Wei pointed to:
> http://xxx.lanl.gov/abs/quant-ph/0107070
>
> Is the Universe Really So Simple?
> Authors: Milan M. Cirkovic
> Comments: Significantly improved version of a comment on quant-ph/9603008;
> Found. Phys. Lett. accepted for publication
>
> The intriguing suggestion of Tegmark (1996) that the universe---contrary
> to all our experiences and expectations---contains only a small amount of
> information due to an extremely high degree of internal symmetry is
> critically examined.
I wasn't too impressed by this paper. I'm surprised it is getting
published.
One thing to note is that the paper of Tegmark's which is getting
criticized is not the one we usually comment on, which proposes
that all mathematical structures exist and some contain conscious
beings. Instead it is another paper which adopts the Many Worlds
Interpretation (MWI) and argues that the universe is consistent with a
cosmological model where the Big Bang was in an extremely simple state.
Then quantum fluctuations, which can be thought of as a consequence of
the Heisenberg Uncertainty Principle, will become naturally amplified
through gravitational instability and decohere, producing separate
MWI branches of the universe. The result is that an extremely simple
initial state can separate into a multitude of complicated branches,
each of which has its own intricate, detailed history.
To digress, the MWI model of the universe is in contrast to others which
we have considered here, such as Schmidhuber's recent paper in which he
supposes that there must exist an underlying random number generator in
order to produce the vast amount of quantum information which seemingly
appears throughout space and time. It seems curious to me when people
propose to accept that all universes exist but not that our own universe
is a many-worlds version of QM.
In criticizing Tegmark, Circovic is really criticizing the MWI.
Most of his points are against that model rather than Tegmark's specific
application. I think Tegmark's paper is really a very straightforward
application of the MWI and does not add too much new, other than the
recognition that the MWI does simplify the cosmological problem.
The main technical point Circovic raises is the problem of black hole
evaporation, which appears to destroy information. One of the basic
principles of QM is that time evolution is unitary, which is equivalent
in the MWI model to conservation of information. Black hole evaporation,
to the limited degree it is understood today, appears to be non-unitary.
This would be inconsistent with the MWI and hence with Tegmark's proposal.
However it is also inconsistent with other QM interpretations as well!
Black hole evaporation is an unsolved problem in QM and will require a
full theory of quantum gravity to be resolved. Until that time it is
hardly fair to point to the problems that this phenomenon raises with
the MWI without mentioning that it also causes problems with other views.
Circovic also raises some philosophical arguments, such as the proposed
experiments to test the MWI. He refers to that paper by Plaga that
would supposedly allow inter-world communication, but I am convinced
that that is impossible. Then there is the old proposal by Deutsch for
an intelligent, world-spanning conscious quantum computer, but IMO even
that will not resolve the question. Either it will be impossible to
construct the required system, or if it is successful, then everyone
will agree that the outcome is what the MWI predicts while denying
the reality of other worlds. All Deutsch is really doing is putting a
system into a superposition, and we do that all the time. The system is
supposedly conscious, but it's a highly artificial system and is taking on
attributes which ordinary conscious brains cannot, so skeptics of the MWI
have many opportunities to distinguish this artificial state from a true
demonstration of the existence of parallel worlds. Quantum computers
by themselves won't convince people and putting a supposed AI program
on one won't make any difference.
Overall I think Circovic is aiming at the wrong target. Most of his
arguments are directed against the MWI rather than Tegmark's paper.
If he presented them in that form I think they would be more appropriate
for publication in an appropriate journal.
Hal
Received on Wed Jun 19 2002 - 12:52:16 PDT