Alternate View Column AV-83
Keywords: space drive Mach's Principle Dean Drive antigravity weight mass reduction wormholes gravitational shielding
Published in the March-1997 issue of Analog Science Fiction & Fact Magazine;
This column was written and submitted 9/28/96 and is copyrighted ©1996 by John G. Cramer.
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Over 35 years ago, in an editorial published in the September-1960 issue of this magazine, the great SF editor John W. Campbell, Jr., broke the news of a new gravity- defying invention, the Dean Drive. It was a contraption of weights, gears, and springs, officially registered with the U. S. Patent Office, that operated so as to produce an oscillating force. According to Campbell, when the Dean Drive was operating under power, it registered significantly less than its normal power-off weight on a bathroom scale. This was taken as evidence that a new anti-gravity breakthrough had been made and that one of the mainstays of physics, Newton's 3rd Law of Motion (conservation of momentum) had fallen. One Analog cover of the period depicted a converted submarine, operating under Dean Drive power, landing on the Moon.
Alas, the work reported by Campbell served principally to demonstrate that bathroom scales are not reliable instruments for investigating antigravity or for overthrowing the laws of physics. Later more detailed studies showed that the Dean Drive developed no net time- averaged force and that Newton's 3rd Law remained intact.
This Alternate View column is about two new reports of possible antigravity breakthroughs. Perhaps, like the Dean Drive, they will prove to be bogus. But the subject continues to have interesting SF implications, and the payoff, if an antigravity route out of Earth's gravity well could be found, would be enormous.
The first of these "sightings" was recently published by J. F. Woodward in the prominent journal Foundations of Physics Letters . I have always regarded proposed antigravity devices with considerable skepticism. It's likely that this work has a hidden flaw somewhere too, but it is certainly the most plausible I've seen. Woodward's paper reports an apparently successful table-top laboratory test of Mach's Principle.
Let me begin by explaining what Mach's Principle is. The physical property of mass has two distinct aspects, gravitational mass and inertial mass. Gravitational mass produces and responds to gravitational fields. It supplies the mass factors in Newton's famous inverse-square law of gravity (F12 = G m1m2/r122). Inertial mass is the tendency of matter to resists acceleration. It is the mass factor in Newton's 2nd Law of Motion (F=ma). One of the deep mysteries of physics is the relationship between these two aspects of mass.
Mach's Principle attempts to connect inertia with gravitation by suggesting that inertial mass comes from the long-range gravitational forces on a massive object from all the other masses in the universe (so that in an empty universe there would be no inertia). Mach said that inertial and gravitational mass must be the same because inertia is a gravitational effect. Albert Einstein liked Mach's Principle and used its implications to formulate his famous Equivalence Principle, a cornerstone of general relativity, which asserts that gravitational and inertial mass are indistinguishable. In a small isolated room it would be impossible, according to the Equivalence Principle, to tell from local measurements whether the room was on the surface of the Earth in a 1 g gravitational field or in a rocket ship accelerating at 1 g through gravity-free space. The Equivalence Principle is now generally accepted in physics, but its underlying basis in Mach's Principle has never been properly understood or tested until now.
Woodward may have accomplished this. He has formulated a nonlocal mathematical theory embodying Mach's Principle. Woodward's theory can be tested because it predicts a remarkable effect: if the mass-energy density of a system is made to change with time, the mass of the system should vary by an amount that is proportional to the second time derivative of the density change. For example, if a capacitor is charged positively and negatively by a voltage that varies as a 10 kHz sine wave and delivers a power of 100 watts to the capacitor, Woodward predicts that the mass of the capacitor should vary from its normal mass by about ±30 milligrams at a frequency of 20 kHz.
This is a prediction that can be tested in the laboratory, and Woodward has devised a clever way of doing this. He describes his method in terms of throwing a ball in the air. His explanation reminds me of the old puzzle of the Juggler and the Bridge: A juggler who weighs 252 pounds carries with him three juggling pins that weigh 6 pounds each. He comes to a bridge that has a precisely determined load limit of 260 pounds. How can he cross the bridge with his juggling pins without breaking the bridge?
The conventional (but wrong) answer is that if he juggles the pins while crossing the bridge, at any given time he will be supporting only one pin (with the other two in the air), so his net weight should be only 252 + 6 = 258 pounds. Therefore, it is concluded, he can safely cross the bridge.
Actually, the situation is not so simple. Every time the juggler catches or tosses a pin, his hand experiences a downward reaction force. This force is added to his weight as he stands on the bridge, producing a momentarily "spike" of increased weight. Newton's 3rd law requires that the time-average of his weight, including the increase spikes, must be 270 pounds, the same weight as if he were simply holding the pins at rest. Thus, if he tries to cross the bridge while juggling he will surely break it.
But now consider what happens if we provide the juggler with the advantages of Woodward's effect. Suppose that by some mechanism we can make the masses of the pins vary with time so that the weight of each has an average value of 6 pounds but varies with time between 2 pounds and 10 pounds. If we carefully match the weight variation to the juggling cycle so that the pins weigh only 2 pounds when the juggler catches a pin and throws it up, then his average weight while juggling will be only 258 pounds, the same as if he were juggling with three 2 pound pins. Then, assuming the bridge responds only to the average load, he can cross it without mishap.
Woodward's test of Mach's Principle works in much the same way. He mounts his mass-varying bank of capacitors atop a piezoelectric motion device which moves the capacitors up and down. By timing the upward push of the motion device to correspond to the mass minimum of the capacitor bank, he attempts to reduce the net weight of the system, which is mounted atop a sensitive electronic scale. Woodward's published measurements, which appear to have been done with considerable care, record a mass reduction of several milligrams as measured using signal averaging techniques to a statistical accuracy of 10 to 15 standard deviations. He also reports a number of systematic checks which are in good agreement with the predictions of his theory.
