The theory was previously used to explain inertial mass - the property of matter that resists acceleration - but it has been extended to gravitational mass, which is the property of matter that feels the tug of gravity.
For decades, mainstream opinion has held that something called the Higgs field gives matter its mass, mediated by a particle called the Higgs boson. But no one has yet seen the Higgs boson, despite considerable time and money spent looking for it in particle accelerators.
In the 1990s, Alfonso Rueda of California State University in Long Beach and Bernard Haisch, who was then at the California Institute for Physics and Astrophysics in Scotts Valley and is now with ManyOne Networks, suggested that a very different kind of field known as the quantum vacuum might be responsible for mass. This field, which is predicted by quantum theory, is the lowest energy state of space-time and is made of residual electromagnetic vibrations at every point in the universe. It is also called a zeropoint field and is thought to manifest itself as a sea of virtual photons that continually pop into and out of existence.
Rueda and Haisch argued that charged matter particles such as electrons and quarks are unceasingly jiggled around by the zero-point field. If they are at rest, or travelling at a constant speed with respect to the field, then the net effect of all this jiggling is zero: there is no force acting on the particle. But if a particle is accelerating, their calculations in 1994 showed that it would encounter more photons from the quantum vacuum in front than behind it (see Diagram). This would result in a net force pushing against the particle, giving rise to its inertial mass (Physical Review A, vol 49, p 678).
But this work only explained one type of mass. Now the researchers say that the same process can explain gravitational mass. Imagine a massive body that warps the fabric of space-time around it. The object would also warp the zero-point field such that a particle in its vicinity would encounter more photons on the side away from the object than on the nearer side. This would result in a net force towards the massive object, so the particle would feel the tug of gravity. This would be its gravitational mass, or weight (Annalen der Physik, vol 14, p 479).
Rueda and Haisch say this demonstrates the equivalence of inertial and gravitational mass - something that Einstein argued for in his theory of general relativity. "In place of having the particle accelerate through the zero-point field, you have the zero-point field accelerating past the particle," says Haisch. "So the generation of weight is the same as the generation of inertial mass."
The idea is far from winning wide acceptance. To begin with, there's a conundrum about the zero-point field that needs to be solved. The total energy contained in the field is staggeringly large - enough to warp space-time and make the universe collapse in a heartbeat. Obviously this is not happening. Also, the pair's work can only account for the mass of charged particles.
Nobel laureate Sheldon Glashow of Boston University is dismissive. "This stuff, as Wolfgang Pauli would say, is not even wrong," he says. But physicist Paul Wesson of Stanford University in California says Rueda and Haisch's unorthodox approach shows promise, though he adds that the theory needs to be backed up by experimental evidence. "If Haisch [and Rueda] could come up with a concrete prediction, then that would make people sit up and take notice," he says. "We're all looking for something we can measure."
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THIS ARTICLE APPEARS IN NEW SCIENTIST MAGAZINE ISSUE: 13 AUGUST 2005
Written by MARK ANDERSON
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