lördag 28 maj 2011

Monstrosity of Quantum Mechanics 5: Passive Observation Impossible

Is passive observation really impossible in the world of quantum mechanics?

David Albert, together with Barry Loewer inventor of a version of the Many-Worlds Interpretation referred to as Many-Minds (different from the one I suggest), tells us that the physical process of making an observation in the quantum world necessarily interferes with what is being observed. In other words, the ideal of fully passive observation of classical mechanics, cannot be upheld in quantum mechanics. The observer will always interfere more or less with what is being observed. Albert tells us that this is the big difference between classical and quantum mechanics.

But is this true? Is fully passive observation impossible in quantum mechanics? Maybe, or maybe not, depending on what is meant by an observation. A human being can make observations in different forms:
  1. Inspection of an analog physical apparatus capabable of measuring some phenomenon.
  2. Inspection of digital simulation of the phenomen.
Here 2. represents a digital simulation based on solving the Schrödinger equation describing the phenomenon, e g the ground state of an atom, and observing its energy, while 1. would be to directly observe the emission spectrum.

Th nice thing about 2. is that it is a completely passive observation, in the sense that the computational process is independent of the observer making the final observation of the energy as a number coming out of the computation.

So maybe passive observation is possible in quantum mechanics. Maybe quantum mechanics is not so different from classical mechanics. Not so mysterious?

15 kommentarer:

  1. If you are willing to sacrifice locality there is an interesting phenomena called interaction-free measurement where you can observe an object without interacting with it. If you want to know how, study quantum optics.

    When thinking about it, the issues you've been raising the last posts are treated in the field of quantum optics and quantum field theory. Maybe you can find some answer studying the fields.

    Maybe you are reinventing the wheel?

  2. A simulation (digital or not) is NOT an observaton!

  3. I don' t think so. Computational aspects of quantum mechanics have not been properly explored.

  4. But i get the feeling that you are touching on more philosophical issues, like if the Schrödinger equation and its solutions are to be seen as something fundamental, and I guess the answer is no. Nobody these days thinks that. It's only an useful computational device used to calculate stuff in a low energy (non relativistic) setting.

    For instance, look upon how it is used in nuclear physics when calculating properties for certain kinds of nuclei in the shell-model. Sometimes very useful, other times not so much. Nothing fundamental here, only a computational device that sometimes are successful, other times not.

    The whole observational issue is of philosophical nature. Maybe you should read Henry Stapp who touches upon those issues.

  5. How do you know that watching the result of a simulation is not an observation?

  6. If the Schrödinger equation is not fundamental physics, what is it then?

  7. The Schrödinger equation is fundamental in "classical" quantum mechanics yes, but one can not in good faith say that "classical" quantum mechanics is fundamental.

    Non the less, "classical" quantum mechanics is well defined with von Neumanns axiomatisation and the work of Dirac, but not fundamental as in able to describe reality without flaw.

    What is fundamental in your point of view?

  8. Claes, I'm genuinely interested in what you consider to be fundamental physics. Are we talking TOE-fundamental?

    One of the Schrödinger equations biggest shortcomings would probably be its unability to describe particle creation and annihilation, and therefore in extension unfit to describe relativistic phenomena like high energy particle interactions. Well not really that high, a gamma above 1.022MeV does the trick for an electron-positron pair.

    That is a short example showing that the Schrödinger equation are not of a fundamental nature without going through philosophical assumptions about the reasonable/unreasonable reality of n-particle Hilbert spaces.

  9. I think the Schrodinger eq is a fundamental model of quantum mechanics, but a model which is not properly understood, in fact misunderstood, and in this sense
    not as fundamental as it could be. My hope is to make the model meaningful without resort to statistics.

  10. In your work, have you seen any possibility to describe particle creation and annihilation? A fundamental quantum mechanic description must incorporate this phenomenon since it is a more then readily observeable phenomena.

    Without that ingredient the model can not possibly be considered fundamental. Quantum mechanics is so much more than low energy atomic physics.

  11. Why do you require creation and annihilation? I am not at all convinced that
    particle interaction requires creation/annihilation of transmitters of forces.

    I think the field is the primary concept and e g mass appears where the gravitational field is strong. See one of my google knols on this subject: The hen and the egg of gravitation.

  12. You misinterpret my statement about creation/annihilation. It's not solely about force interaction and virtual particles (although quite a deal of the standard model is on solid experimental ground) but about real measurable particles that stems from particle reactions. These kind of reactions, where positron-electron creation/annihilation is one of the simplest, can easily be monitored with simple particle detection and coincidence measurement techniques. A lot more intricate experiments with this flavor are now conducted at CERN in the LHC.

    How do you count particles before and after an reaction with the solutions to the Schrödinger equation?

  13. I have not considered this question which seems to be beyond the Schrodinger equation.

  14. Dear Claes,
    I agree with comments by "anonym":
    "Anonym sa...
    But i get the feeling that you are touching on more philosophical issues, like if the Schrödinger equation and its solutions are to be seen as something fundamental, and I guess the answer is no... It's only an useful computational device used to calculate stuff in a low energy (non relativistic) setting." He gives the obvious limitation :lack of particle-antiparticle creation". I would add more obvious limitation: the the time dependent Schroedinger (TDSE)equation describing so nicely the spectra of a hydrogen atom fails after a nanosecond of time evolution: think about preparing the atom in a excited 2p-state and evolve this state using TDSE which predicts that the system stays in this states infinetely long. To get the decay
    of the 2p state you must introduce new degrees
    of freedom: the second quantized electromagnetic field and couple it with the atom. Thus you get the spontaneous emission from the 2p state but you had enlarged the 2-body (electron-proton) a system containing infinite degrees of freedom with nasty divergences.

  15. Your comment adds to the monstrosity.