Monday, October 31, 2011

FTL Neutrino Predictions

I thought I'd jot down my ideas about the recent OPERA superluminal neutrinos at CERN.  In case you hadn't heard, the experiment found neutrinos that (as far as they can tell) move slightly faster than the speed of light.

If correct, this is a big deal, since "faster than light" in one reference frame means "back in time" in another.  Being able to send information back in time would lead to implausible, crazy new technology.

My best guess as to what's going on is that there’s a systematic error in OPERA we haven’t found yet.
My second best guess: light actually travels a little slower than c, at least around Earth. This could be due to interaction with some unknown particle cloud that’s consistently uniform and has a refractive index of 1.0002.

No, this isn’t the aether, and this isn’t experimentally contradicted by the fact that the speed of light doesn’t change as the Earth changes velocity through this field. Just as the speed of light through a moving glass rod isn’t greater or smaller than through a still glass rod (neglecting dispersion, which comes into play as the Doppler-shifted frequency of light causes n to change slightly), moving through this weakly-interacting particle background doesn’t change the observed velocity of light, unless the medium is dispersive. A good assumption would be the medium isn't noticeably dispersive: whatever transitions the light interacts with are of such high energy that photons we generate all look about the same, and dispersion isn’t measurable.

Heck, the medium could even be dark matter. This hypothesis solves a bunch of problems, like why the neutrinos from the 1987A supernova were coincident with (and not before) the photons. Under this hypothesis, the photons traveling though deep interstellar space would not be slowed by the presumably rarefied dark matter there.

Like I said, my money’s still on the possibility that there’s a systematic experimental error at OPERA. However, I find the idea of a vacuum/dark matter refractive index a lot more palatable than particles that violate causality. I haven’t yet heard a good reason to discredit this idea, so I thought I’d post it.
Background: I have an honours physics undergrad degree, but I’m now a neuroscientist. None of my colleagues are capable of evaluating this idea; if it’s rubbish please don’t hesitate to point out why.

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