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Mar 4, 1992, 12:15:50 PM3/4/92

to

In article <1992Mar4.0...@news.iastate.edu>, i1n...@exnet.iastate.edu (Neal Rauhauser -- ) writes:

|> In article <30...@ganymede.tegra.COM> mcdo...@tegra.UUCP (Steve W McDougall) writes:

|> >In article <68...@netnews.upenn.edu> ri...@tigger.jvnc.net writes:

|> >>Is it dead?? I'm confused.

|> >

|> >You're supposed to be confused. That's the point.

|>

|>

|> And its quite possible to open the lib, see the dead kitty, slam

|> the lid, re-open it, and have a live cat again. Note that this is

|> not a very probable occurence, but it is possible. Confused yet?

|> In article <30...@ganymede.tegra.COM> mcdo...@tegra.UUCP (Steve W McDougall) writes:

|> >In article <68...@netnews.upenn.edu> ri...@tigger.jvnc.net writes:

|> >>Is it dead?? I'm confused.

|> >

|> >You're supposed to be confused. That's the point.

|>

|>

|> And its quite possible to open the lib, see the dead kitty, slam

|> the lid, re-open it, and have a live cat again. Note that this is

|> not a very probable occurence, but it is possible. Confused yet?

There's more -- if it is the observation of the cat that is supposed to determine

its state, does the cat qualify as a valid observer (that is, can it determine its

own state?)? If a cat cannot, how about putting a person into the box... is the

person alive or dead before someone else opened the box, or are observers themselves

subject to being in superpositions of states (when the observer opens the box,

the result is that the observer is in a superposition -- one watching a live cat,

and the other watching a dead cat)?

One comment on one observer seeing a dead cat followed by a live cat... The

live and dead states are orthogonal, and the time-evolution operator for the

system does not transfer amplitude from the dead state to the live state... only

the other way around. In other words, the cross-section for an event that shows

a live cat after seeing a dead cat is zero.

Dan

Mar 4, 1992, 3:57:43 PM3/4/92

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i1n...@exnet.iastate.edu (Neal Rauhauser) says:

> mcdo...@tegra.UUCP (Steve W McDougall) writes:

>> ri...@tigger.jvnc.net writes:

>>> Is it dead?? I'm confused.

>> You're supposed to be confused. That's the point.

> And its quite possible to open the lib, see the dead kitty, slam

> the lid, re-open it, and have a live cat again. Note that this is

> not a very probable occurence, but it is possible. Confused yet?

> mcdo...@tegra.UUCP (Steve W McDougall) writes:

>> ri...@tigger.jvnc.net writes:

>>> Is it dead?? I'm confused.

>> You're supposed to be confused. That's the point.

> And its quite possible to open the lib, see the dead kitty, slam

> the lid, re-open it, and have a live cat again. Note that this is

> not a very probable occurence, but it is possible. Confused yet?

This is not true. Once an observation has been made, it can'tbe unmade.

The wave function can't uncollapse.

Mar 5, 1992, 4:40:06 AM3/5/92

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The collapse of the wave function is such a shonky concept, which lacks

so much in any decent mathematical treatment that "uncollapse" is just as

plausible as "collapse". For more details see: John Bell, "Against

'measurement'", Physics World, August 1990, pp. 33-40, and references

therein. Strictly speaking "wave function collapse" is not a part of QM.

It's an "add on".

--

Zdzislaw Meglicki, gus...@arp.anu.edu.au,

Automated Reasoning Project - CISR, and Plasma Theory Group - RSPhysS,

The Australian National University, G.P.O. Box 4, Canberra, A.C.T., 2601,

Australia, fax: (Australia)-6-249-0747, tel: (Australia)-6-249-0158

Mar 5, 1992, 7:21:03 AM3/5/92

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Isn't the point of Schroedinger's cat that it was used by Schroedinger to show

that Quantum physics did not work on large scales in the same way as it

did on the mircospoic scale. None of this mumbo jumbo about cats observing

their own states.

I suppose I should read Scrhoedinger's oringal article, if any body know the

reference I would be most grateful.

