Today, we try living in a universe made just for us. 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.

A wild new scientific principle is gaining ground. It's called the Anthropic Principle, and it says:

Our Universe must have those properties which allow life to develop within it ...

Scientists are agreed on part of this. It's clear we wouldn't have carbon-based life if our physical laws were just a little different. We wouldn't be around in any other universe. Different worlds might have other kinds of intelligent life, but our world produced us. So in its weakest form, the Anthropic Principle is easy to accept. All it says is:

The observed physical quantities all take on values that make it possible for carbon based life to evolve ...

But if that's true, the only universe that can ever be known is one that has thinking observers in it. The universe itself is wed to the nature of its observers. That threatens the old idea of objective science -- the idea that science isn't tangled in human nature.

You have to stretch this only a little bit, and it comes out in far more startling ways. Able people have recast it in some very strange forms. John Wheeler at the University of Texas asks us to try this one:

Observers are necessary to bring the universe into being. Another wrinkle says that if a species comes into being and then dies out again, it takes back the universe's existence. That gives us the wildest form of the Principle so far:

Intelligent information-processing must come into existence in the Universe, and, once it does, it will never die out.

We don't know how much of the Anthropic Principle will still be around after people have thought it over. But the idea behind it has been with us for a long time. It's an old idea with a new place to stand. 2500 years ago, the Greek thinker Anaxagoras put the human mind at the center of things when he wrote:

... what is now and what will be -- all these the mind ordered.

And 200 years ago the poet William Blake also spoke for a kind of naturalism that centered on us. When Blake said,

Where man is not, nature is barren,

he was very close to this new physical hypothesis that the world is bent to fit its people.

Scientists have always struggled to keep their own subjective nature out of science. If any of the stronger forms of the Anthropic Principle gain a footing, that failing could well turn into a virtue.

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

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