

The idea that nothing can travel faster than light in a vacuum is the cornerstone of Albert Einstein’s special theory of relativity, which itself forms the foundation of modern physics. If neutrinos are traveling faster than light speed, then one of the most fundamental assumptions of science—that the rules of physics are the same for all observers—would be invalidated. "If it’s true, then it’s truly extraordinary," says John Ellis, a theoretical physicist at CERN.

Ereditato says that he is confident enough in the new result to make it public. The researchers claim to have measured the 730-kilometer trip between CERN and its detector to within 20 centimeters. They can measure the time of the trip to within 10 nanoseconds, and they have seen the effect in more than 16,000 events measured over the past two years. Given all this, they believe the result has a significance of six-sigma—the physicists’ way of saying it is certainly correct. The group will present their results September 23 at CERN, and a preprint of their results will be posted on the physics website ArXiv.org.

At least one other experiment has seen a similar effect before, albeit with a much lower confidence level. In 2007, the Main Injector Neutrino Oscillation Search (MINOS) experiment in Minnesota saw neutrinos from the particle-physics facility Fermilab in Illinois arriving slightly ahead of schedule. At the time, the MINOS team downplayed the result, in part because there was too much uncertainty in the detector’s exact position to be sure of its significance, says Jenny Thomas, a spokeswoman for the experiment. Thomas says that MINOS was already planning more accurate follow-up experiments before the latest OPERA result. "I’m hoping that we could get that going and make a measurement in a year or two," she says.

Reasonable doubt

If MINOS were to confirm OPERA’s find, the consequences would be enormous. "If you give up the speed of light, then the construction of special relativity falls down," says Antonino Zichichi​, a theoretical physicist and emeritus professor at the University of Bologna, Italy. Zichichi speculates that the "superluminal" neutrinos detected by OPERA could be slipping through extra dimensions in space, as predicted by theories such as string theory.

Ellis, however, remains skeptical. Many experiments have looked for particles traveling faster than light speed in the past and have come up empty-handed, he says. Most troubling for OPERA is a separate analysis of a pulse of neutrinos from a nearby supernova known as 1987a. If the speeds seen by OPERA were achievable by all neutrinos, then the pulse from the supernova would have shown up years earlier than the exploding star’s flash of light; instead, they arrived within hours of each other. "It’s difficult to reconcile with what OPERA is seeing," Ellis says.

Ereditato says that he welcomes skepticism from outsiders, but adds that the researchers have been unable to find any other explanation for their remarkable result. "Whenever you are in these conditions, then you have to go to the community," he says.

This article is reproduced with permission from the magazine Nature. The article was first published on September 22, 2011.


Those faster-than-light neutrinos. Four things to think about

Having read the paper, seen the seminar and watched the excitement over evidence from the Opera experiment that neutrinos violate the speed limit of the universe, here are four things to ponder.

Jon Butterworth Saturday 24 September 2011,  guardian.co.uk

As you have probably noticed by now, neutrinos from one of the accelerators at CERN are regularly fired 730 km through the Alps and across Italy to the Gran Sasso lab, where some of them are detected by the Opera experiment.

This experiment is designed to measure how the neutrinos change their properties as they go. But they also have some very precise GPS positions and timing measurements. So they know the distance the neutrinos travel, they know how long it takes them, and they can therefore measure the speed. Since neutrinos have a tiny mass, the speed should be very close to the speed of light. But their measurement seems to show the neutrinos arriving early – travelling faster than the speed of light.
What would it mean if true?

If this result is valid, it is an amazing breakthrough.

The speed of light limit is built very deeply into the maths of how we understand the universe. It is a foundation of the theory of relativity. This theory precisely describes all kinds of physics (including that behind the GPS systems used to make the measurements and the accelerators used to make the beam). So it can’t just be thrown out. Some better theory would have to be found which contained and extended Einstein’s edifice.

I have no idea what such a theory might be, though I see the "extra dimensions" people have a plan already, whereby the neutrinos take a shortcut across another dimension. Sort of the equivalent of a 2D Londoner living on the surface of the globe taking a short cut to Sydney via the Earth’s core.

Fun to think about, but …

Isn’t this all a bit premature?

Well, yes, a bit. It’s just one result, and the Opera people themselves can hardly believe it. That said, they have produced a careful paper, and given a scientific seminar at CERN. This is the way science is done, and I don’t blame them for also speaking to the press and being excited about the potential implications of their data. What should they have done, kept it secret? Imagine the conspiracy theories…

Also, what should the media have done, ignored it? Gratifyingly, people are interested in physics and this is a proper story. It may have been over-exposed and in some cases over-hyped, but this is a genuine scientific debate, going on now about an intriguing result. It is not a manufactured controversy. So long as people appreciate that, maybe seeing science done in public will become the new spectator sport. Ideally even a participation sport. That could be a good thing, surely?

What might be wrong?

The reason I didn’t write anything until now is that I have been trying to find time to read the paper, understand the measurement, and comment intelligently on it. It is a careful study, the result of years of work by a pretty big team, so to fire off "It must be wrong" comments without due care would be unfair, even though I must admit that was my immediate reaction.

So in the spirit of doing science in public, I’ll explain my main worry with the results.

They measure the time distribution of the protons at the source, in CERN. These protons hit a target and end up producing neutrinos. They also measure the time distribution of neutrinos arriving at Gran Sasso. They fit one distribution to the other, and when they line up that gives them the time of flight, and thus the speed.

Here’s the figure from the paper:

edges Rising and falling edges of the neutrino pulse. The red is the shape from the start, at CERN, and the points are the neutrino arrival times at Gran Sasso.
From arxiv:1109.4897.

Now they do say in the paper "It is worth stressing that this measurement does not rely on the difference between a start (t0) and a stop signal but on the comparison of two event time distributions." but from the distributions in the paper it really looks like all the power of the measurement comes from these leading (left) and trailing (right) edges.

The claim is that sliding the red line along the horizontal axis and determining when it best matches the points gives an accuracy of about 10 nanoseconds (6.9 statistical and 7.4 systematic uncertainty). As pointed out here*, this seems bold, since the horizontal error on the points (the bin width) is five times bigger than this. But the main worry I have is that they seem to assume the red line and the points should match exactly. As far as I can tell there is no allowance in their systematic uncertainties for the possibility that the red line might not be a true reflection of the shape of the neutrino "turn on" and "turn off" in Gran Sasso. To me this is a odd, possibly serious, omission.

For example, at CERN where the red line is measured, all the protons are included in the time profile. By the time it gets to Gran Sasso the beam has fanned out, and big though it is, Opera only sees neutrinos from part of the beam. So any correlation between the production time of the neutrinos (where they are on the horizontal axes of those plots) and the angle they are produced at (which determines whether they actually get to Opera or not) could distort the shape, leading to an uncertainty in the fit and hence an uncertainty in the speed.

I don’t claim this is a debunking of the result. This has probably been studied already, and there might be very good reasons which I haven’t thought of why it is irrelevant. Certainly the Opera team have spent much longer looking for such effects than I have. But I can’t find an answer to this one in the paper.

There may also be other problems. Many scientists are now poring over the results. My worries above were at least partly raised by other people in the very good question and answer session at CERN after the seminar, but the answers were not (yet) complete in my opinion.

Anyway, science in public. Let’s see what happens next.


If this measurement had agreed with expectations, and showed neutrinos travelling at or below light speed, how carefully would we be examining the uncertainties? How much time would I have spent reading the paper? And if that result had been wrong, would we ever have found out?


Professor Einstein, you can relax. E still equals mc2. Probably …

Renowned physicist Frank Close urges caution before we abandon the theory of relativity and prepare for time travel

Graphic explaining the Cern experiment

Partial view of a graphic explaining Cern’s neutrino experiment. Credit: Giulio Frigieri

The barman said: "Sorry, we don’t serve neutrinos." A neutrino enters a bar.

This is but one of many tweets inspired by the news that neutrinos – ghostly subatomic particles – may travel faster than light. If so, science fiction could become science fact, with wonderful paradoxes such as effects preceding their causes. One example would be the punchline preceding the story (in case, like me, it took a while for you to decode the joke).

As a scientist I have grown up to believe this law of nature: the only thing that travels faster than light is a rumour. The story that scientists at Cern, Europe’s giant particle physics laboratory near Geneva, had apparently created neutrinos that travelled faster than light, hit the news on Friday morning while I was half asleep and seemed to be the latest example of this law.

