Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Indeterminism of Quantum Mechanics and incompatibility with Relativity

  1. Jun 19, 2012 #1
    As a self study it has been difficult to find time to study quantum mechanics and relativity simultaneously while obtaining my aerospace engineering degree. Nonetheless, I've made some progress in the matter.

    My point and or discussion rather herin, is this: With quantum mechanics being inherently indeterminist, and using a statistical approach to experimentation, while Relativity being a completely deterministic, it strikes me as somewhat frustrating that the two are incompatible at the moment, and we must rely on one or the other for large scale or small scale theories.

    Particularly, I find it inconsolably hard to reason that quantum mechanics is correct, in being completely indeterministic, knowing full well that a great many experiments have validated it.

    I do not posit it's invalidity, nor do I have a better idea. For this very reason that it is strange I am drawn to it's implications and consequences that seem to come out of it. Yet, I cannot fathom that it is in fact, correct to be statistical, and that everything is not well defined. I guess my question is simple, does anybody else find it as frustrating as I do that this seems to be so? I quibble intensely over the statistical nature of the wave function, and it's different interpretations, and I simply cannot seem to get a sense that it is in fact, entirely correct. I know this is still an open question, and to some extent a frivolous philosophical discussion that may have already been beaten to death. But, I find myself nonetheless wondering, is anybody else as frustrated as I am in this matter?
  2. jcsd
  3. Jun 19, 2012 #2


    User Avatar

    Staff: Mentor

    Frustrated? Nope. Curious? Absolutely.
  4. Jun 19, 2012 #3
    I should rephrase that I guess. I am absolutely curious. My frustration stems, I guess from the fact that I never seem to have enough mathematical background and/or foundation in the physics to address the formalisms and come to my own conclusion. Most of the books I've come across ask the reader to take things based on faith, without derivation, or motivation. I have so much skepticism and curiosity, but I find it difficult to satisfy it because most of the time things are motivated on faith alone, or get brushed off as being to advanced to entertain at the moment. Sidenote: I'm going into school as a fifth year senior.
    so I should have the background to at least motivate my own self study. But I always seem to get stopped in my tracks with the fact that I'm missing a real analysis class, a topology class here, or an abstract algebra class there, etc.
  5. Jun 19, 2012 #4


    Staff: Mentor

    What makes you think they are incompatible? It is not incompatible with Special Relativity and only incompatible up to a point with General Relativity - namely its fine up to about the Plank Scale where a perfectly good theory exists.

    I understand the math thing. My advice is to understand bog standard QM first and the best book I know for that is Ballentine - Quantum Mechanics - A Modern Development:

    Get it - study it and you won't be sorry.

  6. Jun 19, 2012 #5

    There are a few approaches to the unification of GR and QM, time will tell how successful they are(provided they can be tested). As Bohr once said -

    "Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it."
  7. Jun 19, 2012 #6
    rather ask yourself
    how a quantum wavefunction can be influenced by general relativity.
  8. Jun 19, 2012 #7
    Can you point me to any of the competing theories? (Other than M-Theory which as you alluded makes no testable predictions right now.)
  9. Jun 19, 2012 #8
    This may be nitpicky, but QM is not completely indeterministic. The wavefunction is deterministic, it is just certain measurements that are not. I know this is slightly different from your question about relativity, so I don't want to side track the discussion; I just wanted to point this out.

    Also, as has been pointed out, SR and QM work fine together and this has been known since Dirac came up with his equation in the 30's.

    As far as GR, I don't know much... but thanks to the beauty of Wikipedia:
    When you get right down to it though, gravity and QM and GR work fine under many circumstances.

    If you're studying aerospace engineering, a real QM book should be fine. Maybe find some friends and get into it. I enjoyed Griffiths, but the Ballentine book looks pretty cool. He uses more modern notation.
  10. Jun 20, 2012 #9

    AFAIK, the more established theories are Loop qunatum gravity and its sister Causal dynamical triangulation. There a number of small team efforts toward more exotic approaches, but it's hard to judge their merit in the abscence of testable predictions. Your questions will be better addressed in the Beyond the Standard Model, as there are people who have most of the recent LHC data and it will likely be crucial for the future unification(though even larger colliders would seem to be needed).
  11. Jun 20, 2012 #10
    I understand what you're say. When I said incompatible I think of black hole applications where it is necessary to use both theories, excluding some of Hawkings work that does in fact successfully use the two theories. But, general relativity predicts a singularity with infinite density and gravity which is just another way of saying they aren't really sure what happens.

    I sight this example, because I think any theory that is to be a true description of what nature is doing should not break down in any respect.

    I would hold merit, that this just means that the theory is incomplete, which is at best what I think is going on. I am by no means a physicist so I don't have wide sweeping knowledge to back this up, so I may be mistake in some manner. But, nonetheless I think this is the general consensus is it not? That is, without a unified theory that brings together gravity and the quantum world, our description of nature is still rather incomplete.
  12. Jun 20, 2012 #11
    I have a similar thought. We can describe a microscopic particle by a wavefunction. When we have millions/billions microscopic particles concentrated in a small area, shouldn't all wavefunctions add up to produce a giant wavefunction? Do they cancel each other out? Why don't we describe earth with a super giant wavefunction?

    Just curious.
  13. Jun 20, 2012 #12
    For a start, we don't (and cannot) know the state of each and every one of those billions of particles.
  14. Jun 20, 2012 #13
    The point of the wave function is that it does not necessarily describe a system but a probability distribution of where it is most likely for a particle to be. There are different interpretations to what the wave function means physically, as you can do a quick google search to see a few. The problem is not the wave function per se, because it is a deterministic mathematical entity. The problem comes from the measurement process which is not well defined, or even well understood as too what it must be. For instance, is it an interaction between a light signal and an electron? There is no real consensus with the issue and it is has become the central issue in interpretation of quantum mechanics. Of course this is not necessarily a problem in some physicist eyes who take the stance, 'shut up and calculate, implying such things as it works, and provides the correct answer so it is just heuristics to some.
  15. Jun 22, 2012 #14
    GR and QM overlap.....
    and test alternative quantum theories.

    general relativistic effects on quantum

    ....The proposed quantum optics experiment may also allow testing some non-standard theories of quantum fields. Some of these alternative models predict a difference in the time evolution of entangled states on a curved background as compared to predictions of standard quantum filed theory on the same space-time (for a flat space-time, such models reduce to the standard quantum field theory and are thus only distinguishable on a curved background). For example, the model proposed in Ref 27*. predicts a decorrelation of entangled photons, which can have a measurable effect on the expected visibility in our setup.


    Last edited: Jun 22, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook