HM:
…consciousness is just one way of interpreting
the functioning of a brain: it is a complex and observer-dependent
attribution like beauty, not a simple physical property like gravity.
SLP: Consciousness in its known forms is a property of brains, which are
physical systems. Therefore it can be reduced to a description in
purely physical terms, which has nothing whatever to do with an
"observer." The term "observer", incidentally, is a very bad one. In
EVERY physical situation, it can be replaced with a wholly neutral term
such as "registering device" or "recording device".
HM
So "you" (accepting "your" existence for the sake of argument!) believe
you are conscious.
But for all that, it is an arbitrary attribution, and doesn't
invalidate the position of my super-alien, who understands your
construction and function precisely, and can predict and affect
your behavior much better than I (or you!) can, and has no need to
attribute a fuzzy, made-up psychological concept like consciousness
to interact effectively with you. The alien finds plain, unadorned
physics a much more satisfactory way to interpret your functioning.
SLP:
This is absolutely correct. Only WE will be the "super-alien".
Sometime in the 21st century brain function will be fully understood in
purely physical terms. Further, in the 21st century also (as your
excellent books point out) conscious computers and robots will make
their appearance. Whether we will still use the term "consciousness"
then is an open question, however. I don't know whether there will be a
smooth reduction of our common and admittedly folk-psychological concept
of consciousness to strict
physics (the position called "reductive materialism") or whether this
concept is so flawed that it will have to be junked completely
("eliminative materialism'). Until we actually understand how brains
work, and what we crudely call "consciousness" is generated, it is
simply premature to attempt an answer.
HM:
In fact, I think our experience of time is also a subjective
attribution tied up in the way our conscious self-defines.
SLP:
No, time is something purely physical. However, an "anthropic" version
of what you are saying is wholly consistent with this. This is clear by
considering Gell-Mann and Hartle's (GMH) work in extending the basic
Everett picture to a full cosmological context. GMH ideas suggest how
perceivable time evolves from a quantum reality that is timeless (i.e.,
lacking a "forced" temporal direction) at its most fundamental level.
In GMH, we see that a given quantum state of the universe can evolve in
many different ways. But most of these are "sterile" from the point of
view of living or self-aware substructures (SASs). Gravity causes
massive objects to clump up, but since life and informational processes
depend on thermodynamic diseqilibrium, there should be at least one
non-clumpy (or smooth) temporal pole in the reality perceived by SASs.
Two such poles (a smooth "beginning" and smooth "end") can be calculated
to be very unlikely, so from the point of view of SASs the most probable
type of perceivable universe is one where there is a smooth beginning
and a tendency to ever-greater clumpiness. This means that an arrow of
time can be defined, but it is an arrow that (as Paul Davies has pointed
out) is analogous to spatial symmetry-breaking. Just as galaxies can
have rotation axes that point in different spatial directions, different
universes containing SASs can (conceivably) have different temporal
axes. Directional time appears to be an evolved phenomenon that comes
out of broken symmetry, just as so many other aspects of fundamental
physics also come out of broken symmetry.
HM:
Self-aware systems are logical constructs involving psychological terms
that can be mapped onto
any(!) physical or abstract systems, though particular observers,
because of their own perspective, will find some mappings easier to make
than others.
SLP:
Self-aware systems are what they are because of their underlying
physics, period. The computational basis of self-awareness is
instantiated in physics. The notion of "psychological terms" is otiose
HM:
Everett only showed that it was consistent to model a measurement
without collapse by expressing it as the superposition of
a number of correlated observer and system states, each representing
a different measurement outcome. I'm for that 100%: gets rid of
ill-defined collapse, and gains you many-worlds. But he didn't
touch the question of why the decomposition should be into the
particular semi-classical alternatives we experience.
SLP:
Right. As you point out, it takes decoherence ideas and GMH to
understand why we perceive things in the narrow, cramped, crippled,
perspectival way we do, being evolved quasiclasscial objects confined to
an effective quasiclasscial domain.
HM:
After all, the wave function just goes on happily evolving in toto. Who
needs any kind of decomposition?
SLP:
Complete understanding of all branches of the universal wave function,
in a full cosmological sense, without any restrictions whatever, is a
proper goal of physical science. With the development of adequate
computational power in the near future, there is no reason for this goal
not to be reached. There are in fact no foreseeable limits to
computational power. Malament-Hogarth space-times, relying on nothing
more than classical general relativity, actually allow explicitly
tranfinite computation. You may already be very familiar with MH
machines. If not, read a fascinating paper by Lucian Wischik on this at
http://www.wischik.com/lu/researcher.html. It shouldn't be very long
(maybe a century or so) before we have the technology to manipulate
spacetime as a building material and constrict MH machines. And MH
machines, giving the ability to do denumerably tranfinite computations
in finite times, are just the beginning. Once time itself can be fully
controlled, or stepped outside of, much more still will be possible.
Once Mind Fire (to use your wonderful term, which is both elegant and
colorful) takes off, there will be no stopping it.
HM:
The chain of cause is not a pyramid, it is a circle. You can stand on
one part of a circle and say all the rest of the circle follows
from this point. But you can also stand elswhere on it and say
the same thing! We physical scientist types tend to think in terms of
how we evolved
under the physical laws. But that doesn't invalidate the position
that these particular physical laws exist because they're necessary
to produce us.
SLP:
The chain of cause is hierarchical, not a circle. And in an ultimate
TOE, such as Tegmark's, physical laws exist because they CAN exist, in
the modal logical sense of consistent possibility. SAS's are purely
consequences, and not causes, of these laws.
HM:
>From what I've seen in the last few days, most of the folks on this
list have positions closer to mine than to yours. In the larger
scientific world, your position is orthodoxy. I love this list!
SLP:
My "position" is simply the consistent application of Ockham's Razor,
which in its turn can be justified rigorously in terms of Kolmogorov
complexity theory, as Li and Vitanyi have demonstrated. And,
unfortunately, I don't think this "position" is very widely followed.
The most egregious counter-example is the fact that for many decades
Bohr's Copenhagen crackpottery was quasi-orthodoxy--and to some older
physicists, still is. In my own field, clinical medicine (which is not
yet a real science), there are still many practitioners who, in their
arrogant primtivism, disparage a purely reductive point of view and talk
of treating the "whole person," as though people were (in some vague,
undefined way) something "more" than physical systems.
Steve Price, MD
Received on Mon Jul 12 1999 - 03:05:21 PDT