FTL Neutrinos: Closing In on a Solution

by Paul Gilster on February 24, 2012

The news that the faster-than-light neutrino results announced to such widespread interest by the OPERA collaboration have now been explained has been spreading irresistibly around the Internet. But the brief piece in ScienceInsider that broke the news was stretching a point with a lead reading “Error Undoes Faster-Then-Light Neutrino Results.” For when you read the story, you see that a fiber optic cable connection is a possible culprit, though as yet an unconfirmed one.

Sean Carroll (Caltech) blogged on Cosmic Variance that while he wanted to pass the news along, he was reserving judgment until a better-sourced statement came to hand. I’ve thought since the beginning that a systematic error would explain the ‘FTL neutrino’ story, but I still was waiting for something with more meat on it than the ScienceInsider news. It came later in the day with an official CERN news release, and this certainly bears quoting:

The OPERA collaboration has informed its funding agencies and host laboratories that it has identified two possible effects that could have an influence on its neutrino timing measurement. These both require further tests with a short pulsed beam.

So we have not just one but two possibilities here, both with ramifications for the neutrino timing measurements and both needing further testing. And let’s go on with the news release:

If confirmed, one would increase the size of the measured effect, the other would diminish it. The first possible effect concerns an oscillator used to provide the time stamps for GPS synchronizations. It could have led to an overestimate of the neutrino’s time of flight. The second concerns the optical fibre connector that brings the external GPS signal to the OPERA master clock, which may not have been functioning correctly when the measurements were taken. If this is the case, it could have led to an underestimate of the time of flight of the neutrinos. The potential extent of these two effects is being studied by the OPERA collaboration. New measurements with short pulsed beams are scheduled for May.

Image: Detectors of the OPERA (Oscillation Project with Emulsion-tRacking Apparatus) experiment at the Italian Gran Sasso underground laboratory. Credit: CERN/AFP/Getty Images.

We may well be closing on an explanation for a result many scientists had found inconceivable. Here’s a BBC story on the possibility of trouble with the oscillator and/or an issue with the optical fiber connection. We learn here that a new measurement of the neutrino velocity will be taken in 2012, taking advantage of international facilities ranging from CERN and the Gran Sasso laboratory in Italy to Fermilab and the Japanese T2K. The story quotes Alfons Weber (Oxford University), who is working on the Minos effort to study the neutrino measurements at Fermilab:

“I can say that Minos will quite definitely go ahead… We’ve already installed most of the equipment we need to make an accurate measurement. Even if Opera now publish that ‘yes, everything is fine’, we still want to make sure that we come up with a consistent, independent measurement, and I assume that the other experiments will go forward with this as well.”

So this is where we are: An anomalous and extremely controversial result is being subjected to a variety of tests to find out what caused it. If I were a betting man, I would put a great deal of money on the proposition that the FTL results will eventually be traced down to something as mundane as the optical fiber connector that is now the subject of so much attention. But we’ll know that when it happens, and this is the way science is supposed to work. OPERA conducted numerous measurements over a three year period before announcing the FTL result. Let’s now give the further work time to sort out what really happened so we can put this issue to rest.

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{ 56 comments }

Avatar2.0 March 4, 2012 at 1:58

Eniac
In esence, what I am climing is that therre are closed timelike curves in GR:
http://en.wikipedia.org/wiki/Closed_timelike_curve#General_relativity

andy March 4, 2012 at 19:33

A spinning singularity creates a frame-dragging effect (as per GR). From the perspective of someone far outside the singularity, this frame-dragging will make an object (locally moving just beneath the speed of light around the singularity) move at above the speed of light.
And once you have that, you can use SR’s relativity of simultaneity to find systems of reference where said object moves backward through time.

Apparent superluminal motion is possible in SR as well. Also if you are near a black hole you have to use full GR – you can’t get away with the SR approximation. (Similarly you can’t get away with the Newtonian approximation when dealing with objects moving near the speed of light).

In esence, what I am climing is that therre are closed timelike curves in GR:
http://en.wikipedia.org/wiki/Closed_timelike_curve#General_relativity

This is not in doubt, you can for example construct a metric containing a wormhole to the past. Whether such things can exist in reality is another matter, there may well be stability issues that prevent you from doing these kind of tricks. As to the specific case of closed timelike curves in the Kerr metric, do these occur inside or outside the event horizon? If it is on the inside then it is a mathematical curiosity that has no bearing on the observable universe.

Eniac March 5, 2012 at 4:00

@Avatar:

In esence, what I am climing is that therre are closed timelike curves in GR

If that is what you are claiming, then you are likely correct.

