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Fine structure constant increase with energy?

  1. Aug 14, 2010 #1
    Hope someone can help, I am currently studying an Open University course and I am a little confused by a statement in one of the textbooks.
    It says that the value of the fine structure constant increases with collision energy (in Electron/Positron annihilation).
    I am probably being stupid, but I thought it was a constant so by it's nature it would not change? Sadly the book does not elaborate further so I hope someone can help me understand this as I've searched everywhere and can't really find anything to explain this statement :) Thank you for your patience.
  2. jcsd
  3. Aug 14, 2010 #2


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    Welcome to PF. I think if you use the search feature and enter: Fine Structure Constant you will find 11 pages of posts that will explain the question you asked, and then some. If you do a little digging, I am sure you will find your answer, just like I did. Good luck. Please report back what you found, and if it opened up a whole new series of questions in your mind, because, I am betting it will.

  4. Aug 14, 2010 #3
    The book is correct. I'm not sure exactly what kind of explanation you'd like, so I guess I'll just point you to the coupling constant article on Wikipedia:


    In a quantum field theory, the coupling constants usually depend on an energy scale. In QED, the coupling grows with energy (unlike QCD, which is asymptotically free at high energy). In the case of QED, it doesn't change very quickly with energy scale, however. (According to the Wikipedia article the fine structure constant only changes from 1/137 to 1/127 when you go from very small energies all the way up to 90 GeV.)

    *Edit: Looks like I was too slow again.
  5. Aug 15, 2010 #4
    Thanks both of you :) Yes I think I understand know, what threw me was that this is a Level one book and it put this in there without any warning and not even a statement like 'while this may seem to make no sense it does, but we will not be exploring why in this course' which it has done for other subjects.
    Thanks again!
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