Today, entropy at the movies. 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 have huge admiration for film-critic Roger Ebert --
the way he combines fine writing with uncanny insight into the meaning of
movies. And his love of the medium is contagious. Still, he's done two
things that really bother me: One was giving four stars to that atrocious
misandrist movie, The Joy Luck Club. Well, we all blow one now
and then -- and there's no settling arguments over taste.
Ebert's greater mistake was a line in his review of the movie,
The Adjustment Bureau. In it, he says,
"... in the long run the universe will entropy and cease." It'll do what!
Richard Armstrong recently did an Engines episode on the verbing of nouns --
that is, our rising inclination to make nouns into verbs: Text becomes texting;
friend becomes friending, and so on. Now Ebert has verbed the noun entropy.
And that makes it very hard on those of us charged with using and explaining science.
You see, entropy is a material property -- like density or elasticity. When we
do things to a material we change its entropy. That much would be straightforward.
But entropy seems mysterious for two reasons. One is that we can't measure it;
we can only calculate it from other properties. We can't just examine two objects
and know which of the two has the greater entropy.
It's also perplexing because, when anything happens, the combined entropy of everything
involved in the event has to increase. The entropy of any object can increase or decrease.
But together, the sum of all entropies is higher when the process is finished. That
fact is called the second law of thermodynamics. It gives time its direction since time
and entropy increase together. The changing entropy of all things defines past and present.
So you see the problem. Here's a concrete physical property that we engineers use when
we design heat pumps or chemical processes, engines or heating systems. But it so happens
that throughout the universe the sum of all entropies can only increase.
Try this: Put a liter of cold water in the refrigerator and let it freeze. After it's frozen,
its entropy -- that technical noun -- will've decreased by around 1.3 kilojoules per
degree Kelvin. Of course the entropy of the air around it will've increased.
The point is, component entropies can change either way.
Try this: Put a liter of cold water in the refrigerator and let it freeze. After it's frozen,
its entropy -- that technical noun -- will've decreased around 1.3 kilojoules per degree Kelvin.
Of course the entropy of the air around it will've increased. The point is, component entropies
can change either way.
So we have the second law, with its cosmic implications of decay. But let's not steal entropy
-- a working tool of engineering -- and make it into a verb meaning second law decay.
We need entropy in our work. And it'll be an impoverished world if we have to develop separate
vocabularies -- one for sensible science and one for media hyperbole. To you, Mr. Ebert, I say
thank you for years of enriching my movie-going. I'll even pretend I never saw that
Joy Luck Club review. But please -- tread carefully on the precise language of engineering.
For it is the coin by which we all negotiate the complex world we live in.
I'm John Lienhard at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
See the Wikipedia articles on
The Second Law of Thermodynamics
and Entropy.
See also the IMDB articles on
The Joy Luck Club
and Ebert's review of it,
as well as Armstrong's episode on verbing
and Lienhard's episodes on
the second law of thermodynamics
and on teaching thermodynamics.
My thanks to engineering colleague Keith Hollingsworth for his counsel.