But as I awoke, and the story refused to go away, I began to panic that I would have to rewrite my book Neutrino – which it seemed was rapidly being overtaken by events. My only consolation was that this revision would be but a small tremor in the unimaginable change to our understanding of life, the universe and, indeed, everything, if this claim turned out to be true. The physics textbooks in the libraries of the world would be wrong; the foundations of science would crumble. Particles travelling faster than light, capable of carrying information, would alter everything. So, what’s going on and why does it matter?

Einstein’s theory of relativity was one of the great revolutions of 20th-century thought, and arguably the greatest theoretical construct of the human mind. When Isaac Newton built his laws of motion in the 17th century, he imagined space and time as some invisible matrix through which we pass without changing them. The metronome ticks steadily on as we move through a permanent static three-dimensional space. Einstein’s vision was that space and time are fluid, intertwined, affected by our motion: the faster you move, the slower you age. This has many wonderful implications, such as the puzzle of the twins – Tweedledum who stays at home while Tweedledee takes a high-speed gap year and returns home wiser but, surprisingly, younger than his sibling.

The fact that space and time are elastic, stretching and warping in synchrony with our passage, is weird, but inescapably true. The beams of particles at Cern, travelling within a mere fraction of light speed, arrive at their destination on time only when the subtleties of relativity are included in the accounting. GPS satellites locate you precisely, but have to include Einstein’s arithmetic in the calculations. Some experiments at Cern agree with the predictions of relativity to better than one part in a trillion – that is like measuring the distance across the Atlantic Ocean to better than the width of a human hair – but only when relativity is taken into account.

For scientists certainly, and for many of us, perhaps surprisingly, Einstein’s theory of relativity is needed to keep track of our daily affairs.

Albert Einstein Albert Einstein believed that nothing can exceed the speed of light. Photograph: Philippe Halsman/AFP

What has any of this to do with the speed of light?

Einstein’s edifice is constructed on an experimental fact: that the velocity of light is independent of your own motion. Whether you are moving towards the source, or away from it, or are stationary, doesn’t matter: speed of light is universal. This is counterintuitive. A fast racing car overtakes a slower one more gradually than it does the static spectators at trackside; however, a light beam passes everyone the same – spectators or Lewis Hamilton would measure the same speed. Counterintutitive certainly, but true, and it led to Einstein’s world-view. And one of the basic consequences of Einstein’s theory is that the speed of light – in a vacuum – is nature’s speed limit. Nothing can travel through a vacuum faster than light.

Has Cern overthrown this paradigm? I doubt it. Light travels slower through water, glass, even air, than through a vacuum. Radio waves do, too. So light can be slowed down, but not sped up: the vacuum is nature’s open road where light travels at the speed limit. We need to be careful when asking what exactly has the Cern experiment done, or, more pertinently, how did it do it?

Cern produces beams of neutrinos, ghostly particles that can travel through the earth as easily as a bullet through a bank of fog. A beam travels down through the surface of the Earth in a straight line, the Earth’s surface curving upwards away from it initially, eventually bending downwards until, 730km later, at Gran Sasso, a laboratory near Rome, the neutrino beam re-emerges. This journey has taken about 1/500th of a second.

If you could send a light beam through the Earth, it should arrive at the same instant as the neutrino – if the neutrino travels at light speed – or slightly before it (if the neutrino travels slower than light) but not later, as that would require the neutrino to travel faster than light. If we could do that experiment, it would be clear cut. The problem is, we cannot. The Earth is transparent to neutrinos, but opaque to light.

If we know the distance from Cern to Rome precisely enough, and the time that the neutrino took to get there, then the ratio of distance to time – kilometres per second – gives the speed. In effect this is what the experiment does, but even this is not straightforward.

Measuring the time to accuracies of nanoseconds involves accounting for the time that electronic signals take to pass through circuits, into readouts and onwards to further parts of the complex of counters, computer chips and the myriad pathways of the nanoworld. If you have all of these measured, and if they are indeed everything you need to know, then you can determine the time elapsed – with some uncertainty. This they have done. However, if there is some unexpected bottleneck, unrecognised and hence unaccounted for, the timing might be a few nanoseconds amiss.

Then there is the measurement of the distance. Determining this to an accuracy of about 10 centimetres in 730km is required – and, apparently, is possible by geodesy. But precisely how this is done is, to me at least, still one of the many mysteries in this experiment. You certainly don’t do it with a tape measure, even if you had one that was accurate to atomic sizes. Sending a radio signal up to a satellite, at the instant the neutrino leaves Cern, which then passes it on down to the receiver in Rome, and comparing which arrives first, and by how much, has its own difficulties. The speed of radio waves through the atmosphere is affected by magnetic fields, and by other phenomena; it is far from simply a radio beam passing through a vacuum at "the speed of light".

I would bet that a subtle error in the measured distance or time is more likely than that their ratio – the inferred speed – exceeds Einstein’s speed limit.

Ultimately nature knows the answers and we have to find them by experiment. If it is possible to travel faster than light – in a vacuum – then it doesn’t matter how many physicists say nay: the truth will out. And if it is true? I shall rewrite Neutrino and replace email with numail (neutrino-mail) – it’s faster.

Frank Close is professor of theoretical physics at Oxford University and emeritus fellow at Exeter College, Oxford, and the author of Neutrino (OUP)


Unthinkable? Faster than light

Professor Antonio Ereditato is releasing his physics data hoping that someone will find a flaw and restore conceptual order

Editorial, guardian.co.uk, Friday 23 September 2011

The tales science tells about the universe star one steadfast hero: the velocity of light. With Einstein, the space and time of Newton’s day lost their uniformity, even the solid idea of matter melted into air. But the steady speed of electromagnetic radiation (the c in E = mc2) proved a sturdy enough foundation stone for the old genius to be able to reconstruct physics, and thereby rescue basic notions of cause and effect. Now Professor Antonio Ereditato, a man with singularly apt initials, is reporting that the tiny neutrinos that his team have been blasting under the Alps have clocked up a superluminal pace.

A mistake? Very likely, which is why Ereditato and co are releasing their data in the expectation that someone out there will find a flaw, and restore the conceptual order. But what if the finding, which is based on 15,000 observations and has passed all the ordinary statistical tests, is instead confirmed? That would be insensible, which is to say profs would be muttering "does not compute"; but the history of science cautions against branding it unthinkable. That was once the verdict passed on heretical talk of the Earth spinning round the sun, as opposed to the other way round. Recall, too, that it was the then inexplicable Michelson-Morley experiment which encouraged the spread of Einstein’s early ideas, and the baffling perihelion precession of Mercury which lent support to his general theory. The first thing in science is to face the facts; making sense of them has to come second.


Faster than light story highlights the difference between science and religion

‘Belief’ means something different to scientists and the faithful … we’re open to the idea Einstein may have been wrong.

Alom Shaha Wednesday 28 September 2011, guardian.co.uk

Palestinian children at the Koran Centre of a mosque

Science does not say, ‘This is the way things are, and it can be no other way.’ Photograph: Nayef Hashlamoun/Reuters

Most physicists believe, as Einstein proposed, that nothing can travel faster than the speed of light in a vacuum. You might say that some, like Jim Al-Khalili who promised to eat his shorts if this was proved untrue, hold this belief religiously. But the recent fuss over the possible existence of faster-than-light neutrinos illustrates precisely how different science and religion are when it comes to questions of "belief" or "knowledge".

As a science teacher, I have met a number of students who have questioned whether scientists simply "believe" in science in the same way religious people "believe" in God. It’s easy to see why they might think this. Children encounter ideas about how the world works from both religion and science and they are often presented with these ideas as "truths" from figures of authority – priests, imams and science teachers – who in turn claim to be informed by even greater sources of authority such as the bible, Qur’an or science textbooks.

But there is a key difference between the way we teach science and religious teachings. Students of science can, at least in principle, test the claims made by science in a way they cannot do for religion. For example, most high school physics courses require students to know that all objects accelerate towards the ground at the same rate, regardless of their mass (providing we ignore air resistance). This is counterintuitive: most people assume that "heavier" objects fall faster. As a teacher, I get my students to find evidence for this claim by designing and carrying out their own experiments. They do not have to take my word for it, or the word of any other authority figure.

