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Brage
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ok yes I understand what you mean then!bhobba said:Observers in QM is something much more general than in normal usage - I added that refinement a bit later in my post.
Thanks
Bill
ok yes I understand what you mean then!bhobba said:Observers in QM is something much more general than in normal usage - I added that refinement a bit later in my post.
Thanks
Bill
Brage said:ok yes I understand what you mean then!
Demystifier said:Yes. Decoherence always involves entanglement, but not the vice versa.
Talisman said:Sorry for bumping an old thread, but can you help me understand when entanglement does not lead to decoherence? Would you say that in the state |0>|0> + |1>|1>, the first qubit exhibits decoherence when measured in the { |0> + |1>, |0> - |1> } basis?
The first qubit is in a mixed state, but that fact by itself is not decoherence. Decoherence will take place when the first qubit is measured, but that's because of the entanglement with the measuring apparatus.Talisman said:Sorry for bumping an old thread, but can you help me understand when entanglement does not lead to decoherence? Would you say that in the state |0>|0> + |1>|1>, the first qubit exhibits decoherence when measured in the { |0> + |1>, |0> - |1> } basis?
jambaugh said:This also is why you'll find me quite reactive in the various QM Interpretation discussions. The orthodox (CI) interpretation is a shift from ontic(object state based) to praxic (positivistic, operational, process based) interpretation and it resolves this as well as the mysteries of e.g. EPR in a less sexy but far more consistent way.
stevendaryl said:I guess my feeling about it is that the orthodox interpretation doesn't actually resolve any of the mysteries of quantum mechanics, but instead takes the point of view that you don't need to resolve them in order to get on with the task of doing physics.
jambaugh said:Realizing a "mystery" isn't really one is a form of resolution.
QM Mystery: "How do distant measurements of EPR pairs communicate FTL and even causally backward through time?"
Orthodox Resolution: "There's nothing in the physics that says they do and the only reason one might think they do is because one is trying to fit an additional classical objective state based interpretation on the quantum physics."
That is exactly the type of "which twin is really older" question that begins with premises contrary to CI. Ask rather "what is actually happening" where "actually" means in the sense of actions and interactions between observer system and environment. You get the same answers when you ask what happens in the lab.Ask Roger Penrose, or ask Sean Carroll, or ask Steven Weinberg about what's really going on in QM, and you'll get three different answers.
jambaugh said:Yes, SR is still a classical theory and there is an objective reality behind it. My point was that the "mystery" in the twin "paradox" case was due to a failure of the thinker to wholly accept the relativity in the theory.
As to consensus among physicists CI is also referred to as the Orthodox interpretation. It still is the leading view: https://arxiv.org/abs/1301.1069
The "sexier" interpretations (EMW, BPW) get over-represented in discussion forums and Sci-Fi media.
That is exactly the type of "which twin is really older" question that begins with premises contrary to CI.
In the logic the set-inclusion lattice of subsets of states transitions to the quantum logic lattice of subspaces in Hilbert space. If you stick to only subspaces which are spans of a given orthogonal basis, you recover a classical logic lattice as a sub-lattice. You can embed classical descriptions in quantum. The thing is though, ALL the other subspaces have operational meaning. There are observables for these "states". There is more happening, more actions available, in a quantum logic lattice than can be expressed as a power set of a maximal set of primary states i.e. than can be expressed as point transitions between objective states. Quantum logic is a language of actions and it is a richer language than classical logic. This is why it is the natural place to start, the justification for actions are primary.
jambaugh said:As to consensus among physicists CI is also referred to as the Orthodox interpretation. It still is the leading view: https://arxiv.org/abs/1301.1069
No it says more, it says it is meaningless* to refer to "what's going on 'under the hood'" (between acts of observation) because that is, by definition unobservable. It is the same as the aether of unrelativity being fundamentally unobservable and thus meaningless*.stevendaryl said:I would dispute that it is an interpretation at all. Instead, it is a "recipe" for getting predictions out of QM. That's why I said that the orthodox interpretation really amounts to saying that we don't care about what's going on "under the hood".
jambaugh said:No it says more, it says it is meaningless* to refer to "what's going on 'under the hood'" (between acts of observation) because that is, by definition unobservable. It is the same as the aether of unrelativity being fundamentally unobservable and thus meaningless*.
jambaugh said:So it is not just a question of sour grapes... to claim one doesn't care because one cannot reach them... it is a deeper question of the meaning of the "grapes" existing at all, (replace the fox and grapes with the "emperor's new clothes"... I put these alternative interpretations in the same story book as the taylors' claims about the invisible cloth.)
stevendaryl said:I think that point of view is nonsense. An observation is a particular kind of interaction. To say that the only thing that is real are those interactions that count as observations is hopelessly solipsistic, in my opinion.
