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QG and Planck units

  1. Aug 30, 2004 #1


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    we could have a thread for talking about Planck units
    and getting accustomed to them

    Planck units are basic and everpresent in QG
    so it helps to develop a feel for them
    even tho LQG is itself based on a continuum
    the underlying spacetime is a continuum and it is only
    the geometric excitations---quantum states of the gravitational field---
    which have a discrete character

    no one says it has to be that way (at least I think they dont!)
    you could have an all-discrete model or an all-continuous model
    and right now no model has a monopoly on the future.
    but Loop is a hybrid, for better or worse, in this sense.

    the underlying spacetime is continuous but the area and volume
    operators turn out to have a discrete spectrum of possible values
    which are some miscellaneous multiples of Planck area and Planck volume

    So one tends to approach Planck units with an attitude of courteous respect, because whenever you get an answer it always turns out to be some number like [tex]\inline{3\pi}[/tex] times some planck quantity.

    So what about these units? Anyway to facilitate getting a handle on them?
  2. jcsd
  3. Aug 30, 2004 #2
    Planck's constant

    Last edited: Aug 30, 2004
  4. Aug 30, 2004 #3


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    that's a good start sol,
    I thought I remembered seeing stuff about Planck units also at
    your Quantum Gravity webpage that has the Egyptian picture with the scales.

    (I wonder if the personage in the pavillion is Maat, the godess of the scales.
    her name in hieroglyph writing is a feather)
  5. Aug 30, 2004 #4
    Use the http://wc0.worldcrossing.com/WebX?126@87.uWONcZfwCDg.0@.1dde3fdf [Broken] Type in Quantum gravity as well.

    Arivero has response here
    Last edited by a moderator: May 1, 2017
  6. Aug 30, 2004 #5
    Marcus, I have been reading about Space-Time and Space length, with corresponding Space geometry (scale), and Time Geometry (distance).

    Space Triangles,

    Eddington stated that if:"You measure with a Scale from A to B and from B to C, the sum of your readings will be greater than the reading with a scale from A to C"

    And now for a Time-Triangle the measurments must be made with an instrument which can measure Time, and the proposition then expresses that:" If you measure with a clock from A to B and from B to C the sum of your readings will be less than the reading obtained by measuring with a clock from A to C ".

    When scale is prescribed upon space as from A to B you can turn your scale around and measure from B to A , obtaining the same result. You cannot turn a clock around, ie make it go backwards in time.

    All Time-Triangles are considerably different from Space-Triangles.

    A well known law of space-trianglation is that any TWO sides are together greater than the third side. There is an analogous, but significantly different law for the time-triangle, viz two of the sides (not any two sides) are together less than the third.

    Loop Quantum GEOMETRY, must have a dual seperate and distinct representation, not of Planck scales, and thus a Planck volume and Area will not share the same Geometrics as Planck Space and Planck Time?

    The Dynamics of Planck Space goes on a different tangent to that of Planck Time!..or you can loop in space, but you cannot loop in Time.
    Last edited: Aug 30, 2004
  7. Aug 30, 2004 #6


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    making a few of the units really concrete

    I'm thinking that for may folks the Planck units are too abstract
    so although theory about them is interesting the priority should
    be direct acquaintance

    I find that planck temperature is an easy one to remember (in kelvin)

    Does anybody else find it so? does anybody happen to know what it is, without having to look it up?
  8. Aug 30, 2004 #7
    1.417 x 1032 kelvin.

    Sorry Marcus I had to look

    http://www.planck.com/plancktemperature.htm [Broken]
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  9. Aug 30, 2004 #8


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    I corrected it to be up to date,

    to be sure of the latest and best data, I hope anybody reading this
    will make it a habit to use NIST site (which gives the so-called
    CODATA recommended values)
    OK, the plug for NIST is over.

