> On 20 Oct 2019, at 08:21, Alan Grayson <agrayson2...@gmail.com> wrote: > > > > On Sunday, October 20, 2019 at 12:14:21 AM UTC-6, Bruno Marchal wrote: > >> On 16 Oct 2019, at 19:35, Alan Grayson <agrays...@gmail.com <javascript:>> >> 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, > > If the box isolates the cat, decoherence of what is in the box will not occur. > > The box contains an environment, the air, heat, etc., so even though the box > is closed, decoherence does occur. AG
Decoherence is just entanglement with the environment. Imagine that the environment ion the cat in the box is just one molecule M (to simplify). M will “measure” the state of the cat by bouncing up to some position M-cat-alive (if the cat was alive) and another position M-cat-dead if the cat was dead. By SWE, before you open the door, the environment “in the box” + the cat is described by the superposition (cat-alive)(molecule at M-cat-alive) + (cat dead)(molecule at M-cat-dead) which is still a superposition. The same with 10^20 molecules, heat, etc. When you open the box, you will just get the state (I see the cat alive)(cat alive)(molecules in the corresponding position) + (I see the cat dead)(cat dead)(molecules in the other corresponding position). As you cannot track the behaviour of all molecules, you are unable to extract interference pattern from that superposition, and it will look like a mixed state. But without collapse of the wave, the cat, the molecules and yourself will remain in the superposition state and this forever, and whatever base is chosen to describe the wave describing you, the molecules and the cat. The apparent collapse is only a term of a superposition seen by an observer described by some factor in that term. Bruno > > Then when the bow is opened, it will take 10^(-20) sec before you are > yourself into a superposition. With the SWE, once the cat is dead + alive, in > box, or out of a box, that state of superposition will never disappear. > > > >> 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 > > Decoherence never destroys any superposition. It only makes harder > (quasi-impossible, impossible in practice) to get the interference back. > That’s how decoherence works well in the no-collapse formulation of QM. > > 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 everyth...@googlegroups.com <javascript:>. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/everything-list/9cdcac4b-ecdb-48d3-bd1d-9ceb8d787ed3%40googlegroups.com >> >> <https://groups.google.com/d/msgid/everything-list/9cdcac4b-ecdb-48d3-bd1d-9ceb8d787ed3%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 everything-list+unsubscr...@googlegroups.com > <mailto:everything-list+unsubscr...@googlegroups.com>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/60558127-3c4d-4b57-a2c0-c2dbdfaad07d%40googlegroups.com > > <https://groups.google.com/d/msgid/everything-list/60558127-3c4d-4b57-a2c0-c2dbdfaad07d%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 everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/EF828CB3-01B7-4175-B476-9EE6F962FC32%40ulb.ac.be.
