• [deleted]

I learned and figured out to do with Linux a year ago, but the cost was a bit much. So I put the plan on hold. Now I am reinspired. I just looked on Craig's list and the price for used ps3s are coming within a price range where I can start getting my personal supercomputer up and running.

Cheers LC

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Is it not true that LQG is a highly speculative theory with no proof whatsoever?

Then why are they modeling it?

    • [deleted]

    LQG has its problems, but since it is based pretty closely to general relativity the idea can't be completely wrong.

    Cheers LC

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    To see if there's any merit to it, in a relatively cheap and easy way, perhaps?

    • [deleted]

    if they are looking to do it inexpensively, why use playstations running linux?

    for half price you could build a far more powerful computer from off the shelf components.

    hmmmm.

    and regarding lqg not being completely wrong--are there other physical theories that are partly right and partly wrong? which part of lqg do you think is right? thanks!

    Hi Kev

    Interesting questions on which parts of LQG are right.

    My guess is the first bit is all a bit loopy, only some teeny bits of the middle part are ok, but the last bit is quite weighty and deadly serious.

    But more serious still, Other 'part right' theries? Almost all, including that there's intelligent life somewhere in our galaxy, and certainly the STR;

    The postulates and principle are fine, but then we go making assumptions, which is where it all went wrong. So can we not tell the difference between two electrons or bunches of protons moving through the vacuum in an accelerator at different speeds? or Voyager 2's similarly impeded progress and disturbance when she left the Heliosphere into the galactic interstellar medium? 'Holy Cow'comes to mind!

    Is that reasonable?

    Peter

    • [deleted]

    Grand Unification?

    Speaking of quantum gravity and SM unification with gravity, has anyone seen this attempt which is built upon the Mobius "Four Color Theorem ?? (URL below)

    http://www.dharwadker.org/standard_model/

    I have not seen a peer reviewed paper on this but there may be one.

    It claims that the standard model is exactly implied as a physical interpretation of the four color (Riemann surface) construction, including all gravitational fields and a neutral Higgs. Speaking of the Higgs, the developer of the model has collaborated to predict the Higgs mass using the four color theorem in the following paper,

    http://arxiv.org/abs/0912.5189

    It is interesting that the construction only allows for standard model particles and fields with Higgs and a gravity spectrum, nothing else. So it should be falsifiable quite soon by the LHC!

    Would be interested to hear anyone's thoughts?!

    Cheers

    • [deleted]

    KeV, you could make a mini-super computer with components. In fact if you use the Motorola chip employed in Macs as permutter that works with 2^n (n = 3,4, ...) Pentium III (or similar level) chips you could have a decent machine. To do this you have to be prepared to do a lot of motherboard building. Parallel linking up PS3s is much easier. If you check Craig's list you can find used PS3s at a reasonable cost. In fact you could probably recover some of the cost if you then sell the controllers.

    LQG is based on Ashtetkar's spinor approach to the ADM formalism of general relativity. That much of the theory is right on a classical level, for this is just a method for putting general relativity in a certain set of variables. The Hamiltonian is formed from the Gauss second fundamental form or extrinsic curvature of a spatial surface in a foliation. The Hamiltonian obeys the constraint NH = 0, for N = lapse function which tells how one spatial surface links to another. There is a similar momentum constraint N^iH_i = 0, for N^I the shift function telling how points are shifted between spatial surfaces. These are constraints which work in the lagrangian of the form

    L = ∫π^{ij}dg_{ij} - NH - N^iH_i,

    for g_{ij} the spatial metric and π^{ij} the momentum conjugate variable to g_{ij}. LQG then takes this and extends it into a quaternionic gauge-like theory of quantized variables. This part becomes a bit tricky, and there are variations on how this is done. This is then a way to construct the Wheeler DeWitt equation HΨ[g] = 0, for Ψ[g] the wave function(al) of spacetime.

    So this is all too close to general relativity to be completely wrong, or to not have some bearing on quantum gravity. There are problems though with the whole idea, in particular the Immirzi-Barbero function or ambiguity with that. This leads to a computation of black hole entropy which is not correct. However, the whole scheme might in the future be shown to be some constraints which can "select" aspects of string theory appropriate for the universe we observe.

    Cheers LC

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      "So this is all too close to general relativity to be completely wrong, or to not have some bearing on quantum gravity. "

      but there is no such thing as quantum gravity.

      what are the central equations of LQG and string theory?

      what do they predict?

      also, what novel physical characteristics do they represent?

      thanks in advance!

      and i have to agree with the above--why spend all that taxpayer money on playstations when a 1/4 of the funding would have bought more power without the playstation logo?

      physics doth seem more and more of a dismal science, day by day.

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      pleaze forgive me as my anglas is not very goot.

      but just because gener relativity is right does nots make lqg right also.

      rather it makes general relativity right which is not quantized

      lqg is quantized as q stands for quantum.

      so lqg which is quantized cannot piggyback on gr which is nots quantized.

      it is like saying that because a man can go into spase on a spase shuttle that the man can fly by flapping his wings.

      no it is the spase shuttle that gets the man to spase and it is general relativity that flies also, not loop quantum gravity.

      loop quantum gravity can flap its wings all it wants but it has not gotten us any sciense.