    CODATA is an international committee of experts on the most accurate scientific measurement of the constants. Its like the roman senate. Picture them in togas and have some respect.
  10. Aug 30, 2004 #9
  11. Aug 31, 2004 #10


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  12. Aug 31, 2004 #11


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    hmm, dejavu
  13. Aug 31, 2004 #12
    Please enlighten

    As we have moved to predefine measures, I thought it important for myself to look at historical information that might help me see this evolution as it came about that quantum gravity, would recogize planck values as a limit from which such geometry might emerge.

    and so it stands as of 25August.
    You know what I find strange, that to medallionize even the experts, I have found limitations in their views? This is not said out of disrespect, but to point out, some are not very familiarized with one sector, specializing in another?

    It is funny to the degree that such specialization could have walked around pround as peacocks displaying all their regalia, and not understand what they are talking about in other areas. So this going for the gold, might have been retrogressively placed badges of honor where they have mistakenly and proundly done so, from good intentions, albeit damaging to a proud tradition of specialization

    Although this historical context might have found some of us entrenched in this past, this does not mean pre-concieve summations should limit it to being so. So I have a challenge I guess, amidst such summations. :sad: :rainbow:

    Of course John Baez goes on to say.....

    So indeed the process has become "easily solved, or the beauty of simplicity" for some to sit back in the rocking chair and take a wonderous view of what we had been given to think about. So what "wisdom of the grand fathers" is to be implored here, to say that all the models of consideration might have worked to a safe and solvent ground of deduction?

    As these grandfathers sit on the porch and gaze to the past, what memories retained help then to put forth a systemic approach that the younger generation, might be endowed with procedures to follow? So we have this comlex organzation structures that must preceed from some basis and given the units of constant in planck length what do we find?

    That the visions of the grandfathers have taken us back to the very origins of our universe? What vision had we been imparted then of this grandiose view of the cosmos?

    Hermeneutics of Quantum Gravity

    Have we gone so far off the deep end then that we shall find Sokal pointing out the defiencies of what dogmas are long held too, and those not? Who is really safe, to think that as a free thinkers, they shall be open for the challenge? Maybe as flexible to undertand that the points of deprture will have told us something about the limits of perception, that today, given our theoretical models, we have a new direction from summation, that helps to point Smolin/Baez in the direction they choose to go. Or those like Lubos, Urs ,Arvin in the direction they choose to go?

    So here we sit, and amongst the toddlers that patiently wait for direction from the grandfathers, we find the stories intriguing, but none the less, the visions imparted and story told, quickly brings reality back to what sits on the horizon for the new generation. Will they warm to the romance a generation brought and find the "new, strangely comforting? It is easily disgarded for some and others, more intriguely captured souls.
    Last edited: Aug 31, 2004
  14. Aug 31, 2004 #13


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    hi sol,

    I liked your post just now because both essays were chosen
    very selectively
    the Gorelik provides good history
    the Baez "planck-node2" essay is exceptionally clearsighted about
    where planck units come from
    (and what is expected of a quantum theory of gravity)

    [edit: darnit sol, your post I was responding to just had two links
    and now you have edited and added more links so it is not so focussed.
    your first version just quoted gorelik
    and baez
    now I'm swamped]

    the two links you provided give a solid historical, theoretical-physics, and philosophical introduction in a short space, I read them with pleasure
    despite still being groggy from choral singing last night.

    I am wondering about something

    suppose the 3 or 4 of us reading this thread (Chronos, sol, olias, myself) were some highschool teachers planning curriculum and we met to think of a strategy to introduce planck units to science students. what ideas would we come up with?

    Here is another way to ask the question:

    planck units are a system of units in which the unit speed is the speed of light-----that is, one unit length per unit time works out to be c.
    And more or less everybody knows the speed of light. They know it is 300,000 kilometers a second or 186,000 miles a second or they can picture it and are familiar. So "everybody in the world" (the world of highschool teachers) knows at least one Planck unit.

    But almost nobody knows more than one. Most people's familiarity with planck units stops with the speed of light.

    If you were going to try to add to a highschool student's consciousness just one more Planck unit, so that he or she would know two units instead of only one, which would you choose?

    Or take yourself as a student. You know c is 3E8 m/s
    what other planck unit do you know by heart?
    or if you dont know any other besides c, what one would you like to know
    without having to look up?

