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I Why do we need time dilation to explain muons reaching earth

  1. Jun 12, 2016 #1
    As I understand it muons have a half life of 2.2 microseconds, thus, at the speed of light cannot get to the earth. But based on exponential decay, of every billion muons which head or way, about 70 will actually get here. Using time dilation the full billion will get here.
    Do we need a billion to say we have muons, or is 70 enough?
     
  2. jcsd
  3. Jun 12, 2016 #2

    Ibix

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    You are correct that the simple arrival of muons at the Earth's surface doesn't tell you anything. However, if you assume that their half life is 2.2μs in our frame then you are making predictions about the numbers you would expect to see at different altitudes (and their production rate in the upper atmosphere, which would need a very good explanation), which can be tested. We have done tests at different altitudes (see the experimental basis for SR sticky thread at the top of this forum) and the decay rates don't support a 2.2μs half life when measured in our frame.
     
  4. Jun 12, 2016 #3
    Many thanks. Your reference to test at altitude would be of great interest. I have found predictions based on time dilation but so far have not found actual tests. If you had a more specific reference for me that would be appreciated.
     
  5. Jun 12, 2016 #4

    Ibix

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    The experimental evidence thread is a single post with a link to an FAQ which is a list of formal references with some discussion.
     
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