How Light Changed the Rules of Opposites

North couldn’t be south. An odd number couldn’t be even. And a particle couldn’t be a wave. Then we saw the light. /

Our earliest rational-scientific descriptions of the universe attached great importance to the existence of opposites. The Pythagoreans, for example, saw the world in terms of ten polar opposites: Limited/Unlimited, Odd/Even, Unity/Plurality, Right/Left, Male/Female, Rest/Motion, Straight/Curved, Light/Darkness, Good/Evil, and Square/Oblong.

Until recently, science’s view of the universe hinged on the existence of another antithetical pair: particle/wave. A particle has a well-defined shape and size. By contrast, a wave is smeared out, like the widening ripples on a pond. A particle’s shape and size don’t change from medium to medium—they are the same in water or molasses. By contrast, the substance and appearance of a wave depend critically on whether it is moving in water, molasses, or some other material. To borrow a phrase from Marshall McLuhan, when it comes to waves, the medium is quite literally the message.

For ages, science considered light to be a wave, not a particle. But that belief was demolished a little more than a century ago.

The experiment that triggered the revolution was performed in the late 1800s, first by Heinrich Hertz and then by his assistant, Philipp Lenard. The setup was simple. When the scientists shone light of different colors and brightness onto a polished metal plate, their instruments detected negatively charged particles—later called electrons—coming off the surface. The men reasoned that electrons in the metal plate were being shoved around by the light waves, the way surfers are by ocean waves. Nothing unusual about that.

But something wasn't quite right. Instead of appearing to be nudged off the metal plate by soft-body waves, the electrons veritably leaped from the surface as if hit by a heavy sledgehammer.

It reminds me of an extraordinary phenomenon I discovered at the Avalon Peninsula in southeast Newfoundland. I came upon a beach made entirely of large pebbles. Every time a wave broke on the shore, it jostled the pebbles, creating a racket. The pebbles behaved exactly as science had expected electrons to behave in Hertz's experiment. The electrons, according to the old theory, should have been jostled around. But instead, they flew off like sharply struck billiard balls.

There was another bit of unexpected strangeness. The brightness of the light made no difference. When hit with dim or bright light, electrons flew off the plate with the same energy, which was ridiculous. It was like saying that tiny ripples and monster waves propel surfers with equal momentum.

There was one final bit of nuttiness. The color of the light—its frequency, the number of cycles per second it has—made a huge difference in the results. Red light pushed electrons off the plate with far less energy than blue light. It made no sense.

In short, everything about the experimental results was backward. The brightness of a light wave, which should determine its wallop, didn't. The color of a light wave, which shouldn't make any difference, did.

Enter 26-year-old Albert Einstein, a total newcomer to the world of professional science. In 1905 he offered an explanation of Hertz’s and Lenard’s so-called photoelectric experiment's crazy results—and it was shocking.

Forget science’s age-old belief, he declared: light is not entirely a wave; sometimes it behaves exactly like—gasp!—a particle. In other words, light is some kind of queer Jekyll-Hyde-like particle-wave—a “quantum,” it came to be called. Incredibly, Einstein ended up being right and was awarded the Nobel Prize in physics.

Einstein’s pronouncement defied everything science had thought was beyond questioning. It was as if he were declaring that odd could be even, right could be left, white could be black. In the history of contemporary science, no one had ever spoken such seemingly contradictory nonsense.

If that weren't a hard enough pill for early 20th-century scientists to swallow, a French aristocrat soon completed the job of destroying science’s cherished belief in the particle-wave dichotomy. In 1924, 32-year-old Prince Louis-Victor de Broglie floated the idea that since a wave can behave like a particle, surely a particle can behave like a wave. “After long reflection in solitude and meditation,” he recounted, “I suddenly had the idea, during the year 1923, that the discovery made by Einstein in 1905 should be generalized by extending it to all material particles and notably to electrons.”

Particles behaving like waves, waves behaving like particles. If it sounds a bit confusing to you, welcome to the dizzying world of 21st-century science. It's a world that sounds senseless but appears to describe very well the universe we live in, a universe that as far as we know comprises objective truth. A world where in certain circumstances, light behaves like a wave, and in others like a particle. Ditto for electrons: sometimes they behave like particles, sometimes like waves.

Please understand, it is not a world where real objects are half one thing and half a completely opposite thing. What science appears to have discovered is that a light ray and an electron are each fully a wave and fully a particle. Each embodies a contradiction. It's a world where our language has met its match, a world where particles and waves are all one hard-to-name, hard-to-comprehend thing—objects with a kind of dissociated identity, whose weird behavior is usually evident only in the teeny-tiny realm of atoms, but not always. Bizarre, seemingly contradictory objects of which we ourselves are made.

It reminds me of Jesus’ identity. The radical notion that Jesus is simultaneously God and man is as confounding as the quantum theoretical idea that light is at once wave and particle, and an electron is concurrently particle and wave. Not half-and-half, but fully one and fully the other.

At the extremities of reality—the realms of the super-tiny and the supernatural—we come face to face with truths for which we have no adequate words. As Niels Bohr, responsible for many of the stunning revelations about particles and waves, reportedly said, “The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.”

Michael Guillen (PhD, Cornell) is former science correspondent for ABC News. Excerpted with permission from Amazing Truths: How Science and the Bible Agree, which releases February 9. See also Chad Meeks’s article in issue 33 of The Behemoth on “The Timeless Life of a Photon.”

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Issue 41 / February 4, 2016
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