From birth to death, gravity pervades our life. Our every step, day-in to day-out, is a struggle against this relentless force. It cuts our baby knees when we fall. It pulls on our limbs so that our every motion is burdened by its enervating presence. It sucks our bodies into the mud, preventing us from soaring into the skies like the birds.
Will there ever by some future technology that will enable us to control gravity—some technology that today is indistinguishable from magic? Can we somehow find a way to "turn off" or "nullify" the gravity field of the Earth? Could we possibly arrange for a mass to push us gently away into the skies instead of hugging us firmly to its crushing bosom?
The answers are: Yes . . . Maybe . . . Someday.
But to control some force in nature, you need to know something about it. You need a theory of how it works, and the more detailed the theory, the better your chances of control. What do we know about gravity? What are the theories? How can we use those theories to nullify gravity?
The first Theory of Gravity, usually attributed to Ug the caveman, was simple:
"Things fall down."
This theory served Ug quite well in its time. Ug used his theory to make gravity his servant rather than his master. Instead of having to walk right up to a saber-toothed tiger to bash it in the head with a sharp rock (and getting all scratched in the process), Ug climbed a tree, and wisely using his theory of gravity, dropped his sharp rock down on the head of the saber-toothed tiger. This was the first use of gravity as a tool for the betterment of the human race.
It wasn't too much later that Ug found a way to use his new theory to nullify the effect of gravity. One day, while sitting high up on a slippery-elm branch waiting for a saber-tooth tiger to walk beneath him, he tossed his favorite sharp rock back and forth from one palm to another. His newly-developed and still-awkward opposed thumb missed a toss and the rock bounced away.
Not wanting to lose his favorite tool, Ug jumped after it. After his jump, Ug noticed a strange thing. The rock no longer fell down. Instead, it just hung there in the rapidly rushing air just an arm length away. By his jump from the branch Ug had made one gigantic leap for mankind toward the conquest of gravity. As he reached out and plucked the floating rock from midair, he thought about all the admiration he would receive around the cave fire that night as he explained the secret of nullifying gravity.
"Just jump," he would tell them . . . At that point the uprushing ground terminated his thought processes.
Ug would be amazed to know that even today we use his simple yet effective technique to nullify gravity. Each flight of the Space Shuttle utilizes his marvelous invention to make multiton communication satellites float weightless so mere men and women can push them around like leaden pillows. To nullify gravity, all the astronauts have to do is to use the Space Shuttle rockets to "jump" high enough that they can go into free-fall.
Unlike Ug, however, whose career as an astronaut ended in a second, the Space Shuttle astronauts can fall forever. That is because while the astronauts are falling vertically ten meters, their orbital velocity takes them horizontally eight kilometers. At this new point, the surface of the Earth below is now ten meters further away than it was before, so the astronauts can fall another ten meters without getting any closer to the dangerous ground. Thus, by using the Ug Theory of Gravity and constantly falling as they move, our astronauts can nullify the effects of Earth gravity.
The Ug Theory of Gravity served the human race well until sailing ships were invented. Then reports began to trickle in from the sailors that the world was round and that there were people living on large island continents on the "other side" of the Earth. Amazingly enough, even though they were obviously upside-down, they didn't have to hang onto trees or handles set into the ground, but instead walked around on their feet in just the same way that people did on the topside of the Earth. It was finally realized that the Ug Theory of Gravity, despite all its advantages, was not the correct theory of gravity and a new theory would have to be found.
Finally, in 1687, Isaac Newton discovered a better theory of gravity. The Newton Theory of Gravity is somewhat more complicated than the Ug Theory of Gravity, but the basic idea is quite simple:
"A mass attracts all other masses."
There is more to the Newton Theory of Gravity than that, but it consists mostly of details that are used for making accurate mathematical predictions.
Using his theory of gravity, Newton was able to predict the motions of the Moon and the planets in the sky to high accuracy. To carry out the calculations he had to invent a new form of mathematics, called "calculus", that revolutionized both science and engineering.
The first use of this new gravitational technology was to predict the future motions of the Moon through the starry background of the sky. Navigators on ships far at sea could measure the position of the Moon in the sky, compare it with the predictions made by the gravitational engineers using the Newton Theory of Gravity, and figure out where the ship was on the trackless sea surface.
Amazingly enough, using only Newton's Theory of Gravity, it is possible to design a simple anti-gravity machine that can "nullify" the gravity field of the Earth. As we shall see, although we know how to design the machine, it will be some time before our engineering technology is up to the task of actually building the machine. To design our Newtonian antigravity machine, we will need to look more closely at the details of the Newton Theory of Gravity.
The basic form of the Newton Theory of Gravity is that masses attract other masses. In a more detailed form, the Newton Theory of Gravity can be expressed as:
"A big mass will attract another mass. The bigger the attracting mass, the stronger the attraction. The closer the two masses, the stronger the attraction. (It goes as the square of the distance between the two masses.)"
How can we use this Newton Theory of Gravity to cancel the gravity field of the Earth?
Well, one way to use the Newton Theory of Gravity to keep the Earth from pulling you down, would be to put another planet, with the same mass as Earth, above your head. The Newtonian antigravity field of the above-Earth will pull you up with the same force as the Newtonian progravity field of the below-Earth is pulling you down. The two forces would cancel each other out and over a broad region between the two "Earths", there would be no gravity. Everyone and everything would be in free fall.
