Article in the CERN newsletter "symmetry breaking" has the following statement:
"Neutrinos are often the first particles to bring news of events in space to Earth, beating even light.". What does this mean?
[Physics] How to neutrinos “beat light”
faster-than-lightneutrinos
Related Solutions
Last (?) Edit: The "problem" is solved: it was mainly a problem in the timing chain, due to a badly screwed optical fibre. A high level description of the problem is given here and a more detailed explanation of the investigation is here.
List of possible systematic biases
I thought it might be a good idea to list the possible systematic biases which could lead xkcd's character to win his bet. As many physicists (including, I guess, many people from the OPERA collaboration), I think it will end like the Pioneer anomaly. Of course, the current list only contains biases which are unlikely, but less unlikely than a causality violation.
Location errors and clocks drifts
The arXiv paper studied them, and seem to exclude it. The distance seems to be known within 20 cm and the synchronisation seems to be within 15 ns (6.9 statistical and 7.4 systematic). If this would however end up to be the explanation, it would be quite boring.
Update: Rumors seems to tell that the boring explanation is the good one.
Not the same neutrinos detected
The neutrinos are emitted on a 10.5 µs window, 175 times longer than the observed effect. It might be possible that the neutrino emitted early are not exactly the same as the one emitted late. Neutrino oscillation might, for example, then make early neutrino more detectable by the distant detector.
However, the detectors were built to measure the oscillation, so I guess that the OPERA collaboration thought about it, and rejected it for whatever reason. I suppose an explanation along these lines would mean interesting new particle physics.
Update: This possibility excluded by a new experiment with 3 ns pulses.
Errors in the statistical timing analysis
The timing itself is based on a quite elaborate statistical analysis. Furthermore, the pulses are quite long (10 μs), so an error in this analysis could easily be of the good order of magnitude.
Update: This possibility excluded by a new experiment with 3 ns pulses.
Both neutrinos and photons were produced in the core of the star but photons have a much stronger probability of interacting with the outer layer of the star than the neutrinos. Thus the photons were trapped whereas the neutrinos easily escaped. This has nothing to do with mass and all to do with the cross-section of interaction with protons/electrons for photons on one hand and for neutrinos on the other.
Reading @dmckee's answer made me realise that the phrasing of the previous paragraph makes it sound like the light flash we observe might be due to those photons eventually escaping. This is not what I meant: it would take millions of years for those photons to escape, as is well known for our own Sun. It is only because the outer layers of the star are eventually blown off that we see a light flash.
I should also have pointed out that electron neutrinos can escape only in the early stages of the collapse of type II supernovae. As the density increases beyond a few times $10^{11} \text{g}\ \text{cm}^{-3}$, the scattering of neutrinos with stellar matter is sufficient to make the timescale of the diffusion of neutrinos out of the star shorter than the collapse timescale. This is a combination of increasing density (and therefore increasing interactions) and accelerating collapse. So the neutrino flash measured on Earth came from the very beginning of the evolution into a supernova.
Let me add some orders of magnitude. The cross-section of photon-electron scattering is of the order of $10^{-24} \text{cm}^2$. Compare this with the neutrino-nucleon scattering. It varies as the square of the neutrino energy:
$$\sigma_\nu \approx 10^{-44} E_\nu^2\ \text{cm}^2$$
with the energy in MeV. So that's 20 orders of magnitude, give or take.
Where does this huge difference come from? Neutrinos interact solely through the weak interaction whereas photons interact through the electromagnetic interaction with charged nuclei and electrons in the star plasma. So this is just a reflection of the relative strength of both interactions. There is no reason it should be like that: it is just the way our universe is! We would not be here to discuss these matters if it were not, actually…
Best Answer
They are probaby talking about supernovae, like how SN1987A was first detected by neutrinos before the light arrived. In that case neutrinos and photons are both produced in the core of the supernovae explosion, but they have dense clouds of gas to get through before they get to empty space and travel freely to us. Since the neutrinos are weakly interacting they can pass through the gas cloud much more easily than the photons and so break free earlier. In a fair race photons beat neutrinos (this was confirmed when the whole OPERA fiasco got sorted out).