The man who oversaw the news that has been shaking up the physics community since a few months back has resigned! Prof. Antonio Ereditato, the man who headed the OPERA experiment, when it announced the faster-than-light neutrino speeds result has quit his job. This comes after a series of setbacks for the original results.
The Unfortunate Part of Science
This is the unfortunate part of physics experiment. The claims were outrageous – flying in the face of a hundred years of physics. At worst, people have ridiculed the experiment and at best, they have had a smirk and a chuckle when they spoke about it. Now, the heads have started rolling.
To give full credit to the experimenters in the collaboration, they were extremely cautious about announcing the results. They did make reruns, but found consistent effects. They searched for errors, but couldn’t find any. That errors were pointed out by the OPERA group itself a few days back, shows the integrity that the group actually showed.
Also, the group didn’t jump the gun and, in fact, came to no physical conclusion at all! Prof. Ereditato always emphasised the need for “words of caution”, since the results would have “potentially great impact on physics”. But, apparently, there have been voices of discontent from within the OPERA collaboration.
The results have all been debunked now, with the Icarus results being the final nail in the coffin. Icarus couldn’t reproduce the faster-than-light effects.
Sandro Centro, spokesperson for the Icarus collaboration, based in the same Gran Sasso lab as the OPERA collaboration, says:
Now we are 100% sure that the speed of neutrinos is the speed of light.
As long as humans do physics, there will be such incidents. Human thoughts are not just scientific and we all know that. The big bad world exists outside – and science just cannot keep that out, no matter how much it tries.
Neutrinos seem to be travelling at speed of light once more! A different experimental group – the Icarus group, tried out the same experiment as the OPERA group in the same lab, but using different equipment and found that the speed of the neutrinos was very much compatible with the speed of light within experimental error bounds! The Icarus group have found that neutrinos travel at the speed of light, not faster. The OPERA result, already fraught by reports of device malfunctions, has received another jolt.
The experimental findings of the Icarus group, also based in Gran Sasso just like OPERA, and also receiving neutrinos from the same CERN source, were published in a paper which is available online here.
A second opinion
The Icarus group intends on studying the different properties of neutrinos and also aspects of any proton decay. They use a Liquid Argon Detector – the T600 – which uses 600 tonnes of liquid nitrogen to detect the presence of neutrinos and also measure their direction and momentum. They have been tweaking their experiment so as to be able to re-check OPERA’s claim.
Of course, OPERA itself has been in a soup with its own problems. We reported the initially reported error of an optical fibre delay here and then followed up with yet another error that might have influenced the speed. With so much at stake, the littlest things might compromise the findings of the biggest experimental groups.
Icarus says that there are more tests to come – as many as four more experiments intend to verify OPERA. The entire physics community is expecting negative results, akin to Icarus’, but to be sure of such a thing would be prejudice.
The neutrino story is still not an open and shut case. You’ve probably read about the supposed computer glitch by now. If you haven’t, we have it right here. However, as more details pour in, more surprises tumble out! It turns out that there wasn’t just one computer error, there were, in fact, two!! And this complicates matters
New York Times reports that one source of error is the GPS measurement system, or more precisely, the optical cable connecting the GPS receiver to the detector. This is a five mile long cable and the faulty wiring could’ve easily put the measurements back by 60 nanoseconds, which was the exact amount of time by which the neutrinos beat the speed of light. This is the story we reported earlier.
However, it seems that there was yet another unaccounted systematic error! There is a piece of equipment that marks the exact time for the GPS measurements, taking into account all sorts of relativistic corrections.
However, this would speed up the neutrinos even more, making the case for the violation of relativity even stronger.
The first error has been corrected, but the second error is yet to be taken care of.
Add and subtract the errors? No? What’s wrong?
As any student of physics would know, errors like these cannot simply be added or subtracted. For extreme precision experiments, like the OPERA experiment, one cannot tweak the experimental data in order to do take into account all technical glitches. The only way to resolve this would be to fix the systematics and run the experiment again!
The experiment would definitely need an independent test to be refuted, now more than ever, since these unexpected question marks have been put up against it.
The supposedly greatest anomaly ever detected in physics, capable of undoing a hundred years of physics, may turn out to be a mere computer glitch. There are rumours that the anomaly may be due to a faulty connection between a GPS unit and a computer receiving signals from it.
