CERN Experiment Indicates Faster-Than-Light Neutrinos

intellitech writes "Puzzling results from Cern, home of the LHC, have confounded physicists — because it appears subatomic particles have exceeded the speed of light. Neutrinos sent through the ground from Cern toward the Gran Sasso laboratory 732km away seemed to show up a few billionths of a second early. The results will soon be online to draw closer scrutiny to a result that, if true, would upend a century of physics. The lab's research director called it 'an apparently unbelievable result.'" Also on the AP wire, as carried by PhysOrg, which similarly emphasizes that the data are preliminary. Update: 09/22 20:43 GMT by T : Reader Curunir_wolf adds a link to the experiment itself, the Oscillation Project with Emulsion-tRacking Apparatus, or OPERA, which "was developed to study the phenomenon of neutrino transmutation (neutrinos changing from one type to another. The speed of the neutrinos, of course, was an entirely unexpected observation."

Comments

Re:That small?

[Daetrin]

And if it's actually an accurate result then it doesn't matter how small the value is. As soon as you break the speed of light by _any_ amount then the theoretical doors are wide open. According to Einstein breaking the speed of light by even just one nanosecond is _exactly_ as impossible as Star Trek variety warp speed.

Re:Einstein replied "Check your measurements, son"

[MozeeToby]

Fermilab has a similar setup which should be able to test the results. So does an experiment in Japan, T2K, but they aren't running at the moment because of the tsunami. The actual experiment shouldn't be too hard to do if you have the equipment to make a beam of neutrinos, just point them at a detector and fire away and see how long time of flight was, which means they could probably start working on it fairly soon, though it will probably take months or years to get enough data points to be statistically significant.

What about a supernova?

[hort_wort]

Neutrinos have been observed coming from supernovae from light years away. There would have been a very noticeable time difference between the neutrinos and the light at that distance if this were true. (Any astrophysicists about to verify this?)

I'm skeptical. I think it was likely a wiring problem. It only takes a few centimeters of wire to make a 60ns delay, and these experiments are notorious for using many wires.

Re:What about a supernova?

[radtea]

Neutrinos have been observed coming from supernovae from light years away. There would have been a very noticeable time difference between the neutrinos and the light at that distance if this were true. (Any astrophysicists about to verify this?)

SN1987A results were consistent with neutrinos moving at c, although the precise detection time of the optical signal was some hours after the neutrino signal (which was found in subsequent analysis.) John Simpson tried to use an argument about times and average energies to argue for a slightly later than expected arrival time, to support his 17 keV neutrino.

These results are 60 ns in about 2 ms, or a factor of 0.00003. The LMC (home of SN1987A) is 160,000 light years away, so this would have the neutrino signal arriving several years ahead of the optical signal.

Ergo, your skepticism is justified. Good call on the comparison measure.

Error in measuring distance perhaps ?

[adisakp]

The detector is 732km away for the emitter and light travels at 299 792 458 m/s. In one billionth of a second, light only travels 29.9 cm. If they are off in the precision of measuring a 732km distance by even as little as 30 cm (~1ft), then their timings will be off by 1 billionth of a second.

Re:Einstein replied "Check your measurements, son"

[History's Coming To]

GPS will do it accurately enough. It's a 17m "error" on the part of the neutrinos, and GPS has an appreciably higher resolution than that. It's the "neutrino bunches" I'm looking at for the experimental error - this could be one of the leading-edge effects that's already known about with photons - the leading edge can arrive faster than c, but the rest of the packet is slowed down so the velocity averages out at c. Still, even if this is the explanation it would be the first time it's been observed in a massive particle as far as I know.

Re:Not so fast...

[epine]

To me a nanosecond seems pretty big. I've spent a chunk of my time over the last couple of years designing consumer circuits sensitive to changes of 10ps in signal arrival time due to changes in the surrounding bulk dielectric.

You haven't lived until you've read a datasheet with the performance spec:

Deterministic jitter: 300 fs.

Probably a PECL part, but still.

And no, they're not using an instantaneous tau to approximate a decay distribution. Anyone who has ever cooked popcorn knows better than that.

Re:Einstein replied "Check your measurements, son"

[MightyMartian]

Well, the proof, if you will, is that the faster anything travels, the more massive it becomes, and thus the more energy is required to accelerate it faster. Basically, any object that accelerates to c would become infinitely massive, or to put it another way, it would require an infinite amount of energy. In short, you cannot accelerate things to the speed of light. Photons basically come into existence at the speed of light.

Since neutrinos do have a mass, it means that CERN couldn't have accelerated them to the speed of light, let alone faster. So either we have a mundane measurement error, or some new never-before seen physical effect has been observed. But considering how intimately linked c is to so many physical constants and laws, I'd say whatever has happened cannot have violated this most essential precept, though beyond the "our ruler is screwy", the possible alternatives make one's head swim.

Re:Einstein replied "Check your measurements, son"

[Savantissimo]

"What's the alternative?"

The alternative is not that Einstein was wrong, but that neutrinos have imaginary mass rather than real mass. This is consistent with observations. We can't measure neutrino mass in experiments, only mass squared, and the error bars on those measurements persistently include some small negative numbers. (And some of these measurements virtually exclude any positive mass^2 values. Other measurements purporting to exclude negative mass^2 values may be the result of over-correction and wishful thinking.)

Imaginary-mass particles are consistent with relativity and were first theorized in the 1960s and given the name "tachyons". High-energy tachyons move near the speed of light; low-energy tachyons move at unlimited velocities. This accounts for the fact that the neutrinos from the 1987A supernova were only 18 hours ahead of the light from the explosion, despite the distance -- they were extremely high energy tachyons.

If neutrinos are tachyons, this could account for a couple of odd things about them - the exceptionally low cross section (likelihood of interaction) and their oscillating between different flavors (electron, muon, tau). Exactly how is a job for the theoreticians, but it seems to me that a neutral particle moving effectively backward in time and at unlimited velocities coupled with low energies is not often going to interact, and imaginary mass could be likened to a rotation or oscillation, much like many other things involving imaginary numbers in physics.

Physicist John Cramer talked about the idea back in 1992 in his Analog column: Neutrino Physics: Curiouser and Curiouser (Alternate View Column AV-54)

of the six most recent experimental determinations of neutrino mass, all have given negative values of the mass-squared to within the statics of the measurements. The experimental observation is that in the vicinity of the end point the yield of electrons lies above the zero-mass line, while for neutrinos with non-zero real mass, the electron yield should lie below this line. The measured mass-squared values are negative to an accuracy of several standard deviations in the most recent of these experiments.

These experimenters have been strangely quiet about mass-squared measurements with negative values. If the results had been positive by the same amount, the literature would be filled with claims that a non-zero value for the neutrino mass had been established. But a negative mass-squared is not something that can be easily publicized.

You obtain the measured mass value from a mass-squared measurement by taking the square root of the measured value. However, the square root of a negative number is an imaginary number. Thus the measurements could, in principle, be taken as an indication that the electron neutrino has an imaginary mass.

What are the physical implications of a particle with an imaginary rest mass? Gerald Feinberg of Columbia University has suggested hypothetical imaginary-mass particles which he has christened "tachyons". Tachyons are particles that always travel at velocities greater than the speed of light. Instead of speeding up when they are given more kinetic energy, they slow down so that their speed moves closer to the velocity of light from the high side as they become more energetic. Feinberg argued that since there are no physical laws forbidding the existence of tachyons, they may well exist and should be looked for.

Here's a link to another, slightly more technical look at the idea: Neutrinos Must be Tachyons by Eue Jin Jeong. Googling "neutrino tachyon" also turns up several previous discussions.