Skip to main content
No. 1265:
Self-Evident Concepts

Today, a closer look at scientific knowledge. 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.

"We hold these truths to be self-evident," said our founding fathers. They were speaking of human rights and liberties. But they were tying into 18th-century scientific thinking. In that rationalist world, Euclid's geometrical axioms were models of the self-evident truths from which all other knowledge derives.

By now, many of Euclid's self-evident axioms have come under question. And we realize that self-evident scientific truth is only scientific misdirection. All science comes to rest on what we call concepts. A concept is a building block that we can't define.

Take the word energy. My dictionary says energy is the capacity for doing work. So I look up work, and find it defined as a transfer of energy. The definitions just take us in a big circle. So what is energy?

The answer's simple, really. But we find it outside science. Energy is something we've all experienced and know in our gut. Energy is what it takes to get us to the mountaintop, or just out of bed in the morning. Energy is what we have to contribute to cold water to make it boil. Energy is what gasoline releases to make our automobiles run. Energy is an essential human experience.

If we look closely at physics books, we'll find that they don't define energy at all. They give examples of its various forms. They show how to calculate work-energy. They show how to translate that into other forms of energy. But they never, never address the question, "What is energy?"

The trouble with most physics texts is that they seldom tell students that energy remains undefined. They create the illusion of a definition to give students confidence. Who wants to say that science comes to rest on the human gut, or in the human heart?

The same is true of other essential quantities. I dare you to define distance, time, or force. Or to prove Newton's laws, for that matter! Any real physical law is simply a statement of human experience in dealing with conceptual quantities.

Science is a strange pursuit. It really is far and away the most careful and accurate attempt we make at understanding the world around us. It is loaded with safeguards against imposing what we want to be true upon what is true. It gives to engineers a vast toolkit for getting things done.

It's just because science is such a formidable tool that we try to take it all the way to absolute truth. But absolute truth is God's province, not ours. In the meantime, this highly-honed, still-imperfect mode of inquiry takes us to Mars and lets us do surgery on our own DNA. For me, the most spectacular thing about the scientific process is that is gives us means for doing so much -- when we can't even define the elementary tools of the trade.

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

(Theme music)

Typical textbook definition of energy.
Notice how incomplete it is.