Landmark: Neutrinos Seem to Break Light Speed Limit – Superluminal Motion Found in 2nd Experiment


Update: Added Glossary and Links to: the original paper, video talk, OPERA website; and step by step explanation of experiment details.

Neutrino Beam Path

Neutrino Beam Path

While working on another problem, a team of physics researchers at CERN and the Gran Sasso Laboratory in central Italy found a potentially revolutionary result seven months three years ago.

They have spent the subsequent seven months three years quietly verifying – that muon Neutrino particles seem to be traveling faster than the speed of light, called Superluminal Motion.

Prof. Dr. Antonio Ereditato

Prof. Dr. Antonio Ereditato, OPERA Spokesman

(A very happy) Team spokesman Prof. Dr. Antonio Ereditato said “We have high confidence in our results. We have checked and rechecked for anything that could have distorted our measurements but we found nothing,” he said. “We now want colleagues to check them independently.” (Quote credit: Reuters reporter Robert Evans)

The team fired some 16,000 neutrino beams from a device deep underground in a Swiss mountain — to a target some 450 miles (731 kilometers (730,534.61 meters)) away in Italy. The particles consistently arrived a few billionths of a second (about 62 nanoseconds) faster than light would have if it had traveled the same distance in a vacuum. The whole trip only takes the Neutrinos about 2.43-milliseconds. The uncertainty is 10 nanoseconds.

The Neutrinos travel through underground rock almost the entire journey, at one spot they are more than 11 kilometers deep; at another they travel almost underneath the city of Florence (Firenze).

OPERA Experiment Detector in Italy

OPERA Experiment Detector in Italy

Neutrinos are beyond invisible, they cannot be seen or detected directly because they do not often interact with ordinary matter. Since they are not affected by electromagnetic forces (that act at all distances), and though they are affected by gravity, Neutrino’s strongest force only works in the incredibly rare instants when they get exquisitely close to an atom’s nucleus. That’s why they can fly through “solid” rocks — because the rock atoms and particles are so far apart.

If confirmed, this seriously undermines Special Relativity (not General Relativity) which requires that nothing can travel faster than the speed of light in a vacuum. It would also undermine the “Standard model” for particle physics.

This does seem to confirm a 2007 experiment where neutrinos from Illinois’ Fermilab showed up early to a detector at the Main Injector Neutrino Oscillation Search (MINOS) experiment in Minnesota.

Experiment Details

The OPERA proton particle beam transforms in several steps :

1. Shooting a pulsed beam of protons at a carbon / graphite target makes charged pions (The proton gun is called SPS).

Neutrino Emitter Device

Neutrino Emitter Device

2. Positive Pions primarily decay into a muon neutrino and an anti-muon.

(The anti-muons are detected at the Swiss emitter and the muon neutrinos get detected in Italy.)

3. The muon neutrinos exit CERN and transit some 731 kilometers of rock and emerge at the Italian Gran Sasso Laboratory detector.

Neutrino Beam Path

Neutrino Beam Path

4. Some muon neutrinos oscillate or transmute (not decay) into Tau-neutrinos.

5. Some Tau-neutrinos decay into Tau-Leptons (kind of a heavy electron) – which do interact with ordinary matter.

OPERA Experiment Detector in Italy

OPERA Experiment Detector in Italy

6. Some of the Tau-Leptons are caught by Lead sheets (1 mm thick) interleaved with photographic emulsion films (along with directional trackers, scintillator strips and magnetic spectrometers).

a) Only one (1) neutrino is measured at the Italian detector, for every quadrillion protons fired from CERN’s SPS (16,111 neutrino hits for 10^20th protons fired over 3 years).

b) When a neutrino hits in Italy (about one per hour), it is timed and associated (extrapolated back) to a recorded proton pulse at CERN by using the time it would take for a photon to travel the same distance.


Paraphrasing Mitchell Porter:

This is a statistical analysis. They are not matching up an individual detection at the emitter in Switzerland with an individual detection at the detector in Italy; they are taking averages and measuring statistical distributions. The interpretation of the starting time depends on which model of meson decay is employed.

(Commentary: I am uncomfortable with the use of statistics and a model to establish when a particle left the “starting gate.” Apparently there is no Neutrino detector at the source, at CERN, to accurately determine when the neutrinos leave Switzerland. Adding one would be a worthwhile improvement (even if only to calibrate the starting time), though still not fully definitive because they are not knowingly measuring an individual Neutrino at both points.)

