re: Many Worlds

Damien Broderick (
Thu, 15 Jan 1998 10:15:00 +0000

At 08:13 AM 1/15/98 +1000, Mitch wrote:

>I would like to see someone explain the operation of a quantum computer
>*using* Many Worlds theory!

Yes, it's not immediately obvious that this model doesn't raise more
difficulties than it resolves. Luckily, David Deutsch addresses this topic
in his THE FABRIC OF REALITY (pp. 216-7):

`I said that [Shor's algorithm] requires only a few thousand arithmetic
operations. I meant, of course, a few thousand operations *in each
universe* that contribute to the answer. All those computations are
performed in parallel, in different universes, and share their results
through interference.'

That much, of course, is the basis for John Clark's claim. The interesting
point follows:

`You may be wondering how we can persuade our counterparts in 10^500-odd
universes to start working on our factorization task. Will they not have
their own agendas for the use of their computers? No... Shor's algorrithm
operates initially only on a set of universes that are *identical* to one
another, and it causes them to become differentiated only within the
confines of the factorization engine. ... There are, no doubt, many other
universes in which we programmed different numbers or never built the
factorization engine at all. But those universe differ from ours in too
many variables - or more precisely, in variables that are not made to
interact in the right way by the programming of Shor's algorithm - and so
do not interfere with our universe.'

Is that the sort of issue you were thinking about, Mitch?

Damien Broderick