We had reported the faster-than-light neutrino results in great detail in several posts earlier. The physics group at Gran Sasso laboratory, near CERN, had detected that neutrinos arrives 60 nanoseconds before they are expected to, if they travelled at light speed. This means that they travelled faster than light, violating the cosmic speed limit imposed by Einstein’s Special Theory of Relativity, by a factor of full one-ten thousandth, which is a huge number when it comes to Lorentz violations.
The rumour is that sources inside Gran Sasso say that when a connection between a GPS receiver and the optic fibre was adjusted, the time of flight comes out exactly 60 seconds longer than measured, exactly cancelling the seen anomaly.
New data from independent experiments is still needed to confirm the non-violation of the cosmic speed limit. If this rumour is true, it is face-saving time for the Gran Sasso scientists.
The fantastic results still stay! The sensational OPERA experiment, which gave us the faster-than-light neutrino results, have repeated the experiment and have found similar results. Neutrinos continue to travel faster than light and the amount by which they break the speed barrier is also the same. The experiment was carried out during 30th October to 2nd November.
The latest results give a 60.7 ns advance for the neutrinos with a 7.4 ns error for the systematic and 6.9 ns statistical error. This means that the previous results are not discredited. The difference between the previous experiment and this present one is the proton bunch size.
Scientists are still skeptical and not willing to accept this result yet. Even OPERA and CERN scientists say that the experiment has to be repeated by MINOS or T2K and only then can the experimental results verified.
Detecting one neutrino at a time
This time, the beam of neutrinos has been bunched in 3 ns bins separated by 520 ns. This means that each bunch in the beam consists of basically one neutrino. The experiment has, thus, been repeated with essentially single neutrinos. The number of events is much less than the last time. While OPERA used 16111 events last time, this time they have stuck to merely 20 events. This has led to many people questioning the statistics of the experiment. OPERA, however, claims that the accuracy is just as good, if not better.
The paper of the repeated experiment is already on ArXiv. Here’s the link to the short paper.
Repeat Experiment Needed!
This experiment re-run proves that the beam bunching has nothing to do with the observed results. The effects have not gone away, but that might depend on the CNGS (Cern Neutrino to Gran Sasso) beam structure as well as the systematics of the OPERA detector. A repeat of the experiment in some other part of the world is the need of the day.
The most common particle in the Universe is also the most mysterious, but it seems that scientists might have got something correctly predicted about it. Neutrinos have been noticed to disappear’ in the Double Chooz experiment and this is being interpreted as the manifestation of the elusive neutrino oscillation signature. Electron anti-neutrinos have been noticed to simply disappear meaning that they are actually turning into tau anti-neutrinos, which we have no way of detecting. Technically, scientists are measuring the third mixing angle’ or Î¸13.
Oscillations of neutrinos
Neutrinos are strange because they do not behave in conventional’ ways. One form of neutrinos can change into another, provided neutrinos have mass, however small it might be. There are three types of neutrinos electron neutrinos, muon neutrinos and tau neutrinos. The names are given according to the particle they accompany in a doublet.
Experimental evidence suggests that one form of neutrinos changes into another and this is through a process called see-saw’ mechanism. In other words, the neutrino exists in a mixed’ state and we detect only one of the constituent states. (If you think this is weird, just know that this is the staple bread-butter of quantum mechanics.) The amount of mixing is given by angles. The electron (type 1) and muon (type 2) type neutrinos mix via the mixing angle Î¸12. The muon (type 2) and tau (type 3) neutrinos mix via the Î¸23 angle. The electron and the tau neutrinos mix via the angle Î¸13, which happens to be out angle of interest. We know that Î¸13 is very small, but we want to know how small it really is. The fact that it is non-zero is, in itself, remarkable.
The value of the mixing angle and the consequence of that
One of the experiments measuring the Î¸13 is the Double Chooz experiment. It just released the first set of results and it gives a definitive value for this third mixing angle. The value, given in terms of sine squared of double the angle, is
sin22Î¸13 = 0.085 + 0.029(stat) + 0.042(syst),
where the last two numbers represent errors and need not concern us too much at the moment.
What is interesting is the fact that the other giant experiment in the field of neutrinos the T2K experiment also gives similar results.
The value of Î¸13 is not zero and the two results corroborate one another to give a 3-sigma level confidence on that fact. There are neutrino oscillations between the electron type and the tau type.
This is a theoretically significant result for scientists, who are knee-deep with questions about neutrinos and their properties (and, before you ask, the faster-than-light results are the least of the worries). This will put further constraints on the neutrino masses.
Special Relativity may have saved itself from disaster. According to a scientist, the OPERA collaboration overlooked a crucial correction to the result, which exactly matches the discrepancy observed. It involved the effect of time dilation of the clocks aboard the GPS satellite.
