Is "empty space" really all that empty?


Demonstrating the existence of zero-point energy is one thing; extracting useful amounts is another. Puthoff’s institute, which he likens to a mini Bureau of Standards, has examined about 10 devices over the past 10 years and found nothing workable.

One contraption, whose Russian inventor claimed could produce kilowatts of excess heat,


supposedly relied on sonoluminescence, the conversion of sound into light. Bombarding water with sound to create air bubbles can, under the right conditions, lead to bubbles that collapse and give off flashes of light. Conventional thinking explains sonoluminescence in terms of a shock wave launched within the collapsing bubble, which heats the interior to a flash point.

Following up on the work of the late Nobelist Julian Schwinger, a few workers cite zero-point energy as the cause. Basically, the surface of the bubble is supposed to act as the Casimir force plates; as the bubble shrinks, it starts to exclude the bigger modes of the vacuum energy, which is converted to light. That theory notwithstanding, Puthoff and his colleague Scott Little tested the device and changed the details a number of times but never found excess energy.

Puthoff believes atoms, not bubbles, offer a better approach. His idea hinges on an unproved hypothesis: that zeropoint energy is what keeps electrons in an atom orbiting the nucleus. In classical physics, circulating charges like an orbiting electron lose energy through radiation; what keeps the electron zipping around the nucleus is, to Puthoff, zero-point energy that the electron continuously absorbs. (Quantum mechanics as originally formulated simply states that an electron in an atom must have some minimum, ground-state energy.)

Physicists have demonstrated that a small enough cavity can suppress the natural inclination of a trapped, excited particle to give up some energy and drop to a lower energy state [see “Cavity Quantum Electrodynamics,” by Serge Haroche and Jean-Michel Raimond; SCIENTIFIC AMERICAN, April 1993]. Basically, the cavity is so small that it can exclude some of the lower-frequency vacuum fluctuations, which the excited atom needs to emit light and drop to a lower energy level. The cavity in effect controls the vacuum fluctuations.

Under the right circumstances, Puthoff reasons, one could effectively manipulate the vacuum so that a new, lower ground state appears. The electron would then drop to the lower ground state–in effect, the atom would become smaller–and give up some energy in the process. “It implies that hydrogen or deuterium injected into cavities might produce excess energy,” Puthoff says. This possibility might explain cold-fusion experiments, he notes–in other words, the occasional positive results reported in cold-fusion tests might really be indicators of zero-point energy (rather than, one would assume, wishful thinking).

Underlying these attempts to tap the vacuum is the assumption that empty space holds enough energy to be tapped. Considering just the fluctuations in the electromagnetic force, the mathematics of quantum mechanics suggest that any given volume of empty space could contain an infinite number of vacuum-energy frequencies–and hence, an infinite supply of energy. (That does not even count the contributions from other forces.) This sea of energy is largely invisible to us, according to the zeropoint-energy chauvinists, because it is completely uniform, bombarding us from all directions such that the net force acting on any object is zero.

But just because equations produce an infinity does not mean that an infinity exists in any practical sense. In fact, physicists quite often “renormalize” equations to get rid of infinities, so that they can ascribe physical meaning to their numbers. An example is the calculation of the electron’s mass from theoretical principles, which at face value leads to an unrealistic, infinite mass. The same kind of mathematical sleight-of-hand might need to be done for vacuum-energy calculations. “Somehow the notion that the energy is infinite is too naive,” Milonni says.

Lamoreaux’s experiment could roughly be considered to have extracted 10^-15 joule. That paltry quantity would seem to be damning evidence that not much can be extracted from empty space. But Puthoff counters that Casimir plates are macroscopic objects. What is needed for practical energy extraction are many plates, say, some 10^23 of them. That might be possible with systems that rely on small particles, such as atoms. “What you lose in energy per interaction, you gain in the number of interactions;” he asserts.

Milonni replies by noting that Lamoreaux’s plates themselves are made of atoms, so that effectively there were 10^23 particles involved. The low Casimir result still indicates, by his figures, that the plates would need to be kilometers long to generate even a kilogram of force. Moreover, there is a cost in extracting the energy of the plates coming together, Milonni says: “You have to pull the plates apart, too.

Another argument for a minuscule vacuum energy is that the fabric of space and time, though slightly curved near objects, is pretty much flat overall. Draw a triangle in space and the sum of its angles is 180 degrees, as it would be on a flat piece of paper. (The angles of a triangle on a sphere, conversely, sum to more than 180 degrees.)

Because energy is equivalent to matter, and matter exerts a gravitational force, cosmologists expect that an energy-rich vacuum would create a strong gravity field that distorts space and time as it is seen today. The whole universe would be evolving in a different manner.

Casimir Effect

CASIMIR EFFECT is the motion of two parallel plates because of quantum fluctuations in a
vacuum. The plates are so dose together that only small fluctuations fit in between; the bigger modes are excluded (above). They exert a total force greater than that by the smaller modes and hence push the plates together. The effect was observed by Steve K. Lamoreaux, now at Los Alamos National Laboratory, who relied on a torsion pendulum (left). A current applied to the piezoelectric stack tried to move the Casimir plate on the pendulum; the compensator plates held the pendulum still. The voltage needed to prevent any twisting served as a measure of the Casimir effect.

By: Philip Yam
From Scientific American Magazine, December 1997, pp. 82-85.

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