Posts Tagged ‘speed of light

New theories emerge to disprove OPERA faster-than-light neutrinos claim

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— It’s been just two weeks since the Oscillation Project with Emulsion-tRacking Apparatus (OPERA) team released its announcement claiming that they have been measuring muon neutrinos moving faster than the speed of light, causing an uproar in the physics community. Since that time, many papers (perhaps as many as 30 to the preprint server arXiv alone) have been published seeking ways to discredit the findings. Thus far though, only two seem credible.

The first is by Carlo Contaldi of Imperial College London. He says that it’s likely the OPERA team failed to take gravity into their math equations and its effect on the clocks used to time the experiment. This because the degree of gravity at the two stations involved in the experiment (Gran Sasso National Laboratory in Italy and the CERN facility in Geneva) were different, thus one of the clocks would have been running slightly faster than the other, resulting in faulty timing. If this turns out to be the case, the OPERA team will most certainly be embarrassed to have overlooked such a basic problem with their study.

The second is by Andrew Cohen and Sheldon Glashow, who together point out that if the neutrinos in the study were in fact traveling as fast as claimed, they should have been radiating particles as they went, leaving behind a measurable trail; this due to the energy transfer that would occur between particles moving at different speeds. And since the OPERA team didn’t observe any such trail (or at least didn’t report it) it follows that the neutrinos weren’t in fact traveling as fast as were claimed and the resultant speed measurements would have to be attributed to something else.

New Constraints on Neutrino Velocities
Andrew G. Cohen, Sheldon L. Glashow
The OPERA collaboration has claimed that muon neutrinos with mean energy of 17.5 GeV travel 730 km from CERN to the Gran Sasso at a speed exceeding that of light by about 7.5 km/s or 25 ppm. However, we show that such superluminal neutrinos would lose energy rapidly via the bremsstrahlung of electron-positron pairs (νμ→νμ+e++e). For the claimed superluminal neutrino velocity and at the stated mean neutrino energy, we find that most of the neutrinos would have suffered several pair emissions en route, causing the beam to be depleted of higher energy neutrinos. Thus we refute the superluminal interpretation of the OPERA result. Furthermore, we appeal to Super-Kamiokande and IceCube data to establish strong new limits on the superluminal propagation of high-energy neutrinos.

Neither of these papers actually disproves the results found by the OPERA team of course, the first merely suggests there may be a problem with the way the measurements were taken, the second takes more of a “it can’t be true because of…” approach which only highlight the general disbelief in the physics community regarding the very possibility of anything, much less the speed of neutrinos traveling faster than the speed of light, messing with Einstein’s most basic theories. The first can be addressed rather easily by the OPERA team if it so desires, and the second, well, if the neutrinos did in fact travel faster than the speed of light and did so without leaving a trail, a lot of physics theory will have to be rethought. Though that may not necessarily be a bad thing, physics is supposed to be about finding answers to explain the natural world around us after all, even if it means going back to the drawing board now and then.
© 2011

Read also: “Is the OPERA Speedy Neutrino Experiment Self-Contradictory?

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October 6, 2011 at 9:07 pm

Live Chat: Have Neutrinos Broken the Speed Limit of Light?

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Nothing can go faster than light, right? Einstein said so. But last week a group of researchers in Italy announced that they’d measured the speed of thousands of neutrinos (tiny, almost massless particles that were fired at their detector from the CERN particle physics lab 730 kilometers away) and found they were traveling slightly faster than light. Is this the beginning of the end for Einstein’s theory of relativity? Have the researchers simply made a mistake in their measurements? Or are the neutrinos, as some versions of string theory allow, taking a shortcut through a higher dimension and arriving in Italy in double-quick time?
Join us for a live chat on this page at 3 p.m. EDT on Thursday, 29 September, to discuss these and other questions with two experts in the field. You can leave your questions in the comments section below before the chat starts.
Upcoming Event:  Have Neutrinos Broken the Speed Limit of Light?

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September 28, 2011 at 4:52 pm

“Relativity without light”, the answer in the superluminal neutrinos;

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Suppose that the result of the OPERA experiment is right and neutrinos travelling faster than light….
This is the end of Einstein’s theory of special relativity and the Lorentz transformations?
Is it possible the special relativity without the second postulation;
The answer is yes.
Read for example:
Simple derivation of the special theory of relativity
without the speed of light axiom
” –
a very simple yet rigorous derivation of the invariance of the space-time interval (and hence the whole special relativity) just from the isotropy, homogeneity and a principle of relativity, without the need of the speed of light axiom.

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September 25, 2011 at 9:26 am


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Potential mistakes in the Opera research

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Almost all theoretical oriented physicists including myself seem to feel almost certain that there is a mistake in the Opera paper and the claimed violation of the relativistic speed limit will go away.

On the other hand, I think that many people who like technology etc. were impressed by the precision work that the Opera folks have demonstrated. It’s a complex piece of work in which particle physicists became top metrologists – their work was endorsed by two teams of professional metrologists, too. In some sense, their measurement is also a pioneering work: as far as I know, the propagation of speed-of-light-in-the-vacuum signals between very distant places on Earth has never been tested against GPS metrology before so it shouldn’t be shocking that one gets a 18-meter discrepancy when he tries it for the first time.