This experiment is analogous to having a billion identical (indistinguishable) invisible cars start a race from New York to LA, and the race begins by having sets (pulses) of drivers run down the stairs of the Empire State Building (which has the effect of spreading them out) before jumping into the cars. Then measuring the time of arrival of the handful of cars which arrive in Los Angeles.

It turns out to be critical to know precisely when the first cars leave New York, and when the first cars reach the LA finish line. (All later timings should be tossed because they can mislead.)

However, if you can credibly establish the earliest time when the first ones leave the starting gate and the earliest time the first ones arrive at the detector – (like using OPERA’s pulsed beams) then you have something that should, not will, override the use of statistics.

No Causality Violation ?

Several physicists seem excessively alarmed and have raised a concern that if this is true “it would violate everything we think we know about causality.

Well, no it doesn’t.

This Causality Violation allegation arises out of a conjecture that is a complex interpretation of Special and General Relativity combined. However, basically causality violation is when an effect occurs before its cause as in —

“There was a young lady named Bright
Who could travel much faster than light.
She took off one day,
In a relative way,
And returned on the previous night.”
Andrew Buller, English poet

Neutrinos arriving a tiny bit early is fundamentally different than Neutrinos arriving before they were sent, and the OPERA Neutrino researchers are not claiming the latter. It is similar to the distinction between “extremely difficult” and “Intrinsically Impossible.”

One analogy is the difference between
1) getting a speeding ticket – or
2) arriving before you left – so that there would be two of you.

Two dramatically different types of “impossible.”

Yes, as the researchers readily acknowledge, Neutrinos are not well understood and there could be some error in the experiment (some reasonable concern is raised about how the start timing of the particles is determined), but causality violation is not one of them.

Update: Sept 23. After listening to the webcast OPERA talk, I am not yet convinced they have this adequately controlled (I hope to replay the talk this weekend.); however this is the only weak link I can find in the experiment.

The formal presentation is set for a conference Friday. I’m not going to attend, but if you do – I would fasten my seatbelt, and expect fireworks. (Update: I am pleased to report that I was wrong. The presentation received warm applause, and sincere compliments.)

It is possible that this result could disappear, or it could withstand scrutiny and get confirmation from another experiment. Remember, that many a beautiful theory has been destroyed by an ugly fact.

If these results hold up, there is no problem for nature – only for one idea, a human created idea – Special Relativity.

Nature has no speed limit, only Special Relativity does.

I take great calm and pleasure knowing that — no idea, conjecture, hypothesis, theory or even law of physics is stronger than simple empirical data.

Verification experiments could involve sending the muon Neutrino beams from CERN’s SPS to the detectors in Japan and Minnesota. Or vice-versa – firing protons from Japan and Minnesota to OPERA. (Yes, I realize both the beams and detectors are not currently lined up.)

Update Sept 30, 2011: To improve the experiment I would like to see clear pulses of detections (as opposed to one hit per hour). To do so they might consider increasing the proton beam density by at least 3, and probably 4 or 5 magnitudes until they get neutrino hits on the order of 1,000 to 10,000 per hour.

This would considerably help my confidence that the proton pulses and detections are truly correlated.

OPERA Experiment Website

The paper: “Measurement of the neutrino velocity with the OPERA detector in the CNGS beam”

CERN Webcast of the Talk

Nature: “Speedy neutrinos challenge physicists”

Reuters article: “Particles found to break speed of light”

BBC: “Speed-of-light experiments give baffling result at Cern”

Physics paper: “About Superluminal motions and Special Relativity: A Discussion of some recent Experiments, and the solution of the Causal Paradoxes”, Erasmo Recami, Flavio Fontana, Roberto Garavaglia

BCT = Beam Current Transformer (used to time proton pulses at the “Starting Line”)

CERN = European Organization for Nuclear Research

CNGS = CERN Neutrinos to Gran Sasso

Extraction = a 10.5 microsecond Pulse of Protons from CERN’s Super Proton Synchrotron

Kicker = Magnetic Beam Switch (at CERN’s SPS) that pulls /aims beam at target 731 km away at LNGS.

LNGS = Gran Sasso Laboratory (Detector in Italy, “Laboratory Neutrino Gran Sasso”)

OPERA = Oscillation Project with Emulsion-tRacking Apparatus (“Finish Line”)

SPS = Super Proton Synchrotron (Proton pulse emitter)

TOF = Time of Flight (time between Start and Finish lines of Neutrinos “flying” from CERN to Italy; about about 2.43-milliseconds.)

TT = Target Tracker (scintillator strips)
(The OPERA paper has a minor grammatical error that could raise a bit of confusion where it says all the distances between devices are added. It is not clear what they really meant.)

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