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A question about Planck units

  1. Jan 25, 2014 #1
    So, the three very small quantities:

    Planck length
    Planck mass
    Planck time

    Does the physical interpretation actually mean for example that when something moves, the smallest distance it can move is one Planck length, that there's no such thing as moving half a planck length?
    And further that all other lengths, masses and times are just integer multiples of their associated Planck units?

    Am I understanding this correctly?

    And if that interpretation is correct, this is proven? (i.e. tried through rigorous and exhaustive experimentation)
  2. jcsd
  3. Jan 25, 2014 #2


    Staff: Mentor

    Check out:

    Its just units that make our equations cleaner an clearer.

    It is however closely related to dimensional analysis which can tell us some profound insights.

    The most profound I know of (it's just what I know of - others may know stuff that's even more profound) is the insight it gives to the renormalization problem and associated infinities that plagued QFT for quite a while until Wilson and others sorted it out:

    It turns out the cause is a dimensional mismatch and a cutoff needed to be introduced to avoid it.

    Last edited: Jan 25, 2014
  4. Jan 25, 2014 #3
    I don't quite understand the paper about the renormalization problem.

    From the wiki article, I've arrived at the following:

    1. These Planck units are just units that are physically derived from small natural hapenstances. i.e. are not plagued by earthly or human units, like the light-year, kg, and second

    2. This DOESN'T necessarily imply that it's the SMALLEST unit of x,y or z.

    3. Most of these Planck units are either too large or small for present instruments to accurately probe to.

    Is this accurate?
  5. Jan 25, 2014 #4


    Staff: Mentor

    Yea - looks about right.

    Don't worry about the renormalisation thing - it was just an aside on how useful dimensional analysis is.

  6. Jan 25, 2014 #5
    Further research (numbers obtained from wiki, take that as you wish)

    Mass of a Proton 1.67262178 × 10-27 kg
    Planck mass 2.17651(13)×10−8 kg

    Clearly, the proton is much less massive than the Planck mass...

    Thank you Bill for clarifying this for me. Too bad, it was a cool idea originally. But, I'm glad that I'm not going to go around spreading misinformation eventually looking like a fool in front of an actual expert.
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