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What can the rest frame of a neutrino possibly mean?

  1. Sep 24, 2011 #1
    this thought was inspired by the recent news about FTL neutrinos. of course i suspect their instruments are broken and that no such thing happened, but regardless, the question stands:

    it's easy to talk about the rest frame of classical objects where the notion of "trajectory" applies and velocity has an unambiguous meaning. but neutrinos and mesons are not little tennis balls zipping about. how does one make sense of boosting into the rest frame of a neutrino, when the "momentum" of such entities is defined by pointwise measurements and not a time derivative of a trajectory? or how does one make sense of the proper time of a meson, and their longer-than-expected observed lifetimes as evidence for relativistic time dilation? a meson is a quantum entity, not a ball! it does not follow a classical trajectory whose time derivative yields its momentum, and hence cannot be interpreted as "moving with velocity v" wrt an earthbound laboratory. i can't see how the relativistic notion of velocity and boosting into a rest frame can possibly apply to a meson, or neutrino, or any atomic entity.
  2. jcsd
  3. Sep 24, 2011 #2
    The concept of trajectory becomes fuzzy, but nevertheless valid to some extent. An analogy would be a trajectory of a short pulse of light in space, or of a ripple in a lake.
  4. Sep 24, 2011 #3


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    Gold Member

    Don't you understand how the extreme dilation of the half-life of the muon was one of the first tests of Special Relativity? From the ground Frame of Reference, the muon's half-life is much longer, allowing them to survive all the way to the ground. From the rest Frame of a muon where its proper time is normal, the ground is much closer to it at the time of its formation so it quickly gets to the ground.
  5. Sep 24, 2011 #4


    Staff: Mentor

    Regardless of whether it is a pointwise measurement or the time derivative of a trajectory there is only one frame where the momentum is 0. That frame is the rest frame.
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