Is to, is to! (We can do that all day until the mods shut us down. How about some point beyond the claim.)No, it's not any deeper. It's just a pretense of being deeper.
I am under the impression that science works the other way around. So let's keep the burden of proof where it belongs.jambaugh said:You, for example cannot empirically disprove those fringe who believe in an aether.
All are. Copenhagen also. They don't go on to prove anything. For that they would need to make a distinguishable claim (experimentally verifiable)jambaugh said:So let me ask you then, which is right, Bohm's Pilot waves, or Everett's Many Worlds?
From my limited layman's knowledge, BM pilot wave is quite deterministic. So it could be possible to prepare a system where all the outcome would be identical. So I suppose there is no harm trying that ?jambaugh said:how can you distinguish my absurdity from theirs?
You are putting cart before the horse. Observations (even more, statistical properties of many similar observations) can't be primitive terms in explanation.jambaugh said:they [interactions] need to be definable in terms of changes they make on observables.
Well, if we take the analogue of flipping a coin, then I'd say that QM measurement is analogous to flipping the coin and looking at the result (value) is just trivial.stevendaryl said:People often say that a physical quantity such as the component of a particle's spin along a particular axis simply doesn't have a value until measured. Okay, but what about after it is measured? Does it have a value then?
If you say it does, then it seems to me that you are assigning one type of physical interaction, a measurement, a role in making things "real" that is different from all other types of physical interaction. If you say it doesn't, then to me, you've got MWI, where nothing has definite values, not even measurements.
forcefield said:Well, if we take the analogue of flipping a coin, then I'd say that QM measurement is analogous to flipping the coin and looking at the result (value) is just trivial.
So there is no mystery why there is no result for the coin or for the "spin" before "measurement".
What do you mean ? I am considering the measurement to consist of the whole experimental configuration.stevendaryl said:That's treating measurement as fundamentally different from other interactions.
forcefield said:What do you mean ? I am considering the measurement to consist of the whole experimental configuration.
I think we are getting off topic here.
I can't make sense of that.stevendaryl said:I mean that if you take the approach that a system doesn't have a value for a property until that property is measured, then that seems to be giving a role to measurement that is different from the role of any other measurement.
Then I would say that there is something wrong in the logic that does not lead to single unique values.stevendaryl said:To me, it seems exactly what the thread is about---whether single-world interpretations are consistent. The reason for thinking that maybe they aren't consistent is because if you treat a measurement process as just like other types of interactions, then measurement would not result in a single unique value any more than any other interaction does.
forcefield said:I can't make sense of that.
Yeah well I don't buy that. I'm pretty sure Bohr didn't agree with that either.stevendaryl said:If the device were described by quantum mechanics, then you wouldn't get a definite result---either [itex]|U\rangle[/itex] or [itex]|D\rangle[/itex]---you would get a superposition of possibilities. That's what Many-Worlds says happens.
forcefield said:Yeah well I don't buy that. I'm pretty sure Bohr didn't agree with that either.
zonde said:Electron is quantized (discrete) unit. It is unclear then what is the meaning of ##\alpha |u \rangle + \beta |d\rangle## after measuring apparatus when ##|u \rangle## and ##|d\rangle## components appear at spatially different outputs. If we say that ##|\alpha|^2## and ##|\beta|^2## are probabilities then there should be collapse i.e. ##\alpha |u \rangle + \beta |d\rangle## physically changes to ##|u \rangle## or ##|d\rangle## (and later detectors simply finds out in which output electron ended up).
So you say that in quantum mechanics electron can only change it's relative phase relationship between components as a result of interaction i.e. [itex]\alpha |u \rangle + \beta |d\rangle \Longrightarrow \alpha |u\rangle \otimes \beta |d\rangle[/itex]stevendaryl said:I'm not sure exactly what you're talking about, but there is no process in quantum mechanics by which a state [itex]\alpha |u\rangle + \beta |d\rangle[/itex] changes nondeterministically into either the state [itex]|u\rangle[/itex] or the state [itex]|d\rangle[/itex]. If the measuring device is itself governed by the laws of quantum mechanics, you're never going to get a unique result.
stevendaryl said:[itex]|?\rangle \otimes (\alpha |u \rangle + \beta |d\rangle) \Longrightarrow \alpha |U\rangle \otimes |u\rangle + \beta |D\rangle \otimes |d\rangle[/itex]