There is no question that from a mathematical point of view, that this method of nullifying the gravity field of the Earth using the Newton Theory of Gravity would work. But it is also obvious that this not a very practical solution. Even though there is a way to keep two Earth-sized bodies that close to each other without them falling onto each other due to their mutual gravity attraction (read my novel Rocheworld to find out how), we do not have another Earth handy to use as the above-Earth. Notice, however, that the Newton Theory of Gravity says that the gravitational attraction gets stronger as the two masses get closer to each other. It turns out there is a way we can use that aspect of the Newton Theory of Gravity to create antigravity.
Let us look at the gravity field of a large knob of rock about 100 meters, a football field, in diameter. (Single rocks of this size are often found in the Sequoia and Yellowstone National Parks in the U.S.A. and many other places around the world.) If it is a very dense rock, it will weigh about four million tons. Although it would admittedly be difficult, we could imagine that we could hire a team of gravitational engineers to lift that rock up on strong pillars and make a small room underneath it. We now have a small asteroid perched on manmade pillars sitting on the roof of our room. In that room, fifty meters from the center of the rock overhead, the gravity field of the Earth would be decreased by the gravity pull of the rock. The amount of gravity decrease would be about ten microgravities (ten millionths of Earth gravity). We have antigravity of a sort, but not very much.
Now, mindful of the admonition of the Newton Theory of Gravity, which says that the amount of attraction varies as the square of the distance between you and the attracting body, suppose we could get closer to the four million ton rock. If we could get ten times closer or about five meters away, then the gravity from the rock would increase to one thousandth of Earth gravity. If we could get a hundred times closer or fifty centimeters away, the attraction would increase to one-tenth of Earth gravity. The rock is now beginning to have a significant effect on the gravity of the Earth. If we could get sixteen centimeters away from a four million ton mass, the gravity attraction would rise to one Earth gravity. The gravity field of the rock is now strong enough to cancel out the gravity field of the Earth, which is a trillion times more massive than the rock.
But how do you get very close to a rock? It doesn't work to dig a hole and crawl inside. You have to make the rock smaller while maintaining its mass so you can get closer to the center while still staying outside. That means we have to find a way to make matter more dense than it normally is.
An atom in normal matter contains a lot of nothing. In the center of the atom is the nucleus, which contains the protons and neutrons that have most of the mass of the atom. Surrounding the nucleus is a tenuous cloud of electrons. An oxygen atom, for example, has a nucleus with eight protons and eight neutrons that is about a trillionth of a centimeter across.
The eight units of positive charge in the nucleus of an oxygen atom are balanced out by eight negatively charged electrons that orbit around the nucleus. It is this outer electron cloud that is the surface that connects the atom to the rest of the atoms in your body (and the outside world). This electron cloud is thousands of times larger than the nucleus of an atom and weighs practically nothing. Thus, an atom is mostly made up of empty space between the nucleus and the outer electron shells.
We know that more dense forms of matter exist. We can see white-dwarf stars in the sky that have the mass of a sun condensed into a ball the size of the Earth. White-dwarf-star densities are about a million times greater than normal densities. We also know that neutron stars exist. Here the mass of a sun has been condensed into a sphere that is only twenty kilometers across! Neutron-star densities are a hundred trillion times greater than normal densities.
Thus, one future magic key to controlling gravity using the Newton Theory of Gravity is to find a method to collapse ordinary matter with its bloated electron orbits into matter with white-dwarf-star densities or greater. We can't do it now, but one of these days we may develop the technology. When we do, we can envision our four million ton rock condensed into a ball thirty-two centimeters or one foot in diameter, with a surface gravitational attraction of one Earth gravity. Even better would be to make it in the shape of a disc that is forty-five centimeters (eighteen inches) in diameter and ten centimeters (four inches) thick. This disc would have the property that the gravitational attraction would be the same on both sides of the disc and would be fairly uniform near the center of the disc. The strength of the gravitational attraction near the center of the disc would be one Earth gravity. If this disc were somehow supported on the surface of the Earth, then on top of the disc there would be a gravity field of two Earth gravities; one gravity from the gravitational attraction of the dense mass in the disc, plus one gravity due to the Earth. On the bottom of the disc, near the center, the one-gravity attraction the disc would cancel the one-gravity attraction of the Earth. There would be a gravity-free region under the disc where we could carry out free-fall experiments.
But now we come to another problem. How do we hold the four million ton antigravity roof up over our heads? The pressure on the roof supports works out to four million atmospheres! It would take a remarkable material to stand that sort of pressure. The material exists, however, and it is remarkable. It is diamond. The highest pressure ever made in the laboratory to date has been about two million atmospheres. It was achieved by pressing the flat surfaces of two diamond anvils together using a turn-screw. Believe it or not, since the total area under pressure between the two diamonds is so small, the turn-screw is turned by hand! At two million atmospheres, one of the two diamond anvils used in the high pressure machine "flowed". The other diamond, however, being made of sterner stuff, did not.
