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Half a Photon Here, Half a Photon There

The Einstein-Hopf process would be an interesting, but irrelevant, curiosity were it not for one peculiarity that sets the electromagnetic quantum vacuum apart from other radiation fields: the shape of its spectrum. The shape is exactly proportional to the frequency cubed -- precisely the right shape to be ``Lorentz invariant.'' A spectrum with this shape does not produce a Doppler effect. The photons that a gas particle meets head-on in the quantum vacuum are no more energetic than those that strike the particle from behind. Consequently, the photons can offer no concerted resistance to uniform motion. (The spectrum and directional distribution of photons, however, do change for particles that are accelerating; this is the origin of inertia in our theory, as discussed in the box on p. 15.)

This idiosyncrasy of the vacuum electromagnetic field throws the Einstein-Hopf process out of balance (see figure on p. 14). Once gas particles are set in motion by the random fluctuations of the electromagnetic field, nothing can stop them. Over millions of years they accelerate steadily, reaching velocities near to that of light and moving across astronomical distances.

Astrophysicists are no strangers to this mechanism. Twenty years ago, one of us proposed it as a possible source of the most energetic cosmic rays. Most cosmic rays consist of electrons, protons, and ions, but those of extremely high energy are missing the electrons. The Einstein-Hopf process would explain this, because it operates more efficiently on protons and ions than on electrons. What no one had considered was that this process could also segregate matter on a cosmological scale.

When we first looked into the matter, the Einstein-Hopf process sounded too good to be true. By transferring energy from virtual photons into real particles, would the process yield something for nothing? To check, we teamed up with IBM physicist Daniel Cole, an expert on the quantum vacuum. For over five years, Cole had been assessing whether theories of the vacuum violate any basic principles, such as the conservation of mass-energy or the second law of thermodynamics. He was able to find nothing amiss with the quantum Einstein-Hopf mechanism.

Emptiness Begets Emptiness

The theory rests on many assumptions, and the one that worries us is the most fundamental: that the quantum vacuum produces a real electromagnetic field. Physicists normally treat the virtual photons as just that: virtual, hence unable to produce any far-reaching real effects. But numerous experiments indicate the field may indeed influence matter. The quantum vacuum creates an attraction between neutral parallel plates, as predicted by Dutch physicist Hendrick Casimir in 1948 and confirmed experimentally several years later. The interaction of the vacuum electromagnetic field with electrons causes a shift of hydrogen spectral lines, as discovered by American physicists Willis Lamb Jr. and Robert Retherford in 1947 and explained later that year by Hans Bethe. And the spontaneous emission of photons can be altered by changing the electromagnetic environment of atoms; this suggests that ``spontaneous'' emission is actually stimulated by the fluctuations of the vacuum.

If the zero-point field is real, it should be possible to reproduce the Einstein-Hopf process in the laboratory. The main obstacle would be achieving densities comparable to those in the cosmic voids: less than one particle per cubic meter. But if we could even approximate this, the effect might be measurable. One possibility would be to create an extremely low temperature magnetic trap and inject anti-protons into it. If the Einstein-Hopf process ejected the anti-protons, the experimenter should see them annihilate with protons in the matter surrounding the trap.

The idea that the zero-point field might really exist dates to the early 20th century, when there was not yet a clear division between classical and quantum physics. Quantum mechanics emerged from a radical, and unsupported, assumption that German physicist Max Planck made in 1900: that the energy of a system can only take on certain discrete, or quantized, values. >From this hypothesis, he was able to explain the blackbody spectrum of the light that stars and other glowing bodies give off. Planck searched for something to explain the quantization, and one possibility he considered was that space is filled with unseen energy, a proposal also made by Walther Nernst in 1916.

During the 1920s, quantum mechanics proved so successful that physicists abandoned the search for an underlying cause of quantization. Quantization, like inertia, came to be regarded as just a given, a new law of nature. But in a series of papers beginning in 1969, Timothy Boyer appears to have vindicated Planck by deriving the blackbody spectrum directly from classical physics, without quantization -- by positing a background zero- point field. This reopens the questions that concerned Planck.

Is it possible that quantum mechanics is classical physics done in the presence of a zero-point field? Could the counterintuitive laws of quantum physics someday go the way of Ptolemaic epicycles? Quantum mechanics is certainly successful in terms of predicting observations, but so was Ptolemaic astronomy. In fact, the Ptolemaic system predicted planetary positions much better than Nicolaus Copernicus's initial theory. If astronomers had simply rejected the Copernican model, rather than worked to fix its shortcomings, we would still think Earth is the center of the universe.

