What is Planck scale: Definition and 41 Discussions

In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of four universal physical constants, in such a manner that these physical constants take on the numerical value of 1 when expressed in terms of these units.
Originally proposed in 1899 by German physicist Max Planck, these units are a system of natural units because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are only one of several systems of natural units, but Planck units are not based on properties of any prototype object or particle (the choice of which is inherently arbitrary), but rather on only the properties of free space. They are relevant in research on unified theories such as quantum gravity.
The term Planck scale refers to quantities of space, time, energy and other units that are similar in magnitude to corresponding Planck units. This region may be characterized by energies of around 1019 GeV, time intervals of around 10−43 s and lengths of around 10−35 m (approximately respectively the energy-equivalent of the Planck mass, the Planck time and the Planck length). At the Planck scale, the predictions of the Standard Model, quantum field theory and general relativity are not expected to apply, and quantum effects of gravity are expected to dominate. The best-known example is represented by the conditions in the first 10−43 seconds of our universe after the Big Bang, approximately 13.8 billion years ago.
The four universal constants that, by definition, have a numeric value 1 when expressed in these units are:

the speed of light in a vacuum, c,
the gravitational constant, G,
the reduced Planck constant, ħ,
the Boltzmann constant, kB.Planck units do not incorporate an electromagnetic dimension. Some authors choose to extend the system to electromagnetism by, for example, adding either the electric constant ε0 or 4πε0 to this list. Similarly, authors choose to use variants of the system that give other numeric values to one or more of the four constants above.

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  1. D

    Can Ant-Man Reach Below the Planck Scale?

    Ant-Man can shrink to the subatomic quantum realm where space and time cease to have meaning. Can he reaches inside the Planck scale? I wanted to use the words "below" or "above" the Planck scale. But when describing inside it.. do you use "below" or "above" the Planck scale to describe inside...
  2. Jezza

    I Are Planck Units Merely a Pop-Science Fad?

    As a physics undergrad, a set of natural units is nothing strange to me, we use them all the time. Having said this, I've never used Planck units. Does any area of research use them on a typical day in the office? There also seems to be this idea that I hear from time to time, perpetuated by...
  3. A

    I Testing GR to What Energy Level?

    When we talk about energy scales, we often hear that we need new theories of gravity and particle physics when we hit the barrier that is the Planck scale. In particle physics we've only probed up to about 13TeV, which is way WAY below that level. It's easy for us to designate the energy to...
  4. kyphysics

    B Question About Planck Scale Unit

    Can someone clarify this for me. Is it the case that Planck scale unit is the smallest unit of measurement that can can observe/make, but not the smallest unit of measurement that exists? If so, is there some name for that which is smaller? Is there some fundamental measuring unit that...
  5. MSparks6

    B How can something be "Zero Dimensional?"

    I am not a physicist by trade nor do I have any experience other than what I've read over the past few years. I once read a book by Stephen Hawking or Michio Kaku (or maybe Brian Green, I can't remember) in which they said something to the effect of "even if we had the technology to see down to...
  6. O

    B Exploring the Mysterious Planck Scale: The Secrets of the Smallest Unit of Space

    It will take a particle accelerator that size of the solar system or more to peek inside the Planck scale.. does this mean the Planck scale is a no man's land.. or empty? but for a passing electromagnetic field or strong field.. doesn't it pass thru or touch the Planck scale at all? If it...
  7. A

    I Vacuum cutoff, normal ordering, Planck scale and 10^120....

    Hi all, This is a followup to a question from a couple of months ago regarding vacuum energy and cutoffs, basically to clarify some ideas. Given the usual picture of the vacuum as containing quantized harmonic oscillators at every point, it is not possible to apply a 'fixed' energy cutoff (at...
  8. F

    I Length Contraction & Time Dilation Beyond Planck Scale: Correct?

    If an object was traveling fast enough relative to an observer such that it's length is contracted down to the Planck scale (as with time), I would imagine that any further increase in speed would result in no more observable relativistic effects? Please correct me if I'm wrong.
  9. C

    B How Does Changing Gravity and Speed of Light Affect the Planck Scale?

    If gravity becomes stronger. would the Planck length becomes longer or bigger? Would speed of light c also have the same effect of changing the Planck length size? Would anyone know any java website that can make you adjust the strength of gravity and c and see how big or small the Planck scale...
  10. G

    B Below and above the Planck Scale

    Below Planck scale means inside the Planck scale, and above Planck scale means outside of Planck scale? If the term is correct.. why doesn't quantum gravity theory like Loop Quantum Gravity affect low energy experiments above the Planck scale (outside of Planck scale)? Quantum field theory is...
  11. Ken Gallock

    B Is it possible to do experiment on the Planck scale?

