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Does radioactivity suffer time dilation?

  1. Jan 15, 2012 #1
    I want to know that if one sends a radioactive material in a spaceship at high speed and bring it back, do we find that the radioactive material has decayed slower than it would on Earth or the same rate?

    As radioactivity doesn't depend on the Coulombic interaction (photons), rather other particles that are responsible for forces between nucleons, does that make any difference?
  2. jcsd
  3. Jan 15, 2012 #2


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    It is affected the same way. I don't know if an experiment such as you describe has been done, but we know that the half life of rapidly moving muons greatly increased. Otherwise very few of the muons created by cosmic rays in the atmosphere would reach the ground. A given muon would have a 50% chance of decaying within 600 meters without time dilation of the decay.
  4. Jan 16, 2012 #3


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    We know that EM is time dilated as well as the weak nuclear force and the strong nuclear force. The EM can be seen in the relativistic Doppler shift of a moving laser as well as many emission and absorption experiments. The weak can be seen in muon decay experiments. The strong can be seen in pion decay experiments.
  5. Jan 16, 2012 #4


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    Isn't the whole of high energy physics proof enough such time dilation is correct? Or are we making a distinction between atoms decaying and particle decay?
  6. Jan 16, 2012 #5


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    No. Our currently-accepted theories of the electromagnetic, weak, and strong interactions are all relativistic ones.

    When I was in graduate school 30+ years ago, one of my office-mates worked on an experiment that used beams of hyperons (sigmas or xis or both, I don't remember which). If the particle lifetimes hadn't been time-dilated, the experiment would have been impossible because the beams would have decayed before reaching the detector.
  7. Jan 16, 2012 #6
    This is only partially related to the original question, but it struck me from reading this thread.

    Can photons be said to experience time at all? Or is the duration of time in the photon's frame of reference between emission and absorption the same regardless of whether it was emitted from a quasar 10 billion light years away and hits our retina compared to if it is emitted from our LCD tv 5 feet away and hits our retina?
  8. Jan 16, 2012 #7


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    There's no sensible way of speaking of a "photon's frame of reference"... but if you could construct a massless clock that could follow the lightlike path of a photon through spacetime, the clock wouldn't tick at all. (I am being sloppy here, as this "but if you could..." statement is of the form "IF false THEN foo", and such a statement is true for all values of foo. The non-sloppy statement is more along the lines of "the spacetime interval between any two points on a lightlike path is zero").

    So in both cases (quasar ten billion light years away in our frame of reference; and LCD TV five feet away in our frame of reference), not only is the "duration of time experienced by the photon" the same, it is zero.

    You could reasonably choose to interpret this as saying that photons do not "experience time" at all... but you might equally reasonably ask what it would mean to say that they do "experience time", or how anything observable would be different if they do or do not "experience time".
  9. Jan 17, 2012 #8
    I think I was wrong to make a distinction, I realize now, 'coz the weak and the strong nuclear forces are both time dilated.

    That means that they will indeed decay slower as the strong nuclear force is involved?
  10. Jan 17, 2012 #9
    Exactly, what does "experience time" even mean for any elementary particle? I doubt we can give it a meaning, after all it's just a theoretical picture that uses particles to realize forces.
  11. Jan 17, 2012 #10


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