From: Anders Sandberg (asa@nada.kth.se)
Date: Sun Jun 15 2003 - 17:09:46 MDT
On Sun, Jun 15, 2003 at 05:09:13PM -0500, Kevin Freels wrote:
> The basic properties of all of the elements of the periodic table have
> been know for some time. If we had a computer with sufficient
> processing power, couldn't we have simulation software that could tell
> us pretty much every chemical compound/material that could be made?
> This would eleminate the trial and error approach and solve possible
> every disease!
The problem is combinatorics. The number of chemicals that you can make
increase very fast with the number of atoms. For ten carbon atoms there
are 75 different alkanes, for 20 366,319, for 30 4,111,846,763 and for
40 62,491,178,805,831 (from http://www.rod.beavon.clara.net/quiz.htm).
And that was just combining carbon and hydrogen. The real problem is
that each bond in these molecules can also turn in different directions
so you end up with a number of configurations growing roughly
exponentially with size for *each* possible molecule. So finding which
chemical in which low-energy configuration would fit a receptor or have
a neat property would require searching through a space that increases
superexponentially with the number of atoms involved. This is
impractical given most advances in computing, and even quantum computers
would only make the problem very expensive.
> I began thinking about this when I was watching a program that
> discussed how snake venom was being used to develop treatment for
> diseases. I estimated that there are so many possible chemicals out
> there in nature that we could probably never get to a point where we
> could try them all on everything.
Yes, isn't it annoying?
> I know that we currently don;t have the processing power to do this,
> but does anyone on this board know roughly how much processing power
> we would need?
Let's say that the number of chemicals containing N atoms selected from
a repertoire of 92 are roughly (92^N)*(N!) (select the atoms, order them
in some order; this is an overestimate). The atoms have on the order of
N bonds which can have ~7 degrees of freedom (length, direction,
torsion), so for each molecule we have to search through a 7N
dimensional space to look for minimum energy/fitness maximum
configurations. So the total amount of work of finding the best by brute
force is on the order of (K^N)(N!) for a large K - very slow. Even an
exponential speedup only turns it into a N^2 log N search with a bad
constant.
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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