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Post by fascinating on Dec 29, 2015 21:10:20 GMT 1
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Post by mrsonde on Dec 30, 2015 18:25:48 GMT 1
I think so - I'll give it a good go anyway. Where do you get lost, exactly? I should say that a large part of the incomprehensibility lies in the precipitous decline in journalistic standards of the New Scientist over the past 50 years - a sure and steady dumbing-down. On top of that, the writer has overlain an interpretative theory - the Copenhagen Interpretation of QM - that predetermines what little sense he's managed to convey.
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Post by fascinating on Dec 31, 2015 11:09:01 GMT 1
I didn't say I got "lost", but I wasn't sure I understood from about the first sentence. It talks about superposition, which I took to mean a situation in which a particle is in 2 alternative states (or in an indeterminate state), at the same time, until it is "observed" and the particle assumes one state or the other. I thought this was nothing to do with the particle being at 2 places at once.
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Post by mrsonde on Dec 31, 2015 14:23:06 GMT 1
Yes, I'd say your understanding is correct - that is how the author has taken "superposition", and quite probably it's how the researchers understand the term. This is what I meant by the sense being determined by an overlaying of the Copenhagen Interpretation - or rather two forms of it, which you might term Realist and, Abacus' old favourite, Idealist. The Realist form says the particle is in both states at the same time (the cat is dead and alive). The Idealist version says it's literally in neither - it only comes into existence as one or the other when someone or something "observes" it and "collapses the wavefunction".
Both forms are suppositions of metaphysics (as they stand, at least). What "superposition" actually refers to are mathematical solutions to the wave equations describing the original observed particles, extrapolated into the future over the path(s) that are not observed -"paths" in a multi-dimensional (many thousands of them in this case) mathematical invention called a phase space. (I say "as they stand" because there are extraordinary experiments that may go beyond this - the so-called quantum eraser and delayed choice quantum eraser experiments - which I confess I'm still mulling over in the rare moments I can consider it without sinking into utter stupefaction.) But at no point is any actual particle observed in anything other than one place at any one time.
My own personal view is that these descriptive metaphysics that derive from Copenhagen are so confused, and confusing, because either the wavefunction is misinterpreted as a probability wave (leading to the "indeterminate", literally "non-existing" conclusion) or it's taken as a literal description of real particles' trajectories (leading to the two-places-at-once conclusion.) Both of these are traditional camps within the Copenhagen Interpretation - Born and Heisenberg liked the former, others such as Pauli and Dirac preferred the latter, and Bohr seemed reluctant to pin his mast to either.
My view is fairly simple and mundane, as interpretations of QM go, though of course pretty hair-raising all the same. It's fairly close to Schrodinger's (and David Bohm's - and Roger Penrose's, I think, insofar as he's made himself clear about it.). I think the wavefunctions are descriptions of waves rather than trajectories - real waves, that is, not probabilities. It's the only solution that makes sense to me - and all the evidence - actual observations - back me up as far as I'm aware (whereas, of course, there can be no possible observations of either of the metaphysical hypotheses above.)
Has that helped any?
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Post by jean on Dec 31, 2015 15:35:49 GMT 1
An exemplary post, and I mean that quite sincerely. I particularly like this bit: My own personal view is...
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Post by fascinating on Dec 31, 2015 20:41:27 GMT 1
Yes, a little, thank you. But I still don't understand how anybody says it means that particles were in 2 places at the same time.
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Post by nickrr on Jan 1, 2016 14:13:45 GMT 1
I'll give it a go with my understanding.
According to quantum mechanics if a particle (often a sub-atomic particle but it can be a larger object like an atom or a group of atoms) is not interacting with any other particle it has no definite position. It is only when it interacts with another particle that it's position then becomes known. This might be, for instance, when someone tries to measure it's position which necessarily involves interacting with the particle.
Before any interaction the particle's position is defined by a series of probabilities. So it may be the case that there's a 25% chance of the particle being found here, 25% there etc. In total these probabilities have to add up to 100% because we know it is definitely somewhere. When an interaction occurs, as described above, it will be found in one of the positions depending on the probabilities. I'd stress that before any interaction, it is not just the case that we don't know where it is, the particle itself has an indeterminate position.
Normally the uncertainty of where a particle might be covers very small distances, such as atomic scales. However in the experiment described scientists claim to have created a group of atoms whose uncertainty in position is over half a metre. Note that it's not strictly speaking correct to say that the group is in two places at once. It could be at either end of the probability distribution or any point in between so actually the group is at many places at the same time.
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Post by mrsonde on Jan 3, 2016 11:08:04 GMT 1
Alright, Hughie.
You'd do well to take it on board then. It simply ackowledges that this view is a metaphysical supposition itself, as much as its alternatives, with no experientia crucis to decide the issue. Yet, anyway - it's unwise to rule one out from possibility.
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Post by mrsonde on Jan 4, 2016 7:28:32 GMT 1
No - as particles, they weren't. Sloppy journalism.
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Post by mrsonde on Jan 4, 2016 9:04:50 GMT 1
I'll give it a go with my understanding. According to quantum mechanics if a particle (often a sub-atomic particle but it can be a larger object like an atom or a group of atoms) is not interacting with any other particle it has no definite position. It is only when it interacts with another particle that it's position then becomes known. This might be, for instance, when someone tries to measure it's position which necessarily involves interacting with the particle. Before any interaction the particle's position is defined by a series of probabilities. So it may be the case that there's a 25% chance of the particle being found here, 25% there etc. In total these probabilities have to add up to 100% because we know it is definitely somewhere. When an interaction occurs, as described above, it will be found in one of the positions depending on the probabilities. I'd stress that before any interaction, it is not just the case that we don't know where it is, the particle itself has an indeterminate position. Normally the uncertainty of where a particle might be covers very small distances, such as atomic scales. However in the experiment described scientists claim to have created a group of atoms whose uncertainty in position is over half a metre. Note that it's not strictly speaking correct to say that the group is in two places at once. It could be at either end of the probability distribution or any point in between so actually the group is at many places at the same time. Welcome back nick. Yes, this is the "Idealist" version outlined above. This needs to be qualified though: This is only true for small systems considered in small periods of time. That uncertainty expands through time, and if your "particle" is travelling at an appreciable speed - a photon, say - then such an "evolution" very quickly covers vast distances. Also, of course, with this metaphysical interpretation, you are obliged to agree with Abacus that the universe in the past, or those vast stretches of it that are unobserved, only exists to the extent that it's been observed. Thankfully, I won't be around to trudge through all that again!
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