Today, let's see what happens when two or more technologies join forces. 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 want you to try a little experiment the next time you have a moment. First find three metal masses -- nuts, bolts, lead sinkers -- whatever's handy. Now hang one on the end of a thread and swing it. The motion is simple -- a little pendulum that moves back and forth in just one way. Next, take a longer length of thread and attach all three masses along its length. Space them about two feet apart. Then hang this string of masses from the ceiling.

Start this system swinging and watch what happens. No matter how they start out, they're soon moving in the most unexpected ways. The middle one might momentarily stop dead, while the other two gyrate around it. They might all move in the same plane, or they might swing in circles. And the patterns of movement keep changing. Going from one mass to a system of three masses takes us from a motion we can easily understand to one that mystifies us.

Our technological systems are like that. In October 1987 we saw what happened when a computer-controlled stock-market responded to a ripple in the economy. We'd told our computers how to respond to certain changes, but we weren't at all prepared for their aggregate response. We were stunned to see them flock together into the greatest one-day stock-market crash the world had ever seen.

That same sort of thing was true of the Three Mile Island and Chernobyl reactor failures -- so many elements were interconnected that an operator couldn't diagnose a change quickly enough to take the right corrective action.

And yet, complex systems of technologies are at the heart of the machinery of today's society. A friend of mine -- an engineering designer -- recently came back from Europe. "John," he said, "I had a remarkable experience. I had to call home, so I picked up the phone in my hotel, pushed a few buttons, and found myself talking to America." I looked at him and said, "So what?"

He said, "Stop and think. How many terribly complex systems had to be put together to give me that convenience -- the space technology to put up a satellite, the electronic technologies on the ground, the radio technologies in the sky, the hotel management systems, and so on and on!"

So I did stop and think. Today's engineers have to worry as much about combining technologies effectively as they have to worry about inventing them. Ill-concieved systems threaten us with terrible mischief. Well-combined technologies stand to present us with amazing benefits and conveniences. And the intellectual challenges of complex-systems design are dazzling.

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

(Theme music)

This episode has been greatly revised as Episode 1434.