    Hi. I was wondering if experiments on the Planck length (about 10-35 m) are possible or not. If it is possible, what kind of experiment would that be? If it's not, then what is the problem? Or what is need to be done? Thanks.
  12. Isaac0427

    Understanding the Planck Scale

    Hi, So I am a little confused on the Planck scale. Correct me if I'm wrong (I hope this doesn't sound idiotic) but I believe that any field on a classical scale should be able to be quantized and work on a quantum scale/Planck scale, where the Planck length and the Planck time are the...
  13. V

    Understanding Planck Scale Derivation: Energy, Length, and Uncertainty

    I see that Planck scale of mass-energy is related to the corresponding length scale by application of the uncertainty principle. What is not clear for me is how we find either energy or length scale to compute the other one? What goes wrong if we assume a higher energy level than the Planck...
  14. nomadreid

    Assigning a Size to Particles and Strings: From Planck Scale to the Universe

    Except for associating a statistical mean to a large number of measurements, how can one assign a single point to a particle ? Indeed, how can one assign a size of anything less than the Planck scale? A similar question about strings: how can one talk about one-dimensional objects? A similar...
  15. F

    The end all be all of the planck scale

    I have always understood Planck time as being the the smallest amount of time that has any physical significance and the Planck scale as being the region where space and time collapse on each other and all of our mathematics fail. Why are these seemingly magic numbers the end all be all of...
  16. A

    Insight on holography at the planck scale

    Part of my basic understanding of the holographic principal is that the amount information in a given area of space is less than the surface area that surrounds that region (measured in Planck units squared). The exception being that in the case of a black hole the information stored within an...
  17. Chronos

    Is a tabletop search for Planck scale signals feasible

    This paper - http://arxiv.org/abs/1211.3816 - by Beckenstein is fascinating. I would like to know if the experimental test proposal is realistic.
  18. S

    Unraveling the Mysteries of Planck Scale Physics and Quantum Gravity

    Quantum Gravity only becomes a problem when we probe below the Planck scale. This is because we don't know what occurs inside a singularity in a Black Hole or in the initial condition of the Big Bang when the universe was supposed to be in Planck density. The Planck scale is also the origin of...
  19. K

    Why Planck Scale? Reasons & String Theory

    What are the reasons for scientists believing the Planck scale is the smallest unit of length? I have been hearing a lot of this length scale recently and i know we can't even do expiremental research at these small of levels. I'm wondering where they got the idea that strings [from string...
  20. J

    Theoretical Particles @ Planck Scale: Is there a maximum wavelength of light?

    First time poster so please be gentle... E = h * f f = c / wavelength 1) Is there a theoretical limit on maximum f (minimum wavelength of Planck length)? 2) Is there a theoretical limit on minimum f of 1 (maximum wavelength of c)? (ie// the maximum distance that a photon can cover in...
  21. R

    World within Planck Scale & QM/GR Unification

    After reading more about Loop Quantum Gravity. I realized they tried to solve quantum gravity by literally sweeping Planck scale under the rug. That is. The smallest volume and area of the spin networks in LQG is Planck size. In String Theory, they make the string Planck size too. They are just...
  22. R

    Is Quantum Gravity only related to Planck Scale?

    Is the need for Quantum Gravity only related to understand what goes on in the Planck Scale between quantum fields and curvature of spacetime where they collide. Or is it a more general solution to how quantum object is connected to spacetime (or quantum spacetime)? Let's take the example of a...
  23. R

    Exploring the Connection between Planck Scale Mass and Gravity

    Lisa Randall's states in the book "Warped Passages" dealing with the Hierarchy Problem: "The Plank scale energy determines the strength of gravitational interactions...the strength is inversely proportional to the second power of that energy...A huge Plank scale mass is equivalent to...
  24. marcus

    New Limits on Planck Scale Lorentz Violation (Floyd Stecker)

    http://arxiv.org/abs/1102.2784 New Limits on Planck Scale Lorentz Violation from Gamma-ray Burst Polarization Floyd W. Stecker 3 pages, submitted to Phys. Rev. Letters (Submitted on 14 Feb 2011) "Constraints on possible Lorentz invariance violation to first order in E/M_{Planck} for photons...
  25. D

    How could spacetime become discretised at the Planck scale?

    In early 2010 I attended this inaugural lecture by string theorist- Prof. Mavromatos entitled 'MAGIC strings'. In it he proposes that some string theory models may violate Lorentz symmetry at the Planck scale resulting in a kind-of foamy spacetime that could be observed by differing arrival...
  26. MTd2

    What is the Planck Scale for AS gravity?