We cannot do this easily for all the claims science makes. For example, it’s quite difficult to prove that atoms and electrons exist. In fact, many prominent scientists refused to believe atoms existed well into the late 19th century and it took Einstein to come up with a proof that was widely accepted. However, even if my students cannot prove for themselves that atoms and electrons exist, even if they cannot grasp the mathematics of Einstein’s proof, I can point them to the fact that the physical world behaves as if our theories about these entities were true. For example, modern telecommunications would not work if what science tells us about electrons were not true in some sense. We cannot say the same for that other invisible thing so many people are asked to believe in, God.

Of course, we do not usually go out and test every single scientific claim we encounter (it would be impractical) and so, in that sense, you could argue that scientists and science teachers have "faith" in science, but it is certainly not the same kind of faith that is demanded of people who believe in God.

One of the things that appeals to me about science is that, unlike religion, science is not dogmatic. It does not say: "This is the way things are, and it can be no other way." Instead it says something like: "Based on the evidence we have so far, this is how things probably are; if clear and solid evidence is discovered that shows this is not how things are, then we will need to change our minds."

Science can seem rather weak in comparison to the certainties religion offers. But it is this very "weakness", this refusal to issue absolute statements of truth, that allows science to progress, and to come up with increasingly better ways of explaining the world.

This is why, even though their existence might mean that "the foundations of science would crumble", science will not shy away from considering the possibility that faster-than-light neutrinos are real. The issue will not be settled by consulting some supposedly infallible text but rather by close scrutiny of the controversial data and further experimentation if necessary.

And anyone who is capable of doing that work is entitled to put forward their conclusions: there are no hierarchies that absolutely must be respected, there is no single person who will have the final say. If, after scientists have done their work, we find that faster-than-light neutrinos do indeed exist, science may go through some kind of crisis, but it will emerge stronger, with even better ideas about the true nature of the universe.


Τα πιο γρήγορα ταξίδια στο σύμπαν

TA NEA, 23 Σεπτεμβρίου 2011

Προβληματισμό έχει προκαλέσει στην επιστημονική κοινότητα η ανακοίνωση ευρωπαίων φυσικών ότι εντόπισαν υποατομικά σωματίδια (νετρίνα) που φαίνεται να ταξιδεύουν ταχύτερα από το φως. Αν αυτό επιβεβαιωθεί-αφού προς το παρόν υπάρχουν επιφυλάξεις-μπορεί να ανατρέψει επιστημονικά δεδομένα της σύγχρονης φυσικής αλλά και την ίδια τη θεωρία του Αϊνστάιν.

Ομάδα επιστημόνων που εργάζεται στις εγκαταστάσεις του ερευνητικού κέντρου CERN, κοντά στη Γενεύη, μετά από τρία χρόνια μετρήσεων κατέγραψαν νετρίνα που κινούνται, όπως είπαν, με ταχύτητα μεγαλύτερη του φωτός, το απόλυτο όριο ταχύτητας στο σύμπαν.
Τα νετρίνα είναι υποατομικά σωματίδια με ελάχιστη μάζα και μηδενικό φορτίο τα οποία δεν αλληλεπιδρούν σχεδόν καθόλου με άλλα σωματίδια. Κινούνται με την ταχύτητα του φωτός, δηλαδή 300.000 χιλιόμετρα το δευτερόλεπτο, ενώ είναι επίσης δυνατόν να αλλάξουν αυθόρμητα από τον ένα τύπο στον άλλο.
Έτσι ένα νετρίνο, για παράδειγμα από τον Ήλιο μπορεί θεωρητικά να διασχίσει ολόκληρο τον πλανήτη χωρίς να προσκρούσει σε κανένα άτομο. Ωστόσο, μία τέτοια σύγκρουση δεν είναι εντελώς απίθανη και μπορεί να καταγραφεί.
Η ομάδα των επιστημόνων εξέπεμψε από το CERN μία δέσμη νετρίνων μ και μέτρησε πόσα νετρίνα τ έφτασαν στο ερευνητικό κέντρο του Γκραν Σάσο στην Ιταλία.
Σύμφωνα με τις μετρήσεις τους, εντόπισαν νετρίνα που διένυσαν την απόσταση των 730 χιλιομέτρων 60 νανοδευτερόλεπτα ταχύτερα από το χρόνο που χρειάζεται το φως. Το περιθώριο λάθους είναι μονο 10 νανοδευτερόλεπτα.


Βγάζουν λάθος τον Αϊνστάιν!

imageΙταλοί επιστήμονες σε συνεργασία με το CERN διαπίστωσαν ότι τα νετρίνα κινούνται γρηγορότερα από το φως


Ρωγμές στη θεωρία της ειδικής σχετικότητας του Αϊνστάιν και κατ’ επέκταση στο οικοδόμημα της σύγχρονης φυσικής θα μπορούσαν να προκαλέσουν τα αποτελέσματα ενός πειράματος από ευρωπαίους επιστήμονες που διαπίστωσαν ότι υπάρχουν σωματίδια που ταξιδεύουν γρηγορότερα από το φως.

Οι μετρήσεις που πρέπει τώρα να επαληθευτούν από αντίστοιχα πειράματα έγιναν σε ένα από τα μεγαλύτερα εργαστήρια φυσικής στον κόσμο, το λεγόμενο OPERA, που βρίσκεται κάτω από τα βουνά της Κεντρικής Ιταλίας.

Εκεί, στην περιοχή του Γραν Σάσο που βρίσκεται σε ευθεία γραμμή 730 χιλιόμετρα μακριά από τη Γενεύη και το CERN, οι επιστήμονες διαπίστωσαν ότι τα υποατομικά σωματίδια νετρίνα, η φύση των οποίων δεν έχει πλήρως κατανοηθεί, κινούνταν με ταχύτητα λίγο μεγαλύτερη από εκείνη του φωτός. Τα νετρίνα αποστέλλονταν μέσω δεσμών υψηλής ενέργειας από το CERN στο εργαστήριο της Ιταλίας, υπογείως, στο πλαίσιο ενός πειράματος για τη μελέτη του φαινομένου της ταλάντωσης αυτών των σωματιδίων.

Θεωρητικά, για να φθάσουν τα νετρίνα από το υπερ-σύγχροτρο πρωτονίων του CERN στους ηλεκτρονικούς ανιχνευτές του ιταλικού εργαστηρίου θα χρειάζονταν 2,4 εκατομμυριοστά του δευτερολέπτου.

Ομως, στη διάρκεια των τριών τελευταίων χρόνων που επαναλαμβανόταν το πείραμα και αφού από τη… γραμμή τερματισμού είχαν περάσει περί τα 15.000 νετρίνα, οι επιστήμονες ανακάλυψαν ότι τα αινιγματικά σωματίδια ολοκλήρωναν το αστραπιαίο ταξίδι τους 60 δισεκατομμυριοστά του δευτερολέπτου γρηγορότερα, με μια απόκλιση της τάξης των 10 δισεκατομμυριοστών του δευτερολέπτου.

Το αποτέλεσμα των μετρήσεων προκάλεσε μεγάλη έκπληξη στους επιστήμονες στο Σαν Γκράσο και παρά το γεγονός ότι τα πειράματα διενεργήθηκαν αρκετές φορές, οι ίδιοι εμφανίζονταν αρκετά συγκρατημένοι. Θα πρέπει και άλλα εργαστήρια στον κόσμο να επαληθεύσουν το πείραμα και να καταλήξουν στο ίδιο συμπέρασμα ώστε να αποδειχτεί ότι πράγματι υπάρχουν στο σύμπαν σωματίδια που ταξιδεύουν γρηγορότερα από το φως.

«Είμαστε συγκλονισμένοι από τα αποτελέσματα του πειράματος, όμως ένα επιστημονικό αποτέλεσμα δεν μπορεί ν’ αποτελεί ανακάλυψη παρά μόνο αφότου επαληθευτεί και από άλλους ειδικούς», ανέφερε ο δρ Αντόνιο Ερεντιτάτο, που είναι συντονιστής του προγράμματος στο εργαστήριο OPERA.

