I'll have to look more closely at those papers, but I have a couple
of quick comments.
Jeff Bone, <jbone.domain.name.hidden>, writes:
> 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."
I think this is an unfortunate terminology choice, although it is true
that we have occasionally used it here. The truth is, there is nothing
remarkable about white rabbits. Our world is full of white rabbits.
Using the term to refer to worlds which are utterly improbable is
confusing. I think we got into it by reference to Alice in Wonderland,
where the White Rabbit character walks, talks and wears clothes, but
by itself, especially without capitals, the term white rabbit does not
connote improbability. I would prefer "flying rabbit" or just "magical".
> 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.
It's not clear to me that causality and time are inherent properties
of worlds. I include worlds which can be thought of as n-dimensional
cells that satisfy some constraints. Among those constraints could be
ones which induce the effects we identify as causality and time. For
example, a two-dimensional cell where C[i,j] == C[i-1,j] XOR C[i-1,j-1].
This particular definition has the property that C[i,.] depends only on
C[i-1,.], which lets us identify i as time, and introduce a notion of
causality where conditions at time i depend on conditions at time i-1.
But we could just as easily create a cell system where there was no
natural definition of time, where C[i,j] depended on i+1, i-1, j+1
and j-1. You could still imaging satisfying this via some constraint
satisfaction algorithm.
Now these jinni worlds are ones which mostly have these conditions we
identify as time and causality, but which locally, or perhaps rarely,
do not satisfy such rules. Seen in this perspective, there is a full
range of possibilities, from fully causal worlds, to ones which are
99.999% causal and only .0001% noncausal, to ones which are 50-50, to
ones for which no meaningful concept of causality can be defined.
Your perspective seems to be that those worlds which are very, very
slightly non-causal are particularly interesting. If all you thought
existed were causal worlds, then opening the door to slight non-causality
may seem like a big step. But from my perspective, causality is not
that significant, it is merely an accidental property of some worlds,
so it is no big deal to imagine non-causal universes of varying degrees.
[Skipping...]
> 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.
I'll have to look at this. It doesn't sound quite right. If
probabilities are non-unitary that violates the fundamental rules of QM,
which would suggest that jinns and QM cannot exist, or in other words,
that if QM describes our universe, we have no jinns.
Now, I do recall some earlier famous papers by Novikov in which he found
consistent solutions for closed timelike paths, which were presumably
unitary. So I will have to look more closely and see how these results
compare.
> 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.
I think you're getting awfully speculative here. I don't know where
all this is coming from, why you think that jinn would particularly make
unlikely events even less likely to occur.
[skipping]
> 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.
It sounds like you are suggesting that it would be simpler to suppose
that "all universes exist which contain jinn" than "all universes exist".
That doesn't seem at all plausble to me. My heuristic is that any rule
of the form "all universes exist except X" is going to be more complicated
than one of the form "all universes exist".
Hal Finney
Received on Thu Aug 19 2004 - 16:21:48 PDT