--

------------------------------------------------------------------------------

Justin Pearson, | So what do you thinks going on? |

University of Kent at Canterbury | |

U.K. | |

Mar 5, 1992, 11:35:12 AM3/5/92

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gus...@arp.anu.edu.au (Zdzislaw Meglicki) says:

> DOC...@SLACVM.SLAC.STANFORD.EDU (Jon J Thaler) writes:

>> i1n...@exnet.iastate.edu (Neal Rauhauser) says:

>>> And its quite possible to open the lib, see the dead kitty, slam

>>> the lid, re-open it, and have a live cat again. Note that this is

>>> not a very probable occurence, but it is possible. Confused yet?

>> This is not true. Once an observation has been made, it can'tbe unmade.

>> The wave function can't uncollapse.

> The collapse of the wave function is such a shonky concept, which lacks

> so much in any decent mathematical treatment that "uncollapse" is just as

> plausible as "collapse". For more details see: John Bell, "Against

> 'measurement'", Physics World, August 1990, pp. 33-40, and references

> therein. Strictly speaking "wave function collapse" is not a part of QM.

> It's an "add on".

I don't know what point you are trying to make. Measurement repeatibility

is a feature of every interpretation of QM. You can use wavefunction

collapse, many worlds, or hidden variables, but none of them predict

that the cat, once observed to be dead, will ever again be seen alive.

Only Elvis has that property.

I like that, "shonky". What does it mean, precisely?

Mar 7, 1992, 12:12:23 PM3/7/92

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In article <Mar.6.19.52....@ruhets.rutgers.edu> bwe...@ruhets.rutgers.edu (Benjamin Weiner) writes:

>

> Zdzislaw Meglicki writes

>>The collapse of the wave function is such a shonky concept, which lacks

>>so much in any decent mathematical treatment that "uncollapse" is just as

>>plausible as "collapse". For more details see: John Bell, "Against

>>'measurement'", Physics World, August 1990, pp. 33-40, and references

>>therein. Strictly speaking "wave function collapse" is not a part of

>>QM. It's an "add on".

>

> Zdzislaw Meglicki writes

>>The collapse of the wave function is such a shonky concept, which lacks

>>so much in any decent mathematical treatment that "uncollapse" is just as

>>plausible as "collapse". For more details see: John Bell, "Against

>>'measurement'", Physics World, August 1990, pp. 33-40, and references

>>therein. Strictly speaking "wave function collapse" is not a part of

>>QM. It's an "add on".

>"uncollapse" is not plausible

Barring any evidence for this statement, much less any definition of

"collapse" or "uncollapse", this doesn't mean very much.

I've always been against the notion of "wave function collapse" as some

kind of physical process caused by "observation" (a term which has no

clear definition anyway). If one insists on "collapse" one either has

to aceept "uncollapse" or concoct a tale about how time-reversal

invariance is thwarted by thermodynamic subtleties... actually I think

some story along these lines is needed to account for the curious

time-reversal asymmetry of what we call observation -- but I think that

dragging in "wave function collapse" only makes matters murkier.

Mar 5, 1992, 6:15:07 PM3/5/92

to

In article <68...@netnews.upenn.edu>, wee...@libra.wistar.upenn.edu (Matthew P

Wiener) says:

>

>In article <92065.083...@SLACVM.SLAC.STANFORD.EDU>, DOCTORJ@SLACVM (JonJ

>Thaler) writes:

>>I don't know what point you are trying to make. Measurement repeatibility

>>is a feature of every interpretation of QM. You can use wavefunction

>>collapse, many worlds, or hidden variables, but none of them predict

>>that the cat, once observed to be dead, will ever again be seen alive.

>

>Not so. There is, in fact, a quantum veterinary procedure to resurrect

>Schroedinger's cat after it died. You observe an appopriate combination

>of live/dead states almost instantaneously after its death, and you have

>a 50% chance of the cat coming back to life. Repeat until satisfied.

