Engines of Our Ingenuity

No. 2270:
LOUIS de BROGLIE

by John H. Lienhard

Today, the prince and the blurred pea. 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.

Quantum physics was formulated during the first three decades of the 20th century. First, Max Planck predicted the way radiant energy varied with wavelength, from very short cosmic rays through X-rays, ultraviolet, visible, infrared, heat, microwave, and radio waves. He succeeded by parceling energy into tiny packets.

That bizarre idea met resistance. But then Einstein used it to predict additional behavior -- so did others. Finally, Heisenberg gave us the Uncertainty Principle, and Schrodinger his famous equation, which encompassed all these strange results. Nature itself shifted upon its axis, and we took up residence in a new quantum world.

But the key link between Plancck's tiny quantum energy packets and the quantum physics in place by 1930, was a very strange idea. And it was put forth by a French prince.

Louis de Broglie He was Louis de Broglie (whose name the French pronounce more like de Broy.) He was born in Dieppe, in 1891 -- youngest son of the fifth duke de Broglie. His older brother Maurice became the sixth duke and, when Maurice died in 1960, Louis became the seventh -- until his own death, at almost 95.

De Broglie was raised as a prince. He was educated at home by tutors, then finished a university course in math and philosophy at the age of 17. Maurice, by the way, was an experimental physicist, but Louis always tilted more strongly toward theoretical ideas.

Before WW-I, Louis de Broglie was doing graduate work in law at the Sorbonne, and spending a lot time reading current work in physics. He'd been floundering, and now was drafted into the army. He began in mine removal, then transferred to radiotelegraphy.

When he got out six years later, he had direction. He plunged into quantum theory and, in 1922, wrote a doctoral thesis in which he set forth a new principle: That all bodies have a wavelength associated with them. That wavelength is Planck's constant divided by the body's momentum. Your wavelength or mine is immeasurably small. That's because Planck's constant is tiny and we're so large. But what about a pea -- at least a figurative pea?

The wavelength for a tiny electron is much larger than the electron itself. On the micro-scale, objects are smeared out in space. By 1924, Prince de Broglie's Principle was fully formulated. Three years later it was confirmed experimentally; and, in 1929, de Broglie won the Nobel Prize.

He went on to teach at the University of Paris, then became secretary of the Académie of Sciences. Few scientists were ever as unremittingly cheerful and well-loved as de Broglie. In 1952 he won the first Kalinga Prize for his work in popularizing science.

But what he'd really done was to build the bridge between quanta as simple packets of energy, and the new quantum physics of matter blurred and smeared. This prince truly did reshape the very pea that so troubled the sleep of scientists, a century ago.

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

(Theme music)


I. James, Remarkable Physicists. (Cambridge, UK: Cambridge University Press, 2004): see From de Broglie to Fermi, pp. 305-315.

C. L. Tien and J. H. Lienhard, Statistical Thermodynamics. (New York: Taylor and Francis, 1979/1971): Ch. 4, Development of Quantum Mechanics.

See also the Wikipedia article on de Broglie, from which the photo of de Broglie above is taken.

If is not familiar, here is the story of The Princess an the Pea.

Dulac's illustration of The Princess and the Pea
Edmund Dulac's art nouveau illustration of Han Christian Andersen's story of The Princess and the Pea, 1910.


The Engines of Our Ingenuity is Copyright © 1988-2006 by John H. Lienhard.