Και πρόσθεσε πως «όταν έχεις στα χέρια σου ένα τέτοιο αποτέλεσμα, πρέπει να είσαι σίγουρος ότι δεν έχεις κάνει το παραμικρό λάθος. Επί μήνες ελέγχαμε εξονυχιστικά τα αποτελέσματά μας και δεν στάθηκε δυνατό να εντοπίσουμε κάποιο λάθος».

Στο ιταλικό εργαστήριο, τα νετρίνα που αποστέλλονταν από το CERN καταγράφονταν σε έναν μεγάλο ανιχνευτή που ζυγίζει 1.300 τόνους. Ο Σουμπίρ Σαρκάρ που είναι ειδικός στη Σωματιδιακή Φυσική στο Πανεπιστήμιο της Οξφόρδης ανέφερε στην εφημερίδα «Guardian» ότι «αν αποδειχτούν πραγματικά τα αποτελέσματα, θα πρόκειται για ένα πολύ, μα παρά πολύ σοβαρό γεγονός».

Ο ίδιος εξηγεί ότι η σταθερότητα της ταχύτητας του φωτός σηματοδοτεί την κατανόησή μας για τον χώρο, τον χρόνο και την αιτιότητα. Η αιτιότητα σημαίνει ότι μία αιτία προηγείται του αποτελέσματος και όχι το αντίστροφο. Πρόκειται για μια απολύτως θεμελιώδη αρχή πάνω στην οποία έχει χτιστεί η σύγχρονη φυσική.

Κατά τον Σαρκάρ, η απόδειξη ότι υπάρχουν σωματίδια ταχύτερα από το φως μπορεί να σημάνει ότι αλλάζει ο τρόπος κατανόησης του Σύμπαντος, ενώ ο θεωρητικός φυσικός στο Πανεπιστήμιο της Ιντιάνα, Αλαν Κοστελέσκι, προχώρησε τον συλλογισμό του ένα βήμα περισσότερο εκτιμώντας ότι μπορεί ν’ ανοίξει ο δρόμος για τη διατύπωση μιας μεγάλης θεωρίας που θα παντρεύει τη βαρύτητα με την κβαντική μηχανική, επιλύοντας έτσι ένα μυστήριο που βασανίζει εδώ και δεκαετίες τους φυσικούς. Ωστόσο, ο ίδιος επισημαίνει ότι η αξία της θεωρίας της ειδικής σχετικότητας του Αϊνστάιν δεν χάνει το παραμικρό από την αξία της. «Σε κάθε θεωρία υπάρχουν φορές που χρειάζονται ορισμένες επιπρόσθετες διορθώσεις». Γεγονός πάντως είναι ότι προτού ακόμη επιχειρηθεί η επαλήθευση των αποτελεσμάτων, ορισμένοι επιστήμονες εξέφραζαν τη βεβαιότητά τους για την ύπαρξη κάποιου λάθους, όπως ο Τσανγκ Γιουνγκ που είναι θεωρητικός φυσικός στο Πολιτειακό Πανεπιστήμιο της Νέας Υόρκης.

Το ίδιο πιστεύει και ο Ντριου Μπέιντεν που είναι πρόεδρος του Τομέα Φυσικής στο Πανεπιστήμιο του Μέριλαντ που θεωρεί ότι είναι πολύ πιο πιθανό να υπάρχει λάθος στους υπολογισμούς του ιταλικού εργαστηρίου. «Μου ακούγεται σαν να εφηύραν το ιπτάμενο χαλί», είπε χαρακτηριστικά.


Νετρίνο εντοπίστηκαν να ταξιδεύουν ταχύτερα από το φως

kathimerini.gr με πληροφορίες από ΑΠΕ-ΜΠΕ, 23.9.11

Νετρίνο «αστραπή», απειλούν τον Αϊνστάιν και τη σύγχρονη φυσική.

Μεγάλη αναστάτωση έχει προκαλέσει στην επιστημονική κοινότητα η ανακοίνωση Ευρωπαίων φυσικών ότι εντόπισαν υποατομικά σωματίδια (νετρίνο) που φαίνεται να σπάνε το ρεκόρ ταχύτητας στο σύμπαν, ταξιδεύοντας ταχύτερα και από το φως. Αν αυτό επιβεβαιωθεί -προς το παρόν υπάρχουν επιφυλάξεις- τότε απειλείται όχι μόνο η θεωρία του Άλμπερτ Αϊνστάιν, αλλά και όλο το οικοδόμημα της σύγχρονης Φυσικής, αν όχι ο τρόπος που βλέπουμε τον κόσμο, ενώ μπορεί να ανοίξει ο δρόμος για ταξίδια στον χρόνο, ακόμα και στο παρελθόν.

Η θεωρία της ειδικής σχετικότητας από το 1905 -ο ακρογωνιαίος λίθος της Φυσικής- απαγορεύει οτιδήποτε να κινηθεί πιο γρήγορα από την ταχύτητα των 299.792.458 μέτρων ανά δευτερόλεπτο του φωτός. Μέχρι τώρα καμία έρευνα δεν είχε βρει το παραμικρό μεγάλο σώμα ή μικροσκοπικό σωματίδιο να κινείται πιο γρήγορα από το φως.

Όμως, Ιταλοί φυσικοί του πειράματος «Opera», που πραγματοποιείται 1.400 μέτρα κάτω από το έδαφος, στο υπόγειο Εθνικό Εργαστήριο Γκραν Σάσο, σε συνεργασία με το Cern στα γαλλο-ελβετικά σύνορα, από όπου στέλνονται στην Ιταλία ακτίνες νετρίνο, βρήκαν ενδείξεις ότι τα συγκεκριμένα σωματίδια ταξιδεύουν ταχύτερα και από το φως, σύμφωνα με το BBC, το «Nature», τους «Τάιμς της Νέας Υόρκης» και τις βρετανικές «Γκάρντιαν» και «Τέλεγκραφ».

Τα νετρίνο είναι ηλεκτρικά ουδέτερα, σπανίως αλληλεπιδρούν με την κοινή ύλη (περνάνε μέσα από τοίχους και πλανήτες) κι έχουν πολύ μικρή μάζα, αλλά υπάρχουν ολόγυρά μας, καθώς αποτελούν υποπροϊόν των πυρηνικών αντιδράσεων στο εσωτερικό του ήλιου. Δισεκατομμύρια τέτοια υποατομικά σωματίδια περνάνε κάθε δευτερόλεπτο μπροστά από τα μάτια μας, χωρίς να το αντιλαμβανόμαστε.

Ο τεράστιος ανιχνευτής του πειράματος «Opera» (βάρους 1.800 τόννων) εκτίμησε ότι τα νετρίνο που καταλήγουν σε αυτόν από το Cern, διανύοντας μια απόσταση περίπου 732 χιλιομέτρων, φθάνουν 60 νανοδευτερόλεπτα πιο γρήγορα από ό,τι θα επέτρεπε η ταχύτητα του φωτός (δηλαδή κινούνται με ταχύτητα περίπου 0,0025% ταχύτερη από το φως).

«Είμαστε σοκαρισμένοι», δήλωσε ο Αντόνιο Ερεντιτάτο, φυσικός του πανεπιστημίου της Βέρνης, επικεφαλής και εκπρόσωπος του «Opera». «Αν είναι αλήθεια, τότε είναι πραγματικά εντυπωσιακό», δήλωσε ο φυσικός Τζον Έλις, εκπρόσωπος του Cern, αλλά τόνισε την ανάγκη να υπάρξει ανεξάρτητη επιβεβαίωση του γεγονότος.

Οι φυσικοί του «Opera» ανέφεραν ότι έχουν πλέον αρκετή εμπιστοσύνη στα στοιχεία τους για να τα δημοσιοποιήσουν, καθώς έχουν καταγράψει ίδια αποτελέσματα σε περίπου 16.000 μετρήσεις κατά την τελευταία διετία, συνεπώς δηλώνουν σίγουροι ότι δεν έχουν πέσει θύμα κάποιας πλάνης ή λάθους.

Είχε προηγηθεί ένα παρόμοιο πείραμα, το Minos στην Μινεσότα των ΗΠΑ, το 2007, όταν επίσης είχαν φανεί νετρίνο που κατέφθαναν από τον επιταχυντή Fermilab του Σικάγο, να κινούνται οριακά ταχύτερα από το φως, αλλά τότε υπήρχε μεγαλύτερη αβεβαιότητα για τις μετρήσεις. Όμως, οι αμερικανοί φυσικοί, ετοιμάζουν νέα πειράματα που αναμένεται να έχουν ευρήματα σε ένα – δύο χρόνια. Αν το Minos όντως επιβεβαιώσει τις μετρήσεις του «Opera», οι συνέπειες για τη φυσική και την επιστήμη γενικότερα θα είναι κολοσσιαίες.