    Any ideas?
    Last edited: Aug 31, 2004
  15. Aug 31, 2004 #14
    The quote in this link was chosen for a specific reason and was in response to your post. Reductionistic processes have to be scaled as well. There is a result from doing this?

    The view must include a look at the early unverse and a understanding of the Planck Epoch.

    Such a point was raise at a different time in response to what I am going to "tell my eight year old grandson?"

    The expansion of the post, reveals the thinking behind the post as well as what we have to be aware of as Grandfathers?
    Last edited: Aug 31, 2004
  16. Aug 31, 2004 #15
    GrandFather Archibald Wheeler Greatest Blunder?

    Reductionistc processes and the uncertainty

    Even in our long held dogmas there is always room to grow. This is a important lesson and no body has enshrined this principal more then Self Adjoint. I have watched the years in his developement along with my own.

    We have to be careful about our summations.
    Last edited: Aug 31, 2004
  17. Aug 31, 2004 #16


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    stop right there, dont add anything to this post by further editing
    you have a good idea to think about
    the grandson problem. lets focus
  18. Aug 31, 2004 #17


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    you have put the problem more clearly than I did (with my curriculum committee of science teachers)
    it is the 8-year-old grandson problem

    our culture knows the speed of light in the sense
    that 8-year-olds know 186,000 miles-----or 300,000 kilometers---a second
    and sometimes talk about it with the Baba
    this is a sign that it has seeped into our culture

    what other planck quantity (if any) can the Baba
    and the grandchild discuss? and how could it be introduced
    in a natural way (as if not in school)?
  19. Aug 31, 2004 #18
    It is indeed a perplexing problem :smile:

    So indeed a amplitude of the string virbationally helped us to envision sound as a value in how the vacuum might be disturbed? How simple this view when we are amazed at the valuation of sound might garner geometrical proclivites to arrange things this way, or that.

    Here son, watch what happens to a string when I weight the gourd full of water. Can we not alter the sound? Watch son, as the particles arrange themselves on the drum. Let's take this aluminum bar and see why it rings, from beyond the scope of our vision?

    Imagine son, that if we could shrink this bubble that we have created from this vast ocean of the Planck epoch, how we could shrink it's shape using sound. So in this place of sound, nodal points like the patterns on the drum tells us something about the nature of the universe?

    I do not want to defer from the problem posed.
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  20. Aug 31, 2004 #19


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    indeed we are focusing on planck units (rather than on stringtheory as in your earlier post)
    but the idea of music still applies----and can be culture doorway.

    all the planck units are so closely interrelated that they are, in a certain sense the same unit

    the planck frequency is the one which has planck length as its wavelength
    and also a photon with that frequency has one planck unit of energy

    and so in this case the "feather" or unit is several things at once: both a temperature and a speed, a length and an energy, a brief duration of time and a frequency too high to be heard...

    "For the ancient Egyptians, exactitude was symbolized by a feather that served as a weight on scales used for the weighing of souls. this light feather was called Maat, goddess of the scales. The hieroglyph for Maat also stood for the unit of length---the 33 centimeters of the standard brick---and for the fundamental note of the flute."
    Last edited: Aug 31, 2004
  21. Aug 31, 2004 #20

    Consider the amplitude of the string then in relation.

    There are all kinds of measures in that picture? Look at the chair :smile: But the deepest and most troubling, is that we associate heat with extreme energies and how capable would this be of relevance in any mind?

    So we change our glasses. Now all we see is vibration. Some notes, very high and some very low? I have a model for such reductionistic processes. It's called a pyramid. At the tip, is the finest matter dstinction we have. At the base, our earth. Now consider the "amplitude of the string" in relation to the matters.

    Some of the paths energy(uncertainty asks which path will emerge) can take, are as diverse as the choices given to us in Pascal's triangle, but all pathways are conclusive, as sound is, in its consolidation(earth)

    But indeed imagine 3(triangle) in to 4(square) :smile:
    Last edited: Aug 31, 2004
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