Spooky subatomic behavior seen on grander scale

Keay Davidson, Chronicle Science Writer
Sunday, February 22, 2004
From: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/22/QUANTUM.TMP&type=science

Eight decades after one of the weirdest discoveries in the history of science -- that subatomic matter is wavelike -- Austrian scientists are studying the same phenomenon on a much bigger scale, in giant molecules of carbon.

Such research is more dramatic evidence that the spooky phenomena of quantum physics aren't confined to the infinitesimally tiny world within the atom. In fact, quantum effects influence objects much, much bigger than atoms, possibly even important molecules in the human body.

Such research has been under way for several years, and the latest findings are discussed in the current issue of the journal Nature. The years of research by Markus Arndt, Anton Zeilinger and their colleagues at the University of Vienna is worthy of the Nobel Prize, says a spokesperson for the largest organization of physicists in North America.

Zeilinger is "one of the most exciting scientists on the planet ... I'm sure he will get the Nobel someday for his studies of quantum weirdness," said Phil Schewe, a physicist and science writer for the American Institute of Physics. Schewe isn't connected with the Zeilinger team.

"It's marvelous work," said physicist Wojciech Zurek, a leading authority on quantum theory at Los Alamos National Laboratory in New Mexico. The Nature article is "sort of the next step in a progression of very nice papers from the Vienna group."

In the everyday world of classical physics, buildings continually occupy the same position. For example: The Transamerica Building is at 600 Montgomery St. That's also where it was yesterday, and, barring a really awful earthquake, it'll occupy the same location tomorrow.

But in the eerie world of quantum physics, subatomic particles don't have fixed addresses. Take an electron, for example: One moment it's in one place, then it instantaneously appears in another place, then another, etc. Recall the golfing comedy "Caddyshack," in which the golf course gopher poked its head from one hole, then another, then another, and so on.

However, a subatomic particle's positions aren't hopelessly unpredictable. At any given moment, the probability of finding the particle at any given spot is determined by a "probability distribution," which spreads out like a wave; the particle is likelier to be found at the crest of the wave than at its trough. Bizarre as such wavelike matter sounds, physicists have long accepted it as a reality of the subatomic realm.

In recent years, though, they've realized that much bigger particles, namely molecules (clusters of atoms), can also behave in a wavelike fashion.

First, a little history: Light behaves in a wavelike fashion, as scientists have known for centuries. This is revealed by passing light through a series of slits perpendicular to the direction of the light beam. As light waves pass through the slits, they diffract and interfere with each other, creating "interference patterns" on an adjacent wall. These are just like the interference patterns created by waves of water when they pass through the slits in a partly submerged fence along a shoreline.

In the 1920s, as part of his doctoral dissertation, the French physicist Louis de Broglie proposed that subatomic matter also behaves like waves. Members of the dissertation committee were scandalized by his idea; they assumed that atomic-scale objects behaved as predictably as little marbles. But the great physicist Albert Einstein assured them de Broglie was on to something important, so they gave de Broglie his doctorate. He later won the Nobel Prize in physics.

Subsequent experiments by other scientists proved de Broglie was right: Electrons behave not like marbles but like little waves. The discovery became one of the key foundations for "quantum mechanics," now the reigning theory of the subatomic world. Even so, for decades after, most scientists assumed that quantum effects disappeared in objects larger than electrons or atoms.

They were wrong. In 1999, Zeilinger and his colleagues fired beams of "carbon-60" or "carbon-70" molecules (so named because each molecule contains 60 or 70 carbon atoms) at a device called a diffraction grating. The individual molecules spread out in wavelike patterns, creating "interference patterns" visible on a monitor. This proved that even very hefty molecules can experience quantum effects -- and, thus, can literally be in more than one place at a time, crazy though this sounds.

The wavelike behavior of a particle means that in a very real sense, it "exists" not at a single, easily definable spot but, rather, exists simultaneously across a broad area.

In the Zeilinger experiments, a carbon-70 molecule is "instantaneously located" at innumerable spots across an area 1,000 times wider than the molecule itself. (The molecule is one nanometer wide -- that is, one-millionth of a millimeter.) To grasp how weird this is, imagine a person trying to "walk at the same time through two doors that are separated by 1,000 meters," says a statement by the University of Vienna's Institute for Theoretical Physics, the Zeilinger team's home.

In an e-mail to The Chronicle, Arndt said the team might next try to detect quantum effects in even bigger molecules, say a protein such as insulin, a hormone secreted by the human pancreas.

"However, there are also still many technological challenges to be overcome" before achieving such a feat, Arndt said. Also, "we have only started to think" about ways in which the research might improve human understanding of biochemical phenomena.

Such research also stirs philosophical squabbles. Since the early 20th century, the Einsteinian and quantum revolutions have inspired scientists and philosophers of science to reassess traditional conceptions of "matter," "energy," "space," "time," "causality," "locality" and other seemingly commonsensical notions.

True, said Zurek, of Los Alamos National Laboratory, quantum theory violates our everyday notions of "reality." When laypeople ask physicists why the universe acts so strangely, most shrug their shoulders and say that's just the way it is and we might as well get used to it.

With good reason, Zurek says: "The only theory we know that has been found correct in all the experiments ever done is quantum theory. Quantum theory has been tested much, much more rigorously and with much more sensitive experiments than Einstein's relativity."