Re: Information content of the brain

From: Gilles HENRI <Gilles.Henri.domain.name.hidden>
Date: Fri, 19 Mar 1999 10:57:52 +0100

I just rediscovered this mail from Hal that I forgot to read carefully!


>We also need to simulate the brain's input. This is pretty hard since we
>didn't want to simulate the universe that was going to give it the input.
>What we need to do is to hard-wire the input which the brain will receive
>over that 70 year period. Everything the brain will see, hear, touch,
>smell and taste over 70 years is going to be sitting in a table that our
>program will provide.
>
>How much information is this? How much "bandwidth" does the brain consume?
>
>TV is about 1E7 bits per second. If we increase this by a factor of
>10 it would roughly account for our visual input (we don't see as much
>as it seems like; only a small part of our visual field is seen in high
>resolution). That gives 1E8 bits per second for vision. Vision is the
>primary sense modality for humans, but let's multiply it by a factor of
>5 to account for the other senses (handwaving madly here!). That gives
>5E8 bits per second of input, over all modalities, for the human brain.
>Over 70 years, which is 2E9 seconds, that gives a total of 1E18 bits
>of input.
>
>This falls between the estimates above of brain information. When we
>encode this information in a table so that we can present it to our
>simulated brain, we have to add it as part of the size of the input.
>The result is to narrow our bracket, and put it from about 1E18 to
>2E27 bits.
>
>That is the information for this method of simulating an entire human
>lifetime, without trying to actually simulate the universe which the
>human appears to live in.
>

it's ok, but a brain would work properly only if it can observe a
physically coherent input. So the problem is not the number of bits, but
how to choose them. I see only two solutions:
* interfacing the simulated brain with a real I/O interface (CCD,
microphons, and output devices because you expect the environment to react
to your own outputs).
* simulating the whole Universe as proposed below.

>
>Simulating a universe which evolves a brain
>
>We then ask how hard it would be to simulate a brain the old fashioned
>way, by setting up a universe which uses the laws of physics that we
>observe, and running it.
>
>We face a problem right at the beginning, here. Our universe appears
>to have a random component. So we have some choices. We can simulate
>the universe as it appears, and include some mechanism in the program to
>make random selections as specified by quantum mechanical measurements.
>This mechanism could either be a software random number generator, or a
>table of random bits which would be used to make the random choices.
>Or, we could adopt a many-worlds approach, and simulate the universe
>state without collapse.
>
>In any case, the physics involved is probably pretty simple. We don't
>have a full theory, but our best shots at it, the superstring and
>membrane theories that try to marry QM and relativity, really aren't
>very complicated. I'm sure you could capture their essence in a few
>megabytes or even kilobytes.
>
>The initial conditions, as far as we can tell, are also simple. Matter
>appears to have been quite uniformly distributed in the Big Bang. This
>bodes well for us, as it takes little information to specify a uniform
>distribution, at least if we don't care about the details.

Sorry, I may have missed something? First the Universe must have been
slightly inhomogeneous to generate galaxies, stars, planets and so on.
However simple gaussian fluctuations are enough *at the beginning* The
problem is that the subsequent evolution makes its state more and more
complicated *at all scales*. To have a chance to see life appear, you most
describe at least from a DNA molecule to a galaxy (stars can form only
under precise conditions of the intersteller meium!), and may be even with
a higher dynamics. Our galaxy contains maybe 10^67 atoms, whose position
must be given with a uncertainty of 10-10 m in about 10^20 m (10 kpc). So
you are facing a requirement of at least 10^70 bits ! ( I estimated this
number to raise to 10^400 if you want to describe the observable Universe
up to the Planck scale....)

Clearly it is impossible to store this information in any machine smaller
than our galaxy! It is BTW logically and physically impossible to simulate
a *real* Universe with a machine embedded in this Universe! Nothing to say
about a many-worlds wavefunction...

>
>A trivial counting program, once it counts up to about 1E39, will produce
>a number which encodes the entire 1E39 bits of a human brain's state all
>through its lifetime. And there we have it, a fully simulated brain,
>70 years of human lifetime in living color, produced by a program which
>is about 1E2 bits long.
>
>
>Accounting for the costs to localize the brain
>
>We can apply Wei's approach, which is to count the size of the program
>needed to locate the brain, and add it to the size of the program that
>produces the output. With the counting program, it will take 1E39 bits
>to specify where in the output that brain is located. Add that to the
>1E2 bits of the counting program and the overall cost is 1E39 bits, very
>high, making this program give a small contribution.
>
>In the case of many-worlds, then, the challenge is to estimate how hard
>it would be to locate a human-like brain, or even more, a specific human
>brain, among the 1E100+ universes it has created.
>
>To find a human brain, without asking for a specific one, should not be
>that hard. We could create a pattern or template which we would use to
>look for a match. It could perhaps be a specification for a generic
>brain, perhaps a young person's brain. The program to search through the
>multiverse and look for matches to this would be easy to write.

Here again either you or I missed something. If you know how to write a
pattern specifying a brain, you have solved your problem. You don't have to
enumerate stupidly up to 10^39 to recognize a pattern you already know!
Conversely, if you don't know the pattern, it is useless to count (just as
to let a UD run!), because you will be unable to recognize (and to prove to
other people!) the existence of a "living" entity. The problem is entirely
how is this pattern like?

I think that nobody answered me satisfactorily on the problem of
"interpreting" or recognizing" a string. I could compare this problem to
gauge invariance in physics. It's well known that all physical theories
admit many equivalent representations or gauge transformations. However, to
represent "physically" something, they must contain quantities invariant
upon these transformations, that allow to recognize intrinsic features :
e.g. proper interval in general relativity, curvature of space-time and
more generally the action in any known theory.
You seem to admit as obvious that a computation or a string can represent,
or better *be* a physical state of the Universe. However when you think of
a real way to connect them, it seems obvious that you have to precize a way
of doing that. If you want to describe the positions of all atoms, or the
values of a field, you have to precise the coding of real numbers and so
on. When Bruno says that the UD will solve Wheeler-DeWitt equation, it
assumes some coding that allows to recognize the solution in a string. I
may be wrong, but I don't see how you can definie intrinsic physical
quantities (like the curvature of the space time for example) independantly
on these representations (same problem with the "matching pattern" of Hal).
It means also that the same string can represent (under different coding
schemes) different, and even quite different Universes. So it cannot posses
intrinsically all physical properties, and for example the presence of
living beings. Maybe I am wrong and you know works proving the contrary?


Gilles
Received on Fri Mar 19 1999 - 02:00:39 PST