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Question:
In 'A brief History of Time' Hawkings explains, that Heisenberg's uncertainty principle arises because you cannot observe a particle without disturbing it, which is because you would need to 'touch' it with something, like a photon or some other particle, and this will transfer energy to the observed particle. Further, says Hawkings: 'We could still imagine that there is a set of laws that determines events completely for some supernatural being, who could observe the present state of the universe without disturbing it'. From this it would seem that the uncertainty principle is a sort of 'add on' to quantum mechanics, that has been added for practical reasons. When I was introduced to quantum mechanics, it was stated as a basic truth, maybe even THE basic TRUTH about the world: 'Everything is basicly random, and it is only statistics that makes things look ordered'. But would it not be more 'fair' to say that the uncertainty principle is simply a way of taking into account the insecurity our observation introduces to the measurement?



Replies:
The observer is part of the observation. Usually this is stated as: "the observer is part of the experiment." Look for the book, Margins of Reality, by Robert Jahn; then tell me what you think...

John Hawley


This has actually been a question of some interest in the philosophy of quantum mechanics, and there are actually certain conditions (Bell's inequalities) that predict quite different results for quantum mechanics as normally understood and for the simplest theories that assume an underlying determinism (so-called local theories). Experiments have recently been done that show that the inequalities are actually violated by the real world, meaning that at least these local deterministic theories are wrong. But there could still be some kind of determinism behind quantum mechanics - it is hard for us to find, at least!


In addition to the previous responses: It is incorrect to say that the uncertainty principle is an "add-on" to quantum mechanics. Quantum mechanics is a consequence of the uncertainty principle. I think that the best explanation is in Heisenberg's little book "Physical Principles of the Quantum Theory."

Jack L. Uretsky



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