As Planck did when he first derived the blackbody spectrum, we have taken a pragmatic approach: suppose that the quantum vacuum does produce real effects and consider the implications. Many new theories are ad hoc, conjured up to explain one thing and unable to explain anything else. The fact that the zero-point field might account for inertia, gravity, quantization, and, now, cosmic voids indicates that it is worth investigating.

BERNHARD M. HAISCH is an astrophysicist at the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif. He is a scientific editor of The Astrophysical Journal and the managing editor of the Journal of Scientific Exploration. When he is not rethinking scientific paradigms, Haisch, writing under the name of Bernie Sims, is a songwriter and producer. His and his wife's first commercially released song on a major label, Common Ground, will be on the forthcoming album by new Nashville artist Paul Jefferson. Haisch's email address is haisch@sag.space.lockheed.com.

ALFONSO RUEDA is a professor of electrical engineering at California State University in Long Beach. His email address is arueda@csulb.edu. For more information on the zero-point field theory, see the authors' article ``Beyond E=mc2'' in the November/December 1994 issue of The Sciences. Their technical papers appeared in Physical Review A, volume 49, p. 678 and The Astrophysical Journal, volume 445, p. 7.

Illustration captions

The Einstein-Hopf process. In a near-vacuum, collisions between gas particles are rare; collisions between particles and photons are more important. The photons are part of whatever electromagnetic field the particles happen to be immersed in. These photons are always hitting each particle from all sides, but not with equal strength. Those that hit a moving particle head- on are more energetic than those striking from behind, because of the Doppler effect. This imbalance automatically keeps the particle velocities in check (top). There is one exception: If the dominant electromagnetic field is the zero-point field, the spectrum of the field cancels out the Doppler effect, so that photons striking head-on are no more energetic than any other photons (bottom). As a result, the particles are free to move without restraint. Diagrams by Bernhard M. Haisch.

The Illusion of Mass

Einstein's theory states that energy produces gravity in the same way that matter does. Just as a planet attracts other bodies gravitationally, an electromagnetic field attracts bodies gravitationally. A uniform zero-point field that filled the universe would be an enormous source of gravitation -- so enormous that it should reduce the universe to microscopic size. This is clearly not the case.

Two linked theories have been proposed to resolve this paradox. If correct, they would constitute a paradigm shift in our view of matter itself. The first theory grew out of a suggestion made by the Russian physicist Andrei Sakharov in 1968 that gravity could originate in the quantum vacuum. Harold Puthoff published a quantitative, albeit preliminary, development of this idea in 1989. According to his theory, the zero-point field would cause charged particles, such as the electron or the quarks inside protons and neutrons, to oscillate. Whenever a charged particle oscillates, it emits electromagnetic waves of its own. These secondary fields would attract other charged particles.

If true, this theory would unify gravity with electromagnetism -- an unexpected resolution to the long search for a unified theory. It would neatly answer the general relativity paradox. In this view, gravitation is caused by secondary fields induced by the zero-point field; the zero-point field, in and of itself, cannot produce gravitation.

The second theory is our proposed mechanism for inertia. Einstein's principle of equivalence tells us that inertial and gravitational mass are the same. If gravitation is electromagnetic, inertia must be, too. This implies a complete rethinking of what matter really is.

The zero-point field is completely uniform for observers in uniform motion. But it is asymmetric for observers in accelerated motion. In 1994, we and Puthoff examined a phenomenon no one had thought to investigate before: how the magnetic component of the zero-point field interacts with matter during acceleration. The result was surprising, to say the least. The magnetic Lorentz force opposed acceleration with a strength that varied in direct proportion to the magnitude of the acceleration (see figure). It looked like a derivation of Newton's second law, F=ma, heretofore considered an underivable postulate.

What we feel and interpret as ``mass'' is, in this theory, an electromagnetic resistance arising out of the zero-point field. If it is true that mass is a consequence of charge, rather than an inherent property of matter, it might be possible (in the distant future) to build anti-gravity devices that would switch off the inertia of objects.

Are there objections to this theory? Certainly. We propose it not as a done-deal, but as a new approach to long-standing, unresolved fundamental problems. There are two major reservations. First, we treated the quantum vacuum as if it were a perfectly real electromagnetic field. The available evidence on this issue is ambiguous, and more experiments need to be done -- ranging from laboratory measurements of the Casimir force to astronomical observations of large-scale structure in the universe.

Second, even our simple model demanded a complex mathematical analysis, which is difficult to verify. For instance, we ignored non-electromagnetic vacuum fields, such as those associated with the gluon particles that bind quarks together. We are now completing a different approach that avoids this and other problems, and the preliminary results have confirmed the first approach. We hope that more researchers will look into these problems, drawn by the appeal of unsuspected deep connections.

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