Re: Quantum suicide without suicide

From: Bruno Marchal <>
Date: Thu, 9 Jan 2003 10:53:27 +0100

Tim May wrote

>On Wednesday, January 8, 2003, at 10:58 AM, George Levy wrote:
>>In the original verision of Quantum Suicide (QS), as understood in
>>this list, the experimenter sets up a suicide machine that kills
>>him if the world does not conform to his wishes. Hence, in the
>>branching many-worlds, his consciousness is erased in those worlds,
>>and remains intact in the worlds that do satisfy him.
>>Is it possible to perform such a feat without suicide? What is the
>>minimum "attrition" that is required and still get the effect of
>Hawking had a good line: "When I hear about Schrodinger's Cat, I
>reach for my gun."

Good line? I would say it is rather stupid (with all my respect for Hawking).
Come on. The Schroedinger's Cat paper is one of the deepest early paper on
QM conceptual issues. The notion of entanglement appears in it. It prepares
both EPR and quantum computing, which arises from taking seriously the QM
superpositions. You can only mock Schroedinger's Cat by taking a purely
instrumentalist view of QM, and with such a view quantum computing
would not have

>Slightly modify the QS conditions in another direction: instead of
>dying immediately, one goes onto death row to await execution. Or
>one is locked in a box with the air running out. And so on.
>This removes the security blanket of saying "Suicide is painless,
>and in all the worlds you have not died in, you are rich!" In
>99.9999...99% of all worlds, you sit in the box waiting for the air
>to run out.

It reminds me a novel I wrote (a long time ago) where computationalist
practitioners always wait for complete reconstitution before annihilating
the "original". It can be consider as a fair practice letting imagine the
risk of such "immortality" use.

>I don't know if there are other worlds in the DeWitt/Graham sense
>(there is no reason to believe Everett ever thought in these terms),
>but if they "exist" they appear to be either unreachable by us, or
>inaccessible beyond short times and distances (coherence issues).

I disagree. It is only by playing with word that you can suppress the many
worlds in Everett. Some of Everett's footnote are rather explicit. See
the Michael Clive Price FAQ for more on this.
People like Roland Omnes which agree with pure QM (QM without collapse)
and still postulate a unique world acknowledge their irrationality.

>In particular, it seems to me there's a "causal decision theory"
>argument which says that one should make decisions based on the
>maximization of the payout. And based on everything we observe in
>the world around us, which is overwhelmingly classical at the scales
>we interact in, this means the QS outlook is deprecated.

You confuse first and third person point of view. If you put yourself at the
place of Schroedinger Cat you will survive in company of people which will
*necessarily* be more and more astonished, and which should continue to bet
you will not survive. Although *where* you will survive they will
lose their bets.

>Consider this thought experiment: Alice is facing her quantum
>mechanics exam at Berkeley. She sees two main approaches to take.
>First, study hard and try to answer all of the questions as if they
>mattered. Second, take the lessons of her QS readings and simply
>_guess_, or write gibberish, killing herself if she fails to get an
>"A." (Or, as above, facing execution, torture, running out of air,
>etc., just to repudiate the "suicide is painless" aspect of some
>people's argument.)
>From rationality, or causal decision theory, which option should she pick?

It depends of Alice's goal. If she just want the diplom (and not the knowledge
corresponding to the field she studies) then QS is ok, but quite
egoist and vain
at some other level. If she want the knowledge, she will be unable to find a
working criteria for her quantum suicide. By the "Benacerraf
principle" we cannot
know our own level of implementation code. (I use comp here).

>All indications are that there are virtually no worlds in which
>random guessers do well.

Of course! From a 3-person point of view quantum suicide is ordinary suicide.
Tegmark (and myself before in french) made this completely clear.
Also, it is an open problem if some feature in the apparition of life or even
"matter-appearance" does not rely on some quantum guess.

>(The odds are readily calcuable, given the type of exam, grading
>details, etc. We can fairly easily see that a random guesser in the
>SATs will score around 550-600 combined, but that a random guesser
>in a non-multiple-choice QM exam will flunk with ovewhelming
>What should one do? What did all of you actually do? What did
>Moravec do, what did I do, what did Tegmark do?

I think the QS point is not practical, and it is highly unethical. It is the
most egoist act possible. But QS just illustrate well conceptual nuances in the
possible interpretation of QM and MWI.

Received on Thu Jan 09 2003 - 04:55:28 PST

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