There’s Something in the Way That Nothing Behaves

There really is something to nothing.

It took “Seinfeld,” the enormously popular television show that purports to be about nothing, to demonstrate that for a nation. But physicists have known for most of the 20th century that emptiness is really kind of full.

The vacuum, as physicists call it, is chock-full of particles that pop into existence for such short periods of time that they can’t be detected directly. But the particles can have real, observable effects, as a recent experiment by Steve Lamoreaux of the Los Alamos National Laboratory demonstrates.

While working at the University of Washington in Seattle, Lamoreaux set out to demonstrate an effect predicted nearly 50 years ago by Dutch physicist Hendrik Casimir. Casimir calculated in 1948 that so-called virtual photons, which spontaneously burst into existence like kernels of popping corn and then disappear almost instantly, ought to push two narrowly separated metal plates together.

For five decades, nobody bothered to call Casimir on the intellectual carpet. The theory behind the prediction, known as quantum electrodynamics, is so sound that almost nobody dreamed it could be wrong.

A cornerstone of modern physics, quantum electrodynamics describes how particles behave in electromagnetic fields. The theory describes natural phenomena so well that some physicists consider it the most successful scientific theory going.

“Nowadays quantum electrodynamics needs confirmation no more than Newton’s laws or Einstein’s special relativity,” said Michael Eides, a physics professor at Pennsylvania State University.

So nobody ever bothered to test Casimir’s prediction. Everybody just assumed it must be true, because it was based on such ironclad physics.

But in a fit of prankishness, and as a demonstration for his students at the University of Washington, where he taught until last summer, Lamoreaux figured, “Why not measure it?”

“You never know what you’re going to find when you do an experiment,” he said.

To no one’s surprise, the theory worked just fine. As Lamoreaux incrementally moved a pair of metal plates closer and closer to one another, to distances a hundredth the thickness of a human hair, the plates began to feel an attraction to one another in exact accordance with Casimir’s quantum electrodynamical predictions.

“It’s a real property of space itself,” Lamoreaux said. “It’s really a weird thing.”

The two plates felt only a minuscule force, about what’s exerted by a protozoan’s flapping flagellum. But no matter how slightly, the presence of the two metal plates changed the character of empty space so as to generate the force.

The two plates attract each other because the space between them is like a box, explained Charles Sukenik, a University of Wisconsin physicist who has also demonstrated phenomena predicted by Casimir. Virtual photons can be thought of as waves coming in a range of sizes, and when the plates are extremely close the longest waves are excluded from the box.

Since those longest wavelength photons can’t pop into existence between the plates, the total energy of virtual photons inside the box is lower than it is outside. That energy difference is what pushes the plates together.

“We have given an unambiguous demonstration of the Casimir force with accuracy of order 5%,” Lamoreaux wrote in a paper describing his experiment. The paper appeared in the January issue of Physical Review Letters.

Although some researchers have speculated that the popping particles could be harnessed as an energy source, most physicists find no apparent practical value to Lamoreaux’s experiment. It does demonstrate, however, that on the size scale of smoke particles, Casimir’s is a force to be reckoned with.

That may be of practical concern in the future, when researchers hope to build machines that operate in such tiny realms. Nanomachines, as they’re known, could cruise the capillaries to repair damage caused by atherosclerosis, or be launched on space missions at incredibly low costs.

Right now the possibilities of nanotechnology are as endless as the imaginations of the field’s most enthusiastic proponents. But in the future, nanotechnology will rely on understanding the Casimir force and similar effects.

“As we go into the area of nanotechnology and things get very small,” Sukenik said, “one has to start to take them into account.”