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Indeterminism in Quantum Mechanics and....
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...Determinism in Classical Physics. Sorry for the long title, the header won't allow it. Given that Quantum Mechanics is based on indeterminism, is it really a problem to consolidate the two positions. Having read about 'd Hooft it interests me to see what consequences if indeterminism is just a lack of knowledge, or just a failure of the equipment we have at hand to truly understand the world around us. Of course, this would mean a problem for causation (as if it isn't problematic in its own right), given that there appears to be retrocausation in quantum mechanics. It just seems to me that quantum theory relies upon determinism to achieve results anyway. Or am I missing something?
Wait a minute, are you sure about that?
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Re: Indeterminism in Quantum Mechanics and....
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by
on 2007-11-24 14:57:04 (edited 2007-11-24 14:57:53)
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woah, woah, wooaaah there! QM is NOT "based" on indeterminism per se. (at least, no more than statistics is?) It is based on a theory that light (all energy, actually) arrives in discrete packets called quanta. The indeterminism mindset comes as a result of the interference measurement has on later results. When you measure the position of an electron, say, you chance it's momentum. If you setup your experiment so you know the momentum quite well, you'll find a wide range of positions. This is part of nature, not the theory. It is incorrect to say that classical mechanics is any more or less deterministic than quantum mechanics. They have very different "feels" to them, but that's due to the way nature works, not the theories themselves. If you wanted to classically measure an electron's position and momentum, you'd end up with this error, because there's no way to make a small enough vice to hold the darn little thing in place. And, when you bounce this photon (let's classically think of it as a billiard ball) off the poor electron, it goes bouncing all over the place. What a mess! How do we make sense of all this? That's what quantum mechanics does: tries to make sense of it all. You're using words that have particular philosophical meaning, like "causation" and "determinism". Look out! This can get you into trouble in physics! Should you panic and cry out, "what about causation?!", I would put my hand on your shoulder, and calmly reassure you, causation is not lost in QM. You don't need to feel anxiety just because physicists use scary words like "imaginary time" and "entanglement". I was anxious about those, myself, once. It all boils down to the regular science stuff: What's going on here? How can I explain it? How can I talk to my peer about it? What is often forgotten in science is: How do I explain this to my 9 year old daughter or 80 year old grandmother? This is an important part of science that some scientists procrastinate on and eventually forget all about. To answer your concerns more concisely: 1. QM does not loose determinism. It is, however, honest about the inherent minimum error in experiments. 2. QM does not loose causation. There are, however, unusual ways of talking about time as well as very unintuitive statistical problems which can confuse people. 
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Re: Indeterminism in Quantum Mechanics and....
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Thanks for the reply, though there are certain parts that I still don't think are resolved. And yes, I'm questioning it with a philosophical twist, though my degree in theoretical physics is a bit rusty I readily admit. Part of the problem, and I fully understand your point on the problem of measurement involving photons, essentially boils down to good old Heisenberg's Uncertainty Principle. And that is a point I would like to follow up. The problem for any quantum physicist seems to be that limitation of what we can use to investigate the particles under scrutiny. Because the actual things we're using to determine their position or momentum is affected by the very thing we're throwing at it, hence the uncertainty? (Like I say, my physics is rusty.) I would use the analogy of the billiard ball, and that all we can rely on finding out the desired measurement is by 'chucking' something else whose mass is actually enough to change the particle's path of trajectory and other factors. Imaginary time doesn't sound so scary. I'd like to see someone do something with Einstein's Relativity and bring up the idea of imaginary speed. Thanks all the same, Gendou. (Actually, I wouldn't mind having a crack at philosophy of physics. Sounds like it could be a laugh.)
Wait a minute, are you sure about that?
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Re: Indeterminism in Quantum Mechanics and....
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by kudoushinichi
on 2007-11-25 06:48:40
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Well, how do you expect to know the position of an electron without chucking photons at it? Even observing a billiard ball requires us to look at it (photons reflecting of the billiard ball surface and enters our eyes). So it's just nature, I guess, like Gendou said... the uncertainty is inherent in nature...
Shinjitsu wa itsumo hitotsu!
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Re: Indeterminism in Quantum Mechanics and....
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Yeah... Some of this is going over my head but I'm learning a lot in these physics threads So I wanted to thank you Guys (and girls) I'm only secondary final year level though that explains a lot!!! But back to what I was posting I found a lot of this discussion was explored inthe book Black Holes, Wormholes & Time Machines by Jim Al-Khalili Thought you might like to know cana |
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Re: Indeterminism in Quantum Mechanics and....
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by
on 2007-12-11 12:37:54 (edited 2007-12-11 12:45:58)
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Not sure if I made this point already, but redundancy never hurt anyone, but redundancy never hurt anyone. Determinism means you can predict the state of the system at any time if you know the initial conditions. It requires that initial conditions be definable and attainable. In nature, initial conditions are be definable by a theory, but not fully attainable, in practice, due to error of measurement. There are things in nature we cannot predict. For example, we cannot predict if a coin will land heads or tails, or when a radioactive isotope will decay. We can, however, make meaningful predictions about the probability of these events! I stick to the philosophical viewpoint that QM is a deterministic theory of the system of nature. It does not answer every question in nature - heads or tails, for example - but it does give us the probabilities in a deterministic fashion. For example, the superposition of a particle is the square of the wave function. That's no less deterministic than the acceleration is the time derivative of the velocity, right? You say: "The problem for any quantum physicist seems to be that limitation of what we can use to investigate the particles under scrutiny." And I say: "The problem for any cosmologist seems to be that limitation of what we can use to investigate the stars under scrutiny."
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Re: Indeterminism in Quantum Mechanics and....
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by SuicidopoliS
on 2007-12-11 13:40:18
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I recently read this book called "Quantum Physics: Illusion or reality?", written by Alastair I. M. Rae, in which he tackles some of the basics of Q.P., as well as the problems associated with it, one of the most important ones being the measurement problem. He wrote a bit about different suggestions that have been made in order to solve this problem, if even possible, and one of those possibilities was a theory brought forward by a certain Prigogine. Quite frankly, i forgot the essence of Prigogine's theory, but i do remember it implied some thermal physics concepts, and Rae let believe that following Prigogine's idea, indeterminism would in fact become an intrinsic part of all of physics, including classical physics, which seemed quite a radical idea. I'll try to remember to look this up once again, as i had lend this book from the library and had to turn it back in a few weeks ago... .oO° Life's THE CURE, the rest are details! °Oo. |