Ορισμένοι, όπως ο επίτιμος καθηγητής φυσικής του πανεπιστημίου της Μπολόνια Αντονίνο Ζιτσίτσι, πιθανολογούν ότι τα νετρίνο κινούνται μέσα από έξτρα διαστάσεις στο χώρο, όπως προβλέπει η θεωρία των χορδών, για αυτό κινούνται ταχύτερα από το φως. Ίδια ακριβώς άποψη εξέφρασε και ο αστρονόμος νετρίνο Τζον Λέρντ του πανεπιστημίου της Χαβάης.

Άλλοι παραμένουν σκεπτικιστές και δεν βιάζονται να κάνουν τη νεκρολογία της θεωρίας του Αϊνστάιν, θεωρώντας ότι κάποιο πειραματικό λάθος έχει συμβεί. «Αν είναι αλήθεια, τότε πραγματικά δεν έχουμε καταλάβει τίποτε για τίποτε. Ακούγεται πολύ μεγάλο, για να είναι αληθινό», σχολίασε ο φυσικός Αλβάρο ντε Ρουχούλα του Cern.

Ο Ερεντιτάτο του «Opera» επιμένει πάντως ότι οι φυσικοί του πειράματος δεν έχουν μπορέσει να βρουν κάποια άλλη εξήγηση για τα απρόσμενα ευρήματά τους. Γι’ αυτό κάλεσε την επιστημονική κοινότητα να εκφράσει τις δικές της απόψεις ανοιχτά.


Σωματίδια κινούνται ταχύτερα από το φως!

Θ. Τσώλη, ΤΟ ΒΗΜΑ, 22.9.11

Νετρίνα ταξιδεύουν στο CERN με ταχύτητες που ανατρέπουν τη Θεωρία της Σχετικότητας

Σωματίδια κινούνται ταχύτερα από το φως!

Νετρίνα ταξίδεψαν ταχύτερα από το φως στο CERN


Διεθνής ομάδα επιστημόνων κατέγραψε υποατομικά σωματίδια τα οποία ταξίδευαν με ταχύτητα μεγαλύτερη του φωτός! Εάν αυτό το πείραμα που διεξάγεται στο CERN επιβεβαιωθεί, τότε αναμένεται να ταράξει συθέμελα μια από τις βασικές αρχές της φυσικής.

Ο Αντόνιο Ερεντιτάτο που εργάζεται στο CERN δήλωσε στο ειδησεογραφικό πρακτορείο Reuters ότι μετρήσεις που διεξάγονται τα τελευταία τρία χρόνια αποκάλυψαν νετρίνα τα οποία κινούνταν με ταχύτητα μεγαλύτερη κατά 60 δισεκατομμυριοστά του δευτερολέπτου (nanosecond) σε σύγκριση με εκείνη του φωτός καλύπτοντας μια απόσταση 730 χιλιομέτρων μεταξύ της Γενεύης και ενός εργαστηρίου στο Γκραν Σάσο της Ιταλίας.

Τα νετρίνα εμφανίζονται με διαφορετικούς τύπους («γεύσεις») και πρόσφατα αποδείχθηκε ότι μπορούν να αλλάξουν αυθόρμητα τύπο. Ο δρ Ερεντιτάτο και η ομάδα του δημιούργησαν μια δέσμη ενός τύπου νετρίνων – μιονικά νετρίνα- και τα έστειλαν από το CERN στο εργαστήριο στο Γκραν Σάσο. Στόχος τους ήταν να δουν πόσα από αυτά τα σωματίδια θα άλλαζαν τύπο (θα μετατρέπονταν συγκεκριμένα σε ταυ-νετρίνα).

Απίστευτη παρατήρηση

Διεξάγοντας αυτά τα πειράματα όμως οι ειδικοί παρατήρησαν ότι τα σωματίδια κάλυπταν την απόσταση των 730 χιλιομέτρων ταχύτερα από ό,τι το φως. Εμειναν τόσο έκπληκτοι από τα αποτελέσματά τους ώστε επανέλαβαν το πείραμα περί τις 15.000 φορές. Ετσι τα ευρήματά τους είναι στατιστικά σημαντικά, τόσο ώστε να ταράξουν για καλά τα νερά της φυσικής.

«Εχουμε μεγάλη εμπιστοσύνη στα αποτελέσματά μας. Ωστόσο χρειάζεται να διεξαγάγουν άλλοι συνάδελφοι αντίστοιχα πειράματα προκειμένου να τα επιβεβαιώσουν» ανέφερε ο δρ Ερεντιτάτο στο Reuters. Ο ερευνητής ζήτησε περαιτέρω ανάλυση των απίστευτων αυτών αποτελεσμάτων καθώς εάν επιβεβαιωθούν τότε θα ανατρέψουν μια βασική αρχή της Ειδικής Θεωρίας της Σχετικότητας που θεμελίωσε το 1905 ο Αλβέρτος Αϊνστάιν. Σύμφωνα με αυτήν τίποτα στο Σύμπαν δεν μπορεί να ταξιδέψει ταχύτερα από το φως.

Ο δρ Ερεντιτάτο ανέφερε ότι τα ευρήματα θα εμφανιστούν σύντομα σε δικτυακή μορφή προκειμένου να αποτελέσουν αντικείμενο ενδελεχούς μελέτης και από άλλες ομάδες. Παράλληλα η ερευνητική ομάδα οργάνωσε σήμερα Παρασκευή  συνάντηση ειδικών στο CERN ώστε να συζητηθούν τα… φωτεινά της αποτελέσματα.

Στη συνάντηση ο δρ Ερεντιτάτο ζήτησε για άλλη μια φορά νέες ανεξάρτητες μετρήσεις από άλλες ομάδες, καθώς όπως είπε, τα ευρήματα της ομάδας του, εάν ευσταθούν, θα αλλάξουν τη φυσική. «Δεν ισχυριζόμαστε τίποτα, θέλουμε απλώς να βοηθηθούμε από την επιστημονική κοινότητα προκειμένου να καταλάβουμε τα »τρελά» μας αποτελέσματα, διότι πρόκειται πράγματι για »τρελά» αποτελέσματα» κατέληξε ο επιστήμονας.


Ταχύτερα του φωτός


Η κίνηση με ταχύτητα που ξεπερνά αυτή του φωτός ήταν, μέχρι σήμερα τουλάχιστον, χαρακτηριστικό των υπερ-ηρώων στις ταινίες επιστημονικής φαντασίας. Τώρα, ομάδα ερευνητών τού Cern ανακοινώνουν ότι κατέγραψαν σωματίδια που κινούνται πιο γρήγορα από το φως, ξεπερνώντας το απόλυτο όριο ταχύτητας στο Σύμπαν.

Οι ερευνητές εξέπεμψαν δέσμη νετρίνων από το CERN στη Γενεύη και κατέγραψαν πόσα από αυτά έφτασαν στο ερευνητικό κέντρο Γκραν Σάσο στην Ιταλία. Τα νετρίνα διένυσαν την απόσταση των 730 χιλιομέτρων 60 νανοδευτερόλεπτα γρηγορότερα απ' ό,τι το φως (φωτ. Reuters) Οι ερευνητές εξέπεμψαν δέσμη νετρίνων από το CERN στη Γενεύη και κατέγραψαν πόσα από αυτά έφτασαν στο ερευνητικό κέντρο Γκραν Σάσο στην Ιταλία. Τα νετρίνα διένυσαν την απόσταση των 730 χιλιομέτρων 60 νανοδευτερόλεπτα γρηγορότερα απ’ ό,τι το φως (φωτ. Reuters) Η ανακοίνωσή τους, με αποτελέσματα που ήδη επανελέγχονται εξονυχιστικά, εάν αποδειχθεί σωστή, ενδέχεται να κλονίσει τη θεωρία της σχετικότητας του Αϊνστάιν και μαζί της το οικοδόμημα της σύγχρονης φυσικής.

