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B Is quantum physics a theory of unknowledge ?

  1. Aug 9, 2015 #1
    In quantum physics we don't describe the trajectories of particles is that because it is just the description or is it because there is no more fundamental way to do it ?

    Could we say that the fact we don't know the intermediate position change the result ?
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  3. Aug 9, 2015 #2


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    Everything in physics is "just because it is the description". This is what science is about, finding a description which is as good as possible. Older and worse descriptions may still be good enough in certain situations, such as classical mechanics in the classical limit.

    It is not clear to me what you mean by "there being a more fundamental way". What we have found is that at the quantum level, it simply does not make sense to talk of the trajectory of a particle.
  4. Aug 9, 2015 #3
    A. There is no experimental means to know both the trajectory and position of particles at any one point in time. The best scientists are extremely cautious. If something can't be proved experimentally, they don't claim that it is true, no matter how intuitive it might seem. When we look in at a Schrödinger's cat in the center of a cubic box measuring one light year along all edges, you cannot know what happens in the center of that box for half a year. Not only that, but the observer must have mass, and that mass that will have at least a gravitational effect on the cat after half a year or perhaps earlier. The cat might be alive or dead when you peer into the box, and you wouldn't know for half a year because of the speed of light limit, so as far you are concerned the cat's being alive or not is a wave function - it spans the possibility of being both dead and alive at the same time. When looking at a subatomic particle in a confined space of a few nanometers, the particle could have been in any number of places before the information of its trajectory or position reaches our sensors, plus the act of observation will have an effect on the particle being observed. Also at some point the notion of describing particles as being made of still smaller particles must stop, otherwise it would be an endless recursion. So instead we have a wave function instead, covering all possibilities of position and trajectory.

    What is actually going on in the real world is unknowable by scientific experiment. It would be paradoxical to suggest that the most fundamental particles are made of still finer particles, hence they must be made of something else, and at that non-particle level the concept of simultaneous trajectory and position becomes meaningless.

    [Mentor's note: edited to fix the formatting]
    Last edited by a moderator: Aug 9, 2015
  5. Aug 9, 2015 #4
    Quantum physics is a theory of observables. With no scientific means to elucidate any quantum object's "intermediate" workings, it strictly adheres to representing the probability of observations.
    Bell's inequality says quantum objects CAN'T have local hidden variables. They do not add up to a realistic description of observable probabilities.
  6. Aug 9, 2015 #5


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    It is possible that there is some deeper hidden variable theory underlying QM and which would supply the values of those things that QM is silent about. Bell's Theorem about the predictions of quantum mechanics and the experiments validating these predictions together make a fairly strong case that if such a theory is ever discovered, it will be no less weird and offensive to our classical intuition than QM itself.

    However there is no accepted candidate for such theory today, so this discussion is too speculative to accept under the PF rules and this thread is closed.
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