However, FTL neutrinos do not fall in this category, and neither does this phenomenon you describe:

… this frame-dragging will make an object (locally moving just beneath the speed of light around the singularity) move at above the speed of light.

Both describe space-like trajectories, which are pretty much implied by definition when you say “faster than light”: The notation ‘faster than light’ clearly puts them outside of the light-cone, making them space-like.

ljk March 14, 2012 at 22:08

Researchers send ‘wireless’ message using neutrinos

March 14, 2012

(PhysOrg.com) — A group of scientists led by researchers from the University of Rochester and North Carolina State University have for the first time sent a message using a beam of neutrinos – nearly massless particles that travel at almost the speed of light. The message was sent through 240 meters of stone and said simply, “Neutrino.”

“Using neutrinos, it would be possible to communicate between any two points on Earth without using satellites or cables,” said Dan Stancil, professor of electrical and computer engineering at NC State and lead author of a paper describing the research.

“Neutrino communication systems would be much more complicated than today’s systems, but may have important strategic uses.”

Many have theorized about the possible uses of neutrinos in communication because of one particularly valuable property: they can penetrate almost anything they encounter. If this technology could be applied to submarines, for instance, then they could conceivably communicate over long distances through water, which is difficult, if not impossible, with present technology.

And if we wanted to communicate with something in outer space that was on the far side of a moon or a planet, our message could travel straight through without impediment.

Full article here:

http://www.physorg.com/news/2012-03-wireless-message-neutrinos.html

ljk March 15, 2012 at 9:32

http://www.technologyreview.com/blog/arxiv/27648/

First Digital Message Sent Using Neutrinos

Physicists commandeer a beam of neutrinos to send a message through solid rock but at a painfully slow data rate

kfc 03/14/2012

A couple of years ago, we looked at the possibility of using neutrinos to communicate with submarines.

The problem with underwater comms is that only the lowest frequency electromagnetic waves penetrate water to any depth and these are only capable of data rates of around 50 bits per second.

Neutrinos on the other hand pass more or less unhindered through anything. That makes them ideal for submarine communication, except for one thing. Neutrinos are somewhat reluctant to interact with matter and this makes them hard to measure. So any neutrino communications beam would have to be hugely powerful and any neutrino detector extremely big.

Nevertheless, neutrinos raise the possibility of communication at data rates some three orders of magnitude higher than is currently possible with submarines.

Today, a team at FermiLab in Batavia, Illinois, reveal that they have sent a digital message using a neutrino beam for the first time.

These guys used an experiment called NuMI (NeUtrino beam at the Main Injector) to generate an intense beam of neutrinos. The beam consisted of about 25 pulses each separated by 2 seconds or so, with each pulse containing some 10^13 neutrinos.

The beam is pointed at a detector called MINERvA weighing about 170 tonnes and sitting in an underground cavern about a kilometre away. To reach MINERvA, the beam has to travel through 240 metres of solid rock.

MINERvA is one of world’s most sensitive neutrino detectors and yet, out of 10^13 neutrinos in each pulse, it detects only about 0.8 of them on average.

Nevertheless, that’s enough to send a message. The FermiLab team used a simple on-off protocol to represent the 0s and 1s of digital code and transmitted the word “neutrino”.

The entire message took about 140 minutes to send at a data rate that these guys later worked out to be about 0.1 bits per second with an error rate of less than 1 per cent.

That’s not quite the three order of magnitude improvement submariners have been hoping for but at least it’s a proof-of-principle. “This result illustrates the feasibility, but also shows the significant improvements in neutrino beams and detectors required for practical applications,” say the team.

Better results ought to be possible with more intense beams and larger detectors, such as the IceCube detector at the South Pole which uses the Antarctic icepack as a detector.

And submarine communication is not the only potential use. The FermiLab team mention various other alternatives such as interstellar communication and communication with spacecraft hidden on the far side of distant planets.

If that ever comes to pass, this experiment will be the equivalent of Alexander Graham Bell’s famous first telephone call in 1876, which consisted of the message: “Watson, come here. i want you”. By 1880, just four years later, there were some 60,000 telephone sets in the US.

Neutrino communication may take a little longer to catch on. On the other hand, if there’s anything in the faster-than-the-speed-of-light result from the OPERA neutrino experiment at last year, who knows what could happen.

Ref: http://arxiv.org/abs/1203.2847: Demonstration of Communication using Neutrinos

andy March 16, 2012 at 15:02

Measurement of the neutrino velocity with the ICARUS detector at the CNGS beam

Result is that the neutrino velocity is compatible with the speed of light and is inconsistent with the OPERA results.

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