Οι ερευνητές τού Cern δηλώνουν «έκπληκτοι» και οι ίδιοι με την ανακάλυψή τους, τονίζοντας ότι χρειάζονται τη συνεργασία και άλλων εργαστηρίων στον κόσμο προκειμένου να είναι απολύτως σίγουροι για το εύρημα.

Οπως εξηγούν, εξέπεμψαν δέσμη νετρίνων από το CERN στη Γενεύη και στη συνέχεια κατέγραψαν πόσα από αυτά έφτασαν στο ερευνητικό κέντρο Γκραν Σάσο στην Ιταλία. «Τα νετρίνα διένυσαν την απόσταση των 730 χιλιομέτρων 60 νανοδευτερόλεπτα γρηγορότερα απ’ό,τι το φως», δήλωσε χαρακτηριστικά ο Αντόνιο Ερεντιτάτο της ερευνητικής ομάδας. Σημειώνεται ότι το περιθώριο λάθους είναι μόνο 10 νανοδευτερόλεπτα.

Μόνον άλλα δύο εργαστήρια στον κόσμο μπορούν να προχωρήσουν σε αντίστοιχο πείραμα, το Fernilab στο Σικάγο και ένα ιαπωνικό εργαστήριο που ύστερα από το σεισμό και το τσουνάμι στη Φουκουσίμα δεν λειτουργεί. Ο επικεφαλής του Fernilab, Ρομπ Πλάνκετ, δήλωσε ότι ήδη η ομάδα του εξετάζει τις «συγκλονιστικές» πληροφορίες αλλά στάθηκε επιφυλακτικός.

Αποκλειστική συνέντευξη στην «Ε» του φυσικού Σταύρου Κατσανέβα για τη νέα εντυπωσιακή ανακοίνωση στο CERN

Τα νετρίνα ταξιδεύουν ταχύτερα από το φως!


Προχθές το απόγευμα στο Ευρωπαϊκό Κέντρο Πυρηνικών Ερευνών (CERN) της Γενεύης πραγματοποιήθηκε η πολυαναμενόμενη ανακοίνωση για τα απρόσμενα πειραματικά δεδομένα σχετικά με τα νετρίνα.

Η επίσημη ανακοίνωση ήλθε -με καθυστέρηση μιας εβδομάδας- να θέσει ένα τέλος στις υπερβολές και τα κουτσομπολιά που από μέρες κυκλοφορούσαν στο Διαδίκτυο σχετικά με τα τελευταία και ιδιαίτερα ανατρεπτικά δεδομένα που μόλις προέκυψαν από το ερευνητικό πρόγραμμα OPERA (Oscillation Project with Emulsion-tRacking Apparatus).

Το πρόγραμμα OPERA είναι ένα διεθνές πείραμα που ξεκίνησε το 2006 στη Γενεύη και συνίσταται στην εκπομπή μιας πυκνής δέσμης νετρίνων, η οποία παράγεται από τον μεγάλο επιταχυντή του CERN, διασχίζει μια απόσταση 732 χιλιομέτρων μέσα από την οροσειρά των Αλπεων και φτάνει, μέσα σε χιλιοστά του δευτερολέπτου, στο υπόγειο εργαστήριο του Ιταλικού Ινστιτούτου Πυρηνικής Φυσικής (INFN) στο Gran Sasso, όπου βρίσκεται ένας πανίσχυρος ανιχνευτής νετρίνων: μια γιγάντια «φωτογραφική μηχανή» που ονομάζεται OPERA, ζυγίζει 1,3 τόνους και είναι ειδικά κατασκευασμένη για να «απαθανατίζει» όλα τα νετρίνα που φτάνουν σε αυτήν (βλ. σχετικά άρθρα μας στην «Ε» 12-06-10 και 03-07-10).

Ζητήσαμε από τον Σταύρο Κατσανέβα, διαπρεπή αστροσωματιδιακό φυσικό και έναν από τους σχεδιαστές του πειράματος OPERA, να μας πει ποια είναι τα νέα δεδομένα που μόλις ανακοίνωσαν στη Γενεύη και γιατί πολλοί ειδικοί πιστεύουν ότι αυτά μπορεί να ανατρέψουν το σκηνικό στη σύγχρονη φυσική.

* Μόλις χθες έγινε στο CERN μια πολύ σημαντική επιστημονική ανακοίνωση. Τι ακριβώς ανακοινώθηκε;

«Ανακοινώθηκαν τα τελευταία αποτελέσματα που προέκυψαν από το πείραμα OPERA. Η ανάλυση των δεδομένων, τα οποία αφορούσαν τη μέτρηση της ταχύτητας κίνησης των νετρίνων, έδωσε ένα πραγματικά απροσδόκητο αποτέλεσμα: τα νετρίνα που ταξιδεύουν από τη Γενεύη έως το Gran Sasso της Ιταλίας και ανιχνεύονται από τον ισχυρότατο ανιχνευτή OPERA, φτάνουν εκεί 60 δισεκατομμυριοστά του δευτερολέπτου πριν από τον χρόνο που θα χρειαζόταν το φως για να διανύσει στο κενό την ίδια απόσταση. Με άλλα λόγια, φαίνεται ότι τα νετρίνα ταξιδεύουν με ταχύτητα κατά 25 εκατομμυριοστά του δευτερολέπτου υψηλότερη από την ταχύτητα του φωτός στο κενό!

Για να πραγματοποιήσουν αυτή την έρευνα, οι ερευνητές του OPERA, σε συνεργασία με ειδικούς από το CERN και με ειδικά ινστιτούτα μετρολογίας, έπρεπε να κάνουν μια σειρά από μετρήσεις υψηλής ακριβείας προκειμένου να υπολογίσουν επακριβώς τόσο την απόσταση CERN-Gran Sasso όσο και τον χρόνο πτήσης των νετρίνων.

Η απόσταση μεταξύ της πηγής της δέσμης νετρίνων στη Γενεύη (στο CERN) και του ανιχνευτή στην Ιταλία μετρήθηκε με περιθώριο σφάλματος μερικών εκατοστών, ενώ ο χρόνος πτήσης των νετρίνων προσδιορίστηκε χρησιμοποιώντας προηγμένα συστήματα GPS και ατομικά ρολόγια και λαμβάνοντας υπ’ όψιν τον χρόνο απόκρισης όλων των στοιχείων της δέσμης νετρίνων και του ανιχνευτή.

Ολα αυτά περιορίζουν το ποσοστό των συστηματικών σφαλμάτων κατά τη μέτρηση σε ένα επίπεδο μικρότερο των 10 εκατομμυριοστών του δευτερολέπτου: η καταμετρημένη διαφορά χρόνου είναι 6 φορές μεγαλύτερη από το συστηματικό σφάλμα μέτρησης. Η πιθανότητα λοιπόν το σήμα να είναι απλώς μια στατιστική διακύμανση είναι 3 στο εκατομμύριο».

* Γιατί όμως αυτή η ανακάλυψη θεωρείται τόσο σημαντική και έχει προκαλέσει τέτοια αναστάτωση στη διεθνή επιστημονική κοινότητα;

«Το αποτέλεσμα είναι τόσο αναπάντεχο και ο πιθανός αντίκτυπός του στη φυσική τόσο μεγάλος, ώστε θα ήταν μάλλον πρόωρο να επιχειρήσουμε να εξάγουμε συμπεράσματα ή να προτείνουμε ερμηνείες.

Το βέβαιο είναι ότι αυτή η ανακοίνωση θα αποτελέσει την αφορμή για νέα ανάλογα πειράματα, προκειμένου να επιβεβαιωθεί ή να διαψευσθεί το τελευταίο αποτέλεσμα του OPERA. Αρμόζει λοιπόν, προς το παρόν, να υιοθετήσουμε τη στάση του Gellmann, ο οποίος όταν δημοσίευσε τη μελέτη του που προέβλεπε την ύπαρξη των κουάρκς, δήλωσε χαρακτηριστικά: "Ιδού η θεωρία μου για τα κουάρκς, ας ελπίσουμε ότι κάποιος θα βρει πού βρίσκεται το λάθος"».

