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Question: how do we know where (what direction, orientation, velocity) neutrinos come from? (lemmy.world)

submitted 2 months ago by [email protected] to c/[email protected]

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I've seen a few articles about neutrinos recently, high energy ones, super fast ones, ones from open space, others from "sources", and my understanding of the particle is that it's very hard to detect, passes through light-years of lead without interaction, etc. don't headings and speed require multiple readings to make? How do we know the velocity of a neutrino when we can only detect them at single points?

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[–] [email protected] 1 points 2 months ago* (last edited 2 months ago)

In the case of velocity, all neutrinos move at essentially the speed of light (they have the slightest amount of mass which slows them down, each of the three types of neutrino a different mass compared to the other two but still very, very, extremely low masses). Only neutrinos less than 2 eV are noticeably slower than light, and that's quite a low energy. The almost-exactly-light-speed has been confirmed by, among other methods, comparing bursts of neutrinos from supernovas and other intense sources to the photons coming from the same sources.

The photons move at the speed of light by definition and MeV and GeV energy neutrinos show up in detectors at the exact same time down to as close as we've been able to measure it (roughly one part in a billion, I think it is).