Philip Ball, Nature, Feb. 2004
http://www.nature.com/Physics/Physic...07899240295C0F
Empty space can set objects in motion, a physicist claims.
The empty space between stars contains energy from virtual particles.
© NASA
Motion can be conjured out of thin air, according to a physicist in Israel.
Alexander Feigel of the Weizmann Institute of Science in Rehovot says that objects can achieve speeds of several centimetres an hour by getting a push from the empty space of a vacuum.
No one has yet measured anything being set in motion by emptiness. But Feigel thinks it should theoretically be possible to make use of the effect to shunt tiny amounts of liquids around on a lab chip, for example. Such small-scale experiments could be useful for chemists interested in testing thousands of different drugs at the same time, or for forensic scientists who need to do analyses on tiny amounts of material.
The whole idea of getting movement from nothing sounds like a gift to advocates of perpetual-motion machines. But there's nothing in Feigel's theory that violates the fundamental laws of physics, so this doesn’t provide a way to cheat the Universe and get free energy.
Instead, Feigel draws on the well-established notion that empty space does contain a little bit of energy. This ‘vacuum energy’ is a consequence of the uncertainty principle — one of the cornerstones of quantum mechanics.
Because of the uncertainty principle, subatomic particles or photons can appear spontaneously in empty space — provided that they promptly vanish again. This constant production and destruction of 'virtual particles' in a vacuum imbues the vacuum with a small amount of energy.
Moving in a Vacuum
Feigel considered the effects of virtual photons on the momentum — a property defined as mass multiplied by velocity — of objects placed in a vacuum, and came to a surprising conclusion.
He started with the fact that electrical and magnetic forces between objects are mediated by photons that flit between them. So an object placed in strong electric and magnetic fields can be considered to be immersed in a sea of these transitory, virtual photons.
Feigel then showed that the momentum of the virtual photons that pop up inside a vacuum can depend upon the direction in which they are travelling. He concludes that if the electric field points up and the magnetic field points north, for example, then east-heading photons will have a different momentum from west-heading photons.
So the vacuum acquires a net momentum in one direction — it’s as though the empty space is ‘moving’ in that direction, even though it is empty.
It is a general principle of physics that momentum is ‘conserved’ — if something moves one way, another thing must move the other way, as a gun recoils when it shoots a bullet. So when the vacuum acquires some momentum from these virtual photons, the object placed within it itself starts to move in the opposite direction.
Feigel estimates that in an electric field of 100,000 volts per metre and a magnetic field of 17 tesla — both big values, but attainable with current technology — an object as dense as water would move at around 18 centimetres per hour.
References
1. Feigel, A. Quantum vacuum contribution to the momentum of dielectric media. Physical Review Letters, 92, 020404, doi:10.1103/PhysRevLett.92.020404 (2004).
Re: Zero Point Field
