On Thu, Apr 29, 2010 at 9:53 PM, rexallen...@gmail.com <
rexallen...@gmail.com> wrote:
> Probably most of you are familiar with this already, BUT, just in case
> anyone has any interesting comments...
>
> If physicalism is true, your memories are almost certainly false.
>
> Consider:
>
> Entropy is a measure of the disorder of a system. The higher the
> entropy, the higher the disorder.
>
> If a deck of cards is ordered by suit and then within each suit by
> ascending rank, then that’s a low entropy state. This is because out
> of the 8.06 * 10 to the 67th (52!) possible unique arrangements of the
> cards in a standard 52 card deck, there’s only 24 that fit that
> particular description.
>
> A “random looking” arrangement of the deck is a high entropy state,
> because there are trillions of unique arrangements of a standard 52
> card deck that will fit the description of looking “randomly
> shuffled”.
>
> Same with the egg. There are (relatively) few ways to arrange the
> molecules of an egg that will result in it looking unbroken, compared
> to the huge number of ways that will result in it looking broken. SO,
> unbroken egg…low entropy. Broken egg…high entropy.
>
> AND the same with the universe…there are (again, relatively) few ways
> to arrange the atoms of the universe in a way that makes it resemble
> what we see with people and trees and planets and stars and galaxies,
> compared with the gargantuan number of ways to arrange things so that
> it resembles a generic looking cloud of dust.
>
> OKAY. Now.
>
> Of the relatively few ways that the elementary particles of the
> universe can be arranged so as to resemble what we see around us
> today, only a tiny fraction of those particle arrangements will have
> values for momentum and position that are consistent with them having
> arrived at that state 13.7 billion years after something like the Big
> Bang.
>
> The vast majority of the particle arrangements that macroscopically
> resemble the world around us will *instead* have particles in states
> (e.g., with positions and velocities) that are consistent with the
> particles having previously been in something more like a giant dust
> cloud.
>
> By which I mean: If we take their current positions and velocities,
> and work backwards to see where they came from, and go back far enough
> in time, eventually we will not arrive at the Big Bang. Instead we
> will arrive at a state resembling a giant dust cloud (probably a very
> thin, spread-out dust cloud).
>
> SO, bottom line:
>
> Out of all the possible configurations that the universe could be in,
> ones that have people, and planets, and stars, and galaxies are
> extremely rare.
>
> Further, even if we then only consider those extremely rare possible
> configurations that have people, and planets, and stars, and galaxies
> – the ones with particles in states (e.g., with positions and
> velocities) that are consistent with having arrived at this
> configuration 13.7 billion years after something like the Big Bang are
> STILL rare.
>
> We don’t know the exact state of our universe’s particles, but in
> statistical mechanics the Principle of Indifference requires us to
> consider all possible microscopic states that are consistent with our
> current macroscopic state equally likely.
>
> So given all of the above, and our current knowledge of the laws of
> physics, the most likely explanation is that all of your current
> memories are false and that yesterday the universe was in a HIGHER
> state of entropy, not a lower state (as would be required by any
> variation of the Big Bang theory).
>
> Physical systems with low states of entropy are very rare, by
> definition. So it’s very improbable (but not impossible) that the
> unlikely low entropy state of the universe of today is the result of
> having evolved from an EVEN MORE UNLIKELY lower entropy universe that
> existed yesterday.
>
> Instead, statistically it’s overwhelmingly more probable that the
> unlikely low entropy state of the universe today is the result of a
> random fluctuation from a HIGHER entropy universe that existed
> yesterday.
>
> And thus your memories of a lower entropy yesterday are most likely
> due to this random fluctuation, not due to yesterday actually having
> had a lower entropy than today.
>
>
I think you've got the argument wrong. The idea is *not* that any physicists
actually believe our memories are false and that the entropy was higher in
the past, it's just a sort of reductio ad absurdum argument that points out
you *would* be forced to this conclusion *if* you assumed there was no
process that could have naturally led to a high probability that our
universe would start out in low-entropy state. But in fact there is thought
to be such a process: inflation, which could cause a very small region of an
earlier universe (a small region which had somewhat lower entropy than
average due to a random fluctuation) to expand to a very large and smooth
initial state for our universe (which would be at tremendously low entropy
for its size, since gravity causes higher-entropy states to be more clumpy).
See the discussion in chapter 11 of Brian Greene's "Fabric of the Cosmos",
for example. Another physicist named Sean Carroll has extended this idea and
argued that in the long-term future, our universe will likely evolve into
something called a "de sitter space", so if you *start* with a de sitter
space and evolve it both forward and backward in time, you get a multiverse
where small regions constantly inflate into new universes, and that this
process actually increases the entropy of the multiverse ('increasing' in
both the forward and backward direction in time from that initial de sitter
space, with no ultimate upper bound to the total entropy) in spite of the
fact that each inflation event produces a large smooth region which has a
low entropy for its size. Carroll discusses this in his book "From Eternity
to Here", and also in these articles and papers:
http://preposterousuniverse.blogspot.com/2004_10_01_preposterousuniverse_archive.html#109892415875650212
http://arxiv.org/abs/gr-qc/0505037
http://arxiv.org/abs/hep-th/0410270
Carroll also discusses the reductio ad absurdum argument that entropy was
higher in the past and therefore all our memories are false in this post:
http://blogs.discovermagazine.com/cosmicvariance/2006/08/01/boltzmanns-anthropic-brain/
Jesse
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