Woodward's reported mass reduction effect is small, and both his measurements and his interpretation in terms of Mach's Principle need to be checked by others before they can be accepted as scientific facts. But, taken at face value, his result is a remarkable demonstration that the mass and weight of an object can be reduced in the laboratory. This would be a new physical phenomenon that raises a number of interesting questions. How can it be reconciled with the laws of physics? Can the mass change be used to reduce the net system weight to zero or less (antigravity)? Can the capacitor mass be driven to momentary values of less than zero (negative mass)? And so on. Woodward's paper does not confront most of these issues, but let me attempt to do so here.
(1) Conservation Laws: If the mass of an isolated object in motion changes spontaneously, either its kinetic energy or its momentum (or both) much change. As I read Woodward's paper, it is the momentum of the object that changes with the mass, while its kinetic energy remains constant. In other words, it is the law of conservation of momentum (Newton's 3rd Law) that is placed under attack by Woodward's effect.
However, Woodward, in formulating his version of Mach's Principle, assumes that the interaction of the isolated object with the other masses of the universe is nonlocal, in analogy with the nonlocal character of quantum mechanics as demonstrated by the Einstein-Podolsky-Rosen experiments. Thus, Woodward's effect implicitly assumes an immediate nonlocal momentum transfer between the varying mass of interest and the rest of the universe. Therefore Newton's 3rd Law is preserved, but in a rather peculiar way.
(2) Weight Reduction and Antigravity: Woodward's effect, as implemented in his measurements, produces a mass change of a few milligrams in a object that must have a mass on the order of a few grams. Therefore the fractional change in weight is 0.1% or less.
The question of burning interest to SF readers and writers is whether the weight reduction effect can be made large enough to produce actual lift against gravity. The answer appears to be yes. The weight reduction magnitude depends on the product of the mass variation and the acceleration applied to the varying mass by the piezoelectric motion device. The size of the mass variation depends on the amount of electric power flowing to the capacitor and on the frequency f of its charging current. The magnitude of the applied acceleration depends on the distance "stroke" of the piezoelectric motion device and on the square of the frequency (f2) at which it is operated. This means that the overall size of the weight reduction should grow as the third power of the driving frequency (f3).
Woodward's measurements at a frequency of about 10 kHz (a rather modest audio frequency) observed a weight change of about 1 part in 1000. Increasing the frequency by a factor of 20 to 200 kHz while holding the other variables fixed (if that is possible) should make the weight reduction considerably larger than the weight itself, therefore achieving lift. In other words, Woodward's effect, if it is real, should be usable as an antigravity device or a space drive, in the sense that these terms are normally used in science fiction.
(3) Mass Reduction and Wormholes: Several previous AV columns have pointed out that negative mass seems to be required to stabilize wormholes (see my AV columns in Analog, June-89, May-90, July-92, and Mid-Dec-94) or to produce a "warp drive" of the kind described by Alcubierre ( Analog, Nov-96). This raises the question of whether Woodward's effect could also be used to produce negative mass for this purpose.
For Woodward's apparatus, even if the weight were driven negative by the strong f3 frequency dependence of the effect, the average mass of the capacitor bank would remain unchanged and its instantaneous mass, which depends only on the first power of f, would not be likely to go negative.
However, in the conclusion of his paper Woodward speculates on the possibility of producing negative mass, at least momentarily, that might be used to create and stabilize transversable wormholes. This might be done by raising the frequency and power level at which the capacitor bank (or its equivalent) is operated. It is not clear, however, whether with available materials it would be possible to achieve a negative mass, even momentarily, or if this would be sufficient to produce a transversable wormhole, since the negative mass condition would exist, at best, for a very brief time period.
In any case, Woodward's laboratory demonstration of Mach's Principle, if it can withstand closer scrutiny, is a very important new development in fundamental physics. Time will tell ...
The second recent antigravity "siting" was an article in the Sunday Telegraph of London, September 1, 1996, describing "one of the most astonishing scientific developments of this century, ... the world's first antigravity device." It went on to relate how physicists at Tampere University of Technology in Finland, led by Dr. Eugene Podkletnov had a paper accepted for publication in the prestigious Journal of Physics-D: Applied Physics, which described a new effect, gravitational shielding. The experimenters used a "high-Tc" superconducting disk cooled to liquid nitrogen temperature, levitated in a magnetic field, and spun up to a high rotation speed with auxiliary magnetic coils. It was claimed that objects suspended over the spinning superconducting disk were shielded from the effects of gravity and were reduced in weight.
However, there are already indications of problems with this work. After the article appeared, the editors of Journal of Physics-D informed a Telegraph reporter that the gravitational shielding paper had been withdrawn by its principal author on September 9 and would not be published in the foreseeable future. I note that a previous paper about the same shielding effect had been published in 1992, but I did not find the effect reported there convincing, since it could probably be explained by induced eddy currents.
AV Columns On-line: Electronic versions of more than eighty past "The Alternate View" columns by John G. Cramer are available on-line on WorldWideWeb at the URL: http://www.npl.washington.edu/AV.
The Dean Drive:
"Report on the Dean Drive," John W. Campbell, Jr., Analog, Sept-1960;
"Instrumentation for the Dean Drive," John W. Campbell, Jr., Analog, Nov-1960;
"Final Report on the Dean Device," John W. Campbell, Jr., Analog, Dec-1960;
"Detesters, Phasers, and Dean Drives," G. Harry Stine, Analog, June-1976.
Mach's Principle and Weight Reduction:
James F. Woodward, Foundations of Physics Letters 9, 247-293 (1996).
E. E. Podkletnov and R. Nieminen, Physica C 203, 441-444 (1992)
This page was created by John G. Cramer on 10/8/96.