On Sunday, October 20, 2019 at 12:14:21 AM UTC-6, Bruno Marchal wrote: > > > On 16 Oct 2019, at 19:35, Alan Grayson <[email protected] <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 >>> >>> 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 * > 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 [email protected] <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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/60558127-3c4d-4b57-a2c0-c2dbdfaad07d%40googlegroups.com.
