Such claims emit a strong scent of fantasy, but researchers say incremental successes could open the door to significant breakthroughs in key areas of nanotechnology, and perhaps larger structures. "What I can contribute is to understand the role of the Casimir force in real working devices, such as microwave switches, MEMS oscillators and gyroscopes, that normally are made of silicon crystals, not perfect metals," Tang says.
The request for proposals closed in September. The project received "a lot of interest," Kenny says. "I was surprised at the creativity of the proposals, and at the practicality," he adds, although he declined to reveal how many teams submitted proposals. "It wasn't pure theory. There were real designs that looked buildable, and the physics looked well understood."
Still, the Casimir project was a "hard sell" for DARPA administrators, Kenny acknowledges. "It's very fundamental, very risky, and even speculative on the physics side," he says. "Convincing the agency management that the timing was right was difficult, especially given the number of programs that must compete for money within the agency."
DARPA managers certainly would be satisfied if the Casimir project produced anything tangible, because earlier attempts had failed. Between 1996 and 2003, for example, NASA had a program to explore what it calls Breakthrough Propulsion Physics to build spacecraft capable of traveling at speeds faster than light (299,790 kilometers per second). One way to do that is by harnessing the Casimir force in a vacuum and using the energy to power a propulsion system. The program closed with this epitaph on its Web site: "No breakthroughs appear imminent."
One of many problems with breakthrough propulsion based on the Casimir force is that whereas zero-point energy may be theoretically infinite, it is not necessarily limitless in practice—or even minutely accessible. "It's not so much that these look like really good energy schemes so much as they are clever ways of broaching some really hard questions and testing them," says Marc Millis, the NASA physicist who oversaw the propulsion program.
The DARPA program faces several formidable obstacles, as well, cautions Jeremy Munday, a physicist at California Institute of Technology who studies the Casimir effect. For starters, simply measuring the Casimir force is difficult enough. These experiments take many years to complete, adds Munday, who recently published a paper in Nature (Scientific American is part of the Nature Publishing Group) describing his own research. What's more, he says, although several groups have measured the Casimir force, only a few have been able to modify it significantly. Still, Munday adds, the exploratory nature of the program means its goals and expectations are "quite reasonable."
Tang is pragmatic about his efforts, given the unlikelihood that Casimir force will ever provide much energy to harness. "The force is really small," he says. "After all, a vacuum is a vacuum."
Yet sometimes the best science can hope for is baby steps. "To come up with anything that can lead to a viable energy conversion or a viable force producing effect, we're not anywhere close," Millis says. "But then, of course, you don't make progress unless you try.