Engines of Our Ingenuity

No. 368:
THE SIZE OF IT

by John H. Lienhard

Click here for audio of Episode 368.

Today, we wonder: How big is big? How small is small? 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.

The extent of our universe is some 15 billion light years. It's about 10-to-the-nineteenth times bigger than earth. Earth in turn is about 10-to-the-nineteenth times bigger than an electron. As far as size goes, we're curiously placed right in the middle. Things reach just as far inward as they do outward.

The universe, expanding at the speed of light, is one light year larger each year. That's around ten trillion miles. It seems like a lot, but the universe is already so big that it expands by only a ten trillionth of a percent in a year.

These enormities do funny things. When I say we breathe 10-to-the-22 molecules in each breath, that's just a number. But see it another way: Consider the first breath you exhaled when you got off the plane in -- say -- London, 15 years ago. That breath diffused into the air. It blew off into the trade winds. It has circled the earth, mixed into hurricanes and blizzards. Over the years it's been stirred into the air over every land and every sea. Right now, as you listen to my voice, no matter where you are, you take in one molecule of that single 15-year-old breath that you spent in another land -- every time you inhale. That's what the number 10-to-the-22 means.

And we're centered in all this magnitude. Our ability to comprehend is also centered. We can understand distances up to about 1000 times our length. We can see lengths down to about 1/1000th of our length. Beyond that, we fly on instruments.

If we look at a germ under a microscope, the experience of seeing becomes synthetic. We can gaze at the moon and stars, but we have no idea whether they lie one mile or a billion miles away. To find out, we have to use analysis and instruments. We resort to synthetic experience.

So we play the delicious magnitude game. The earth is as much larger than you, as you are larger than the cells that make up your body. We're oddly centered in a world that's both too large and too small to comprehend. We could be no smaller than we are and still own that great computer called a brain. And our immense universe is as small as it could be and yet be old enough to have spawned us. It took 15 billion years for the expanding stars and planets to ripen -- for earth to cool until it could sustain carbon-based life.

So we dwell in the right place at the right time. It's a huge and ancient place made to our measure. It's large enough to contain a free people. And it's small enough that we can either spoil it or shape it into a fit dwelling.

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

(Theme music)


Barrow, J.D. and Tipler, F., The Anthropic Cosmological Principle. New York: Oxford University Press, 1988.

Tien, C-l. and Lienhard, J.H., Statistical Thermodynamics. New York: Hemisphere Pub. Corp., 1979 (See especially Example 2.2.)

Schrödinger, E., What is Life? & Other Scientific Essays. New York: Doubleday Anchor Books, 1956




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

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