Suffering from inertia? Gravity got you down? You are not alone. Gravity and inertia are among the most fundamental attributes of anything possessing mass. But researchers have never attained a satisfactory understanding of the fundamental nature of gravity. Inertia has proved an even more elusive problem. Ever since Isaac Newton articulated his three laws of motion, scientists have simply accepted the existence of inertia as a given: bodies in motion remain in motion, and those at rest stay at rest, unless acted on by an outside force.

Bernhard M. Haisch of the Lockheed Palo Alto Research Laboratory, Alfonso Rueda of California Sate University at Long Beach and Harold E. Puthoff of the Institute for Advanced Studies in Austin, Tex., think they may at last have a clue to the process that gives rise to inertia. That process, Haisch argues, must be connected to gravitation as well, neatly unifying intertial and gravitational mass, the two ways that physicists define the mass of an object.

Writing in the February issue of Physical Review A, the three researchers describe inertia as the consequence of the bizarre subatomic happenings that take place in ostensibly empty space. Quantum theory predicts that, on such tiny scales, random quantum fluctuations roil the vacuum, creating a soup of virtual particles. Those particles continuously pop in and out of existence before they can be directly detected.

Haisch and his collaborators started by assuming the existence of such small-scale electromagnetic fluctuations, known as the zero-point field. They then examined the effects of the field on normal matter. In the mid-1970's several researchers showed that an object accelerating through the zero-point field should be exposed to a glow of radiation stirred up from the vacuum. Haisch, whose background is in astrophysics, wondered whether that radiation would exert a "pressure" opposing the acceleration; such a pressure exactly fits the description of inertia.

Rueda cast those ideas in mathematical form and became convinced that Haisch was on to something. "Intuitively, it made a lot of sense," he says. "The only thing that can resist the accelerating agent is the vacuum — what else is there?" He notes that the zero-point field is present at all times and in all places, which would explain the instantaneous, universal nature of inertia.

The two scientists soon teamed up with Puthoff, who had been exploring possible connections between gravity and the zero-point field. Although theorists have had considerable success understanding the other three forces of nature (electromagetism and the two nuclear forces), "gravity has always been the oddball," Haisch reflects. Puthoff, drawing on earlier work by the late Russian physicist Andrei Sakharov, seeks to explain gravity as a long-range effect of zero-point electromagnetic fluctuations. Linking gravity to the zero-point field automatically draws inertia into the explanation and so naturally accounts for the equivalence of inertial and gravitational mass.

The ambitious, unconventional theory of inertia immediately faces a dubious audience. "I like the philosophical idea of what they are trying to do," says astrophysicist Paul S. Wesson of the University of Waterloo, "but I'm skeptical about the details." He points out, for example, that the zero-point field contains a great deal of energy. Because energy is equivalent to matter (according to Einstein's famous equation), the zero-point field might be expected to generate an intense gravitational tug, in blatant conflict with the observed structure of the cosmos. Haisch suggests that if the zero-point field gives rise to gravity, as Sakharov proposed, the energy within that field would not itself produce gravitational effects.

Peter W. Milonni of Los Alamos National Laboratory voices far more serious reservations. He worries that the theory ascribes real significance to a term describing the mass of particles, one that is normally considered to have no physical meaning and so is subtracted out of quantum-mechanical equations. And he sees "many inconsistencies" in the theory resulting from idealized or ad hoc assumptions. Nevertheless, he admits the appeal of Haisch's approach. "Sometimes wrong ideas lead people to the right one," he comments.

Haisch and his co-authors plan to reformulate their results in more conventional quantum-mechanical terminology, which may make them more appealing. "This is the first step in a new way to look at things," Haisch explains. "You can't expect us to solve everything in one fell swoop." The three researchers also look to observational support from an upcoming experiment at the Stanford Linear Collider, which will measure the effect of electromagnetic radiation on the apparent mass of the electron.

That phenomenon raises the highly speculative prospect that the proper electromagnetic field could elminate the inertia of any object, thereby permitting levitation. Controlling inertia may be possible, Haisch reluctantly concedes, but "God knows if it's ever going to become a reality." Still, for those people trying to make their lives a little lighter, it is nice to know that science may be able - someday - to lend a hand.