Building machines
from a multitude of parts on a production line was a triumph of the
industrial revolution.
A lathe can make
many useful things, but it can't duplicate its parts and put them
together to make a baby lathe identical to itself. To do so would
require deep knowledge of its own construction-the lathe would have
to know itself. No machine ever has, but recently engineers and
scientists at NASA have shown that a self- replicating machine
could be built. With a relatively modest investment, a self-
replicating factory could be built by early in this century.
The Japanese have reached a similar conclusion.
Self-replicating
machines would produce factories as well as products, so that self-
replicating machines would be the ultimate tools for increasing
productivity. One application investigated by the NASA group was to
use a self- reproducing machine on the surface of the moon to make
solar cells, which could be cheaply hauled to vast solar- power
satellites that would beam solar energy back to earth. The
researchers considered the task of making one million solar cells
out of the moon dust. A $1 billion, 100-ton conventional factory
would take about 6,000 years to perform this task. A self-
replicating factory of the same initial size and cost could do the
job in just 20 years, because it makes not only Solar cells but
more solar-cell factories. Marvin Minsky, artificial- intelligence
expert at the Massachusetts Institute of Technology and former
president of the American Association for Artificial Intelligence,
recently wrote, "Teaching computers how to build copies of
themselves could begin a flood of automatic self-replication
machines making more machines at very low cost. Then we'll have to
learn to cope with the resulting explosive growth of wealth and
productivity."
It was not until
1948 that scientists became convinced that machines could be taught
to replicate themselves. In that year John von Neumann, the
Hungarian- American mathematician who helped design the first
stored-programme computer, gave a series of historic lectures at
the University of Illinois. He showed that to duplicate itself, a
device must have available its own blueprint, some manipulators-
hands, essentially- and a set of rules for building things. The
beauty of von Neumann's approach was that he was able to prove,
with mathematical rigour, the possibility of building
self-reproducing machines.
The simplest
self-reproducing machine von Neumann imagined would sit in a giant
stockroom filled with replacement parts- extra arms, legs, eyes,
circuit boards, and the other paraphernalia from which it was
built. The machine would have a memory tape containing all the
instructions needed to build a copy of itself from these spare
parts. Using its robot arm and its ability to move around, the
machine would find and connect parts. The tape programme would
instruct the device to reach out and pick up a part, look to see if
it's the right one, and if not, put it back and grab another.
Eventually the correct one would be found, then the next, and the
two joined in accordance with the master checklist. The machine
would continue to follow the instructions, never knowing what it is
making, until it finishes assembling a physical duplicate of
itself. But the new robot would be "uneducated"; it would have no
instructions on its tape. The parent would then copy its own memory
tape onto the blank tape of its offspring. The last instruction of
the parent's tape would be to activate its
progeny.
Some simple examples
of machines that reproduce without human intervention do exist.
Small mechanical contrivances capable of self-assembly from simpler
parts are easy to build. Roger Penrose, a British physicist,
fabricated a set of simple blocks that could hook together using a
set of ratchets and levers. When single parts are placed in a box-a
track shaped like a long trough- and shaken, they do not join
together. However, when an interlocked, two-block unit is placed in
the box and shaken, a simple form of reproduction takes place.
Collisions between the two- block unit and other parts in the
box cause new two- block units to form, each identical to the
original. Penrose successfully tested replicating units of up to
four blocks, using several different block types.
It is important to
recognize that a complex robot is not essential to make a useful
machine. It is possible to design a modular growing robot system,
like the early lathes that could produce parts that could make
better lathes, which could then produce parts that made better
lathes, and so on. But the exercise has not been done.
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