> On 20 Oct 2019, at 03:56, Alan Grayson <[email protected]> wrote: > > > > On Wednesday, October 16, 2019 at 11:35:58 AM UTC-6, Alan Grayson wrote: > > On Monday, October 14, 2019 at 3:50:46 PM UTC-6, Alan Grayson wrote > > On Monday, October 14, 2019 at 10:51:03 AM UTC-6, Brent wrote: > > On 10/13/2019 9:10 PM, Alan Grayson wrote: >> On Sunday, October 13, 2019 at 5:50:35 PM UTC-6, Brent wrote: >> >> >> On 10/13/2019 1:08 PM, Alan Grayson wrote: >> > What are YOU talking about? I just made a GUESS about the decoherence >> > time! Whatever it is, it doesn't change my conclusion. If there's a >> > uncertainty in time, are you claiming the cat can be alive and dead >> > during any duration? Is this what decoherence theory offers? AG >> >> Yes, part of the cat can be alive and part dead over a period seconds. >> Or looked at another way, there is a transistion period in which the cat >> is both alive and dead. >> >> But the main point is that this time had nothing to do with >> Schroedinger's argument (he knew perfectly well the time of death was >> vague); his argument was that Bohr's interpretation implied that the cat >> was in a super-position of alive and dead from the time the box was >> closed until someone looked in. >> >> Brent >> >> Agreed. Without decoherence, the cat would be in a superposition of >> alive and dead from the time the box was closed until someone opened >> it. With decoherence, it would be in that superposition for a very short >> time, the decoherence time, when it would be in state, |decayed>|dead> >> or |undecayed> |alive> before the box was opened, provided it was >> opened after the decoherence time. So, as I see it, decoherence just >> moves the "collapse" earlier, before the box is opened, and does not >> resolve S's problem with superposition. > > True, but it resolves the problem about whether conscious observers are > necessary to "collapse" the wave function (or split the world). > > I think Feynman answer this question before the advent of decoherence theory. > I recall reading his comments that an instrument was sufficient for observing > a double slit experiment, and even destroying the interference if rigged to > determine which-way. AG > > The idea of decoherence is that, it not carefully isolated, systems are > continuously "monitored" by the environment and so act classically. > > Here's a good analysis which casts the Schroedinger cat story into a double > slit-experiment. > > https://arxiv.org/pdf/1405.7612.pdf <https://arxiv.org/pdf/1405.7612.pdf> > >> The cause of the problem, or >> paradox if you will, is the superposition interpretation of the radioactive >> source. AG > > Yes, that's the problem. The radioactive nucleus is effectively isolated > until it decays, after which it is not isolated...it has interacted with the > detector. So in the MWI the system is splitting continuously into the branch > were the atom hasn't decayed and the branch where is has just decayed and > interacted with the environment. The atom is in a superposition of decayed > and not decayed with amplitudes varying in time: psi = sqrt[exp(-at)]|not > decayed> +sqrt[1-expt(-at)]|decayed> . > > But isn't this superposition, interpreted to mean the source is in both > states simultaneously before measurement, responsible for the paradox of a > cat which is alive and dead simultaneously, even if for a very short time if > decoherence is considered? If so, isn't this sufficient to question the > validity of said interpretation? AG > > Sean says the decoherence time is 10^(-20) sec. So when the box is closed, > the cat is in a superposition of alive and dead during that time interval, > assuming the decay hasn't happened. If that's the case, I don't see how > decoherence solves the paradox, unless we can assume an initial condition > where the probability of one component of the superposition, that the cat is > dead, is zero. Maybe this is the solution. What do you think? AG > > Maybe this is an easier question; after decoherence, assuming the radioactive > source hasn't decayed, what is the wf of the cat? Is the cat in a mixed > state, alive or dead with some probabIlity for each? AG
Without collapse, the cat never get into a mixed state. That never happen. But the SWE explains entirely why, from the perspective of the observer (him/herself analysed with the SWE), it looks like a mixed state has occurred. Bruno > > Brent > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/2a9e57dc-8480-43cf-83f4-3e1ff8998806%40googlegroups.com > > <https://groups.google.com/d/msgid/everything-list/2a9e57dc-8480-43cf-83f4-3e1ff8998806%40googlegroups.com?utm_medium=email&utm_source=footer>. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/D428BA2C-D9E6-4898-B92B-4420797693A0%40ulb.ac.be.