* Ωστόσο, θα πρέπει να επιμείνουμε: η επιβεβαίωση και από άλλα πειράματα αυτού του εντυπωσιακού αποτελέσματος τι συνέπειες θα έχει στη μικροφυσική αλλά και, γενικότερα, στις τρέχουσες φυσικές θεωρίες μας;

«Η αδιαμφισβήτητη, μέχρι σήμερα, υπόθεση ότι η ταχύτητα του φωτός στο κενό αποτελεί την ανώτερη δυνατή ταχύτητα συνδέεται άρρηκτα με το "αναλλοίωτο" των νόμων της φύσης κάτω από τους λεγόμενους μετασχηματισμούς Lorentz.

Το "αναλλοίωτο" εδώ σημαίνει ότι αυτοί οι μετασχηματισμοί εξασφαλίζουν τη μετάβαση από το ένα αδρανειακό σύστημα αναφοράς στο άλλο χωρίς οι νόμοι της φύσης να αλλάξουν μορφή. Εξάλλου, το αναλλοίωτο των μετασχηματισμών του Lorentz αποτελεί το θεμέλιο της θεωρίας της Γενικής Σχετικότητας του Αϊνστάιν, της μόνης θεωρίας για τη βαρύτητα που διαθέτουμε σήμερα, δηλαδή της μοναδικής θεωρίας για το "απείρως" μεγάλο. Η ανυπαρξία σωματιδίων ικανών να κινούνται με ταχύτητα μεγαλύτερη αυτής του φωτός είναι η θεμελιακή υπόθεση όχι μόνο της Θεωρίας της Σχετικότητας αλλά και των περισσότερων σύγχρονων θεωριών. Και αυτή ακριβώς τη θεμελιακή υπόθεση φαίνεται πως διαψεύδουν τα νέα πειραματικά δεδομένα.

Ωστόσο, ο εικοστός αιώνας μάς άφησε ως κληρονομιά, εκτός από τη Γενική Σχετικότητα, και μια άλλη σπουδαία θεωρία, την Κβαντομηχανική, η οποία περιγράφει με ακρίβεια το "απείρως" μικρό.

Το πιο προχωρημένο ερευνητικό-θεωρητικό μέτωπο των τελευταίων 40 χρόνων είναι η μεγάλη, αλλά δυστυχώς ανεπιτυχής, προσπάθεια να βρεθεί μια ενοποιημένη θεωρία ικανή να συμπεριλαμβάνει, χωρίς αντιφάσεις, τόσο τη Γενική Σχετικότητα όσο και την Κβαντομηχανική. Σε αυτή τη μεγάλη ενοποίηση αποβλέπουν π.χ. οι θεωρίες των χορδών, της κβαντικής βαρύτητας βρόγχων, οι θεωρίες πολλαπλών διαστάσεων και μεμβρανών κ.ο.κ.

Ομως για μερικές από τις παραπάνω θεωρίες η χωροχρονική δομή αλλάζει σε υψηλές ενέργειες, το συνεχές του χωροχρόνου διαρρηγνύεται σε έναν "κβαντικό αφρό", ο χωροχρόνος γίνεται μια "αναδυόμενη" ιδιότητα των θεμελειωδέστερων αντιδράσεων κ.ο.κ. Γι’ αυτές τις θεωρίες το "αναλλοίωτο" των μετασχηματισμών Lorentz δεν είναι παρά μια προσεγγιστική συμμετρία που παραβιάζεται· όσο για την ύπαρξη σωματιδίων που κινούνται ταχύτερα από το φως, παύει να θεωρείται ταμπού. Συνεπώς, οι θεωρίες αυτές προβλέπουν εν γένει τη δυνατότητα ταχυτήτων μεγαλύτερων από την ταχύτητα του φωτός.

Εξάλλου, η ιστορία της φυσικής μάς διδάσκει ότι οι περισσότεροι φυσικοί νόμοι έχουν "ημερομηνία λήξης": κάποια στιγμή ανακαλύπτουμε μια γενικότερη θεωρία και οι μέχρι τότε καθιερωμένη "νόμοι" μετατρέπονται σε περιορισμένες προσεγγίσεις στο πλαίσιο ενός νέου νόμου με πολύ ευρύτερες εφαρμογές. Αυτό ακριβώς συνέβη στη Νευτώνεια Μηχανική, η οποία στις αρχές του εικοστού αιώνα μετετράπη σε επιμέρους προσέγγιση της θεωρίας του Αϊνστάιν για τις πολύ χαμηλές ταχύτητες σε σχέση με την ταχύτητα του φωτός.

Το πρόγραμμα OPERA, μεταξύ άλλων, ελέγχει τη θεωρία του Αϊνστάιν σε ένα καθεστώς όπου η ενέργεια είναι τουλάχιστον 100 δισεκατομμύρια φορές μεγαλύτερη από την πιθανή μάζα των νετρίνων. Αντίστοιχο καθεστώς συναντάται στην κοσμική ακτινοβολία πολύ υψηλής ενέργειας που μελετάται στο πείραμα AUGER στην Αργεντινή, ή στα νετρίνα και τα φωτόνια υψηλής ενέργειας που εκπέμπονται από τα βίαια κοσμικά φαινόμενα.

Είναι λοιπόν απολύτως δικαιολογημένος ο ενθουσιασμός αλλά και η μεγάλη αναστάτωση για αυτή την ανακάλυψη: αν η μέτρηση αυτή επιβεβαιωθεί από άλλα σχετικά πειράματα, τότε το ερευνητικό και θεωρητικό έργο που διανοίγεται για το άμεσο μέλλον είναι τεράστιο. Ισως ανοίξαμε ένα καινούργιο παράθυρο στον κόσμο».

Ποιος είναι ο Σταύρος Κατσανέβας

Γεννήθηκε στην Αθήνα το 1953. Σπούδασε Φυσική στο Πανεπιστήμιο Αθηνών και στο Πανεπιστήμιο Paris 11-Orsay. Εργάστηκε για τρία χρόνια στο Εθνικό Εργαστήριο του επιταχυντή Fermi στο Σικάγο των ΗΠΑ, και πέντε χρόνια στο CERN της Γενεύης. Σήμερα διδάσκει στο Πανεπιστήμιο Paris 7 και είναι υπεύθυνος για την έρευνα στην αστροσωματιδιακή Φυσική και την Κοσμολογία στο ΙΝ2Ρ3 (Εθνικό Ινστιτούτο Πυρηνικής Φυσικής και Στοιχειωδών Σωματιδίων) του CNRS. Από το 2006 είναι ο πρώτος συντονιστής του ευρωπαϊκού προγράμματος ASPERA (Astroparticle Physics European Research Area Network) με στόχο τη συνεργασία των ευρωπαϊκών κρατών για τη χρηματοδότηση των μεγάλων αστροσωματιδιακών προγραμμάτων του προσεχούς μέλλοντος.


«Τα νετρίνα ίσως κόβουν δρόμο από τον χωρόχρονο»

Ο γερμανός επιστήμονας Χάινριχ Πάες θεωρεί πιθανό το ενδεχόμενο τα σωματίδια να είναι ταχύτερα από το φως


Την ώρα που συγγραφείς επιστημονικής φαντασίας και όχι μόνο, οραματίζονται ταξίδια στο άγνωστο παρελθόν της Γης, στους κόλπους των επιστημόνων ακούγονται επιφυλακτικές φωνές και εκφράζεται σκεπτικισμός για την ικανότητα των νετρίνων να ξεπερνούν σε ταχύτητα το φως.

Ηδη το περασμένο Σαββατοκύριακο, 30 από τους 160 επιστήμονες που συμμετείχαν από 11 χώρες στο τριετές πείραμα, δεν υπέγραψαν το τελικό κείμενο συμπερασμάτων που δόθηκε στη δημοσιότητα, εκφράζοντας την άποψη ότι τα αποτελέσματα θα έπρεπε να σταλούν προς δημοσίευση σε επιστημονικό περιοδικό και να μην κοινοποιηθούν μέσω συνέντευξης Τύπου.

Ο συντονιστής του πειράματος OPERA στο ιταλικό εργαστήριο όπου καταγράφηκαν οι εκπληκτικές ταχύτητες των νετρίνων, δρ Αντόνιο Ερεντιτάτο, ανέφερε ότι τα αποτελέσματα των μετρήσεων που επί τρία χρόνια διενεργούσε η επιστημονική του ομάδα είναι στη διάθεση της διεθνούς επιστημονικής κοινότητας για να τα υποβάλει σε εξονυχιστικό έλεγχο.

