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Ratio of real and virtual

  1. Nov 3, 2006 #1

    wolram

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    Sad i know but it is just a thought that, the ratio of real to virtual particles
    that are present at any one time may have some outcome for QG, if any one could even calculate such a thing.
     
  2. jcsd
  3. Nov 3, 2006 #2
    The ratio real/virtual is zero, since 'real' is just one value of p^2 while for virtual particles p^2 can potentially take any value.
     
  4. Nov 3, 2006 #3

    turbo

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    The ratio is dependent upon the scale at which you impose a UV cutoff for the virtual particle pairs of the vacuum. If you don't impose a cutoff, the calculated vacuum energy runs to infinity.

    If you want to read some interesting papers on this subject (the intersection of quantum theory and gravitation) Thanu Padmanabhan has authored many. Here is a link to his home page. Just click on "My Research", then "list of publications". For the past few years, he has been treating the vacuum as an elastic solid (as Sakharov did), though he has not yet given it a dynamical nature, as it must have if it is to play a critical role in gravitation.

    http://www.iucaa.ernet.in/~paddy/

    If anybody is going to make a QG breakthrough, I expect that it will be Padmanabhan or someone following a similar path - perhaps someone in the LQG field.
     
  5. Nov 3, 2006 #4

    selfAdjoint

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    In the density formalism Carl Brannen has been championing, there isn't any quantum vacumm and hance no virtual particles. For that matter Schwinger had his own formalism that eliminated the QV. Schwinger had an explanation for the Casimit effect without a vacuum or virtual particles too, I don't know if Brannen does.

    But it looks like we should take seriously the idea that virtual particles, and the quantum vacuum they live in, is just a "coordinate frame" or "gauge choice" kind of thing.
     
    Last edited: Nov 3, 2006
  6. Nov 3, 2006 #5

    wolram

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    Thank you, Turbo, SA, at least what i am thinking is not total rubbish then
    :smile: , thanks for links.
     
  7. Nov 3, 2006 #6

    turbo

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    I have Googled these fellows and have had no luck in finding relevant papers. Do you have links?

    By the way, a relevant blog with lots of interesting links is Christine Dantas' "Background Independence". I found the blog by searching for "Padmanabhan" and stumbling across a paper of his that she had linked and commented on.

    http://christinedantas.blogspot.com/
     
  8. Nov 3, 2006 #7

    selfAdjoint

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    I misspelled Carl Brannen's name, it's fixed now. He's our CarlB of "CarlB in Hawaii". His draft of his book on density formalism is at http://www.brannenworks.com/dmaa.pdf. Schwinger of course is Julian Schwinger the famous contemporary of Richard Feynman and co-discoverer of QED. His anti-vacuum formalism is called Source Theory, google on Schwinger Source.
     
  9. Nov 3, 2006 #8

    CarlB

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    Actually I believe in virtual particles, probably to a degree more than the average guy. I do have trouble believing in the vacuum.

    In my (admittedly naive) view, virtual particles are particles that are not on their mass shell. I'm not a big believer in mass, so I don't really have a problem with things running around not on their mass shell. In fact I would prefer to think that mass shells are a result of the mathematics.

    The problem is that in physics, we define a particle as something that is a eigenstate of mass. This causes difficulties when the neutrinos are analyzed because historically they were assumed to be massless, and now we have come to find out that the flavor neutrinos are not mass eigenstates. It's kind of like thinking of a mixture of the muon and electron as being a well defined particle.

    Here's what Wikipedia says:
    http://en.wikipedia.org/wiki/Virtual_particle

    Where I differ in the above is that I believe that all states are intermediate. That is, the above Wiki article says that virtual particles do not appear in the initial and final states, and so are an artifact of perturbation theory (which I think is untrue). In my version of reality, you can't talk about the initial and final states separately any more than you can talk about the intermediate states as existing separately. All these things need to be treated on an equal footing.

    Please pardon me for being completely wrong on this, I don't mean to waste your time thinking of philosophy when you could be calculating.

    Carl
     
  10. Nov 3, 2006 #9

    selfAdjoint

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    When you get some time, could you post a little more about this, if you prefer, on the Philosophy of Math and Science forum?
     
  11. Nov 3, 2006 #10

    wolram

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    It seem CarlB is thinking by (much higher methods) exactly the same as me
    sorry i do not even have a clue how to expand the idea.
     
  12. Nov 5, 2006 #11

    CarlB

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    Let me explain it this way. I'm very simple minded, but sometimes I'm not very good at saying what I'm thinking.

    To make a calculation in QM that you can compare against experiment you calculate a probability. To do this, you have to include an initial state and a final state. In the usual way that QM is done, you think of these two states as existing individually, but that is not how QM is compared with experiment.

    To compare QM with experiment, you need to have both an initial state and a final state, and it is only together that you can calculate a probability.

    So when someone comes up to you and tells you that if you rotate an initial state by 2\pi, the initial state is multiplied by -1, they are telling you something that cannot be verified by experiment. It is not a fact of physics, it is only an opinion.

    If you tell them back "no, if you rotate the inital state by 2 pi you also have to rotate the final state the same amount, and therefore you will get an overall multiplication of 1", what can they say? All they can do is tell you that they believe in the initial states and final states separately, despite there being no experimental evidence for this.

    The density operator formalism gives you a way of keeping the initial state and final state linked together so you can't go around rotating just half of the durned thing. To me, that makes it a lot simpler to understand. The density operator prevents you from going on about things that do not have anything to do with experiments.

    Plus, the density operator formalism can be geometrized (as in how David Hestenes did) very simply, much more simply than the spinors can separately. This is why I started writing a book on the density operator formalism of quantum mechanics:
    http://www.brannenworks.com/dmaa.pdf

    Now I need to add a lot more chapters to the book, but even the first chapter covers the arguments I have made above in much greater detail. What I really need is for someone to read it carefully who will look for mistakes, confusing arguments, and things that are just ugly. I'm putting out word to two of the universities I've been a member of (i.e. U. California, Irvine, and U. of Washington), looking for a graduate student who wishes to earn some pay for this, but no luck so far. I can pay with PayPal, so we can do this easily over the net.

    It's not so good as a QG fellowship in France, but it should amount to a reasonable sum of money in places in the world that are cheaper to live than California or the US.

    Carl
     
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