Wiener) says:

>

>In article <92065.083...@SLACVM.SLAC.STANFORD.EDU>, DOCTORJ@SLACVM (JonJ

>Thaler) writes:

>>I don't know what point you are trying to make. Measurement repeatibility

>>is a feature of every interpretation of QM. You can use wavefunction

>>collapse, many worlds, or hidden variables, but none of them predict

>>that the cat, once observed to be dead, will ever again be seen alive.

>

>Schroedinger's cat after it died. You observe an appopriate combination

>of live/dead states almost instantaneously after its death, and you have

>a 50% chance of the cat coming back to life. Repeat until satisfied.

I stand partially corrected. To the extent that 'alive' and 'dead' are

quantum eigenstates of some 'life' operator, the state of the cat can be

changed from one state to the other in much the same way that the polarization

of light can be rotated by a succession of linear polarizers.

Mar 6, 1992, 7:52:11 PM3/6/92

to

Zdzislaw Meglicki writes

>The collapse of the wave function is such a shonky concept, which lacks

>so much in any decent mathematical treatment that "uncollapse" is just as

>plausible as "collapse". For more details see: John Bell, "Against

>'measurement'", Physics World, August 1990, pp. 33-40, and references

>therein. Strictly speaking "wave function collapse" is not a part of

>QM. It's an "add on".

Don't over-interpret Bell. Sure, wavefunction collapse is a poorly

defined process which isn't part of (or reconcilable with) the

smooth time-evolution of QM states. But what really bothers lots

of people is the fact that the reduction occurs on interaction

with the classical measuring apparatus. Where is the split?

"uncollapse" is not plausible

Mar 9, 1992, 11:10:41 AM3/9/92

to

In the context of the above, there are a few points I'd like to complain about

when it comes to wave-function collapse -- particularly as formulated in

Cohen-Tanoudji et al and in Dirac's monograph:

1) The time evolution operator involving observation does not seem to be

unitary (same class of complaint as the time-reversal asymmetry).

2) If you wanted to construct a Hamiltonian (it would have to be non-Hermitian

to produce a non-unitary time-evolution operator) to represent the impact of

observation, it would have to account the effective scattering from the input state

to the output (observed) state... ie you'd have to do work. Yet, observing the cat

is essentially a passive process. Somehow, I'm producing a profound scattering of

states with essentially no energy (no interaction term in the Hamiltonian) coupling

the cat's state to my observation of its state.

3) The observations one can see in quantum experiments can be explained

by solving Schrodinger's equation for the system+observation process in question, and

looking at the observables. For example, you can look at the production of

bubble-chamber tracks (look in Schiff for a nice discussion), or you can look at

linear response theory (Kubo) to see how a system's quantum states interact with an

applied field in a way that can be examined at a macroscopic level (both these

techniques treat the measurement process as a part of the quantum system...).

(NOTE that the probability of seeing weird non-conservative events, or seeing a live

cat following seeing a dead cat is very small -- as calculated from the stand-point

of cross-sections.)

If it is clear from 1) and 2) that the impact of collapse produces scattering of

states in a way that is completely divorced from dynamical processes (Schrodinger's

equation), and by 3) handles a problem that is already handled by looking at

cross-sections that follow from simple dynamic considerations, why would one NEED

collapse?

Dan

Mar 9, 1992, 11:30:37 PM3/9/92

to

DOC...@SLACVM.SLAC.STANFORD.EDU (Jon J Thaler) writes:

> I like that, "shonky". What does it mean, precisely?

> I like that, "shonky". What does it mean, precisely?

G'day, mate!!

It's an Oz-tralian-ism. It means the same as "dodgy" :)

Tee hee... Actually, it means something of questionable

reliability or doubtful character. It can be applied to people. We

have a comedy show here which features the "Dodgy Brothers" who go in

for things like Used Car Selling and the like. Hope this has enriched

you in some way. :)

We now return you to your regular programme.

--

Joe Voros

Department of Physics, Monash University, Clayton, VIC, 3168, Australia.

Quantum Mechanics is God's way of telling you to mind your P_i's and Q_i's.

