How fast do neutrinos actually go?

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    Neutrinos
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Discussion Overview

The discussion revolves around the speed of neutrinos, particularly whether they travel at the speed of light or slower, and how their mass influences their velocity. Participants explore theoretical implications, observational evidence, and the relationship between neutrino flavor change and speed.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks to determine the percentage of the speed of light (C) at which neutrinos travel, noting conflicting information found online.
  • Another participant suggests that the speed of neutrinos depends on their energy and posits that if neutrinos are massive, they could theoretically travel at any speed up to the speed of light.
  • A different participant proposes that uncertainty in neutrino flavor indicates uncertainty in mass, implying that neutrinos can travel at speeds lower than C. They reference the standard model, which posits massless neutrinos traveling at C, but acknowledge observational evidence suggesting neutrinos have non-zero mass.
  • One participant provides a calculation related to the energy of neutrinos from nuclear reactions, suggesting that if neutrinos have a non-zero mass, their speed is very close to the speed of light, with a specific mathematical expression to illustrate this point.

Areas of Agreement / Disagreement

Participants express differing views on whether neutrinos can travel at the speed of light or if they are necessarily slower due to their mass. There is no consensus on the exact speed or the implications of neutrino mass on their velocity.

Contextual Notes

The discussion includes assumptions about the mass of neutrinos and its implications for their speed, as well as references to the standard model of particle physics. The mathematical expressions presented may depend on specific conditions or definitions that are not fully resolved in the conversation.

fbsthreads
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i wanted to find out what percent of C neutrinos travel at.

so i got on the web and found pages quoting 'light speed' and 'almost light speed'.

my understanding was that they travel slower than light because they change flavour as they travel, (they couldn't change if going at light speed).

so how fast do they travel through space?
 
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I depends on their energy. If they are actually massive (as seems to be the case), it should be possible to find neutrinos at any speed (up to c).
 
Yes, *I think* inorder for there to be uncertainty in the flavour there must be unceratnity in the mass, so the mass must be non-zero. Therefore they can travel at any speed lower than c.

Of course in the standard model neutrinos don't have mass and therefore travel at c (which is why some siters say they travel at c), but as far as I'm aware observational evidence overwhelmingly suggest that neutrinos do have a non-zero mass.
 
Neutrinos from nuclear reactions have energies on the order of 1 MeV. Their mass if nonzero is thought to be around .1 eV. This means
[tex]\gamma=10^7[/tex]
But
[tex]\gamma={1\over\sqrt{1-\beta^2}[/tex]
so [itex]\beta[/itex] which is the ratio of speed to speed of light, is veryvery close to 1:
[tex]1-\beta\sim 10^{-14}[/tex]
 

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