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Domains for relativity vs quantum mechanics

  1. May 22, 2010 #1
    Popularized treatments of quantum mechanics describe it as applicable to the behavior of submicroscopic particles, while relativity applies to the very large (i.e., astronomical). This seems totally arbitrary to me. Where is the boundary between the 2 domains? Atoms? Neutrons? Quarks? Or is it perhaps the nature/properties of the bodies whose behavior is being described rather than their absolute size which is critical? I realize this may be a meaningless question to the expert but what am I missing?
  2. jcsd
  3. May 23, 2010 #2


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    It's very hard to see quantum mechanical effects in systems that aren't really small. This has to do with the fact that the bigger they get, the harder it is to isolate them from their environments. Interactions with the environment tend to "move" the quantum mechanical behavior into the environment (e.g. the air in the room where the experiment is performed) and make the system we're interested in behave classically.

    Gravitational effects are very hard to observe in microscopic systems because they are so small compared to the effects of other kinds of interactions. Consider e.g. what Newton's law of gravity and Coulomb's law say about the forces between two classical point particles each carrying the charge of an electron. They say that the electromagnetic force is 1036 times stronger than the gravitational force. (I was too lazy to do the calculation myself, so I just googled and got the number from here).
  4. May 23, 2010 #3


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    A bit in line with Fredrik's respons, but with a different perspective; an important disctinction is if you consider the relation between the observer and the system that's observed.

    QM, in it's tested domains (ie particle physics) the reference of the observer, is effectively massive. It's the entire laboratory frame, which is working as a fixed background, relative to which the interactions of the small subsystem (atom, or subatomic systems) are examined. This is how the environment, can be more or less fully controlled, and the approximation of the observer beeing a static reference reall does make sense for all practical purposes.

    This is not true for cosmological models. Some people argue, for example Smolin, and I fully agree, that for this reason the logic implicit in the quantum framework fails for cosmologial models because the approxiamation of (fixed massive reference) studying a subsystem whose environment are monitored fails. In this view, regular "quantum theories" of the entire universe, talking about the wavefunction of the universe etc, does not make any sense since it's applying a framwork that's probably valid only on small subsystems in a controlled environment, to the entire universe where clearly that assumption is totally wrong.

    So the unification of QM and GR not only concernts the quantum mechanics of hypotetical small black holes and such, or extreme high energy particle experiments where small black holes may in theory form, it is also concerned with how to unify the framework valid for isolated subsystems (where the timless dynamical laws determined the future from initial conditions in a timeless statespace) with the cosmologial models where the state space generally is evolving, and the laws can only be assessed at a particular moment in time, and the meaning of timeless laws is lost.

    For more input see these talks see

    "On the reality of time and the evolution of laws"
    and the recent
    "Laws and time in cosmology" (which I haven't had time to watch yet myself)

    found at http://pirsa.org/index.php?p=speaker&name=Lee_Smolin

    If you understand and agree with the points here, it motivates the quest for a new framework where causal laws are emergent and evolving as per some darwinian scheme, similar to what we have in biology and social interaction models.

  5. May 23, 2010 #4
    It's the Planck scale. If you have an elementary particle big enough to reach the Planck mass, or a black hole small enough to approach the Planck mass from upside, one theory would replace the another. Or rather, neither theory will work.
  6. May 24, 2010 #5
    You're missing what everyone is missing, a correct QM theory of GR.

    It seems natural to me that the solution to this long standing puzzle will be that GR operates on a different space to QM, so there is no "QM theory of GR".

    By this I mean that the QM mechanical wavefunction is a real entitity which is generated by FTL signals in a space appended to the classical (3D) space of GR. The space may be extra dimensions or some other construction which "meshes" with classical space.

    By proposing that QM operates in a different space we solve nearly all the paradoxes of QM, since FTL is allowed as long as classical information is not transmitted, and in a non-classical space SR restrictions need not apply

    I think suspicions must be aroused that this is the case, since the attempts to model everything in classical space is leading to rather ridiculous extra dimensional constructs anyway.

    Why not bite the bullet and just assume a non-classical space exists which permeates the classical universe? (eg Either continuously or as a discrete mesh?)

    I could go further and specify how this naturally allows us to explain consciousness and free-will but it'll sound a little too crazy and I'll scare people off :smile:

    A scientific test that would provide strong evidence for this (or rule it out) is to show that entanglement correlations are not instantaneous. I outlined some simple ideas in the EPR thread, https://www.physicsforums.com/showthread.php?t=395509
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