Today, we look in the mirror and find something
strange. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
"Why don't you do a program
on mirror images?"
says my wife. Now I'm in trouble! On the
one hand, she's clearly on to something. On my other
(mirror image) hand, I realize mirrors are such a
familiar paradox we hardly have a vocabulary to talk
about them.
Her remark was triggered by a program I did on
chiral chemistry. A chiral material is one whose
molecules are identical in every feature but one,
and that one has to do with mirrors.
Suppose your mirror self were to step out of the
mirror. His hair would be parted on the wrong side.
His watch would be on the wrong wrist. There's no
way you could turn him around to make him into you.
He would not be you. That creature would be wrong
in the same way as a left-handed handshake from a
friend is wrong.
The word chiral comes from the Greek for hand,
because our hands are mirror images. One chiral
molecule is the reversed mirror image of the other.
That means there's no way to rotate one molecule to
make it into the other. That tiny difference is
enough to make otherwise identical materials behave
differently.
When I was young I saw the 1945 Michael Redgrave
movie, The Dead of Night -- a set of
six horror stories. The Dead of Night
created conventions of movie terror we've used ever
since. Everything in it has been copied 'til it's
hackneyed. That was the first time I saw the trick
of a mirror reflecting a scene unlike the one in
front of it. Mirrors made me uncomfortable for
years after that.
Engineers make great use of mirror images. Suppose
a pipe carries hot water inside a concrete block,
parallel with an insulated surface of the block.
How to calculate heat flow in the concrete? The
easiest way is to replace the insulation with a
mirror image of the concrete and the pipe. It's far
simpler to calculate the effect of the mirror
image. And the answer's just the same as it is for
the single real pipe.
The subtlety of mirror images shows itself in how
long it took chemists to learn why seemingly
identical molecules don't behave the same. Pasteur
first found such molecules in 1847. But it was this
century before people figured out the part of about
chirality -- that the two molecules reflected each
another.
Mirror imaging has become a regular tool in our bag
of scientific and engineering tricks. Opposed
images cut through complexity and disorient us at
the same time. No wonder our legends teem with
mirrors. Think of vampires, fun houses, bad luck,
the infinite regress of self in the barber shop,
and the face of Medusa.
Perhaps that's what the seventeenth-century mystic,
George Herbert, meant when he said, "The best
mirror is an old friend." For old friendships
invariably prove to be just as dear -- and just as
subtly complex and puzzling -- as that seemingly
simple mirror we look into, first thing every
morning.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