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      yah i am also puzzled by the need 4 expenisve playstion3 xbox type stations

      in my country that would buy much food for physicists who work on real topics and not wild turkey chases that are over forty years old now.

      it is as the elderly funders of wild turekey chases need to keep feeding the wild turkey even though it is not to be found ever.

      one musts wonder what physics would be like if we did physics not dead turkies

      • [deleted]

      Gravity may not quantize effectively beyond the one or two-loop limit. Gravity on the quantum tree level, with internal graphs of order ħ is not at all hard to quantize. If this is done on the post-Newtonian level is not much different from quantizing Maxwell's equation. I will say that I think fundamentally something else takes over from gravitation as the quantum field, but that is a bit of a long story. In this way quantum gravity is not some exponentially difficult nest of perturbative terms, but is a soliton dynamics. However, LQG may provide some answers for how quantum gravity should look at the O(ħ^2) level.

      PS3's are not that expensive. Building a mini-parallel processor or super computer with them is within a pretty modest budget.

      Cheers LC

        • [deleted]

        thanks lawrence,

        you seem to write many thinsg without really signifying anything. for instance, you write:

        "Gravity may not quantize effectively beyond the one or two-loop limit."

        do you mean to see that

        a) gravity has been quantized at the one loop limit

        b) gravity has been quantized at the two loop limit

        c) gravity has been *effectively* quantized at the one loop limit

        d) gravity has been *effectively* quantized at the two loop limit

        e) gravity has been quantized at the one loop limit but it has not *Effectively* been quantized at the one loop limit.

        f) gravity has been quantized at the two loop limit but it has not *Effectively* been quantized at the two loop limit.

        e) gravity has been *effectively* quantized at the one loop limit but it has not been quantized at the one loop limit.

        f) gravity has been *effectively* quantized at the two loop limit but it has not been quantized at the two loop limit.

        Gravity on the quantum tree level, with internal graphs of order ħ is not at all hard to quantize.

        So do you mean that you have quantized gravity?

        "If this is done on the post-Newtonian level is not much different from quantizing Maxwell's equation."

        What do you mean by post-Newtownian level? GR? How, if done on a different level, is it different from quantizing Maxwell's equations? When you say that it is " not much different from quantizing Maxwell's equation," what are the differences?

        "I will say that I think fundamentally something else takes over from gravitation as the quantum field, but that is a bit of a long story."

        Where can I find this long story? What takes over from gravity? Have they measures/found this yet?

        "In this way quantum gravity is not some exponentially difficult nest of perturbative terms, but is a soliton dynamics. However, LQG may provide some answers for how quantum gravity should look at the O(ħ^2) level."

        You say that LQG "may provide some answers for how quantum gravity should look at the O(ħ^2) level."

        What percentage chances would you ascribe to your use of "may." 10%, 50%. .0001%?

        That would be great if you could please provide some equations to show that LQG quantizes gravity as after researching this on the web, it appears that LQG fails to quantize gravity in any way shape or form.

        I would be happy to provide you links, if you could please provide me with definitive equations of LQG.

        • [deleted]

        hello again lawrence,

        you write in a highly speculative, unscientific manner, so that makes it hard for us to understand anything you are saying.

        for instance, consider your phraseology which i have capitalized to illustrated your non-committal obfuscation:

        Gravity MAY NOT quantize EFFECTIVELY beyond the one or two-loop limit. Gravity on the quantum tree level, with internal graphs of order ħ is NOT AT ALL HARD TO quantize. IF THIS is done on the post-Newtonian level is NOT MUCH DIFFERENT from quantizing Maxwell's equation. I WILL SAY that I THINK fundamentally SOMETHINGH ELSE takes over from gravitation as the quantum field, but that is A BIT OF A LONG STORY. IN THIS WAY quantum gravity is not SOME exponentially difficult nest of perturbative terms, but is a soliton dynamics. HOWEVER, LQG MAY PROVIDE some answers for how quantum gravity SHOULD LOOK at the O(ħ^2) level.

        So you can see, Lawrence, that I will say that I think you may not have said anything of substance in your non-committally written, unscientific paragraph. "In this way, a bit of a long story may be told, while something else may provide how it all should look which is not all that hard to do and not much different from quantizing Maxwell's equations, if this is done on the proper level."

        you write, "PS3's are not that expensive. Building a mini-parallel processor or super computer with them is within a pretty modest budget."

        yes but every penny counts when a nation is 15 trillion in debt and the above posters' points was that there is no need to advertise for playstation but that the whole point of linux is that one can save thousands by using generic processors, especially when one's "science" consists of "In this way, a bit of a long story may be told, while something else may provide how it all should look which is not all that hard to do and not much different from quantizing Maxwell's equations, if this is done on the proper level."