How strong is a perfect diamond? Strong enough to help make antigravity possible? Dare we envision a future where one of the attractions at a Disney park is a Freefall Pavilion, rising upwards on massive swooping buttresses of pure diamond, which support a brilliantly reflecting roof of ultradense matter—and under that roof floats a crowd of funseekers, swimming through the warm air with colorful feathered wings attached to their arms, living out the legend of Icarus for the price of an E coupon?
Because of the unfortunate coincidence that the Earth is massive and its surface gravity is strong, while the density of matter that we can make is small, so that its surface gravity is weak, antigravity machines using the Newton Theory of Gravity still involve technologies that are presently indistinguishable from magic. Even though we know how to design such antigravity machines, we cannot yet build them. As we shall see later, this will still hold true for antigravity machines built using the secrets of the Einstein Theory of Gravity. To make any antigravity machine capable of canceling out the gravity field of the Earth will require the use of ultradense matter, and the method of making ultradense matter is still a form of magic practiced only by white-dwarf and neutron stars.
There is a form of gravity cancellation, however, that can be practiced right now. It uses a combination of Ug antigravity and Newtonian antigravity to create a large volume that is completely free of gravity forces even though the volume is embedded in the gravity field of the Earth and even when the volume has gravity producing masses in it! This gravity free volume could be built in a few years and profitably used to make exotic materials that cannot be made under the influence of gravity.
Many of the experiments presently carried out on Space Shuttle flights, especially those where the Spacelab is flown as cargo, are called "zero-gravity" materials processing experiments. Some involve forming "perfect" spheres of metal or latex by squeezing out drops of liquid into free-fall. The surface tension forces form the drops into spheres and then the drops solidify into balls. Others involve mixing two metals with greatly differing density, such as lithium and lead (to make a bearing alloy). If you attempted to cast such an alloy on Earth, the bottom of the crucible would contain mostly lead and the top would contain mostly lithium. Another space manufacturing process, called electrophoresis, uses the flow of strong electrical currents through a liquid to collect dilute quantities of precious biological chemicals from blood samples or a watery mass of bacteria and their excretions. The purity of the end product depends strongly on the dominance of the electrochemical currents over the convention currents in the liquid caused by the heated water "rising" in any residual gravity forces.
At the present time, these "zero-gravity" space manufacturing experiments are done using only the Ug form of antigravity. The Space Shuttle "jumps" into space and goes into a free-fall orbit around the Earth. This effectively cancels most of the gravity field of the Earth, but not all of it. The only part of the Space Shuttle that is under absolutely zero net gravity force is the center of mass of the spacecraft. The rest of the Space Shuttle, especially the nose, tail, and wingtips, is experiencing gravity forces due to the tides of the Earth. These residual gravity forces are not large, a few microgravities, and do not cause any large effects in the present crude space manufacturing experiments. But as the manufacturing apparatus goes from the experimental stage on the Space Shuttle to the "making money" manufacturing phase on the Space Station, the apparatus will become larger, the residual gravity tidal forces will become larger, and the tidal forces will begin to affect the quality of the manufactured product.
I have invented a way to reduce these gravity effects by another factor of a million, so that the residual forces are less than a picogravity (a trillionth of Earth gravity). I do this by using various arrangements of massive dense spheres, disks, and rings to nullify the residual gravity effects inside the processing apparatus. (Those interested in the details can read my technical paper in "Recommended Reading" at the end of the chapter.)
Suppose you were floating around in the bay of the Space Shuttle. The Shuttle has all of its control thrusters off and is floating in free-fall, its nose pointing to the ground below. If you were floating at the point in the middle of the bay that is the center of mass of the Shuttle, you would stay at that point, since both you and the Shuttle are in exactly the same orbit. If, however, you were up in the nose of the Shuttle, fifteen meters away from the center of mass, you would find that after two minutes of time that you would have drifted some thirty centimeters away from the center of mass of the Shuttle, closer to the nose. Your motion was caused by a residual tidal force of 4.5 microgravities. In two minutes under this intense gravity force you will have reached the tremendous velocity of five millimeters per second and are about to be smashed against the forward bulkhead, where you will be crushed by the intense 4.5 microgravity acceleration. Although you are perfectly capable of surviving this experience, a space manufacturing facility located in the nose of the Space Shuttle would be significantly affected by these residual gravity tidal forces. The "perfect" ball bearings would be elliptical, the "uniform" alloy would have density gradations, and the "pure" biological extract would be contaminated with impurities.
There are two ways to look at how these residual tidal forces occur. One picture uses the concept of orbital motion and the other uses the concept of gravity gradients. The two ways are equivalent as long as the region we are interested in (the inside of a Space Shuttle or a manufacturing facility on the Space Station) is much smaller than the distance to the center of the Earth.
In the orbital picture, the center of mass of the Space Shuttle is in orbit around the Earth, moving at a certain speed appropriate for that orbit. You are in the nose of the Space Shuttle, fifteen meters closer to the Earth. However, at the start of the experiment you have arranged your velocity so that you are not moving with respect to the walls of the Shuttle. You are now moving with the velocity of the Space Shuttle, but you are in a lower orbit which requires a higher velocity than the Space Shuttle velocity if it is to be a circular orbit. Since your velocity is too low for your altitude, you are not in a circular orbit, but at the peak of an elliptical orbit. As you and the Space Shuttle continue in orbit, the Space Shuttle remains at the same distance above the Earth, while you drop away in your elliptical orbit and soon smash against the front bulkhead. The same picture applies if you start out near the tail of the Space Shuttle, only now in your higher orbit you are going too fast for your altitude and rise up away from the Shuttle orbit.
