Engines of Our Ingenuity

No. 855:

by John H. Lienhard

Click here for audio of Episode 855.

Today, we learn to look for the door into summer. 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.

I've been asking friends what they hear when I say the word tunnel. None have given me the common Freudian stuff, and only a few mentioned claustrophobia. A different theme entirely emerged -- far stronger and far more positive.

One said, "Tunnels are connections." One recalled that Greek oracles always spoke from within caves. One way or another, tunnels remind us of the subtle ways we get to the other side of trouble. For some, going through a tunnel is death and rebirth.

When I put the question to a theoretical chemist, she hesitated -- then said, "Oh, you mean underground tunnels!" Her first thoughts had not been of subways and caves, but of quantum physics. But even there the word is a metaphor for breaking free.

Here's how it works: Electrons are bound to atoms by electric forces. They seem to be trapped. Classical physics says that it is "impossible" for them to escape.

But when we study quantum physics, we find that a tiny electron is far less definite than objects in our much-larger world. It doesn't have a precise location. The electron is most likely here -- but it might also be over there at the very same instant.

If that sounds like nonsense, it's because we're too large. We can't experience that vagueness directly. When we talk about matter in so small a form as an electron, our whole solid vocabulary for material existence breaks down.

Sixty-five years ago, classical physicists imagined that electrons were held to atoms by an insurmountable energy barrier -- a wall they couldn't get through. Now quantum physics says that a few electrons can walk right through the wall -- as though it weren't even there.

Scientists who traffic in those mysteries call such an escape "tunneling." The electrons seem to tunnel through the energy barrier and escape their inescapable prison just as surely as occasional captives tunnel their way to freedom. Jean Paul Sartre described what that electron does. He said,

Let us not look for the door, and the way out, anywhere but in the wall against which we are living.

That image of escape where we thought escape was impossible recurs. Remember the story about the house cat who went from door to door, on a cold winter's day, looking for the one door that led into summer. Well, the metaphor of the tunnel -- and of the quantum mechanical tunnel -- reminds us that we can pass through the wall. We can find the door into summer. There are ways to tunnel through our impossible troubles -- after all.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

I am grateful to Theresa Kavenaugh Lienhard, Brown University Chemistry Department, and Don Kouri, UH Chemistry Department, for their cogent discussions of quantum tunneling. Sartre credits Ralph Waldo Emerson with the "wall" idea that I quote.

For more on the matter of tunneling, see the proceedings of the Smithsonian Institution's symposium on its tunneling exhibition, Down Under: Tunnels Past, Present, and Future, National Museum of American History, Saturday, October 23, 1993.

I say more about tunnelling as a metaphor in Episodes 51, 664, and 849. For a more technical look at tunnelling, try the search function, using the word "tunnel."

The Engines of Our Ingenuity is Copyright © 1988-1997 by John H. Lienhard.

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