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Planck length.

  1. Sep 30, 2009 #1
    "The Planck length is the scale at which classical ideas about gravity and space-time cease to be valid, and quantum effects dominate. This is the ‘quantum of length’, the smallest measurement of length with any meaning."

    What I am wondering about this description is the word "dominate". Does this mean quantum effects are all there is at this level? Would Quantum Gravity be needed? Does this mean quantum effects "dominate" more at the the planck scale than they do, on say, the electron? Do quantum effects on the electron get downgraded to something like "significant"? So the planck length is where quantum effects are the strongest and they get a little weaker as we move up the scale from this starting point?

    Thanks.
     
  2. jcsd
  3. Sep 30, 2009 #2

    alxm

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    That's not right. Where did that quote come from?
     
  4. Sep 30, 2009 #3

    jtbell

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  5. Sep 30, 2009 #4

    dx

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    The quote is talking about quantum effects in the description of spacetime, not about quantum effects in general. Quantum effects, of course, are important well above the plank scale in the understanding of atoms, electrons etc.
     
  6. Oct 1, 2009 #5
    Planck length is where space and time interact one on one, time is defined as the length in seconds that a photon takes to cross one planck length. We still have to measure the photon's motion to get time, but time is not one dimensional motion, energy is. Time dilates as an expanding area in all directions it is the motion we measure that gives us a direction, time gives us the possible directions.
     
  7. Oct 2, 2009 #6
    Do you think this is a solid line i.e. does the photon occupy the entire line segment, or like a bit the line segment is a path?

    If time dilates in every direction would the area of time for this measurement be R^3 as in a sphere or because it is a photon would it be a cone?
     
  8. Oct 3, 2009 #7
    Planck length is where space and time interact one on one, time is defined as the length in seconds that a photon takes to cross one planck length.

    Where can I find more about this?
     
  9. Oct 4, 2009 #8

    alxm

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    Planck units are just another set of units that are convenient in some circumstances. If you see the links on the bottom of this page (or use the search function), you can see this has come up again and again. They don't have any special significance, at least not one that's generally accepted.
     
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