Probably what you're thinking of is that neutrinos from a distant super nova will reach earth before the light does. This is similar to the phenomenon of electrons being able to travel through water faster than light can. A neutrino exiting the gravity well of the (ex-)star will be slowed, while a photon will not (it's frequency will shift instead). However, once the two are traveling through "empty" space where there is a negligible gravitational field, the neutrino has an advantage. Photons are effected by electromagnetic fields, while neutrinos are only affected by the weak nuclear force, which is effective only at very short distances (on the order of the diameter of an atomic nucleus). Because of this, the photon's journey through space is disturbed more than the neutrino's. If the distance traveled is great enough, the neutrino can not only catch up to the photon, but actually beat it to the destination.
Talya wrote:
okay...I am still skeptical that neutrinos travelled faster than light, but their argument is flawed, TheRiov.
They are not basing it on any measurement of the speed of the neutrinos, but rather on the fact that if Neutrinos did travel faster than light, it would violate an untested hypothesis by a 1979 scientist, so it cannot be true.
This isn't an accurate portrayal of the paper. It's really quite brilliant. It makes its arguments only from very well established theories (namely conservation laws) and experimental evidence of the maximum possible speed of electrons in a vacuum (hereafter 'e').
In a nutshell, all particle interactions -- including particle decay -- must obey a set of conservation laws. There are no known violations of these laws, at least with respect to the set of conditions over which they have domain (some of them are universal, others only to specific circumstances). The paper observes that if the Opera neutrinos truly were travelling at the velocities apparently demonstrated, they would not only be travelling faster than c, but also faster than e (which according to experimental evidence, could only possibly exceed c by very small amount). That being the case, certain types of neutrino decay are possible for neutrinos travelling faster than both c and e that are not possible for slower neutrinos without violating the laws of conservation. One such decay is the "3 body" decay where a neutrino emits a virtual Z boson, which then decays into a real positron-electron pair. Mass-energy is conserved, so the creation of this real pair reduces the energy of the neutrino. Or, from a broader (observable time scale) perspective, the neutrino decayed into three particles: a lower energy neutrino of the same flavor, a positron, and an electron. This lower energy neutrino has only about 3/4 the energy of the original neutrino.
Crucially, the probability of this decay type occurring is a function of how much the neutrino's velocity exceeds e. At the velocities apparently observed by Opera, and over the distances involved, it is vanishingly unlikely that this decay would not have occurred
at least once for each of the neutrinos emitted in the highest of their three energy brackets. In other words, if the neutrinos were travelling faster than c, then the observed final energies are inexplicable. However, they fit perfectly for sub-luminal, sub-e neutrinos.
Even so, Cohen-Glashow doesn't claim this is proof of impossibility. It merely observes that superluminal neutrinos, as observed by Opera, contradict more than "just" relativity. There is no amount of evidence that can ever really disprove what happened in the Opera experiments. All we can ever say is that we have more evidence for ~P than for P. And if the delta is large enough, we assume that any observations that seem to support P are a fluke. The Cohen-Glashow paper brings more evidence to bear against the proposition that the Opera neutrinos traveled FTL, because now any evidence supporting the laws of conservation and the speed of electrons in a vacuum is evidence against it. Or, from another perspective, it raises the bar for how much evidence will be needed in support of FTL neutrinos to turn the tide in its favor.
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