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BM, initial state and information

  1. May 13, 2009 #1
    I have 3 questions regarding BM

    1. Trans-plankian problem
    Let’s roll all processes back in time from the God’s view (so we see all BM particles and their trajectories are not hidden to us). Like any single-history deterministic theory in BM the future is ‘encoded’ in the past, so, the deeper we go into the past the more precise tuning is required for all particles to end at the places they are right now (the same in true in classical mechanics because it is a single-history deterministic theory too).

    Very soon that precision becomes so high that it requires to the position of particles to be less then planks length. BM predicts that there is no fundamental length. Hence BM might be inconsistent with the future TOE

    2. As we go back in time our Universe becomes more and more dense. But in BM the total amount of information is the same, so the ‘density’ of information becomes higher and higher. Ultimately BM predicts that there should be no limit of the amount of information is a given volume. It is also a consequence of 1

    However, we have very important hints from the Nature (holographic principle and entropy of black holes) that the amount of information is limited.

    3. Finally, I wonder how BM solves the problem of the initial conditions? In single-history non-deterministic theories (CI) all complexity and symmetry breaking can come from very simple initial conditions. MWI, multiple-history theories also can derive everything from simple initial conditions (absolutely symmetric and void false vacuum for example). But it is not the case for the single-history deterministic theories.

    Just think about the deterministic theory in a context of Quantum Loop Gravity Big Bounce. The text I am typing was actually encoded in the pre-bounce universe. Weird, isn’t it?
     
  2. jcsd
  3. May 14, 2009 #2

    Demystifier

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    The problems 1. and 2. are not specific to BM, but to any theory that assumes that quantum field theory is the final theory. These problems can be avoided by string theory. If you consider the Bohmian interpretation of strings, then these problems can be avoided within BM as well.

    The problem 3. is not a problem in the covariant approach:
    http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]
    http://xxx.lanl.gov/abs/0904.2287
    because there the "initial" conditions are distributed at various times, not only at the "beginning" of the universe. This fact helps also in solving the problems 1. and 2. as well.
     
  4. May 14, 2009 #3
    This comment is only my opinion and not accepted fact:

    Information does not need 'volume' to exist - its massless and sizeless. Information creates volumes IMO. A volume is a mathematical device, not a 'real physical' one. It needs information to implement it.

    The amount of information needed to roll back the universe to the big bang is huge. Even computers cannot 'run backwards' without zillion enormous data storage requirements. Its very difficult to role back even a SME website application. (a database can be rolled back, but it needs large transactional files to do it). But the whole system rollback? Nobody does it that I know.
     
  5. May 14, 2009 #4
    All questions 1,2,3 are related. So I will begin from the last one.

    For simplicity, lets talk about the classical mechanics and infinite space. Compare the following scenarious:

    A absolutely void universe
    B Two rocks orbiting each other in an empty space.
    C Earth with Humans orbiting Sun

    All scenarios (A,B,C) are compatible with the classical mechanics. There is no violation of newtonian laws in any scenario. So, we ask a question: but why there are humans on Earth? Classical mechanics does not answer that question: the difference between the scenarios lies in the initial conditions.

    So, in many cases a theory does not answer ALL questions, it just defines evolution laws (state X(N+1) = some function of X(N) (this is oversimplification)) but not the X(0).

    Some theories (non-deterministic or multi-history) can have very simple or null initial conditions. But it is not the case for BM. So we have a question: why between billions of initial conditions, that particular one we live in had been chosen in BM?

    Regarding the superstring theory, yes, nice try, it is very easy to say that we dont know it yet, but the problem with the initial conditions exists no matter how formulas of BM will be changed in TOE, it they still one-history and deterministic.

    You can avoid this problem only by saying that in TOE (planks energies etc) BM breaks apart and becomes non-deterministic or multi-history, but it that case what is a whole point of BM? :)
     
  6. May 14, 2009 #5

    Demystifier

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    BM does not answer this question, but I do not consider this to be a serious problem. Anyway, if you consider this to be a problem, then you should admit that an analogous problem exists in MWI: why between billions of parallel universes you (the frog) observe this particular one?

    You will probably say that MWI is not a theory of consciousness (frogs). That's fine, but likewise I can say that BM is not a theory of initial conditions. So neither MWI nor BM is complete. We don't have a complete theory of everything yet. So what?
     
    Last edited: May 14, 2009
  7. May 14, 2009 #6

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    I can avoid this problem by assuming that something yet unknown determines initial conditions. (You can call it God if you like.) In this case BM still has a point.
     
  8. May 14, 2009 #7

    Demystifier

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    Neither does MWI, as far as observations by particular frogs are concerned.
     
  9. May 14, 2009 #8
    In MWI it is not a problem at all: any branch-frog observes his own Universe, so when being asked, any branch-frog replies with some confusion: "I dont know why i am in that particular branch"

    And yes, I see it as a very serious problem of BM. It is cosmology-impared: while even CI, for example, can say something 'Initial random quantum fluctuations lead to tiny differences in density in early Universe, which lead to the initial condensations of the Dark matter. DM then attracted ordinary matter, forming galaxies and stars.'

