At some point in the past various of us have argued about whether the
simulation argument and / or the multiple worlds interpretation of
quantum mechanics implies an "every possible world" (EPW)
interpretation, i.e. one in which highly improbable events, laws of
physics, etc. obtain.
Stumbled across an interesting if tangential paper that has something
to say about this. First some terminology: let's call events that are
highly improbable "white rabbits" and universes in which such events
happen frequently (or universes with entirely inscrutable laws of
physics) "white rabbit worlds."
Let's further adopt the term "djinni" or (to follow Gott's
nomenclature) "jinni" to refer to closed time-like (causally cyclic)
curves, and "jinn worlds" as worlds (n-dimensional "spacetime" slices
of the higher-order spacetime, or rather n-m dimensional phase-space
volumes where n is the total dimensionality of the phase space) that
contain such causal cycles. In order to explain what this means:
these are causally consistent chains of events in which there is no
ultimate cause, but rather a closed causal chain that traverses both
forward and backward along the time dimension. A peculiarity of this
idea is that, in such a world, information "appears" without cause.
For example a computer employing a closed time-like curve as a register
can compute "hard" problems, but when one examines the execution
history of the computer through time one finds that it never actually
executes the computation! Cf.:
http://arxiv.org/pdf/gr-qc/0209061
Anyway, "jinni" are these little closed curves of causality in the
presence of time travel that are consistent but defy common sense.
David G. Boulware of the University of Washington published this paper
in PRD:
http://arxiv.org/abs/hep-th/9207054
...in which he studies the behavior of quantum fields in spaces with
closed time-like curves. What he finds is that probabilities are not
"conserved", i.e. not unitary, in such spaces. That is, the Feynman
sum-over-histories approach always yields precisely 1 --- except when
space contains one or more jinn. In such cases, there are quantum
events that simply cannot occur.
So: jinn defeat white rabbits. If any world-line through the phase
space is cyclic / allowed to self-intersect, the overall phase-space is
constrained, presumably to those set of configurations which are of
higher probability. The very existence of such causal cycles may
indeed be --- meta-paradoxically ;-) --- essential in stabilizing the
overall structure of the phase space. It would seem that these cycles
act as a kind of strange attractor around which probable configurations
(universes) coalesce.
Speculation: it may be that through studying the impact of such closed
time-like curves in various spacetimes that we ultimately reconcile
Cramer's transactional interpretation (retarded waves moving forward in
time, advance waves reaching back to "handshake" on each quantum event,
producing a kind of causal contract) of QM with MWI --- and ultimately
COMP. Indeed, each retarded wave-advance wave pair *is* a jinni.
Cramer doesn't just embrace jinn in his interpretation --- he bases the
whole idea on their existence! (FWIW: this seems to me an
embarrassment of riches. Why should *every* quantum event require a
jinni, when a few --- acting as strange attractors --- might suffice?
Though admittedly the latter leads to the questions which few, and
why?)
The implication ala Boulware is that if this is a real physical effect,
then this provides a kind of global probabilistic censorship that makes
the world the predictable place that it is! And --- connectionism ---
it's rather ironic that Cramer's transactional hypothesis is based in
part on some of Feynman's own speculation, when Feynman probably didn't
realize the essential seemingly paradoxical consequences of pairing the
histories approach with cyclic causality.
So that's all well and good for physics, but what about the more
algorithmic cosmologies? One school of thought regarding the COMP
hypothesis is that it is easier to simulate all possible worlds than it
is to simulate any subset of them. (Cf. previously-discussed
Champernowne machine / "everything" algorithm.) But what if the
dynamics of the simulation are such that these jinni exist as a priori
structural parameters, "roots" if you will of the computation? In such
an environment, "every computable universe" is NOT every possible
universe.
Curiouser and curiouser,
jb
Received on Thu Aug 19 2004 - 15:20:36 PDT