Mar 10, 1992, 5:53:53 PM3/10/92

to

Since I'm getting quoted on this, I ought to publicly disavow it:

I never intended to post the one-sentence statement, "uncollapse is

not plausible." I was bit by a newsreader glitch. I did think that

the original poster had overinterpreted Bell's Physics World

article, which I felt was more directed toward complaining about

the "shifty split" between measured system and measuring apparatus.

I never intended to post the one-sentence statement, "uncollapse is

not plausible." I was bit by a newsreader glitch. I did think that

the original poster had overinterpreted Bell's Physics World

article, which I felt was more directed toward complaining about

the "shifty split" between measured system and measuring apparatus.

On that subject, it seems to me that most treatments of measurement

as compatible with Schrodinger evolution wind up sneaking the split

back in somewhere along the line - for example, Kurt Gottfried's

treatment as quoted in the Bell article. Basically, Gottfried's

cooked up a dish that's palatable to him; but many other people

find it less than filling. I haven't got Schiff here - but my

instinct is that his treatment is similar.

If I was the only person who was bothered by this, I would figure

that I just didn't understand it. I take comfort from the fact

that a lot of smart physicists don't seem to understand it either.

That may not be scientifically objective, but it's human.

Ben Weiner

Mar 11, 1992, 2:53:32 PM3/11/92

to

Look, I tried the cat experiment. On the third trial, the

cat was dead. On each of the subsequent 413 trials, it remained dead.

Am I doing something wrong?

James Nicoll

Mar 11, 1992, 11:47:00 PM3/11/92

to

Yes, you forgot to uncollapse its wave function.

Mar 12, 1992, 1:41:46 PM3/12/92

to

In article <1992Mar12.0...@galois.mit.edu> jb...@nevanlinna.mit.edu (John C. Baez) writes:

>>In article <1992Mar11.1...@watdragon.waterloo.edu> jdni...@watyew.uwaterloo.ca (James Davis Nicoll) writes:

>>

>>>

>>> Look, I tried the cat experiment. On the third trial, the

>>>cat was dead. On each of the subsequent 413 trials, it remained dead.

>>>Am I doing something wrong?

>>>

>>In article <1992Mar11.1...@watdragon.waterloo.edu> jdni...@watyew.uwaterloo.ca (James Davis Nicoll) writes:

>>

>>>

>>> Look, I tried the cat experiment. On the third trial, the

>>>cat was dead. On each of the subsequent 413 trials, it remained dead.

>>>Am I doing something wrong?

>>>

>Yes, you forgot to uncollapse its wave function.

Um, how exactly do I do that? It is rather urgent; my landlady wants

to know where her cat is.

James Nicoll

Mar 12, 1992, 4:29:53 PM3/12/92

to

jdni...@watyew.uwaterloo.ca (James Davis Nicoll) writes:

Yes - Schrodinger's experiment calls for a randomly selected cat.

By using the same subject you are biasing the results because this

cat has learned from past experiments and is affecting the outcome.:-)

Jim

Mar 12, 1992, 4:13:56 PM3/12/92

to

In article <1992Mar12.1...@watdragon.waterloo.edu> jdni...@watyew.uwaterloo.ca (James Davis Nicoll) writes:

>>>> Look, I tried the cat experiment. On the third trial, the

>>>>cat was dead. On each of the subsequent 413 trials, it remained dead.

>>>>Am I doing something wrong?

>>Yes, you forgot to uncollapse its wave function.

> Um, how exactly do I do that? It is rather urgent; my landlady wants

>to know where her cat is.

There are various ways; I suggest you just switch the sign of the

Hamiltonian and wait for as many days as the cat has been dead. If your

landlady is impatient you may also want to multiply the Hamiltonian by a

large constant.

--------

Senior physicists, labeled by many younger ones as "the establishment,"

contend that an advanced degree in physics is an excellent education, even

if it leads to no job. Besides, physicists are at the pinnacle of science,

they argue, and superbly qualified to take jobs as applied scientists,

engineers or even plumbers. NY Times Tues. Mar. 10 1992, p. C1.

-------

jb...@math.mit.edu

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