# Neutrino arrival time

## Main Question or Discussion Point

If you produce a lot of neutrinos over a short period of time, and then let them travel a distance long enough that their rest mass makes an appreciable difference in their travel time compared to photons emitted at the same time:

Will they arrive:
1) At 3 separate periods of time because the 3 mass eigenstates each have a different rest mass, speed and arrival time, or
2) At the same time, because each neutrino oscillates through all 3 mass eigenstates, and over several oscillation periods has a single average speed and a single valued average rest mass?

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It depends on what exactly you mean by "If you produce a lot of neutrinos over a short period of time".

mfb
Mentor
You can always describe the time-evolution in terms of the independent mass eigenstates (neglecting interaction with matter on its path). The production is a superposition of those 3. If you somehow manage to produce a neutrino with a very precise, well-defined energy and production time, I would expect separation of the mass eigenstates with flight distance.
However, I do not see any way to test this - even with low-energetic neutrinos from fusion processes, the gamma factors are somewhere at ~10^9, giving v=(1-10^18)c or 1ns separation after several years (and light-years!) of flight.

However, I do not see any way to test this - even with low-energetic neutrinos from fusion processes, the gamma factors are somewhere at ~10^9, giving v=(1-10^18)c or 1ns separation after several years (and light-years!) of flight.
Or 1 ms after 10^15 seconds... meaning 30 million years.

Hundreds of millions to a few milliard lightyears are typical distances to gamma ray flashes.

Do gamma ray flashes emit any neutrinos?