Ronald Van Elburg says that the two frames of reference the Gran Sasso laboratory on the ground and the clocks on the GPS satellite in orbit around the Earth – are in relative motion with respect to each other and thus special relativity effects come into the picture. The time of flight, thus, needs to be corrected for this factor too.
From the perspective of the clock, the detector is moving towards the source and consequently the distance travelled by the particles as observed from the clock is shorter
Magnitude of the Effect
Now, for the crucial magnitude of this effect. Van Elburg presents the analysis which shows that this timing should account for 32 ns for the time of flight. Further, this happens at CERN as well as the Gran Sasso Lab in Italy and thus, the number has to be doubled, yielding 64 ns, which exactly compensates the noticed discrepancy of 60 ns.
This solution has recently been released and is yet to be verified properly. The effect seems too obvious and it seems unlikely that OPERA has not taken it into account. OPERA has not responded as yet.
A theoretical attack on the results
Recently, there has been a theoretical attack on the experimental result by Sheldon Glashow (Nobel Laureate, Physics) and his Boston University colleague, Andrew Cohen. They dismiss the results by showing that if the result were true, no high energy neutrino would reach the detector at Gran Sasso. The fact that they detect high energy neutrino (above 12.5 GeV) means that the neutrinos are not travelling faster than light. This is not an experimental result, but a theoretical bound.
We’ll just have to wait and watch. The van Elburg paper is a pre-print and is not yet peer-reviewed.
After the astonishing result from the OPERA collaboration of detecting neutrinos travelling faster than speed of light, Fermilab wants to double-check the claim. This is an inevitable step in the direction of validating the apparent finding. If Fermilab’s MINOS data doesn’t find anything that replicates the OPERA observations with high enough confidence, then the OPERA result, despite its hype, will become null and void.
Here’s the reason why, despite the care and beauty of the OPERA experiment, it needs independent corroboration: every scientific result must be reproducible. Fermilab has an advantage over other neutrino research labs in the world since it already has the data sets from the famous MINOS experiment.
MINOS was Fermilab’s version of the Super Kamiokande experiment,. Neutrinos come in three flavours or types electron, muon and tau. The curious thing is that neutrinos can oscillate’ or change between these types. An electron neutrino can become a muon neutrino. A theoretical mechanism, known as the see-saw mechanism, explains this, using certain unknown parameters, which need to be supplied experimentally. Super Kamiokande performed experiments in 1998 and confirmed the phenomenon of oscillation and measured the mixing angle’ too. Fermilab repeated this experiment and found consistent results. This was the MINOS experiment, MINOS standing for Main Injector Neutrino Oscillation Search.
Well known to scientists in the neutrino field, but virtually unthinkable to the outside world, is that fact that MINOS had actually detected neutrinos moving faster than light. However, these couldn’t survive analysis and presented only a 1.6 to 2 sigma confidence level, below the 3 sigma needed for validation and way below the 5 sigma needed for labeling it as a discovery. MINOS now plans to sift through their data and put it through rigorous analysis. MINOS should take less than 6 months, since the data is already available to them.
It won’t matter if the OPERA experiment isn’t proved wrong. If Fermilab and T2K don’t reproduce the data, OPERA will be up for grabs. Einstein, thou be stillâ€¦ at least for 6 months.
So CERN has stunned us with a result and this one doesn’t even come from the LHC. The premier European high energy research institute has detected neutrinos that seem to move at a speed greater than that of light, violating one of the most sacred pillars of physics Einstein’s Special Relativity. You must have read about it we posted it here. So what about these faster-than-light neutrinos? Why are so many people all excited about them?
In this article, I will try and explain that, touching upon four crucial points. First we need to understand why people are not ready to believe the result in the first place. Next, we’ll understand whether this is believable or not. Is CERN just tricking us or have they put real hard work behind this before publishing it? Next, we shall talk about the implications of this result, if it is proved right. Lastly, we discuss how there can still be flaws and where some glitches might be found in the coming days.
Unlike the popular media, scientists are treading softly on this result. They are not yet ready to say that Einstein was wrong, although that is what it would imply. They are merely reporting facts at this moment, stating the results as got in the experiment. The result is very possibly wrong, but let’s take a closer look.
What on earth are Neutrinos?