Now suppose the Space Shuttle were in a perfect equatorial orbit, always following the equator of the Earth, with its wings pointing north and south. If you started your space-float at the end of the north wingtip, you would be at the same altitude as the Space Shuttle, moving at the same speed as the Space Shuttle, but your orbit started out a wingtip's length north of the equator. Your orbit has to cross the equator after a quarter of an orbit, go south until it reaches a wingtip's length after a half orbit, cross back over the equator again and then return to the north after a full revolution. Since your orbit has to cross over the equatorial orbit of the Space Shuttle, you will find that you will float from the wingtip "toward" the center of mass of the Space Shuttle.
A similar effect occurs if the wings of the Space Shuttle are oriented along the equator. Now, however, the line from the wingtips through the center of mass is a straight line, while the Shuttle orbit is curved. If you start out on a wingtip, you are in a higher orbit than the Space Shuttle and going too fast. As you rise in your elliptical orbit, you slow down and the Space Shuttle overtakes you, bringing you closer to its center of mass.
Thus, from the orbital picture, objects inside the Space Shuttle that are not right at the center of mass of the Shuttle move in their own orbits. From the viewpoint of those in the Shuttle, those objects that are above or below the Space Shuttle center of mass move outward, while those objects in a plane tangent to the Earth move inward.
There is an alternate way of looking at the same effect that uses the concept of gravity gradients, or the change of the gravity field of the Earth with distance. Imagine that the Space Shuttle is not in orbit. Instead it is just dropping nose first toward the Earth. If you were floating in the nose of the Space Shuttle, dropping along with it, you would be closer to the center of the Earth than the center of mass of the Shuttle. Since the Newton Theory of Gravity says that the gravity field of the Earth gets weaker with distance, then the gravity field on you is stronger than the gravity field on the Space Shuttle and you fall faster than the center of mass of the Space Shuttle, pulling you toward the nose. If you were at the back of the Shuttle bay, you would be in a weaker gravity field, while the Shuttle is in a stronger field and is pulled away from you. Thus, because the gravity field of the Earth changes with vertical distance above the Earth, objects at different altitudes fall at different rates. The farther apart the objects are from each other, the greater the difference in their rates of fall.
This gravity gradient or differential acceleration effect is better known to you as the tidal force. The tides in the oceans of the Earth are caused mostly by the gravity gradient forces of the Moon. The Moon pulls on the oceans of the Earth that are underneath it, and pulls them up away from the center of mass of the Earth, causing the below-Moon tidal bulge. At the same time, the Moon is pulling the Earth away from the ocean water on the far side, causing the opposite-Moon tidal bulge. That is why the tides come about every twelve hours instead of every twenty-four hours.
There is also a horizontal gravity gradient. The reason for the horizontal accelerations is a little harder to understand, but the horizontal gradients are always just as important as the vertical gradient. For a spherical attracting mass like the Earth, the horizontal gradients are half the strength of the vertical gradients, but there are two of them. Going back (briefly) to our still-falling Space Shuttle, suppose you were out near one wingtip, falling along with the Shuttle. Both you and the Space Shuttle are falling directly toward the center of the Earth. But since the two trajectories ultimately meet at the center of the Earth, as you fall along your trajectory, your trajectory gets closer to the Space Shuttle trajectory and you observe an inward motion.
If we move our point of view to the center of the mass of the Space Shuttle, we see that the gravity tide pattern from the Earth consists of a tension in the vertical direction that is twice as strong as the uniform compression in the horizontal direction. [See top half of Figure 8.]
To eliminate these residual gravity fields we can use my gravity gradient compensator consisting of six dense masses in a ring around the region to be protected. (A solid ring or any number of masses greater than three can be used instead, but six seems to be optimum.) The plane of the ring of masses is arranged to always be tangent to the surface of the Earth below. The tidal gravity pattern from the six compensator spheres in a ring is almost exactly the same as the tidal gravity pattern from the Earth, except the accelerations are reversed in direction.
This pattern of forces is easily understood if you imagine a small test object in the middle of the ring. If the test object is exactly in the center, the combined gravitational attraction of the six spheres cancels out. If the test object moves above or below the plane, the combined attractions of the spheres will pull it back. If the test object moves toward one of the spheres, the attraction of that sphere increases while the attraction of the sphere on the opposite side of the ring decreases, and the test object is pulled even farther away from the center. By merely adjusting the radius and tilt of the ring of compensator spheres we can "fine tune" the gravity tidal pattern of the compensator to match the tidal pattern of the Earth at any altitude. Since we are not trying to compensate the whole gravity field of the Earth, but only the much weaker tidal forces, we will not need ultradense matter for the compensator spheres, but only normal density materials like lead or tungsten.