          • [deleted]

          I think you are caviling too much over a short paragraph. By effective I am referring to effective theory. Perturbative quantum gravity is complicated and the number of graphs is enormous for anything beyond the two loop level. As for post Newtonian calculations, you can do the calculation with a metric expanded out to two orders beyond flat metric, and the Einstein field equations reduce to Maxwell's equations. Equivalently for g_{ab} = η_{ab} h_{ab},

          then for h'_{ab} = h_{ab} - tr(h)/2 a gravity wave is given by the linear wave equation

          □h'_{ab} = 8πT_{ab}, □ = d'Alembertian

          which is elementary to quantize if you are in a source free region with T_{ab} = 0. If you include the source then you have a perturbative theory in O(ħ^n) similar to QED. So this is a quantization of weak gravity where curvatures are small. For curvatures arbitrary perturbation approach to quantization out to O(ħ^2) has been performed, but not higher.

          The cost for PS3 parallel processing probably costs less than a single mission in Afghanistan, so I don't see this as a budget breaker particularly.

          Anyway, for most of these messages I try to keep them short.

          Cheers LC

          • [deleted]

          thanks lc,

          you keep igoring the elephant in the room--actually two elephants

          1) nobody has ever seen any evidence for quantum gravity

          2) gravity has never been successfully quantized in any theory

          as quantum gravity epic fails on both a theoretical level and experimental level, i am not sure why you keep trumpeting it.

          above you write, "So this is a quantization of weak gravity where curvatures are small."

          actually, it isn't, as "where curvatures are small" is a subjective quality. unlike qed, gravity has never been successfully quantized.

          you write, "The cost for PS3 parallel processing probably costs less than a single mission in Afghanistan, so I don't see this as a budget breaker particularly."

          yes this is true but you logic makes no sense. wasting money on war does not justify wasting money on playstations when far less expensive computers with more power could have been used to demonstrate i am not quite sure what, as loop quantum gravity has never quantized gravity nor ever made any predictions which could be tested experimentally.

          best,

          :) k

          • [deleted]

          I think you are simply negative. Quarks were postulated some years before they were confirmed, and Schwarzschild found a black hole solution decades before they were found. There are some indications of quantum gravity, in particular signatures of AdS-black hole physics at the RHIC.

          Cheers LC

          • [deleted]

          hello lawrence,

          yes both quarks and the black hole were *predicted* via rugged mathemantics, not by mere wishful thinking.

          antimatter was predicted mathematically by dirac.

          so it is that i am not as you say "being simply negative." i am simply statingwhat physics is and what physics has always been.

          there is no working theory today that makes any physical prediction of quantum gravity.

          there is no working theory today that makes any mathematical prediction of quantum gravity.

          gravity has not been quantized.

          there is no evidence for quantized gravity. please do not take this personally, but there just simply isn't.

          these are merely facts, and i think you will agree that as physicists we must deal with facts not merely play with playstations all the time in fantasy worlds of groupthink where true physicits are labeled as "negative" and denied funding while all the cash goes to playstations simulating, in your words, non-theories that "In this way, a bit of a long story may be told, while something else may provide how it all should look which is not all that hard to do and not much different from quantizing Maxwell's equations, if this is done on the proper level.."

          i hope that you do not h8 me for speaking of truth and facts.

          best regards,

          k :)

          • [deleted]

          mr. crowell states, "The cost for PS3 parallel processing probably costs less than a single mission in Afghanistan, so I don't see this as a budget breaker particularly."

          well, this is perhaps an apt comparison as the federal reserve funds both the afghanistan war and modern physics, which is why mr. crowell sounds like someobody working for the federal reserve, as opposed to, say, a physicist.

          for instance, mr. alan greenpsan once said, "I guess I should warn you, if I turn out to be particularly clear, you've probably misunderstood what I've said." :)

          as lqg is alos funded by the fiat dollar, mr. crowell writes, "In this way, a bit of a long story may be told, while something else may provide how it all should look which is not all that hard to do and not much different from quantizing Maxwell's equations, if this is done on the proper level." :)

          Greenspan wrote, "The Fact that our economical models at The Fed, the best in the world, have been wrong for fourteen straight quarters, does not mean they will not be right in the fifteenth quarter," and this is pretty much the philosophy backing lqg at this point, except that lqg is supposed to be physics where hope and good intentions should never be allowed to trump physical reality.

          As millions lose their jobs and homes, I guess it is good to see others getting playstations to support the fanatsy physics that has enriched the elders who sit atop forty years of unprecedented failure exceeded only by unprecedented funding an unparalleled egoes, which have displaced true physics from the academy.

          • [deleted]

          B-modes in the CMB are a prediction of gravitons in the early universe, so this is a prediction. There are also correlations with QCD and black hole or AdS physics. I don't think hammering on a keyboard much on this is a productive use of my time. I think you two are just negative.

          Anyway, to use the economic arguments, why don't we just close out physics entirely? Come on. lets take all these speculative people in universities and throw them out on their butts? Let's close down mathematics departments while we are at it. After all, this is clearly a waste of money and is helping to keep so many millions of people out of work, right? But we gotta keep the wars on, and when the GOP comes roaring back it is possible we may get another war with Iran. Now that is a real productive use of our time and money.

          It is people like you two who have a tendency to set the world into a dark age.

          Cheers LC