«Πραγματικά θέλουμε να μας πουν πού κάναμε λάθος, αν όντως κάναμε. Αντιλαμβάνομαι ότι μπορεί διάφοροι συγγραφείς επιστημονικής φαντασίας να διατυπώσουν τη δική τους εκδοχή για το τι μπορεί να σημαίνουν τα αποτελέσματα, όμως εμείς δεν σκοπεύουμε να μπούμε σε μια τέτοια διαδικασία».

Ορισμένοι από τους επιστήμονες που εξαρχής θεώρησαν ότι είναι πιθανό τα νετρίνα να κινούνται με ταχύτητα μεγαλύτερη από εκείνη του φωτός, είναι ο Χάινριχ Πάες από το Πανεπιστήμιο του Ντόρτμουντ και οι συνάδελφοί του.

Κατά τον Πάες, είναι πιθανό τα νετρίνα να εκμεταλλεύονται άγνωστες διαστάσεις και να κόβουν δρόμο μέσα από τον χωρόχρονο. «Οι επιπλέον διαστάσεις στο σύμπαν μπορεί να είναι έτσι διαμορφωμένες, ώστε τα σωματίδια που κινούνται σε αυτές να τρέχουν γρηγορότερα από τα αντίστοιχα που ταξιδεύουν στις τρεις γνωστές διαστάσεις του Σύμπαντος».

Ο Aλαν Κοστελέσκι από το Πανεπιστήμιο της Ιντιάνας, δεν απέρριψε ούτε κι αυτός το ενδεχόμενο να έχει δίκιο το ιταλικό εργαστήριο, καθώς αρκετά παλιότερα, το 1985, είχε διατυπώσει τη θεωρία ότι ένα ενεργειακό πεδίο που απλώνεται αόρατο στο κενό, θα μπορούσε να επιτρέπει στα νετρίνα να κινούνται ταχύτερα από τα φωτόνια που αποτελούν το φως.

ΕΠΙΦΥΛΑΞΕΙΣ. Ωστόσο, δεν ήταν λίγοι οι επιστήμονες που εξέφρασαν σοβαρές επιφυλάξεις για την ορθότητα των μετρήσεων, προτού αυτά επαληθευτούν από ανεξάρτητους ερευνητές. Ο Τζιμ αλ Χαλίλι από το Πανεπιστήμιο του Σάρεϊ ανέφερε στην εφημερίδα «Guardian» ότι η πιο λογική ερμηνεία είναι να έχει γίνει κάποιο λάθος στην εκτίμηση των αποτελεσμάτων. «Είμαι τόσο σίγουρος γι’ αυτό, ώστε αν κάνω λάθος είμαι διατεθειμένος να φάω το… παντελόνι μου σε ζωντανή μετάδοση»!

Λιγότερο εκδηλωτικός αλλά εξίσου βέβαιος ότι κάτι δεν εκτιμήθηκε σωστά στην ίδια ιστορία, εμφανίστηκε και ο καθηγητής Σωματιδιακής Φυσικής στο Πανεπιστήμιο του Σέφιλντ, Νταν Τόβεϊ. «Η αίσθηση που έχω είναι – και φαντάζομαι το ίδιο θα ισχύει για το μεγαλύτερο μέρος της επιστημονικής κοινότητας – ότι κάποια σημαντική παράμετρος δεν ελήφθη υπόψη και προέκυψαν τα αποτελέσματα αυτά».


Τα νετρίνα και η κρίση

Του Μιχάλη Μητσού, ΤΑ ΝΕΑ 26.9.11

«Δεν σερβίρουμε νετρίνα», λέει ο μπάρμαν. Ενα νετρίνο μπαίνει σ’ ένα μπαρ.

imageΑυτό είναι ένα από τα πολυάριθμα tweets που κυκλοφόρησαν αμέσως μετά την ανακοίνωση των επιστημόνων του CERN ότι τα νετρίνα ταξιδεύουν πιο γρήγορα από το φως. Μέσα σε ελάχιστους χαρακτήρες συμπυκνώνεται η σημασία αυτής της ανακάλυψης, εφόσον βέβαια επαληθευτεί: η επιστημονική φαντασία γίνεται επιστημονική πραγματικότητα, το αιτιατό προηγείται του αιτίου, οι συνέπειες των πράξεων έρχονται πριν από τις πράξεις, όλα ανατρέπονται, όλα πρέπει να αναθεωρηθούν. Ο Λούκι Λουκ ίσως τελικά να μπορεί να πυροβολεί πιο γρήγορα από τη σκιά του. Κι ίσως μια μέρα να μπορέσουμε να ταξιδέψουμε στο παρελθόν.

Θα πρέπει βέβαια να ξεκαθαρίσουμε κάτι από την αρχή. Ο Αϊνστάιν δεν υποστήριξε ποτέ ότι η ταχύτητα του φωτός δεν μπορεί να ξεπεραστεί. Η θεωρία της σχετικότητας προβλέπει απλώς ότι υπάρχει ένα όριο ταχύτητας που δεν μπορεί να ξεπεραστεί. Μέχρι τώρα, τα πειράματα έδειχναν ότι το όριο αυτό αντιστοιχεί στην ταχύτητα του φωτός στο κενό. Ισως αποδειχθεί στο μέλλον ότι τα υποατομικά σωματίδια που λέγονται νετρίνα τρέχουν με απειροελάχιστα μεγαλύτερη ταχύτητα.

Η επιφύλαξη είναι απαραίτητη καθώς, όπως επισημαίνει ο ιταλός μαθηματικός Πιερτζόρτζιο Οντιφρέντι στη «Ρεπούμπλικα», τα νετρίνα έχουν προκαλέσει συζητήσεις και στο παρελθόν. Για καιρό οι επιστήμονες πίστευαν ότι δεν έχουν μάζα, κατά συνέπεια κινούνται με την ταχύτητα του φωτός. Υστερα είπαν ότι έχουν μάζα, άρα κινούνται πιο αργά. Τώρα λένε πως και μάζα έχουν και πιο γρήγορα τρέχουν από το φως. Ολα είναι στο τραπέζι, εκτός από την αμφισβήτηση της θεωρίας της σχετικότητας. Οι οπαδοί των επαναστάσεων μάλλον θα απογοητευτούν και πάλι. Οπως έλεγε άλλωστε και ο ίδιος ο Αϊνστάιν, «η επιστήμη δεν είναι μια δημοκρατία της Μπανανίας όπου γίνονται κάθε μέρα επαναστάσεις»…

Ο Φρανκ Κλόουζ, που διδάσκει θεωρητική φυσική στο Πανεπιστήμιο της Οξφόρδης και έχει γράψει το βιβλίο «Νετρίνο», έχει δύο βασικές αντιρρήσεις. Για να μετρήσεις τον χρόνο με ακρίβεια νανοδευτερολέπτου, γράφει στην «Γκάρντιαν», πρέπει η δίοδος των ηλεκτρονικών σημάτων μέσα από κυκλώματα, τσιπάκια και άλλους διαδρόμους του νανοκόσμου να είναι ανεμπόδιστη. Ενα στιγμιαίο και ανεπαίσθητο μποτιλιάρισμα να γίνει, κι έχεις πέσει έξω. Η άλλη πηγή πιθανού λάθους είναι η μέτρηση της απόστασης. Η ακρίβεια εδώ εξασφαλίζεται με τη χρήση της γεωδαισίας. Ομως η ταχύτητα των ραδιοσημάτων μέσα από την ατμόσφαιρα επηρεάζεται από μαγνητικά πεδία και άλλα φαινόμενα. Οι επιστήμονες του CERN δεν έδωσαν εδώ πειστικές απαντήσεις.

Τα πειράματα έτσι θα συνεχιστούν. Και η αντιπαράθεση ιδεών αναμένεται συναρπαστική. Ο Πολ Κρούγκμαν, μάλιστα, θεωρεί ότι τα νετρίνα μπορούν να δώσουν μια λύση και στην οικονομική κρίση: αρκεί να στείλουν ένα μήνυμα στο παρελθόν ότι δεν πρέπει να απελευθερωθεί η οικονομία (και δεν πρέπει να γίνει δεκτή η Ελλάδα στην ευρωζώνη)…

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