paulfchristiano comments on Decoherent Essences - Less Wrong

16 Post author: Eliezer_Yudkowsky 30 April 2008 06:32AM

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Comment author: paulfchristiano 23 January 2011 07:35:33PM 5 points [-]

"No one had ever thought of decoherence. The question of why a human researcher only saw one thing at a time, was a Great Mystery with no obvious answer."

This is not true, and saying things like this will reduce your credibility in the eyes of intelligent observers. In "The Present State of Quantum Mechanics" Schroedinger writes

As we thus construct an objective picture of this process, like that of any other, we dare hope to clear up, if not altogether avoid, the singular jump of the psi-function [...] it would not be quite right to say that the psi-function of the object which changes otherwise according to a partial differential equation, independent of the observer, should now change leap-fashion because of a mental act.

(This is in translation, but I don't think you can deny in good faith that he understands decoherence and almost certainly grasps the predicted existence of many worlds).

From the form in which the psi-function was last known, to the new in which it reappears, runs no continuous road - it ran indeed through annihilation. Contrasting the two forms, the thing looks like a leap. In truth something of importance happens in between, namely the influence of the two bodies on each other, during which the object possessed no private expectation-catalog nor had any claim thereunto, because it was not independent.

You should consider changing the way you talk about the history of quantum mechanics (and probably learning more about the history) before writing at more length about it.

Comment author: Luke_A_Somers 22 April 2012 03:49:01AM 0 points [-]

Well, that's an interesting quote, but did he come out and say that QM was all there was, no exceptions ever, and collapse is not real? If he did, it was in private and did not spread, for when Everett (re-?)proposed it later, it was exceedingly controversial and derided.

And certainly decoherence is a considerably more complicated beast than that, and simply the notion that QM is all there really is NOT sufficient to understand decoherence, not by a long shot.

Comment author: paulfchristiano 22 April 2012 04:25:10AM 1 point [-]

Well, that's an interesting quote, but did he come out and say that QM was all there was, no exceptions ever, and collapse is not real?

Yes. He said it in the passage I quoted. ("it would not be quite right to say that the psi-function of the object...should now change leap-fashion because of a mental act." You could quibble with the word 'quite,' but I think the surrounding text is plenty clear.) His understanding comes through in his writing more generally. The fact that one person has understood something (or many) does not preclude it from being controversial some time later.

And certainly decoherence is a considerably more complicated beast than that, and simply the notion that QM is all there really is NOT sufficient to understand decoherence, not by a long shot.

I don't know quite what you mean. In what way is decoherence "more complicated," and than what? It looks to me like Schrodinger understands exactly what is going on.

Comment author: endoself 22 April 2012 06:31:52AM 1 point [-]

I think he is expressing dissatisfaction with QM rather than endorsing MWI. I found a different quote, from 1950, that seems to support the former.

For it is just because they prohibit our asking what really “is”, that is, which state of affairs really occurs in the individual case, that the positivists succeed in making us settle for a kind of collective description. They accuse us of metaphysical heresy if we want to adhere to this “reality”. . . . The present quantum mechanics supplies no equivalent. It is not conscious of the problem at all; it passes it by with blithe disinterest.

That isn't that clear a statement of his views, but it is from a letter written in reply to Einstein, who said

I am as convinced as ever that the wave representation of matter is an incomplete representation of the state of affairs, no matter how practically useful it has proved itself to be. The prettiest way to show this is by your example with the cat. . . .

If one attempts to interpret the ψ-function as a complete description of a state, independent of whether or not it is observed, then this means that at the time in question the cat is neither alive nor pulverized. But one or the other situation would be realized by making an observation.

(Both quotes are taken from Karl Przibram's Letters on wave mechanics: Schrodinger, Planck, Einstein, Lorentz p. 35-38.)

This is clearly against quantum mechanics rather in support of MWI. They both realize that QM's ontology needs to be revised, but neither knows how.

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