    The coupling constant runs so the Planck scale changes. What is it at the AS point?
  27. M

    General relativity breaks down at Planck scale

    Why? Some measurements confirm this statement? Or this is a theoretical conclusion?
  28. E

    Does string/M-theory make falsifiable predictions at planck scale?

    Stephen Hawking's recent book The Grand Design uses M-theory to predict a multiverse, which then does away God via the anthropic principle. A common criticism that string theory makes no experimentally falsifiable predictions which is countered that experiments do not have enough energy to...
  29. Orion1

    How Do Planck Scale Dimensions Define Universal Limits?

    Planck energy: E_P = m_P c^2 = \sqrt{\frac{\hbar c^5}{G}} Gravitational radius: r_G = \frac{r_s}{2} = \frac{G m_P}{c^2} Gravitational radius is equivalent to Compton wavelength: r_G = \overline{\lambda}_C \frac{G m_P}{c^2} = \frac{\hbar}{m_P c} Planck force is a constant in the Einstein...
  30. 1

    Help: Planck Scale and Fine Structure Constant

    Could someone explain the relationship between the FSC and the Planck Scale? What are they in relation to each other. I know what the Planck Scale is, and I even have a loose understanding of the FSC, but what of them in contrast and comparison? And how does the FSC affect QM, if at all...
  31. ZapperZ

    Lorentz invariance verified almost to Planck scale?

    So whose quantum gravity theory will crash-and-burn if this is correct? http://physicsworld.com/cws/article/news/40834 Zz.
  32. U

    The structure of quantum geometry of spacetime at the Planck scale

    http://img233.imageshack.us/img233/5816/espaotempoquntico1.th.jpg Two pictures of quantum spacetimes... The theory of quantum gravity (LQG) can perform calculations and predictions on the concrete structure of space and time at the Planck scale. Equations formulas that describe...
  33. N

    Is there a limit to the information contained within the Planck scale?

    In his book THE BLACK HOLE WAR, 2008, Leonard Susskind makes the following comments around page 135-137: In the following he happens to be referring to a Planck scale cube...let's ignore that specific geometric shape... (Later in the book of course he describes his holographic...
  34. marcus

    Videos from Planck Scale conference now online

    http://www.ift.uni.wroc.pl/~planckscale/movie/ The first one I intend to watch is Steve Carlip's He is talking about similarities that have emerged among different approaches to QG. In particular evidence for reduction of dimensionality as you zoom in (inspect the spacetime geometry at smaller...
  35. marcus

    A string theorist reports on the Planck Scale conference

    Jose Figueroa is in the Math Physics group at Edinburgh and his research centers on string and susy: http://www.maths.ed.ac.uk/~jmf/ There was a big conference in Poland just now (ending today 3 July) which was interesting partly because it was mixed. Stringers gave talks alongside nonstring...
  36. L

    Why planck scale? let me explain before kill me

    Why we are searching quantum gravity effect at the Planck scale? The question seems very stupid (and may be) but let me explain. I define a quantum object when his action is of the order of Planck constant \bar h. namely A~E \delta t~\bar h. So if i take a small amount of energy E i can take...
  37. T

    Planck scale in extra dimensions

    Hi everybody, it's my first post on here but as i seem to have hit a brick wall with my work I'm hoping somebody might be able to help me :) Homework Statement I'm looking at how the Planck scale is reduced in higher dimensions (ADD theories) and I've managed to reproduce an expression...
  38. D

    Planck Scale and Unification of Forces- new research studies

    How do Planck's photon theories relate to the belief that all forces may be unified at high speeds? I understand that light waves can act as particles, and particles can act as light waves. Waves/particles emit energy. And Planck's scale is believed to be around the length of convergence of...
  39. D

    What happens with causality at the Planck scale? Can effects precede causes?

    What happens with causality at the Planck scale? Can effects "precede" causes? I would like to know what happens with causality at the Planck scale, explained in "educated layman" terms, if that's possible... :) Might effects "precede" causes in time? Do we have to redefine causality at the...
  40. marcus

    Planck scale Lorentz-symmetry test theories Amelino-Camelia

    "Planck scale Lorentz-symmetry test theories" Amelino-Camelia new paper by Giovanni A-C http://arxiv.org/abs/astro-ph/0410076
  41. marcus

    Physics meets Philosophy at the Planck scale (new book?)

    I have found references to a book that is either "to appear" or has already been published by Cambridge University Press. The book is Physics meets Philosophy at the Planck scale edited by C. Callender and N. Huggett this is apparently a collection of essays by philosophers and...