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Is the Planck length relative?

  1. Jul 6, 2012 #1
    If space contracts relative to the motion of an observer, would two observers traveling at different speeds disagree on the Planck length? Or is the Planck length constant such that two observers would agree on the Planck length, but would disagree about how many Planck lengths long certain objects were. Show them an object one Planck length long and they would both agree about its length. But show them a much longer object and one might say that it is 1000 Planck lengths long while the other would see it as being only 900 Planck lengths long.

    Is the Planck length relative or constant?
  2. jcsd
  3. Jul 6, 2012 #2
    I would say it's relative, as it's just a unit of distance, so I don't see why it would be any different than say a, picometer!

    This is just me thinking, so I would wait until someone who is more knowledgeable on Planck's length posts.
  4. Jul 6, 2012 #3


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    The Planck length is a combination of physical constants that has the dimensions of length: √(ħG/c3). It is only an order of magnitude scale, thought to be the scale at which the quantum effects of gravity become important. It is not the actual length of anything. And since the constants that make it up are the same in every reference frame, so is the Planck length.
  5. Jul 6, 2012 #4
    Bill K, thanks, and sorry, because the formula √(ħG/c3) really doesn't mean much to me, but I'm trying my best to decipher its meaning. I think it means that the Planck length is in some way the relationship between the speed of light and gravity, and that this relationship will hold true no matter the reference frame of the observer, and since C and G are constants, the Planck length will also be constant. So the Planck length is more a relationship, than an actual physical length. Thus it is a misapplication to try to use the Planck length as a measuring tool.

    Am I even close?
  6. Jul 6, 2012 #5


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    And the Planck constant.

    You can say "this object has a length of 10^35 planck lengths" - and this number will be different for observers moving relative to you (as the Planck length is absolute, but the length of the object relative). However, those numbers have no physical meaning itself, like "1m" is just the length relative to a different scale.
  7. Jul 6, 2012 #6


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    Fiziqs, G is Newton's constant of gravitation - it tells how strong the gravitational force is. ħ is Planck's constant - it tell us how much quantum mechanics affects things. c of course is the speed of light. If you're not familiar with these terms, a good place to look them up is Wikipedia.
  8. Jul 6, 2012 #7


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    Being picky but this has always bothered me. h is Planck's constant and ħ is


  9. Jul 6, 2012 #8
    Bill K, I have spent so much time on Wikipedia lately trying to assimilate as much information as I can. But so much of the information contained in the physics articles just goes right over my head. But I'm trying. Slowing but surely I'm putting the pieces together. I can be very tenacious when I want to be.

    I'm trying to teach myself QM using the "Hole in the wall" method. http://www.ted.com/talks/sugata_mitra_the_child_driven_education.html

    Basically I have this box in front of me called the internet, and with it I have access to an amazing world of information. And I've always had a fascination for physics. People have an amazing ability to learn when they're curious. Unfortunately the members here on PF have become my "Granny cloud" Those are the people that I go to when I can't figure something out on my own, or I have an idea that I want to bounce off of someone. Consider me like the two year old with an annoying habit of always asking why. I know that it can be irritating, but I'll try to keep it to a minimum. And I'll try to remember that the members here are much smarter than I am.

    Anyway, I appreciate any and all help. Any input is good input.
  10. Jul 6, 2012 #9


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    Whatever you do then, don't read the sci-fi novel "Eon" by Greg Bear. Throughout the book instead of h-bar he calls it "slash-h" :yuck:
  11. Jul 6, 2012 #10


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    Thanks for the heads up. :approve:
  12. Jul 6, 2012 #11


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    Also try to remember that none of us are getting paid for this, unlike teachers, professors, tutors, etc. :wink:
  13. Oct 3, 2012 #12
    Here is the explanation in this pdf document,which might help you.

    Attached Files:

  14. Oct 3, 2012 #13
    Yes. I have worked on Planck Lengths for about a year, the world is made of fundamental particles only by theory but there is strong evidence that the Planck Length has a fundamentally relative association.
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