VA PRIMER OF ATOMIC ENERGY
The material universe, the earth and everything in it, all things living and non-living, the sun and its planets, the stars and the constellations, the galaxies and the supergalaxies, the infinitely large and the infinitesimally small, manifests itself to our senses in two forms, matter and energy. We do not know, and probably never can know, how the material universe began, and whether, indeed, it ever had a beginning, but we do know that it is constantly changing and that it did not always exist in its present form. We also know that in whatever form the universe may have existed, matter and energy have always been inseparable, no energy being possible without matter, and no matter without energy, each being a form of the other.
While we do not know how and when matter and energy came into being, or whether they ever had a beginning in time as we perceive it, we do know that while the relative amounts of matter and energy are constantly changing, the total amount of both, in one form or the other, always remains the same. When a plant grows, energy from the sun, in the form of heat and light, is converted into matter, so that the total weight of theplant is greater than that of the elementary material constituents, water and carbon-dioxide gas, out of which its substance is built up. When the substance of the plant is again broken up into its original constituents by burning, the residual ashes and gases weigh less than the total weight of the intact plant, the difference corresponding to the amount of matter that had been converted into energy, liberated once again in the form of heat and light.
All energy as we know it manifests itself through motion or change in the physical or chemical state of matter, or both, though these changes and motions may be so slow as to be imperceptible. As the ancient Greek philosopher Heraclitus perceived more than two thousand years ago, all things are in a constant state of flux, this flux being due to an everlasting conversion of matter into energy and energy into matter, everywhere over the vast stretches of the material universe, to its outermost and innermost limits, if any limits there be.
Each manifestation of energy involves either matter in motion or a change in its physical state, which we designate as physical energy; a change in the chemical constitution of matter, which we know as chemical energy; or a combination of the two. Physical energy can be converted into chemical energy and vice versa. For example, heat and light are forms of physical energy, each consisting of a definite band of waves of definite wavelengths in violent, regular, rhythmic oscillations. A mysterious mechanism in the plant, known as photosynthesis, uses the heat and light energy from the sun to create complex substances, such as sugars, starches, and cellulose, out of simpler substances, such as carbon dioxide and water, converting physical energy, heat, and light into the chemical energy required to hold together the complex substances the plant produces. When we burn the cellulose in the form of wood or coal (coal is petrified wood), the chemical energy is once again converted into physical energy in the form of the original heat and light. As we have seen, the chemical energy stored in the plant manifested itself by an increase in the plant’s weight as compared with that of its original constituents. Similarly, the release of the energy manifests itself through a loss in the total weight of the plant’s substance.
It can thus be seen that neither matter nor energy can be created. All we can do is to manipulate certain types of matter in a way that liberates whatever energy had been in existence, in one form or another, since the beginning of time. All the energy that we had been using on earth until the advent of the atomic age had originally come from the sun. Coal, as already said, is a petrified plant that had stored up the energy of the sun in the form of chemical energy millions of years ago, before man made his appearance on the earth. Oilcomes from organic matter that also had stored up light and heat from the sun in the form of chemical energy. Water power and wind power are also made possible by the sun’s heat, since all water would freeze and no winds would blow were it not for the sun’s heat energy keeping the waters flowing and the air moving, the latter by creating differences in the temperature of air masses.
There are two forms of energy that we take advantage of which are not due directly to the sun’s radiations—gravitation and magnetism—but the only way we can utilize these is by employing energy derived from the sun’s heat. In harnessing Niagara, or in the building of great dams, we utilize the fall of the water because of gravitation. But as I have already pointed out, without the sun’s heat water could not flow. To produce electricity we begin with the chemical energy in coal or oil, which is first converted into heat energy, then to mechanical energy, and finally, through the agency of magnetism, into electrical energy.
The radiations of the sun, of the giant stars millions of times larger than the sun, come from an entirely different source, the greatest source of energy in the universe, known as atomic or, more correctly, nuclear energy. But even here the energy comes as the result of the transformation of matter. The difference between nuclear energy and chemical energy is twofold. In chemical energy, such as the burning of coal, the matter lostin the process comes from the outer shell of the atoms, and the amount of matter lost is so small that it cannot be weighed directly by any human scale or other device. In nuclear energy, on the other hand, the matter lost by being transformed into energy comes from the nucleus, the heavy inner core, of the atom, and the amount of matter lost is millions of times greater than in coal, great enough to be weighed.
An atom is the smallest unit of any of the elements of which the physical universe is constituted. Atoms are so small that if a drop of water were magnified to the size of the earth the atoms in the drop would be smaller than oranges.
The structure of atoms is like that of a minuscule solar system, with a heavy nucleus in the center as the sun, and much smaller bodies revolving around it as the planets. The nucleus is made up of two types of particles: protons, carrying a positive charge of electricity, and neutrons, electrically neutral. The planets revolving about the nucleus are electrons, units of negative electricity, which have a mass about one two-thousandth the mass of the proton or the neutron. The number of protons in the nucleus determines the chemical nature of the element, and also the number of planetary electrons, each proton being electrically balanced by an electron in the atom’s outer shells. The total number of protons and neutrons in the nucleus is known as the mass number, which is very close tothe atomic weight of the element but not quite equal. Protons and neutrons are known under the common name “nucleons.”