If we assume that the six spheres in the compensator are each a 100 kilogram ball of tungsten, then the spheres will be twenty-two centimeters (nine inches) in diameter. The match of the compensating fields to the Earth fields is only perfect at the exact center of the ring. The match is fairly good, however, in a significant region about the central point. Calculations show that if the compensator ring were properly adjusted, the residual gravity forces inside a disk-shaped region about the size of a box of bath powder at the center of the compensator ring would be reduced by a factor of one hundred. At geostationary orbit altitude, the tidal fields to be compensated become smaller and the size of the compensated region becomes larger. The compensator ring can now lower the residual accelerations to less than a picogravity (a trillionth of an Earth gravity) over a disk-shaped volume the size of a large hatbox.
These large volumes of force-free space will certainly be valuable for scientific experiments that require a region free from Earth tides. They also will be useful, up to a point, for space manufacturing. The lower acceleration limit for space processing is set by the self-gravity of the molten metals or liquids being processed. A ball of water and bacteria one meter across will have a self-gravity field at its surface of thirty nanogravities, while a molten ball of steel ten centimeters across has a self-gravity field of twenty nanogravities (greater than the accelerations due to the Earth tides). These self-gravity forces will cause convection currents to flow in the liquid, disturbing the desired equilibrium conditions.
It turns out, however, that with a little bit of Newtonian antigravity magic, we can not only cancel any Earth tides that might affect those materials processing experiments, but we can also cancel the self-gravity field everywhere inside the sample! The shape for a space materials processing experiment sample that gives the most volume with the lowest residual gravity is a thick disk. For a specific example, let us assume a disk of material with the density of water that is thirty centimeters in diameter and ten centimeters thick (about the size of a large double-layer cake). The self-gravity field pattern of this thick disk is quite complicated. It is zero at the center and becomes stronger as you go toward the surface, reaching about three nanogravities at the top and bottom and around the rim.
We first can smooth out the variations in the acceleration due to the "edge effects" by surrounding the sample volume with a "guard ring" consisting of a container in the shape of a ring filled with material that has the same density as the material in the sample chamber. The material in the sample volume and the guard ring need to be kept separated by a thin wall. The material in the guard ring will not be free from accelerations, and convection currents will be set up in it. The thin wall will keep the protected material in the sample volume from being disturbed by these currents.
We then add "guard caps" to the top and bottom of the sample volume plus guard ring. With the guard ring and guard caps in place, we find that the original complicated self-gravity force pattern inside the sample has become very regular and increases linearly with distance from the center. How can we cancel these self-gravity accelerations? Let us take them one at a time.
To compensate for the inward vertical component of the self-gravity of the disk we will use the outward vertical acceleration of the Earth tides. If the Earth tide at the altitude of our manufacturing facility is too strong for the self-gravity of the disk, we cancel a portion of it with our six-sphere tidal compensator. If the Earth tide at that altitude is too weak, we augment the Earth tidal forces using my two-sphere tidal augmentor.
A tidal augmentor consists of two 100 kilogram spheres placed above and below the sample disk. The gravity tidal pattern the augmentor produces at the point between the two spheres is identical to the tidal pattern of the Earth. [See Figure 9.] Thus, by judicious use of either the compensator or augmentor, depending upon the orbital altitude and the density of the sample of material undergoing processing, we can adjust the Earth tides so they will compensate for the vertical component of the self-gravity of a properly guarded sample disk.
The horizontal component of acceleration is another matter. The horizontal self-gravity accelerations of the disk are inward directed, as are the accelerations induced by the Earth tides. After we have used the Earth tides to null out the vertical self-gravity, we will find that the horizontal accelerations have been doubled. The combined self-gravity and Earth tide accelerations can now be canceled by a last bit of Newtonian magic. Instead of using the Newton Theory of Gravity, however, we will use the Newton Theory of Mechanics. We can cancel the horizontal accelerations by a slow rotation of the sample disk about its vertical axis.
The rotation of a disk causes an outward centrifugal acceleration that has no component along the vertical spin axis, just a horizontal acceleration that everywhere increases linearly with distance from the axis. A carefully chosen rotation of about one revolution every few hours will now cancel both the inward acceleration of the self-gravity of the sample and the inward acceleration of the Earth tides.
Thus, by a combination of guard rings and guard caps to make the self-gravity more uniform, the use of the Earth tides augmented or compensated by 100-kilogram masses, and a slight rotation of the sample volume, it is possible to cancel all the gravity inside a sample volume of material some thirty centimeters in diameter and ten centimeters thick (the size of a birthday cake). The technique can be used at any orbital altitude, but the best results can be obtained in a space manufacturing facility in geostationary orbit. In one example that I calculated, our birthday-cake sized sample disk of water had the gravity fields inside decreased by a factor of a thousand, so that the maximum gravity acceleration anywhere inside the disk was less than a picogravity or a trillionth of an Earth gravity. At this level of acceleration it would take an atom eight seconds to fall its own diameter!
One of these days there will be large space laboratories in orbit, with special isolated rooms where ultra-low gravity experiments can be carried out. There will be no humans near those rooms, for the gravity of even the most petite experimenter would be enough to disturb the delicate experiments floating inside. From some of the laboratories will come exotic alloys, from others ultra-light, ultra-strong foamed metals. From still other laboratories the valuables extracted will not be tangible products like pharmaceuticals and new materials, but that intangible yet infinitely more valuable product of scientific research—knowledge. Perhaps new knowledge about the innermost secrets of gravity.
