From Jones and Bartlett, a book on Stem Cells from Dr. Ann A. Kiessling and Scott C. Anderson:

Selected Articles:

December 16, 2003

Electrifying News

A long-held theory comes to a shocking end.

Many young people who study science come away with the impression that all the important questions have been answered, and that it would be difficult or impossible to contribute to such a well-researched body of knowledge.

It ain't so. In fact, what we don't know is much more impressive than what we do know. And even what we do know is always subject to revision or refinement.

There's a good reason to revisit old knowledge. The difference between Newton and Einstein is hardly noticeable on typical scales, but philosophically, the two theories couldn't be farther apart. If tiny problems with Newtonian physics hadn't cropped up, Einstein would never have developed the theory of relativity that would lead, ultimately, to atomic power. As measurements get better, we often find that a beloved theory, like a comfortable but ancient sweater, is becoming somewhat threadbare and ill-fitting.

Such is the case with theories of lightning. You may have read that lightning is formed when an electric field builds up between positively charged clouds and the negatively charged earth. Just as rubbing your feet across the carpet leads to a build-up of electrons in your body, the turbulent air of a thunderstorm "rubs" electrons off. And just as touching a door handle causes those electrons to painfully pop out of your finger in a spark, lightning provides a similar shocking way to get rid of the built-up charge.

Time-lapse photography captures lightning in Norman, Oklahoma.
Photo by C. Clark, NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL)

That's a good theory, since there's a 300,000 volt difference across this atmospheric "battery." But there's a problem: To create lightning, the theory requires a field ten times stronger than what can be measured. Scientists have scratched their heads over this for years, and have thought that there must be a problem with the measurements. After all, it's not easy to get precise measurements of the electric field in the middle of a thunderstorm. Not too many people can be convinced to fly a kite in a storm anymore (it's a miracle that Ben Franklin wasn't killed).

So scientists have resorted to firing rockets into the thunderclouds. Behind them, these rockets trail a thin, Kevlar-coated wire (for strength over such long distances), allowing the scientists to probe the electrical nature of the storm. Sure enough, the field they measured is just too weak to provoke lightning strikes - at least according to the standard theory.

In the world most people inhabit, a failure like this would be an extremely distressing event. But in science, it's the exception to the rule that generates the greatest excitement. Whenever there's an incompatibility between theory and measurement, it's time to come up with a better theory. And that, in turn, typically bears even sweeter fruit. In science, failure is just as useful as success as long as it helps to distinguish between competing theories.

So it was back to the drawing board. The standard theory predicted that x-rays of a certain energy should accompany lightning, so Joseph Dwyer at the Florida Institute of Technology (which enjoys a lot of lightning) decided to look for this signature. But what he saw was surprising. Instead of the x-ray energies he expected, he saw something else: x-rays that are usually associated with cosmic rays.

But cosmic rays come from outer space. Can it be that lightning is actually triggered by exotic cosmic events, perhaps billions of light-years away? Dwyer realized that his conclusions gave newfound credibility to a theory advanced in the 1990s by Alexander Gurevich of the Lebedev Institute in Moscow. Gurevich proposed that cosmic rays could initiate a kind of electron chain reaction. When a cosmic ray hits an atom in the air, it can knock off an electron which flies off at high speed. It can hit another electron, which can hit another, etc., analogous to billiard balls on a pool table. But just like billiard balls, the electrons ultimately lose their energy (typically to heat) and then everything settles down again.

But now imagine that we lengthen the pool table, and tilt it very slightly. The felt holds the balls in place at first, provided we don't tilt the table too much. Now, when you hit the balls, they continue moving for as long as there is a table, and in fact they accelerate since they're going downhill. When they hit other balls, there is an increasing cascade of faster and faster-moving balls. For electrons, substitute an electric field for the tilt of the table, and you have what Gurevich called a "runaway breakdown." In fact, all that's needed is about a tenth of the electric field required by the standard theory. Oddly enough, that's just the field that we have.

This is not to say that the story is over and that we now know everything we need to know about lightning. There's plenty of room for improvement, and besides lightning, there are recently discovered electric phenomena fancifully called sprites and elves that require even more theories. But already, we have gained a much greater appreciation for how the earth is affected by its cosmic neighbors - and just how much there is still to learn.


Copyright © 2000-2014 by Scott Anderson
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Here are some other suggested readings about weather and lightning: