Beyond Gravity

Of all the natural forces, gravity is the most mysterious and the most implacable. It controls our lives from birth to death, killing or maiming us if we make the slightest slip. No wonder that, conscious of their earth-bound slavery, men have always looked wistfully at birds and clouds, and have pictured the sky as the abode of the gods. The very phrase "heavenly being" implies a freedom from gravity which, until the present, we have known only in our dreams.

There have been many explanations of those dreams -- some psychologists try to find their origin in our assumed arboreal past -- though it is unlikely that many of our direct ancestors ever spent their lives jumping from tree to tree. One could argue just as convincingly that the familiar levitation dream is not a memory from the past, but a premonition of the future. Some day weightlessness or reduced gravity will be a common, and perhaps even a normal, state of mankind. The day may come when there are more people living on space stations and worlds of low gravity than on this planet; indeed, when the ultimate history of the human race is written, the estimated 100 billion men who have already spent laborious lives struggling against gravitation may turn out to be a tiny minority. Perhaps our spacefaring descendants will be as little concerned with gravity as were our remote ancestors who floated effortlessly in the buoyant sea.

Even now, most of the creatures on this planet are hardly aware that gravity exists. Though it dominates the lives of large land animals such as elephants, horses, men and dogs, it is seldom more than a mild inconvenience to anything much smaller than a mouse. To the insects it is not even that; flies and mosquitoes are so light and fragile that the air itself buoys them up, and gravity bothers them no more than it does a fish.

But it bothers us a great deal, especially now that we are making determined efforts to escape from it. Quite apart from our current interest in space flight, the problem of gravitation has always worried physicists. It seems to stand completely apart from all the other forces -- light, heat, electricity, magnetism -- which can be generated in many different ways and are freely interconvertible. Indeed, most of modern technology is based upon such conversions -- of heat into electricity, electricity into light, and so on.

Yet we cannot generate gravity at all, and it appears completely indifferent to all the influences that we may bring to bear on it. As far as we know, the only way a gravitational field can be produced is by the presence of matter. Every particle of matter has an attraction for every other particle of matter in the universe, and the sum total of those attractions, in any one spot, is the local gravity. Naturally, this varies from world to world, since some planets contain large amounts of matter and others very little. In our solar system the four giant planets -- Jupiter, Saturn, Uranus and Neptune -- all have surface gravities greater than Earth's, two-and-a-half times greater in the case of Jupiter. At the other extreme, there are moons and asteroids where gravity is so low that one would have to look hard at a falling object for the first few seconds to see that it was moving.

Gravitation is an incredibly, almost unimaginably, weak force. This may seem to contradict both common sense and everyday experience, yet when we consider the statement it is obviously true. Really gigantic quantities of matter -- the 6000 million million million tons of the (continued on page 80)Beyond Gravity(continued from page 71) Earth -- are required to produce the rather modest gravity field in which we live. We can generate magnetic or electric forces hundreds of times more powerful with a few pounds of iron or copper. When you lift a piece of iron with a simple horseshoe magnet, the amount of metal the magnet contains is outpulling the whole Earth. The extreme weakness of gravitational forces makes our total inability to control or modify them all the more puzzling and exasperating.

From time to time, one hears rumors that research teams are working on the problem of gravity control, or antigravity, but these stories always turn out to be misinterpretations. No competent scientist, at this stage of our ignorance, would deliberately set out to look for a way of overcoming gravity. What a number of physicists and mathematicians are doing, however, is something less ambitious; they are simply trying to uncover basic knowledge about gravity. If this plodding, fundamental work does lead to some form of gravity control, that will be wonderful; but I doubt if many people in the field believe that it will. The opinion of most scientists is probably well summed up by a remark made recently by Dr. John Pierce of the Bell Telephone Laboratories. "Antigravity," he said, "is strictly for the birds." But the birds don't need it, and we do.

We still know so little about gravitation that we are not even sure if it travels through space at a definite speed -- like radio or light waves -- or whether it is "always there." Until the time of Einstein, scientists thought that the latter was the case, and that gravitation was propagated instantaneously. Today, the general opinion is that it travels at the speed of light and that, also like light, it has some kind of wave structure.

If gravitational waves do exist, they will be fantastically difficult to detect, because they carry very little energy. It has been calculated that the gravity waves radiated by the whole Earth have an energy of about a millionth of a horsepower, and the total emission from the entire solar system -- the Sun and all the planets -- is only half a horsepower. Any conceivable man-made gravitational-wave generator would be billions of billions of times feebler then this.

Nevertheless, attempts are now being made to produce and detect these waves. In some of these experiments, it is planned to use the whole Earth as an antenna; the waves to be looked for would have a frequency of only about one cycle per hour. (Ordinary TV and radio waves run to tens of millions of cycles per second.) Even if these extremely delicate experiments succeed, it will be a long time before we can expect any practical applications from them. And it may be never.

Yet every few years, some hopeful inventor builds and actually demonstrates, at least to his own satisfaction, an anti-gravity device. These are always laboratory models, producing only a very tiny lift. Some of the machines are electrical, others purely mechanical, based on what might be called the bootstrap principle, and containing unbalanced flywheels, cranks, springs and oscillating weights. The idea behind these is that action and reaction may not always be equal and opposite, and sometimes there may be a little net force left over in one direction. Thus, though everyone agrees that you can't lift yourself by a steady pull on your bootstraps, perhaps a series of properly timed jerks might have a different result.

Put this way, the idea seems completely absurd, but it is not easy to refute an intelligent and sincere inventor with a beautifully made machine containing dozens of parts, moving in every possible direction, who maintains that his oscillating contraption produces a net lift of half an ounce and that a bigger model could take you to the Moon. You may be 99.999 percent sure that he is wrong, yet be quite unable to prove it. If gravity control is ever discovered, it will surely depend upon much more sophisticated techniques than mechanical devices -- and it will probably be found as a byproduct of work in some completely unexpected field of physics.

It is also probable that we will not make much progress in understanding gravity until we are able to isolate ourselves and our instruments from it, by establishing laboratories in space. Attempting to study it on the Earth's surface is rather like testing hi-fi equipment in a boiler factory; the effects we are looking for may be swamped by the background. Only in a satellite laboratory will we be able to investigate the properties of matter under weightless conditions.

The reason why objects are -- usually -- weightless in space is one of those elusive simplicities that is almost invariably misunderstood. Many people, misled by careless journalists, are still under the impression that an astronaut is weightless because he is beyond the pull of gravity.

This is completely wrong. Nowhere in the universe -- not even in the remotest galaxy that appears as a faint smudge on a Palomar photograph -- would one be literally beyond the pull of Earth's gravity, though a few million miles away it is almost negligible. It falls off slowly with distance, and at the modest altitudes reached by human travelers so far, it is still almost as powerful as at sea level. When an astronaut looked down upon the Earth from a height of nearly 200 miles, the gravity field in which he was moving still had 90 percent of its normal value. Yet, despite that, he weighed exactly nothing.

If this seems confusing, it is largely due to poor semantics. The trouble is that we dwellers on the Earth's surface have grown accustomed to using the words gravity and weight almost interchangeably. In ordinary terrestrial situations, this is safe enough; whenever there's weight there's gravity, and vice versa. But they are really quite separate entities, and either can occur independently of the other. In space, they normally do.

On occasion, they can do so on Earth, as the following experiment will prove. I suggest you think about it rather than actually conduct it, but if you are unconvinced by my logic, go right ahead. You will have the tremendous precedent of Galileo, who also refused to accept argument and appealed to experimental proof. However, I disclaim all responsibility for any damage.

You will need a quick-acting trap door (one of those used by hangmen will do admirably) and a bathroom scale. Put the scale on the trap door and stand on it. It will, of course, register your weight.

Now, while your eyes are fixed on the scale, get one of your acquaintances ("That's not an office for a friend, my lord," as Volumnius said to Brutus on a slightly similar occasion) to spring the trap door. At once the needle will drop to zero; you will be weightless. But you will certainly not be beyond the pull of gravity; you will be 100 percent under its influence, as you will discover a fraction of a second later.

Why are you weightless in these circumstances? Well, weight is a force, and a force cannot be felt if it has no point of application, if there is nothing for it to push against. You cannot feel any force when you push against a freely swinging door; nor can you feel any weight when you have no support and are falling freely. An astronaut, except when he is firing his rockets, is always falling freely. The "fall" may be downwards or upwards or sideways -- as in the case of an orbiting satellite, which is in an eternal fall around the world. The direction does not matter; as long as the fall is free and unrestrained, anyone experiencing it will be weightless.

You can be weightless, therefore, even where there is plenty of gravity. The reverse is also true: you don't need gravity to give you weight. A change of speed -- in other words, an acceleration -- will do just as well.

To prove this, let us imagine a still more improbable experiment than the one just described. Take your bathroom (continued on page 112)Beyond Gravity (continued from page 80) scale to a remote spot between the stars, where gravity, for all practical purposes, is zero. Floating there in space, you will again be weightless; as you stand on the scale, it will read zero.

Now attach a rocket motor to the underside of the scale, and start it firing. As the scale presses against your feet, you will feel a perfectly convincing sensation of weight. If the thrust of the rocket motor is correctly adjusted, it can give you, by virtue of your acceleration, exactly the same weight that you have on Earth. For all that you could tell, unless your other senses revealed the truth, you might be standing still on the surface of the Earth, feeling its gravity, instead of speeding between the stars.

This sensation of weight produced by acceleration is quite familiar; we notice it in an elevator starting to move upwards, and -- in the horizontal, not the vertical direction -- in a car making a fast getaway or suddenly braking. It is possible to produce artificial weight to an almost unlimited extent by the simple means of acceleration, and quite surprising amounts of it are encountered in everyday life.

We measure such forces in terms of so many gravities or g's, meaning that a person experiencing, say, 10 g's would feel 10 times his ordinary weight. But the actual gravity of the Earth is not involved when the weight force is produced wholly by acceleration, and it is unfortunate that the same word is used to describe an effect which may have two completely different causes.

The most convenient way of producing artificial weight is not acceleration in a straight line -- which would quickly take one over the horizon -- but motion in a circle. As anybody who has ridden a carrousel knows, swift circular movement can generate substantial forces; this was the principle of the cream separators that some of us country boys can still remember from our days on the farm. The modern versions of these machines are the giant centrifuges now used in space-medicine research, that can increase a man's weight 10 or 20 times.

Small laboratory models can do far better than this. The Beams Ultracentrifuge, spinning at the unbelievable rate of 1,500,000 revolutions a second (not a minute!), produces forces of more than a billion gravities. Here, at any rate, we have far outdone Nature: it seems most unlikely that there exist gravitational fields anywhere in the universe more than a few hundred thousand times more powerful than Earth's.

It is easy enough, therefore, to produce artificial weight, and we may do just this in our spaceships and space stations when we get tired of floating around inside them. A gentle spin will give a sensation that is indistinguishable from gravity -- except for the minor point that "up" is toward the center of the vehicle, not away from it as in the case of the Earth.

We can imitate gravity, then, but we cannot control it. Above all, we cannot cancel or neutralize it. True levitation is still a dream. The only ways in which we can hover in mid-air are by floating, with the aid of balloons, or by reaction, as with airplanes, helicopters, rockets and jet-lift devices. The first method is limited in scope and demands very large volumes of expensive or inflammable gases; the second is not only expensive but exceedingly noisy, and liable to let one down with a bump. What we would like is some nice, clean way, probably electrical or atomic, of abolishing gravity at the throw of a switch.

Despite the skepticism of the physicists, there seems no fundamental impossibility about such a device -- as long as it obeys certain well-established natural laws. The most important of these is the principle of the conservation of energy, which may be paraphrased as: "You can't get something for nothing."

The conservation of energy at once rules out the delightfully simple gravity screen used by H. G. Wells in The First Men in the Moon. In this greatest of all space fantasies, the scientist Cavor manufactured a material that was opaque to gravity, just as a sheet of metal is to light or an insulator to electricity. A sphere coated with "Cavorite" was able, according to Wells, to float away from the Earth with all its contents. By opening and closing the shutters, the space travelers could move in any desired direction.

The idea sounded plausible -- especially when Wells had finished with it -- but unfortunately it just won't work. Cavorite involves a physical contradiction, like the phrases "an irresistible force" and "an immovable object." If Cavorite did exist, it could be used as a limitless source of energy. You could employ it to lift a heavy weight -- then let the weight fall again under gravity to do work. The cycle could be repeated endlessly, producing that dream of all motorists -- a fuelless engine. This, to everyone except inventors of perpetual-motion machines, is an obvious impossibility.

Though gravity screens of this simple type can be dismissed, there is nothing inherently absurd in the idea that there may be substances that possess negative gravity, so that they fall upward instead of downward. From the nature of things, we would hardly expect to find such materials on Earth; they would float around out in space, avoiding the planets like the plague.

Negative gravity matter should not be confused with the equally hypothetical antimatter, whose existence is postulated by some physicists. This is matter made up of fundamental particles with electric charges opposed to those in normal matter: thus electrons are replaced by positrons, and so on. Such a substance would still fall downward, not upward, in an ordinary gravitational field: but as soon as it came into contact with normal matter, the two masses would annihilate each other in a burst of energy far fiercer than that from an atomic bomb.

Antigravity matter would not be quite so tricky as this to handle, but it would certainly pose problems. To bring it down to Earth would require just as much energy as lifting the same amount of normal matter from Earth out into space. Thus an asteroid miner who filled the hold of his space jeep with negative-gravity matter would have a terrible time getting home. Earth would repel him with all its force, and he would have to fight every foot of the way downward.

Thus negative-gravity substances, even if they exist, would have rather a restricted use. They might be employed as structural materials: buildings containing equal amounts of normal and negative-gravity matter would weigh exactly nothing, so could be of unlimited height. The architect's main problem would be anchoring them against high winds.

It is conceivable that by some treatment we might permanently degravitize ordinary substances, in much the same way that we can turn a piece of iron into a permanent magnet. (Less well known is the fact that continuously charged bodies -- permanent electrets -- can also be made.) To do so would require a great expenditure of energy, for to degravitize one ton of matter is equivalent to lifting it completely away from the Earth. As any rocket engineer will tell you, this requires as much energy as raising 4000 tons to a height of one mile. That 4000 mile-tons of energy is the price of weightlessness, the entrance fee to the universe. There are no concessions and no cheap rates. You may have to pay more, but you can never pay less.

On the whole, a permanently degravitized or weightless substance seems less plausible than the gravity neutralizer or gravitator. This would be a device, supplied with energy from some external power source, that would cancel gravity as long as it was switched on. It is important to realize that such a machine would give not only weightlessness, but something even more valuable -- propulsion.

For if we neutralized weight exactly, we would float motionless in mid-air: but if we overneutralized it, we would shoot upward with steadily increasing speed. Thus, any form of gravity control would also be a propulsion system: we should expect this, as gravity and acceleration are so intimately linked. It would be a wholly novel form of propulsion, and it is difficult to see what it would push against. Every prime mover must have some point of reaction; even the rocket, the only known device that can give us a thrust in a vacuum, pushes on its own burnt exhaust gases.

The term Space Drive, or just plain Drive, has been coined for such non-existent but highly desirable propulsion systems, not to be confused with the Overdrives and Underdrives peddled by Detroit. It is an act of faith among science-fiction writers, and an increasing number of people in the astronautics business, that there must be some safer, quieter, cheaper and generally less messy way of getting to the planets than the rocket. Within a few years, the monsters standing at Cape Canaveral will contain as much energy as the first atomic bomb in their fuel tanks -- and it will be much less reliably controlled. Sooner or later there is going to be a really nasty accident: we need a space drive urgently, not only to explore the solar system, but to protect the state of Florida.

It may seem a little premature to speculate about the uses of a device which may not even be possible, and is certainly beyond the present horizon of science. But it is a general rule that, whenever there is a technical need, something always comes along to satisfy it -- or to bypass it. For this reason, I feel sure that eventually we will have some means of either neutralizing gravity or overpowering it by brute force. In any event, it will give us both levitation and propulsion in amounts determined only by the available power.

If antigravity devices turn out to be bulky and expensive, their use will be limited to fixed installations and to large vehicles -- perhaps of a size that we have not yet seen on this planet. Much of the energy of mankind is expended in moving vast quantities of oil, coal, ores and other raw materials from point to point -- quantities measured in hundreds of millions of tons per year. Many of the world's mineral deposits are useless, because they are inaccessible; perhaps we may be able to open them up through the air, by the use of relatively slow-moving antigravity freighters hauling a few hundred thousand tons at a time across the sky.

One can even imagine the bulk movement of freight or raw materials along gravity pipelines -- directed and focused fields in which objects would be supported and would move like iron toward a magnet. Our descendants may be quite accustomed to seeing their goods and chattels sailing from place to place without visible means of support. On an even larger scale, gravity and propulsion fields might be used to control and redirect the winds and the ocean currents: if weather modification is ever to be practical, something of this sort is certainly necessary.

The value of gravity control for space vehicles, both for propulsion and the comfort of their occupants, needs no further are not so obvious. Jupiter, the largest of the planets, is barred from direct human exploration by its high gravity, two-and-a-half times that of Earth. This giant world has so many other unpleasant characteristics (an enormously dense, turbulent and poisonous atmosphere, for example) that few people take very seriously the idea that we will ever attempt its manned exploration; the assumption is that we will always rely on robots.

I doubt this. In any event, there are always going to be cases when robots will run into trouble and men will have to get them out of it. Sooner or later there will be scientific and operational requirements for the human exploration of Jupiter: one day we may even wish to establish a permanent base there. This will demand some kind of gravity control -- unless we breed a special class of colonists with the physiques of gorillas.

If this seems a little remote and fantastic, let me remind you that much closer to home there is an even more important example of a high-gravity planet which, perhaps less than 50 years from now, men may not be able to visit. That planet is our own Earth.

Without gravity control, we may be condemning the space travelers and settlers of the future to perpetual exile. A man who has lived for a few years on the Moon, where he has known only a sixth of his terrestrial weight, would be a helpless cripple back on Earth. It might take him months of painful practice before he could walk again, and children born on the Moon (as they will be within another generation) might never be able to make the adjustment. One can think of few things more likely to breed interplanetary discord than such gravitational expatriation.

To avoid this we need a really portable gravity-control unit, so compact that a man could strap it on his shoulders or around his waist. Indeed, it might even be a permanent part of his clothing, taken as much for granted as his wrist watch. He could use it to reduce his apparent weight down to zero, or to provide propulsion.

Anyone who is prepared to admit that gravity control is possible at all should not boggle at this further development. Miniaturization is one of the everyday miracles of our age, for better or for worse. The first thermonuclear bomb was almost as big as a house: today's economy-sized war heads are the size of wastepaper baskets -- and from one of those baskets comes enough energy to carry the liner Queen Elizabeth to Mars. This everyday fact of modern missilery is, I submit, far more fantastic than the possibility of personal gravity control.

The one-man gravitator, if it could be made cheaply enough, would be among the most revolutionary inventions of all time. Like birds and fish, we would have escaped from the tyranny of the vertical -- we would have gained the freedom of the third dimension. In the city, no one would use the elevator if there were a convenient window. The degree of effortless mobility that would be attained would demand re-education to an entirely new way of life, an almost avian order of existence.

Even if the extreme of personal, one-man levitation turns out to be impossible, we may still be able to build small vehicles in which we can drift slowly and silently (both are important) through the sky. The very idea of hovering in space was a fantasy a generation ago, until the helicopter opened our eyes. Now that experimental ground-effect machines are floating off in every direction on cushions of air, we will not be satisfied until we can roam at will over the face of the Earth, with a freedom that neither the automobile nor the airplane can ever give.

What the ultimate outcome of that freedom may be, no one can guess, but I have one final suggestion. When gravity can be controlled, our very homes may take to the air. Houses would no longer be rooted in a single spot: they would be far more mobile than today's trailers, free to move across land and sea, from continent to continent. And from climate to climate, for they would follow the sun with the changing seasons or head into the mountains for the winter sports.

The first men were nomads: so may be the last, on an infinitely more advanced technical level. The completely mobile home would require -- quite apart from its presently unattainable propulsion system -- power, communication and other services equally beyond today's technology. But not, I think, beyond tomorrow's.

This would mean the end of cities, which may well be doomed for other reasons. And it would mean the end of all geographical and regional loyalties, at least in the intense form that we know today. Man might become a wanderer over the face of the Earth, a gypsy driving a nuclear-powered caravan from oasis to oasis, across the deserts of the sky.

Yet when that day comes, he will not feel like a rootless exile with no place to call his own. A globe that can be circumnavigated in 90 minutes can never again mean what it did to our ancestors. For those who come after us, the only true loneliness will lie between the stars. Wherever they may fly or float on this little Earth, they will always be at home.