The Newton Theory of Gravity served the human race well for over 200 years. As the followers of Newton carried out more and more detailed calculations of the motion of the Moon and planets, the better the Newton Theory of Gravity looked. For example, the motion of Mars in its orbit is predominantly due to the gravitational attraction of the Sun, but the mass of nearby Jupiter causes perturbations in that orbit, and the mass of Earth causes perturbations in that perturbed orbit, and the mass of Saturn causes perturbations in that perturbed, perturbed orbit, etc. Finally, perturbation calculations were carried out for the effect of every planet around the Sun on every other planet. All the observations of the planets agreed with the predictions of the amazing Newton Theory of Gravity . . . almost. There was a "slight discrepancy" in the predictions for the orbit of Mercury that wouldn't go away.
The orbit of Mercury is not circular. It is distinctly elliptical. With an orbital period of only 88 days, the astronomers have followed Mercury through hundreds of revolutions around the sun and have been able to measure the parameters of the orbit to high accuracy. The major axis of the orbital ellipse of Mercury shifts a little each revolution, 5599.74±0.41 seconds of arc per century to be exact (about four degrees of total precessional shift since people started measuring a few centuries ago). Calculations using the Newton Theory of Gravity indicate that the perturbations introduced by the other planets in the solar system cause most of this shift, but not all of it. Even after many refinements, the maximum calculated orbital shift due to the planetary perturbations was found to be 5557.18+0.85 seconds of arc per century, leaving a discrepancy of 42.56+0.94 seconds of arc per century between the measurements and predictions of the Newton Theory of Gravity.
Finally, along came Albert Einstein with his new Theory of Gravity. Using his new theory, Einstein calculated the orbit of Mercury and found that in his theory the major axis of the orbital ellipse of Mercury should precess an additional 42.9 seconds of arc per century, in excellent agreement with the measurements. Other competing theories of gravity, when applied to the precession of the orbit of Mercury, give an incorrect value or even the wrong sign.
The Einstein Theory of Gravity is more complex than the two previous theories of gravity. In a simplified form it can be expressed as:
"A mass causes space to curve. Other masses move in that curved space."
In the Einstein view of gravity, mass does not cause gravity. Instead mass curves space and curved space causes gravity. A good analogy is to imagine a rubber sheet stretched over a frame. If you put a heavy ball bearing in the center of the rubber sheet, the weight of the ball would cause a curved depression. The mass of the heavy ball bearing has "curved" the rubber sheet "space". If you then drop a tiny marble on the curved rubber sheet, the marble would immediately start to roll toward the center as if the large ball were attracting it. But there is no direct attraction between the ball bearing and the marble, the ball bearing is curving the rubber sheet and the marble is responding to the curvature of the rubber (and the gravity of the Earth). If the marble were tossed properly into the curved depression in the rubber sheet, it would go into an "orbit" around the heavy ball bearing at the center.
Because Mercury is close to the sun, the space curvature caused by the Sun has two effects on the motion of Mercury. First, the curved space produced by the Sun causes Mercury to move in an orbit about the sun, just like all the other planets do under the influence of the curved space caused by the Sun. But, in addition, the space near the Sun where Mercury orbits is so curved, that some of the space is missing!
A circle drawn around the Sun out near the orbit of Earth has a full 360 degrees of angle in it. But a circle drawn around the Sun in near the orbit of Mercury does not have a full 360 degrees in it, it is missing roughly 0.1 seconds of arc. So every time Mercury orbits the sun, it comes up short by that much. After a century, or some 415 orbits, this missing piece of angle in Mercury's orbit adds up to a noticeable precession of 42 seconds of arc. The prediction and confirmation of the existence of this tiny little amount of missing space by the Einstein Theory of Gravity has led to many other and more dramatic predictions by the theory, such as the big bang, black holes, gravitational waves, space warps, time machines, and even gravity control. Some of the predictions, such as the big bang and black holes, now seem to be verified by observation. The others are still indistinguishable from magic, but we are beginning to envision how they might turn into future reality.
Because the Einstein Theory of Gravity is more complex than the Ug or Newton theories, it can give us more handles by which we can control gravity. There are at least two ways that we can use the Einstein Theory of Gravity to negate the gravity field of the Earth. There are also two ways we can use the Einstein Theory of Gravity to make a mass push instead of pull.
In the scientific studies of electricity, it has been found that electricity and magnetism are related. If you change or move electricity, you make magnetism, and if you change or move magnetism, you make electricity again. This transformation between electricity and magnetism is used to make your automobile run. The electricity in your car battery is only twelve volts, not strong enough to run your spark plugs. This low voltage electricity is used to create magnetism in the spark coil. The magnetism temporarily stored in the coil is then released very rapidly when the points open. This rapidly changing magnetic field then generates the powerful, high-voltage sparks that are used by the spark plugs. By using the magnetic field as an intermediate step, the automotive engineers have found a way to convert weak electric forces into strong electric forces.
The Einstein Theory of Gravity says that gravity behaves the same way as electricity. If you take a mass and the gravity field that surrounds it, and move the mass very rapidly, you can create a new field, the gravitational equivalent of magnetism. It is not magnetism, but a completely new field. If you can then cause that new field to change, then you can create a stronger gravity field than you started with. More importantly, that stronger gravity field can be made to appear at a place where there is no mass, and can be made either attractive or repulsive.
