The Whole Universe as a Finite Binary String?

SETH LLOYD is Professor of Mechanical Engineering at MIT and a
principal investigator at the Research Laboratory of Electronics. He
is also adjunct assistant professor at the Santa Fe Institute. He
works on problems having to do with information and complex systems
from the very small-how do atoms process information, how can you make
them compute, to the very large - how does society process
information?

http://www.edge.org/3rd_culture/lloyd2/lloyd2_index.html

One of the things we do with our quantum computers is to use them as
analog computers to simulate other physical systems. They're very good
at simulating other quantum systems, at simulating quantum field
theories, at simulating all sort of effects, down to the quantum
mechanical scale that is hard to understand and hard to simulate
classically. These numbers are a lower limit to the size of a computer
that could simulate the whole universe, because to simulate something
you need at least as much stuff as is there. You need as many bits in
your simulator as there are bits registered in the system if you are
going to simulate it accurately. And if you're going to follow it step
by step throughout its evolution, you need at least as many steps in
your simulator as the number of steps that occur in the system itself.
So these numbers, 10[120] (10 to the 120) ops, 10[90] (10 to the 90)
bits of matter -10[120] if you believe in something like holography ­
also form a lower bound on the size of a computer you would need to
simulate the universe as a whole, accurately and exactly. That's also
uncontroversial. . .

From my perspective, it's also uncontroversial that the universe
registers 10[90] bits of information, transforms and processes that
information at a rate which is determined by its energy divided by
Planck's constant. All physical systems can be thought of as
registering and processing information, and how one wishes to define
computation will determine your view of what computation consists
of. . .

If you look at a quantum computer you don't see anything, because
these molecules are too small. But if you look at what's happening in
a quantum computer, it's actually attaining these limits that I
described before, these fundamental limits of computation. I have a
little molecule, and each atom in the molecule registers a bit of
information, because spin up is zero, spin down is one. I flip this
bit, by putting it in an NMR spectrometer, zapping it with microwaves
and making the bit flip. I ask, how fast does that bit flip, given the
energy of interaction between the electromagnetic field I'm putting on
that spin and the amount of time it takes to flip? You find out that
the bit flips in exactly this time that's given by this ultimate limit
to computation. . . It goes exactly at the speed that it's allowed to
go and no faster. It's saturating its bound for how fast you can
perform a computation. . .

The other neat thing about these quantum computers is that they're
also storing a bit of information on every available degree of
freedom. Every nuclear spin in the molecules stores exactly one bit of
information. We have examples of computers that saturate these
ultimate limits of computation, and they look like actual physical
systems. They look like alanine molecules, or amino acids, or like
chloroform. Similarly, when we do quantum computation using photons,
etc. we also perform computation at this limit. . .

http://www.edge.org/3rd_culture/lloyd2/lloyd2_p4.html
________________

Just a few interesting if not controversial thoughts . . .

Sean Pitman
www.DetectingDesign.com


.