On 5/1/2010 10:43 AM, Rex Allen wrote:
On Thu, Apr 29, 2010 at 10:58 PM, Jesse Mazer<laserma...@gmail.com> wrote:
I think you've got the argument wrong.
I think you're wrong about my getting the argument wrong. :)
Carroll discusses this in his book "From Eternity to Here"
> From Eternity To Here, Pg. 182 (my comments follow the quote):
I know from experience that not everyone is convinced by this
argument. One stumbling block is the crucial assertion that what we
start with is knowledge of our present macrostate, including some
small-scale details about a photograph or a history book or a memory
lurking in our brains. Although it seems like a fairly innocent
assumption, we have an intuitive feeling that we don't know something
only about the present; we *know* something about the past, because we
see it, in a way that we don't see the future.
But this argument assumes that "knowing" is timeless and that if we
reversed all the momenta we would still perceive the physical evolution
of systems per the same time-symmetric laws but with things going
"backwards". But I don't see how knowledge, perception, etc can be
timeless. They already imply an evolution in time and they pick out a
direction. So if you say you know that the micro-physics of the
universe, including your brain, are time-symmetric then you must also
give an account of how they *seem* time-asymmetric. This is usually
done by a statistical mechanics kind of argument relating local entropy
growth (including formation of memories) to expansion of the universe
and quantum decoherence. This argument is not definitive mainly because
we don't have a definitive theory of consciousness, but to the extent we
assume a physical basis for consciousness it seems pretty good.
Cosmology is a good
example, just because the speed of light plays an important role, and
we have a palpable sense of "looking at an event in the past." When
we try to reconstruct the history of the universe it's tempting to
look at (for example) the cosmic microwave background and say, "I can
*see* what the universe was like almost 14 billion years ago; I don't
have to appeal to any fancy Past Hypothesis to reason my way into
drawing any conclusions."
That's not right. When we look at the cosmic microwave background (or
light from any other distant source, or a photograph of any purported
past event), we're not looking at the past. We're observing what
certain photons are doing right here and now.
But "observing", i.e. forming a thought about a perception is not
timeless and already assumes both duration and direction. If you
reversed everything via a CPT transformation, then according to a
physical model of the world nothing would change - including your
perceptions and thoughts.
When we scan our radio
telescope across the sky and observe a bath of radiation at about 2.7
Kelvin that is very close to uniform in every direction, we've learned
something about the radiation passing through our *present* location,
which we then need to extrapolate backward to infer something about
the past. It's conceivable that this uniform radiation came from a
past that was actually highly non-uniform, but from which a set of
finely tuned conspiracies between temperatures and Doppler shifts and
gravitational effects produced a very smooth-looking set of photons
arriving at us today. You may say that's very unlikely, but the
time-reverse of that is exactly what we would expect if we took a
typical microstate within our present macrostate and evolved it toward
a Big Crunch. The truth is, we don't have any more direct empirical
access to the past than we have to the future, unless we allow
ourselves to assume a Past Hypothesis.
Indeed, the Past Hypothesis is more than just "allowed"; it's
completely necessary, if we hope to tell a sensible story about the
universe. Imagine that we simply refused to invoke such an idea and
stuck solely with the data given to us by our current macrostate,
How could any "data" be "given" if we didn't have thoughts with duration
and direction? There is no "macrostate" as a static thing with no
implicit or explicit direction. This is very clear in Newtonian
mechanics since evolution equations are second-order and include momenta
as well as position. It's not so clear in QM where the evolution
equations are first-order. This results in the cosmological
"problem-of-time" illustrated by the Wheeler-Dewitt equation having no
time variable. But there is still a continuous topology and physical
time can presumably be recovered as a statistical approximation.
including the state of our brains and our photographs and our history
books. We would then predict with strong probability that the past as
well as the future was a high-entropy state, and that all of the
low-entropy features of our present condition arose as random
fluctuations. That sounds bad enough, but the reality is worse.
Under such circumstances, among the things that randomly fluctuated
into existence are all of the pieces of information we traditionally
use to justify our understanding of the laws of physics, or for that
matter all of the mental states (or written-down arguments) we
traditionally use to justify mathematics and logic and the scientific
method. Such assumptions, in other words, give us absolutely no
reason to believe that we have justified anything, including those
David Albert has referred to such a conundrum as *cognitive
instability* - the condition that we face when a set of assumptions
undermines the reasons we might have used to justify those very
assumptions. It is a kind of helplessness that can't be escaped
without reaching beyond the present moment. Without the Past
Hypothesis, we simply can't tell any intelligible story about the
world; so we seem to be stuck with it, or stuck with trying to find a
theory that actually explains it."
So it seems to me that physicalism (the proposal that our experiences
are "caused" by an independently existing material world) is riddled
with "cognative instabilities". As is Bruno's mathematical platonism.
And as is any theory that proposes a causal mechanism for conscious
There is no sensible story to be told about existence.
Sean says: "Without the Past Hypothesis, we simply can't tell any
intelligible story about the world"
I'd go further and say that even with the Past Hypothesis you can't
tell any intelligible story about the world. We *can* say that the
"big bang" theory is consistent with what we observe. But so is a
higher-entropy past. And so is Bruno's AUDA. And so are a lot of
BUT these things all inevitably lead to more questions. There seem to
be only two possible "final" answers:
1) Everything exists.
2) Reality is essentially arbitrary. There is no reason why
existence is this way as opposed to some other way. It just is.
Option 1 can actually be collapsed into option 2: Why does everything
exist? There is no reason, it just does.
Again, Kant's first antinomy:
“Suppose we were to accept the big bang hypothesis concerning the
origin of the universe. Only a short-sighted person would think that
we have then answered the question of how the world began. For what
caused the bang? Any answer will suppose that something already
existed. So the hypothesis cannot explain the origin of things. The
quest for an origin leads us forever backwards into the past. But
either it is unsatisfiable- in which case, how does cosmology explain
the existence of the world? - or it comes to rest in the postulation
of a causa sui - in which case, we have left the scientific question
unanswered and taking refuge in theology. Science itself pushes us
towards the antinomy, by forcing us always to the limits of nature.”
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To post to this group, send email to everything-l...@googlegroups.com.
To unsubscribe from this group, send email to
For more options, visit this group at