(Jan 21, 1997) -- For a half century, physicists have known that there is no such thing as absolute nothingness, and that the vacuum of empty space, devoid of even a single atom of matter, seethes with subtle activity. Now, with the help of a pair of metal plates and a fine wire, a scientist has directly measured the force exerted by fleeting fluctuations in the vacuum that pace the universal pulse of existence.
The sensitive experiment performed at the University of Washington in Seattle by Dr. Steve K. Lamoreaux, an atomic physicist who is now at Los Alamos National Laboratory, was described in a recent issue of the journal Physical Review Letters. Lamoreaux's results almost perfectly matched theoretical predictions based on quantum electrodynamics, a theory that touches on many of the riddles of existence and on the origin and fate of the universe.
The theory has been wonderfully accurate in predicting the results of subatomic particle experiments, and it has also been the basis of speculations verging on science fiction. One of the wilder ones is the possibility that the universal vacuum -- the ubiquitous empty space of the universe -- might actually be a false vacuum.
If that were so, something might cause the present-day universal vacuum to collapse to a different vacuum of a lower energy. The effect, propagating at the speed of light, would be the annihilation of all matter in the universe. There would be no warning for humankind; the earth and its inhabitants would simply cease to exist at the instant the collapsing vacuum reached the planet.
Another suggestion by several theorists is that the phenomenon Lamoreaux has been studying might provide a mechanism by which some advanced civilization in the distant future could construct a time-warp machine, allowing people to tunnel almost instantly through "wormholes" to distant points in space and time.
Lamoreaux's experiment was the first direct and conclusive demonstration of something much less speculative: the Casimir Effect, which has been posited as a force produced solely by activity in the "empty" vacuum. His results came as no surprise to anyone familiar with quantum electrodynamics, but they served as material confirmation of a bizarre theoretical prediction.
Quantum electrodynamics holds that the all-pervading vacuum continuously spawns particles and waves that spontaneously pop into and out of existence on an almost unimaginably short time scale.
This churning quantum "foam," as some physicists call it, is believed to extend throughout the universe. It fills the empty space within the atoms in human bodies, and reaches the emptiest and most remote regions of the cosmos. In this foam, a typical pair of newborn "virtual" particles can survive for only about 10 to the minus 43rd power seconds (that is, a fraction of a second equal to one divided by 10 followed by 42 zeroes).
Quantum electrodynamics became a respectable theory in the 1920s, and since then it has been rigorously tested by many experiments and found to be perfectly sound. But the Casimir Effect had not been directly measured. The effect is named for Hendrick B.G. Casimir, the Dutch physicist who predicted it in 1948. Based on calculations derived from quantum electrodynamics, he concluded that if two parallel metal plates were held very close together, a force generated by vacuum quantum effects alone would push the plates together. If the two plates are so close that their separation is less than the longer wavelengths of fleeting particles in the quantum foam, he reasoned, the longer wavelengths would be excluded from the space between the plates. The vacuum outside the plates, however, would contain its normal full complement of all wavelengths of virtual particles, which would then exert a force tending to push the plates together.
The force, Casimir calculated, would be so small as to be almost undetectable, but it should, in principle, be measurable.
A similar effect, a quantum mechanical force exerted on neutral sodium atoms traveling between a pair of metal plates, was detected and measured in 1992 by Dr. Edward Hinds and his colleagues at Yale University. But Lamoreaux decided to try to conduct the exceedingly difficult experiment of measuring the force between two parallel plates directly.
Aligning the plates to be perfectly parallel while separated by a space only about one micron wide proved to be impossible, he said in an interview. (A micron, one-millionth of a meter, is about one one-hundredth the thickness of a human hair.) Instead, he substituted a lens-shaped plate for one of the flat ones, and with this, constant separation between the plate and the closest point on the curved surface of the lens was easier to maintain.
One of the plates was attached to a bar suspended by a fine tungsten wire -- a torsion pendulum. By linking the other end of the bar to a feedback system, he was able to detect and measure the tiny attractive force between the plates. The amount he found was within 5 percent of the value predicted by quantum electrodynamics for the Casimir Effect.
Lamoreaux said he had been intrigued for many years by the mystery of the vacuum and the paradox that even a vacuum containing no matter embodies enormous complexity in the form of fluctuations and fleeting virtual particles.
"Now that the experiment is done," he said, "I've been thinking a lot about what it means. It's a really funny feeling. Although I'm an atomic physicist and this experiment was a bit out of my line, I found it the most intellectually satisfying experiment I've ever done."
Original file name: CNI - Energy of Vacuum
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