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B What is the Planck length?

  1. Jun 5, 2017 #1
    The definition of the planck length I have found is that it is the shortest length that has meaning. What is meant by that? Can someone give be a better definition of what it is?
     
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  3. Jun 5, 2017 #2

    Nugatory

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    There's a lot of misleading stuff written about the Planck length, and definition you've found is an example. Give this Insights article a try: https://www.physicsforums.com/insights/hand-wavy-discussion-planck-length/
     
  4. Jun 5, 2017 #3
    So does quantum theory only apply to things smaller than the Planck length? That cannot be right.
     
  5. Jun 5, 2017 #4

    Nugatory

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    You're right, it's not right.
    The Planck length is the approximate distance at which quantum gravity starts to matter. Quantum mechanics has not been completely and successfully integrated with gravity, but works just fine above the Planck length, where we don't need a theory of quantum gravity.
     
  6. Jun 5, 2017 #5
    Thanks for the help.
    Side note - for quantum gravity do you believe in String Theory or Loop Quantum Gravity. I go for LQG because I see string theory as a theory of philosophy not science. I do not think it can be proven. But then again - they said that about molecules.
     
  7. Jun 5, 2017 #6

    FactChecker

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    Theories can be supported or can survive a test, but that is not the same as being totally proven. If string theory can not be proven or disproved, that is good enough. It means that it is consistent with reality.
     
  8. Jun 5, 2017 #7
    Your right, but what I am saying is the LQG has more testable proof. Also Occam's Razor suggests LQG as it is much more simple than having the 11 plus dimensions.
     
  9. Jun 5, 2017 #8

    FactChecker

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    Good points. Simpler is better. And if it is stronger and allows some testable predictions that string theory does not, then that is better (assuming that it passes the tests). Simpler and stronger together are much better.
     
  10. Jun 5, 2017 #9
    thanks for the replies
     
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