Conceptually, there are a number of ways that such a gravity machine could be made. One idea is to roll up some hollow pipe to form a long coil, like the curly cord on a telephone. [See Figure 10.] We then bend the long coil around until the two ends meet to form a curly closed ring.
If the pipes are filled with massive liquid and the liquid is moved back and forth in the pipes rapidly enough, then an alternating push-pull gravity field will be generated at the center of the ring. If the machine was big enough, and the liquid was dense enough and moving fast enough, then we would have a gravity catapult that could launch and retrieve space ships by its gravity repulsion and attraction.
How big? How dense? How fast? Unfortunately, the machine has to be as big as the distance over which you want the gravity effects to operate. The liquid has to be as dense or denser than white-dwarf-star material, and the speed of the flow has to be so high that the ultradense liquid will approach the speed of light in a few milliseconds.
I am afraid that it will be some time before we have all that gravitational technology well in hand. But we do have the theory needed to design our gravity catapult, and some time in the long distant future we will have college classes full of bright students taking their first course in Gravitational Engineering, studying the turbulent flow in ultradense matter and producing more and more efficient designs for the gravitational attractor and repulsor beam intensities to minimize passenger discomfort during the launch or retrieval of an interstellar passenger liner.
The Einstein Theory of Gravity can give us yet another way to control gravity. One of the strangest facets of the Einstein Theory of Gravity is the concept of curved space. The method by which a massive object causes a curvature in space is difficult to really comprehend. It is as if the mass had grabbed hold of space and pulled the space into it. This grip of mass on space is still maintained when the mass is moving. The space seems to move along with the mass. This effect, called the "dragging of the space-time coordinate frame", is the basis for another future magic type of antigravity machine.
If you are near a rapidly moving dense mass, you will find yourself "dragged" along in the direction of the moving mass. One could envision a "lift" shaft, lined with pipes full of rapidly flowing ultradense fluid that wafts you rapidly up to the top of a mile-high building. But more likely this "drag" effect will be used in space as a gravity catapult for shipping purposes within the Solar System. This machine would again be in the form of a ring of ultradense matter, but this time the ring would be uniformly whirling from inside-out, like a gigantic smoke-ring.
If a spaceship entered such a toroidal gravity catapult through the hole from one side, it would be expelled out the other side of the hole with a greatly increased velocity. If the spaceship were falling in toward the Sun from the asteroid belt with a high velocity, it would be gently stopped in Earth orbit by threading the torus in the opposite direction. Since the forces on the spaceship during acceleration and deceleration are gravitational forces which act equally on every atom in the ship, all the atoms in the spacecraft are stopped at the same rate and at the same time. So, even though the accelerations and decelerations can be at rates equivalent to hundreds of Earth gravities, the passengers on those spacecraft will not even have to turn in their martini glasses for "landing" in the Earth-Moon system, much less buckle their seatbelts, stow their overhead luggage, raise their seatbacks, and secure their tables.
As unbelievable as these machines for controlling gravity might seem, they at least use a form of matter which we know exists, even if it is presently found only in the interiors of far distant stars. There are speculations that there might exist another type of matter. It has very strange properties. If it ever could be found or made, then a whole new era of gravity control would open up.
All the matter that we know of is the type called regular (positive) matter. Yet both the Newton and the Einstein Theories of Gravity allow the existence of an opposite form of matter, called negative matter. According to the theories of gravity and mechanics, an atom of negative matter would repel all other matter (including other atoms of negative matter).
Now, the first thing you should realize is that negative matter is not "antimatter". Antimatter is different from regular matter in its quantum mechanical properties, not its gravitational properties. Although it has yet to be proven experimentally, we are fairly sure that antimatter attracts other forms of matter, just like normal matter. Negative matter, however, would repel other forms of matter.
We do not know how to make negative matter. But when we do, we will discover that it will not cost us any energy to make that negative matter. Because the rest mass energy of a particle is proportional to its mass (E=mc2), the rest mass energy of a negative mass particle is negative! That means that if we always create equal amounts of positive and negative matter at the same time, it will cost us no net energy to do so! One can imagine a future scene in some huge laboratory, where great machines apply intense electric, magnetic, and gravitational forces to some microscopic point in empty space. The energy levels of the fields are raised higher and higher until the "nothing" itself is ripped apart into a ball of regular matter and an equal sized ball of negative matter, the whole process using no net energy except for the losses in the generating machines.
Once we have our negative matter, we can start using it to make antigravity machines. But we must be very careful how we handle the negative matter. Unlike a chunk of regular matter, which responds to your push by moving away, if you push on a chunk of negative mater, it will come toward you! (If by mistake, you pushed on some negative matter, and it started to move toward you, you must quickly run around behind it and give it a slap on the rear to bring it to a halt!)
Now that we have learned how to control our working material, the simplest antigravity machine that we can make is to form the negative matter into a dense disc and lay it on a good strong floor. If the disc is dense enough and thick enough, then the repulsive gravity field on both sides of the disc will be one Earth gravity. That negative gravity field from the disc would then cancel the gravity field of the Earth. In the region above the disc, the gravity attraction would be zero and you could float there in free fall.
