Robotics Reference
In-Depth Information
In a more recent experiment (2002), Adelman used a simulation of
a DNA computer to solve a logic problem that would be impossible for
a human to complete by hand. The idea was to use a strand of DNA
to represent a mathematical or logic problem, and then generate trillions
of other unique DNA strands, each representing one possible solution.
Exploiting the way that DNA strands bind to each other, the computer
can weed out invalid solutions until it is left with only the strand that
solves the problem exactly. This experiment solves a problem requiring
the evaluation of more than one million possible solutions, far too com-
plex for anyone to solve without the aid of a computer. It required a
set of 20 values that satisfy a complex tangle of relationships. Adleman's
chief scientist, Nickolas Chelyapov, offered this illustration: imagine that
a fussy customer walks into a huge showroom with one million cars on
sale, and gives the car dealer a complicated list of criteria for the car he
wants.
I want it to be either a Cadillac or a convertible or red. If it is a
Cadillac, then it has to have four seats or a locking gas cap. If it
is a convertible, it should not be a Cadillac or it should have two
seats . . . [4]
The customer rattles off a list of 24 such conditions, and the dealer has
to find the one car in stock that meets all the requirements. (Adleman
and his team chose a problem they knew had exactly one solution.) The
dealer will have to run through the customer's entire list of requirements,
and to do this for each of the million cars in turn—a hopeless task unless
he can move and think at superhuman speed. This serial method, exam-
ining one possible solution after another, is the way a digital electronic
computer solves such a problem.
In contrast, a DNA computer operates in parallel, with countless
molecules shimmying around together at once. This is equivalent to
each car having a driver inside it who will listen to the customer read his
list over a public address system, and drive his car away the moment it
fails one of the conditions. By the time the customer finishes his list, his
dream car will be waiting in the showroom—the last one remaining after
all the others have been rejected.
In 2003 a team of Israeli scientists at the Weizmann Institute of Sci-
ence in Rehovot, led by Ehud Shapiro, unveiled a programmable mole-
cular computing machine composed of enzymes and DNA molecules,
that was recognized by
The Guinness Book of World Records
as “the small-
