Quantum Computers [was Read any good books lately?]

Robert J. Bradbury (bradbury@www.aeiveos.com)
Tue, 17 Aug 1999 00:51:32 -0700 (PDT)

> hansen <hansen@best.com>

-- promoted Deutsch's multiverse perspective

> hal@finney.org wrote
> I don't agree with Deutsch's suggestion that quantum computers would
> imply that the Many-Worlds interpretation must be true.

> hanson replied:

> If a QC carries out a computation requiring 10^500 superimposed
> possible states, and actually carries out the computation, then
> those states have to be real, since they had a physical effect, as
> real as the state (after measurement) we observe in this universe.
> Since those states are real, and don't (and can't) exist in this
> (visible) "universe", then those alternate "universes" have to be
> real. (This is the essence of Deutsch's challenge.)

> (Terminological clarification: Deutsch uses "multiverse" to refer
> to the entire collection of alternate "universes", even though
> "universe" is a more logical word for the collection...)

> Then John K Clark jonkc@att.net said:

   >Hal said that a working quantum computer would not prove that the
   >many world interpretation is correct and he's right, but it would
   >make it much more popular.

OK, now, I'm going to go where IMHO we shouldn't be going, i.e. "Magic Physics". We aren't SIs and we shouldn't be talking about it... At any rate, this may seem like a really stupid question and demonstrate my profound ignorance on the subject but nothing ventured, nothing gained:

If, the superimposed states collapse, and *we* get the "result", what do the other universes get? I.e. if we get the factors of the number and they get all the other states (i.e. the non-results), then what good is the method? Can the other universes "work" if they only get the "non-results" of our universe? If so, aren't you "worried" that our universe might one day get allocated some of the "non-results" as well? How do the results get allocated to the various universes (observation?). If we happen to be in the universe capable of observing (and therefore collapsing the states into a useful result), then how can you claim that the other universes exist [when there isn't anyone in them to observe anything?] If any of this argument "holds together" then I think we are living in a universe as strange as and potentially as easily "destroyed" (by belief alone) the one created in Permutation City.