The negative gravitational field of negative matter can also be used for gravity propulsion. If you place a ball of very dense negative matter near a similar dense ball of regular matter (which is incidentally attached to your spaceship), you will find that the negative matter ball will repel the regular matter ball, which in turn will attract the negative matter ball. The two dense balls will start to move off in a straight line at a constantly increasing speed. The acceleration will be the strength of the gravitational attraction of one ball for the other, with the negative matter ball chasing after the positive matter ball and the positive matter ball carrying your spaceship along with it.
You might at first worry that I'm getting something for nothing. First there were two balls of matter, both standing still, with no kinetic energy. Then, after a while they are both moving off together at high speed with no propulsion energy being expended. You might think that would prove that negative matter is impossible, since it looks like the law of conservation of energy is being violated.
But if you look very closely, you will find that negative mass propulsion does not violate any laws of physics. It is true that the ball of regular mass gains speed and increases its kinetic energy [E=1/2(+m)v2], so it looks like it is getting energy out of nowhere. But while it is doing so, the ball of negative matter is gaining negative energy [E=1/2(-m)v2] and the total energy of the two masses is zero, just as it was when they were standing still. Thus, negative mass propulsion does not violate the law of conservation of energy.
By the same type of argument, you can also show that negative mass propulsion does not violate that other important law of physics, the law of conservation of momentum. For while the momentum of the positive ball of mass is increasing, the momentum of the negative ball of mass is decreasing, resulting in zero net momentum, even though the two balls started out standing still and now are moving off at high speeds.
So far as we know, negative matter doesn't exist. We don't know why it doesn't. After all, both the positive and negative forms of electricity exist, so why not the positive and negative forms of mass? Perhaps there is some yet unknown law of physics that prevents it from forming. But even if we can never obtain this indistinguishable from magic material, we can still devise ways to control gravity with just regular matter, if just work hard and use enough energy and intelligence.
The Einstein Theory of Gravity is now serving the human race well, and will until a better Theory of Gravity is discovered. We do not know the correct Theory of Gravity yet. The correct Theory of Gravity must include quantum mechanics—the theory of the behavior of atoms and elementary particles. The Einstein Theory of Gravity, despite all its recognized grandeur, ignores quantum mechanics. Because it does not recognize the world of the small, someday it will be replaced. Many brilliant people are now working hard to find a new Quantum Theory of Gravity that will retain all that was good in the Einstein Theory of Gravity and yet will add the new features of gravity effects into the microcosmic world of the atom.
The new Quantum Theory of Gravity will be even more complex than the Einstein Theory of Gravity. The strange Einsteinian concepts of curved space will be mixed up with the even more exotic zoo of "elementary" particles, with their strangeness, beauty, charm, and color. Yet we should not despair that the theories become more complex. For it is their very complexity that will be the tools that the gravitational engineer of the future will use to invent, design, build, test, and make work the machines that will give us control over our common burden, gravity.
Can we really make an antigravity machine? The answer is: Yes. There are many ways to make a machine that will cancel the gravitational attraction of Earth. It is also theoretically possible to make a machine out of massive bodies that will repel an massive object instead of attracting it. The technology required to build such machines is not here right now, but as we gain control over more energy and move into space where we can manipulate large masses without having to contest Earth for their control, we will move into the realm of gravity control technologies that are presently indistinguishable from magic. When that day comes, the children of the human race (or whoever the human race has evolved into by then) will control gravity as easily as our littlest children now control the awesome power of lightning with the flick of a wall switch.
Albert Einstein, The Meaning of Relativity, p. 102 (Princeton University Press, Princeton, NJ, 1955).
Robert L. Forward, "General Relativity for the Experimentalist," Proceedings of the Institute of Radio Engineers, Vol. 49, pp. 892-904 (May 1961).
Robert L. Forward, "Antigravity," Proceedings of the Institute of Radio Engineers, Vol. 49, p. 1442 (September 1961).
Robert L. Forward, Starquake, Ballantine/Del Rey, NY, 1981. [Science fiction novel that visually describes a number of gravitational machines made with ultradense matter.]
Robert L. Forward, "A New Gravitational Field," Science Digest, Vol. 52, #3, pp. 73-76 (September 1962).
Robert L. Forward, "Guidelines to Antigravity," American Journal of Physics, Vol. 31, #3, pp. 166-170 (March 1963).
Robert L. Forward, "Far Out Physics", Analog Science Fiction/ Science Fact, Vol. 95, pp. 147-166 (August 1975).
Robert L. Forward, "Goodby Gravity," Omni, Vol. 1, #4, pp. 88-91 (January 1979).
Robert L. Forward, "Flattening Spacetime Near the Earth," Physical Review, Vol. D26, pp. 735-744 (15 August 1982).
Robert L. Forward, Rocheworld, Baen Books, NY, 1990. [Science fiction novel that visually describes a zero-gravity region midway between two massive planetoids.]
Robert L. Forward, "Negative Matter Propulsion", J. Propulsion Vol. 6, pp. 28-37 (January-February 1990).
Robert L. Forward, Timemaster, Tor Books, NY, 1992. [Science fiction novel that describes the many technologies that would arise from the discovery and control of negative matter.]
William J. Kaufmann, III, Relativity and Cosmology, Chap. 11 and 12, (Harper and Row, NY, 1973).