There’s a lot of potential for errors. The measurement may be schematically represented as three steps: “measuring the distance”, “bringing the proper universal time to CERN clocks”, and “bringing the proper universal time to Gran Sasso clocks”. So the mistakes may be divided into three basic groups:

  • timing errors at CERN
  • timing errors in Italy
  • errors in the distance measurement

This is just a very rough, “geographic” separation of the possible mistakes. Various numbers in the calculations depend on each other and one should be more specific about the origin of the error, anyway…… Read the rest of this entry »

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September 24, 2011 at 11:23 am

The Phantom of OPERA

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Those working in science are accustomed to receiving emails starting with “dear sir/madam, please look at the attached file where I’m proving einstein theory wrong”. This time it’s a tad more serious because the message comes from a genuine scientific collaboration… As everyone knows by now, the OPERA collaboration announced that muon neutrinos produced at CERN arrive to a detector 700 kilometers away in Gran Sasso about 60 nanoseconds earlier than expected if they traveled at the speed of light (incidentally, trains traveling the same route arrive always late)….. Read the rest of this entry »

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September 24, 2011 at 11:16 am

Some Comments on the Faster Than Light Neutrinos

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Matt Strassler

The OPERA experiment has now presented its results, suggesting that a high-energy neutrino beam has traveled 730 kilometers at a speed just a bit faster than the speed of light.  It is clear the experiment was done very carefully.  Many cross-checks were performed.  No questions were asked for which the speaker did not have at least a reasonable answer.
Some preliminary comments on the experiment (none of which is entirely well-informed, so caution…)

  • They have to measure times and distances to an accuracy of 1 part in a few hundred thousand. This is hard, not impossible, and they have worked with metrology experts to carry these measurements out.
  • The timing measurement is not direct; it has to be made in a statistical fashion. The proton beam pulses that make the neutrino beam pulses [read more about making neutrino beams here] are not sharp spikes in time, but are distributed in time over ten thousand nanoseconds. (Recall the measured early arrival of the neutrinos is only 60 nanoseconds.) And so one cannot measure, for each arriving neutrino, how long it took to travel. Instead one has to measure the properties of the proton beam pulses carefully, infer the properties of the neutrino pulses, measure the timing of the many arriving neutrinos, and work backwards to figure out how much time on average it took for the neutrinos to arrive. This sounds tricky.[Thanks to Ryan Rohm for calling my attention to this a few days ago.]That said, the experimenters do show some evidence that their technique works.  But this could be a weak point.
  • I am a bit concerned about the way in which statistical and systematic errors are combined. The theory for statistical errors is well-defined; one assumes random fluctuations. In combining two statistical errors E1 and E2, one says that the overall error is the square root of E1-squared + E2-squared.  This is called “adding errors in quadrature.”  But systematic errors are much less well-defined, and it is not clear you should combine them in quadrature, or combine them with statistical errors in quadrature. The OPERA experiment combines all errors in quadrature, and says they have a measurement at 6 standard deviations away from the speed of light. If you instead combined systematic errors linearly with statistical errors (E1+E2 instead of as above) you would get 4 standard deviations. If you combined all the systematic errors with each other linearly, and then with the statistical error linearly, you would get 2 standard deviations (though that is surely too conservative). All this is to say that this result is not yet so significant that different and more conservative treatments of the uncertainties would all give a completely convincing result. This is just something to keep in mind when evaluating such an exceptional claim; we need exceptional confidence……

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September 23, 2011 at 6:54 pm

Conclusions from OPERA experiment

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EP Seminar
New results from OPERA on neutrino properties
by Dario Autiero (Institut de Physique Nucleaire de Lyon)
Friday, September 23, 2011 from 16:00 to 18:00 (Europe/Zurich)

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September 23, 2011 at 4:07 pm

Dimension-hop may allow neutrinos to cheat light speed

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What are we seeing here?

A CERN experiment claims to have caught neutrinos breaking the universe’s most fundamental speed limit. The ghostly subatomic particles seem to have zipped faster than light from the particle physics laboratory near Geneva, Switzerland, to a detector in Italy.

Fish that physics textbook back out of the wastebasket, though: the new result contradicts previous measurements of neutrino speed that were based on a supernova explosion. What’s more, there is still room for error in the departure time of the supposed speedsters. And even if the result is correct, thanks to theories that posit extra dimensions, it does not necessarily mean that the speed of light has been beaten.

“If it’s true, it’s fantastic. It will rock the foundation of physics,” saysStephen Parke of Fermilab in Batavia, Illinois. “But we still have to confirm it.”

Neutrinos are nearly massless subatomic particles that are notoriously shy of interacting with other forms of matter. An experiment called OPERA (Oscillation Project with Emusion tRacking Apparatus) sent beams of neutrinos from a particle accelerator at CERN to a detector in the Gran Sasso cavern in Italy, 730 kilometres away.

The neutrinos arrived 60 nanoseconds sooner than they would have if they had been travelling at the speed of light, the team says.

Supernova contradiction

If real, the finding will force a rewrite of Einstein’s theory of special relativity, one of the cornerstones of modern physics (and a theory whose predictions are incorporated into the design of the accelerators at CERN). “It’s not reasonable,” says theorist Marc Sher of the College of William and Mary in Williamsburg, Virginia….. Read the rest of this entry »

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September 23, 2011 at 12:20 pm