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I was reading about the reason why we think neutrinos have mass, and it said that because they evolve over time, they must have mass because they feel the flow of time. But don't photons also evolve over time? They get red shifted, isn't that evolution over time?

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  • $\begingroup$ Where did you read this? $\endgroup$ – probably_someone Jun 12 at 1:46
  • $\begingroup$ On a lot of different sites like: google.com/… $\endgroup$ – Shantanu Jun 12 at 2:03
  • $\begingroup$ Can you quote the specific part of that site that says that neutrinos must have mass because they feel the flow of time? $\endgroup$ – probably_someone Jun 12 at 2:04
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    $\begingroup$ The closest thing I can find is: we know neutrinos have mass because they can oscillate between flavors in flight. But that is a very different statement. $\endgroup$ – probably_someone Jun 12 at 2:11
  • $\begingroup$ Does this express what you are thinking? (There are problems with it.) If you see someone traveling near the speed of light, there clock runs slowly. If they were traveling at the speed of light, their clock would stop Since light evolves, its clock must not have stopped. It must not travel at the speed of light. Things that don't travel at the speed of light have mass. $\endgroup$ – mmesser314 Jun 12 at 2:33
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they must have mass because they feel the flow of time

This is a badly designed sentence to describe a specific mathematically explained behavior of neutrinos.

Neutrinos with a specific energy and momentum vector ( whose length gives the invariant mass of the particle) as they travel change type of neutrino in an observation called neutrino oscillation.. This observation is dependent on time. There are three kinds of neutrinos whereas there is only one type of photon, so this effect cannot happen to photons.

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  • $\begingroup$ Really nice answer. $\endgroup$ – Árpád Szendrei Jun 23 at 16:56
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If you are talking about photons from galaxies and other distant sources, they are red shifted relative to the rest frame of their source because we are moving away from the source rapidly. The photons have nothing to do with it.

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