On 4/29/2010 6:53 PM, 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).

This isn't quite right. If the evolution of the universe is deterministic, then it's time reversible, and reversing all the momenta will take it back to it's initial state - whether that's a Big Bang or not. And even if it's not strictly deterministc or instead of reversing every particle's momentum we just reverse them "roughly" so that the macroscopic level momenta are reversed, then all the stuff we can see will collapse back to a reverse Big Bang - in fact that's why we think there was a Big Bang.

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.

That doesn't follow. Assuming the same laws of physics obtain and the universe is big enough, it may be that having some people and some planets a some stars etc is probable. And if the universe is spatially infinite (and it looks like it is) then all those things are inevitable in some part of the universe.

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).

That's true if by "our current knowledge" you take only the large scale state of the universe.

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.

Yes, that's the problem of Boltzmann's brain.

http://blogs.discovermagazine.com/cosmicvariance/2008/12/29/richard-feynman-on-boltzmann-brains/

But if the universe arose from a quantum fluctuation, it would necessarily start with very low entropy since it would not be big enough to encode more than one or two bits at the Planck scale. If one universe can start that way then arbitrarily many can. So then it is no longer clear that the evolved brain is less probable than the Boltzmann brain.

Brent

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