That whole neutrino thing

The past few days have been rife with headlines of the form "CERN Scientists Claim Neutrinos Travel Faster Than Light."  Sometimes the story underneath explains what's really going on, but too often it veers off into time travel and speculation that Einstein Was Wrong.  In fact, no one at CERN (which produced the neutrinos) or OPERA (which detected them) is claiming any such thing.  As their actual article makes clear, they have a measurement they can't explain and they're asking for help explaining it.

This being a particle physics article, the list of authors takes up the first two pages, but there's plenty of solid information after that.  I haven't read it in detail and, not being a particle physicist, probably wouldn't understand all the detail, but they talk a lot about how they measured both the times and distances involved, including taking into account the movement of the earth's crust and the 2009 Italian earthquake, along with a host of other factors.

They present their data and explain how they analyzed it, but specifically don't make any claims about faster-than-light particles or anything else.  They simply claim they have an anomaly they don't know how to explain and they're still looking into it.  Their precise words:

Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly. We deliberately do not attempt any theoretical or phenomenological interpretation of the results.

Statements I've seen in the press from the actual physicists involved reflect this.  A better headline would be "Scientists Can't Explain Neutrino Speed Measurement."

There is ample reason to doubt that OPERA observed neutrinos traveling faster than light.  First, the measurements underpinning special and general relativity are quite solid by now.  Relativity predicts not just that nothing travels faster than light, but a large number of other effects -- for example that clocks run faster in weaker gravity than stronger -- that have been measured to great accuracy.  The odds that those measurements are wrong are very small.  Much more likely that we just haven't found the flaw in the neutrino measurement.

Second, there is strong evidence from astronomy that neutrinos do not travel faster than light.  Supernovae put out both neutrinos and light, and they arrive here at essentially the same time, having travelled for hundreds of thousands of years.  The OPERA anomaly of one part in 4,000 or so would accumulate to 25 years or so over 100,000 years.  In practice, the neutrinos from a supernova do arrive sooner, but only on the order of hours, and astronomers have good reason to believe this is because they leave about that much sooner.  Physicist Matt Strassler has a good summary on his blog Of Particular Significance.

Even if the measurements did hold up, and it turned out that neutrinos can travel faster than the observed speed of light, we're quite a way from time travel.  It might not even be evidence that relativity is wrong.  I've seen speculation that the photon, as we already know the neutrino is, might actually be ever-so-slightly massive.  This would leave relativity's absolute speed limit intact and imply that we just hadn't had the tools to measure the difference between the speeds of photons and the actual upper limit.  I'm not sure I quite buy that that squares with all the observations of light over the last several decades, but I haven't looked at the details (and I'm still not a physicist).

Failing that, it's quite possible that relativity is only mostly right and breaks down in some extreme cases, the same way that Newtonian physics breaks down at extreme speeds and other places.  Who knows?  Such a breakdown might even clear the way for unifying gravitation and quantum mechanics.

But again, no one involved is claiming we're anywhere near that point.

[Prof. Strassler has added a post about the OPERA anomaly.  Among other things, he says that the speed of light not quite being the ultimate speed limit -- that is, not quite the c in e = mc² -- would be a plausible explanation for slightly-faster-than-light particles.  Since he really is a particle physicist, I'm going to bow out and suggest that non-physicists interested in the subject follow his blog (if you are a physicist, I'm sure you already know where to go, but then what are you doing reading this?) -- D.H.][I had originally referred to the "CERN/OPERA" anomaly, but I've changed that.  Although CERN did produce the neutrinos and its name is now associated with the results, it did not conduct the measurements in question. -- D.H.]
[And, of course, it now appears the measurements were wrong. due to a faulty cable.  Kind of anticlimactic, except to two of the project leads involved, who resigned -- D. H.]