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Question about alpha, the fine structure constant

  1. Sep 13, 2010 #1
    I understand that it's been determined to have a very small value. At the same time, it is also true that gravity is incredibly weak compared to the other fundamental forces. What I'm wondering whether there might be some relationship between them?
  2. jcsd
  3. Sep 13, 2010 #2
    I'm not an expert on physical constants, but I don't think we KNOW of any direct relation between them.


    they explain the gravitational coupling constant and say:

    while the fine structure constant is explained here:

    Note there are no common terms, no apparent joint dependency.

    However, as a purely personal observation and speculation , I'd say they probably ARE related via some unknown mechanism at the big bang. We have been able to unite (unify) three of the four fundamental forces within one mathematical framework (strong,weak, electromagnetic) and these form a cornerstone of the Standard Model of Particle Physics but gravity remains an outside the model. This means that it's likely that all three forces originated from a single very high energy but unstable intial big bang condition and via a phase transition to a lower energy state " degraded" and now appear to us as separate and distinct entities. Sort of analogous to a radioactive decay, but one we can't observe and do not understand.

    So your question is analogous to asking "Are the electron,proton and neutron related?" We do know of some commonalities, but why they appeared from "nothing" (the big bang) and why they have the physical characteristics they do (mass,spin,charge,etc) are unknown.

    What we do think we understand is if any of those constants varied significantly from experimentally measured values we observe, likely our universe would not exist..... and we would not be having this discussion.
  4. Sep 13, 2010 #3

    Jonathan Scott

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    Gold Member

    The fine structure constant is about 1/137, and primarily gives the relative strength of electromagnetic interactions. An approximately equivalent dimensionless gravitational constant could be obtained by comparing the electromagnetic forces between pair of protons and the corresponding gravitational force, which is of the order of 1040 times weaker!

    Some people have speculated about various numerical relationships between them, for example involving exp(-alpha), but no such relationship is supported by standard theory.
  5. Sep 13, 2010 #4
    I should have been more clear. My question made it appear I was seeking a mathematical relationship. Rather, I am wondering if they share some root cause. For example, if gravity is actually just appears diluted due to the effects of higher dimensions, could this possibly be similarly true of alpha?

    These dimensions are often said to be tightly curled up; it seems to me there would be no constraint on the value of alpha where they are concerned.

    That could be wrong on any number of levels but it's mainly for illustration.
  6. Sep 14, 2010 #5
    I answered that: the big bang or whatever sort of "bang" you favor.

    possibly, of course, but not according to any widely studied theory.
  7. Sep 15, 2010 #6
    That isn't really an answer. That's sort of like asking why a stove gets hot when you turn it on and being told because it has a burner. Thanks for playing.
  8. Sep 18, 2010 #7
    I am new to this forum, and this is my first post =)

    I noticed that many of the questions on this site could be answered if the posters had more carefully studied Landau! This question is no exception, although the reference is very obscure.

    Check out "On the Quantum Theory of Fields" in the anthology "Niels Bohr and the Development of Physics" On page 60 in this book (about 5 pages into the paper) Landau conjectures a deep relationship between the FSC and the gravitational constant G. The idea is that the energy scale for which QED breaks down may be the same as that for which the gravitational interaction is no longer negligible. (The reason this is relevant is that if we can derive the energy scale that QED breaks down from first principles, we can determine the FSC without reference to measurement)

    When I was an undergraduate, I used to keep Landau's collected works permanently checked out of the library. If you are up for an enlightening challenge, I suggest you try to work your way through his collected works.
    Last edited: Sep 18, 2010
  9. Sep 19, 2010 #8
    Thanks for the reply. I'll see what I can do.
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