    BM can say only that Earth and our galaxy is here because it was predefined (by God?)
     
  10. May 14, 2009 #9
    Ha!
    I made a post about God before reading yours. So we had agreed again :)
    I believe in God, but I think that the design of the universe is beautiful, while the idea of putting all BM particles into their precisely-calculated initial positions using some tweezers of God (before pressing the big red button 'START') is a very ugly one.
     
  11. May 14, 2009 #10

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    Fine, then keep on with your MWI approach if you find it helpfull. I don't see it as a problem and you cannot convince me.
     
  12. May 14, 2009 #11
    Well, one obvious point is that BM can be reformulated as a non-deterministic stochastic theory just by adding a random component to the trajectories (from some underlying 'background fluctuations').

    There's also some stuff in the Cambridge BM course that I'm following about 'back reaction' where the particles affect the wave function (as well as the other way around - which is all one normally talks about). See the slides http://www.tcm.phy.cam.ac.uk/~mdt26/pilot_waves.html" [Broken] - lecture 8 p. 25 and p.31. He says something about 'life/consciousness being defined as a physical system which uses its own nonlocality in its self-organization' via some kind of particle/wave feedback loop. I liked this course up to Lecture 8 (where in places it veers off into nuttiness) - but I'm not sure I understand this. If I did it would seems to have some implications for 'particle determinism'. Does anyone have any thoughts?
     
    Last edited by a moderator: May 4, 2017
  13. May 14, 2009 #12

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    I don't see any point in adding such an artificial structure. It does not even help to solve the "problem" that Dmitry refers to.
     
  14. May 14, 2009 #13

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    I don't see a big difference between initial conditions chosen by "God" and random fluctuations in the early universe chosen by "God".
     
    Last edited: May 14, 2009
  15. May 14, 2009 #14
    In CI any fluctuation can be traced back to an original 'random' event in spacetime (in MWI the equivalent is a branch). These fluctuations appear all the time.

    In BM any symmetry breaking (by symmetry breaking I mean any symmetry breaking, for example, Earth and void space around is also a symmetry breaking, because it is a violation of isotropy of space) can not be traced to some event in t>0: all violations must exist from the very beginning, any symmetry must be broken from the very beginning, it can not break 'spontaneously'.

    Again, this is important, Deterministic single history theory can not in principle break any symmetry - if some symmetry appears to be broken then it was broken from the very beginning (even on the 'hidden' level may be)

    Hence, mass spectrum, C,P,CP, T voliations, matter over antimatter, CMB anysothropy map should be encoded in the initial conditions. based on BM, this image: http://en.wikipedia.org/wiki/File:WMAP_2008.png is a drawing of God because it was encoded in the initial conditions.
     
  16. May 14, 2009 #15
    "Might be" about some unknown theory is nothing one can object. But of course where is nothing in BM which prevents some fundamental length. For example, in my proposal for a TOE (http://ilja-schmelzer.de/clm" [Broken]) there is, on the one hand, some critical length, one which is critical for the unification of the known
    forces, on the other hand there is a continuous background.

    I would name the holographic principle and black hole entropy highly speculative theory instead of "hints from Nature". The increasing density is something which can be easily avoided, for example by a reinterpretation in terms of shrinking rulers, and, anyway, we need
    a''(tau)>0 in the early universe (something confusingly named "inflation"), so there is no necessity for a singularity. In my proposal (http://ilja-schmelzer.de/glet" [Broken]) there is no big bang singularity.

    I think it doesn't handle this problem.

    This is a weirdness typical for all deterministic theories. But deterministic theories may appear stochastic on a more fundamental level and reverse. Last but not least, for those who prefer for philosophical reasons stochastic theories, there is Nelsonian stochastics - quite close to BM but stochastic.
     
    Last edited by a moderator: May 4, 2017
  17. May 14, 2009 #16

    Singularities appear to be part of reality and the closest one is at the heart of a black hole in the centre of our own galaxy. That we don't understand infinity(yet?) is not IMO a reason to sweep it under the rag.
     
    Last edited: May 14, 2009
  18. May 14, 2009 #17

    Einstein pondered on this, asking "Did God have a choice when building the universe?". If there is only one approach to a theory of everything that could describe the universe we are in, then likely god didn't have much choice(though the term "God" is misleading and overlapping with concepts from naive religions).
     
    Last edited: May 14, 2009
  19. May 15, 2009 #18
    Then there is a hope that at planks scale different interpretations are falsiable, for example, in QLG there is no continious background AFAIK.
     
    Last edited by a moderator: May 4, 2017
  20. May 15, 2009 #19
    Loop quantum gravity has a continuous background, but the operators (for example area) do not have continuous eigenvalues.

    Or at least that is my understanding after it came up a couple time in the BTSM sub-forum.
     
  21. May 15, 2009 #20

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    That is the correct understanding. :approve:
     
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