The real heroes of this story, Neutrinos are the slipperiest of all known particles. They carry no charge, almost no mass and interact extremely feebly with other matter and that too via the weak interaction. They’re nearly impossible to detect. They leave no tracks in bubble chambers (no charge), don’t interact with each other to form clumps (no strong interactions, like those of protons and neutrons) or speak with normal matter particles. Scientists were forced to assume its existence to solve a puzzle (the beta decay problem), and, even though neutrinos have been detected after that by several detectors, their properties remain largely mysterious. They are giving a headache once more.
Why are people not ready to believe it?
Simply put, it’s Einstein. People are not expecting anything new and now they find this! This is just too unexpected. Why take a result so flagrantly conflicting with all known physical results at face value? Wellâ€¦
Is this result Believable?
As an answer the first of our questions, I would go with a Yes‘. The result is totally believable in the sense that the experiment and analysis seem water-tight at this moment. Scientists of the OPERA collaboration have been looking at the data for three years! They have done everything scientifically possible to discredit their own finding, but have only managed to strengthen it.
Remember, we told you in the particle physics articles, what confidence level means? A confidence level, quoted as some n-sigma, n’ being an integer, refers to the amount of confidence the experimenter has on his/her own results. A 3-sigma result is one which is significant enough to be considered a potential for detection’. This means that the doubts are less than 0.3%. We’re just getting warmed up! For a discovery’ we need a minimum of 5-sigma, which is a confidence level of 99.9999%.
The current results are a 6-sigma, at 99.999999% confidence level, high and above the threshold required to get a discovered’ tag!! This still doesn’t mean that it is true. It just means that the possibility that this is merely a statistical fluctuation is extremely small. They two are very close, but not the same.
The real motivation for believing in what CERN has found is the methodology they’ve applied in finding out the results. They had found this result 3 years back, but never jumped the gun in publishing it. They checked and re-checked everything, found crucial error bars and found that this result survives. They added more parameters contributing smaller errors, hoping that they’ll somehow add up and then give the necessary’ error bars. They didn’t.
We’ll just talk about the use of GPS and cesium atomic clocks to measure time and how accurately the distance was measured. Since velocity is simply distance divided by time, we need both parameters accurately.
Particles travelling faster than the speed of light have been found. This startling claim comes from a source as respectable as CERN. This was supposedly observed in a neutrino experiment carried out by CERN. However, it is too early to confirm this startling result.
UPDATE: The ‘discovery’ was made by the OPERA experiment while the neutrinos were beamed from Geneva to a lab in Gran Sasso in Italy. The pre-print of the report, prepared by CERN and published today (23rd September) can be found here: http://arxiv.org/abs/1109.4897
Faster Than The Speed of Light? Real Life Tachyons?
Albert Einstein and his Special Theory of Relativity taught us that nothing having mass can travel at the speed of light or above. Massless particles can travel only at the speed of light. Thus, nothing can travel faster than the speed of light.
CERN’s scientists have now found that neutrinos, one of the most enigmatic particles, have breached this barrier. Neutrinos have nearly no mass, no charge and interact negligibly with ordinary matter. It is due to these properties that they cannot be easily detected. The scientists claim that a neutrino beam fired near Geneva to a lab 730 kilometers away in Italy reached its destination 60 nanoseconds earlier than expected. The experimental and statistical errors combine to deduct 10 nanoseconds, which still leaves 50 nanoseconds unexplained and makes this result significant. There are obvious checks and re-checks being performed.
CERN is now depending on the colliders in America and the T2K neutrino experiment in Japan to reinforce its findings. The findings may need many runs and checks to be confirmed. Once confirmed, it raises many questions, including why such an effect wasn’t noticed before. The big question would be this: What happens to Special Relativity, which is an extremely reliable theory?
John Ellis, a theoretical physicist at CERN, gauges the magnitude of the find, if found true:
This would be such a sensational discovery if it were true that one has to treat it extremely carefully.
About the implication for Special Relativity, Ellis says that It has worked perfectly till now”.
Jury Out On Relativity? Not Really!
A knee-jerk reaction would provoke statements about revolutionizing the whole of physics, since stars to elementary particles, all rely on the Special Theory of Relativity. It has been wonderfully accurate, especially when combined with Quantum Mechanics to form Quantum Field Theory. Personally, at this moment, I don’t think this will throw Relativity out, even if the result is correct – Relativity is too beautiful and has been proved too correct in too many situations for that drastic step. I would even stick my neck out and add that this observation is some sort of experimental glitch and that faster-than-light particles have not really been detected. However, only more tests will testify to that.
The grand old man of physics has been challenged by a tiny, nearly massless particle.