The guest speaker on supernova, in conjunction with Professor Johnson, said that superluminal neutrinos were detected from a supernova. The reasoning was about how we detected neutrinos from the supernova before we detected its light. So we see neutrinos before we see the star go supernova.
The way I understand this is to think of time flowing at the speed of light. So neutrinos leave the star when it goes supernova, but they travel faster than the flow of time (really the light from the supernova) so they pass time and reach us first. But what if you were at the 'surface' of the star when it blew? Would the neutrinos still reach you first, or would you read both at the same time since neither was traveling any distance (I'm assuming neutrinos and photons have the same source location).
This is like when I first learned that infinity wasn't a number. My question here is, is superluminosity a property over distance? If neutrinos travel faster than light, shouldn't they reach you first despite what your distance from the source is? Even if that distance is 0, unless getting from point A to point A requires traveling some warped path.
Hmm... my understanding of what the guest speaker said is that the neutrinos arrived at the time we would expect based on neutrinos traveling at (nearly) the speed of light. The neutrinos arrived before the supernova was detected optically, because the neutrinos are generated when the star initially collapses whereas most of the optical photons come later. The collapse of the star results in a shock wave that passes out through the gas around the star (including some of the gas ejected from the star itself). The shock wave heats up the gas atoms so that they become ionized, and the optical light we see is dominated by the emission that occurs when electrons recombine with the ions. I think what happened is we observed the optical light, and then used our physical understanding to roughly predict when the explosion occurred compared to when the optical light was mostly emitted, and lo and behold! the neutrinos came at the right time. This is a strong constraint because the supernova occured about 50 kiloparsecs away, which means that if the neutrinos had the speed (faster than light) measured by CERN, then they should have arrived 3 years earlier (instead of a few days before the optical light was detected, which is expected).
ReplyDeleteHowever if, as you question in your blog post, superluminal travel time is not linear in distance, then who knows! I think most people assume that d = v * t still applies.