If you were wondering why the Italian(*) OPERA collaboration announced a finding that will almost certainly be proved wrong, wonder no more. They almost certainly don't believe it themselves, but their experiment relies on the techniques that gave the anomalous result. If they are making a mistake somewhere, they badly want to know where it is. If they aren't--they're happy.
I read their paper (arXiv:1109.4897) and don't see where the problem is, but I'd hardly expect to with the level of detail provided in the paper. You need to get deep into the details; testing the cables and the timing every way you can--and I can't do that. I still think there's a mistake somewhere.
But just for fun, suppose there isn't. Suppose that muon and tau neutrinos of > 5 GeV moving through rock in the Earth's gravity do in fact more faster than the speed of light in a vacuum. What could the reason be, and what might happen next?
Before I mention options, bear in mind that we have several outstanding puzzles in physics:
- Reconciling General Relativity (gravity) and the Standard Model (strong and electro/weak forces in a Quantum Mechanical framework). There is no unified model. String theory has been popular for 20 years because it offered a framework for doing this, but so far it hasn't worked. At all.
- Dark matter. Nobody knows what it is, though it pretty plainly seems to be there. Maybe it is particles and DAMA saw it. Maybe not.
- Dark energy aka acceleration of the universe's expansion. It seems as though the universe's expansion is speeding up, and you can account for that and make some models of the history of the universe work if you throw some "dark energy" into the picture. There's no other evidence for it though, so we should really call this the expansion acceleration mystery.
- There are a few little fringe items like the Pioneer probe acceleration, where the devil is in the details: is this the effect of known physics or something new?
OK, let's see, suppose OPERA's result is correct:
- All neutrinos go faster than light
We know from SN1987A that O(10MeV) electron neutrinos and anti-neutrinos move at very nearly lightspeed (within a fraction of 2E-9 of the speed of light)--they arrived only hours before the light arrived. However, the muon and tau neutrinos only a thousand times more energetic move at a fraction of 2.5E-5 faster than light.
This isn't like the tachyon model, where the speed decreases with energy. Nor does it look like special relativity with a different value for C. Maybe something like v=c+ε E or +ε E^2 might describe it. It is pretty hard to motivate something like that from either classical or relativistic physics. But if it is, it is, and there's something very different about neutrinos.
- Only μ and τ neutrinos go faster than light
This is really weird; just like the previous approach but with electrons and electron neutrinos different from other flavors. The elementary particle hierarchy is now tied into the structure of spacetime and superspacetime. This would be wild.
- Neutrinos speed up in a gravity well
They'd have sped up in SN1987A too, but once flying free they'd be back near C again, so there wouldn't be a huge effect.
In this case some particles (neutrinos) see a different spacetime structure than other particles do. Once again we have a new link between particle type and gravity. The hot dark matter models have to be redone--I'd think it would make the halos larger and less dense, so you'd need more cold dark matter.
- Neutrinos have access to extra time dimensions
I tried to figure out the consequences of multiple time dimensions some years ago, but I assumed that the observer would never see anything faster than light. If that assumption was wrong, this is exactly the sort of thing you would see: the particle follows a world-line where it moves at lightspeed (or nearly; neutrinos turn out to have mass after all), but we only see one component of the time, so it seems to be going faster than light. I'll have to go back and rework that analysis, just for laughs.
- Neutrinos interact with rock to "go faster than light"
I have no good model for how this would work, but with time we could come up with some sort of phase velocity description of the neutrino that might allow such an interaction. Beta decay starts to look very strange--we'd have to go back to square one for a new model. UPDATE There's a paper on this option now:, and a hat tip to Dorigo.
But is probably some boring clock problem.
(*)Yes, it has collaborators from Croatia to Korea, but it is sited in Italy and Youngest Daughter loves Rossini, so what else can I call it?
UPDATE: It used to be said that every French soldier had a field-marshal's baton in his knapsack. Something similar is true of physicists...
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