There are two important facts to keep constantly in mind about protons and neutrons. The first is that the two are interchangeable. A proton, under certain conditions, loses its positive charge by emitting a positive electron (positron) and thus becomes a neutron. Similarly, a neutron, when agitated, emits a negative electron and becomes a proton. As we shall see, the latter process is taken advantage of in the transmutation of nonfissionable uranium into plutonium, and of thorium into fissionable uranium 233. The transmutation of all other elements, age-old dream of the alchemists, is made possible by the interchangeability of protons into neutrons, and vice versa.
The second all-important fact about protons and neutrons, basic to the understanding of atomic energy, is that each proton and neutron in the nuclei of the elements weighs less than it does in the free state, the loss of weight being equal to the energy binding the nucleons. This loss becomes progressively greater for the elements in the first half of the periodic table, reaching its maximum in the nucleus of silver, element 47. After that the loss gets progressively smaller. Hence, if we were to combine (fuse) two elements in the first half of the periodic table, the protons and the neutrons would lose weight if the newly formed nucleus isnot heavier than that of silver, but would gain weight if the new nucleus thus formed is heavier than silver. The opposite is true with the elements in the second half of the periodic table, the protons and neutrons losing weight when a heavy element is split into two lighter ones, and gaining weight if two elements are fused into one.
Since each loss of mass manifests itself by the release of energy, it can be seen that to obtain energy from the atom’s nucleus requires either the fusion of two elements in the first half of the periodic table or the fission of an element in the second half. From a practical point of view, however, fusion is possible only with two isotopes (twins) of hydrogen, at the beginning of the periodic table, while fission is possible only with twins of uranium, U-233 and U-235, and with plutonium, at the lower end of the table.
The diameter of the atom is 100,000 times greater than the diameter of the nucleus. This means that the atom is mostly empty space, the volume of the atom being 500,000 billion times the volume of the nucleus. It can thus be seen that most of the matter in the universe is concentrated in the nuclei of the atoms. The density of matter in the nucleus is such that a dime would weigh 600 million tons if its atoms were as tightly packed as are the protons and neutrons in the nucleus.
The atoms of the elements (of which there are ninety-two in nature, and six more man-made elements)have twins, triplets, quadruplets, etc., known as isotopes. The nuclei of these twins all contain the same number of protons and hence all have the same chemical properties. They differ, however, in the number of neutrons in their nuclei and hence have different atomic weights. For example, an ordinary hydrogen atom has a nucleus of one proton. The isotope of hydrogen, deuterium, has one proton plus one neutron in its nucleus. It is thus twice as heavy as ordinary hydrogen. The second hydrogen isotope, tritium, has one proton and two neutrons in its nucleus and hence an atomic mass of three. On the other hand, a nucleus containing two protons and one neutron is no longer hydrogen but helium, also of atomic mass three.
There are hundreds of isotopes, some occurring in nature, others produced artificially by shooting atomic bullets, such as neutrons, into the nuclei of the atoms of various elements. A natural isotope of uranium, the ninety-second and last of the natural elements, contains 92 protons and 143 neutrons in its nucleus, hence its name U-235, one of the two atomic-bomb elements. The most common isotope of uranium has 92 protons and 146 neutrons in its nucleus and hence is known as U-238. It is 140 times more plentiful than U-235, but cannot be used for the release of atomic energy.
Atomic, or rather nuclear, energy is the cosmic force that binds together the protons and the neutronsin the nucleus. It is a force millions of times greater than the electrical repulsion force existing in the nucleus because of the fact that the protons all have like charges. This force, known as the coulomb force, is tremendous, varying inversely as the square of the distance separating the positively charged particles. Professor Frederick Soddy, the noted English physicist, has figured out that two grams (less than the weight of a dime) of protons placed at the opposite poles of the earth would repel each other with a force of twenty-six tons. Yet the nuclear force is millions of times greater than the coulomb force. This force acts as the cosmic cement that holds the material universe together and is responsible for the great density of matter in the nucleus.
We as yet know very little about the basic nature of this force, but we can measure its magnitude by a famous mathematical equation originally presented by Dr. Einstein in his special theory of relativity in 1905. This formula, one of the great intellectual achievements of man, together with the discovery of the radioactive elements by Henri Becquerel and Pierre and Marie Curie, provided the original clues as well as the key to the discovery and the harnessing of nuclear energy.
Einstein’s formula, E =mc², revealed that matter and energy are two different manifestations of one and the same cosmic entity, instead of being two different entities, as had been generally believed.It led to the revolutionary concept that matter, instead of being immutable, was energy in a frozen state, while, conversely, energy was matter in a fluid state. The equation revealed that any one gram of matter was the equivalent in ergs (small units of energy) to the square of the velocity of light in centimeters per second—namely, 900 billion billion ergs. In more familiar terms, this means that one gram of matter represents 25,000,000 kilowatt-hours of energy in the frozen state. This equals the energy liberated in the burning of three billion grams (three thousand tons) of coal.
The liberation of energy in any form, chemical, electrical, or nuclear, involves the loss of an equivalent amount of mass, in accordance with the Einstein formula. When 3,000 metric tons of coal are burned to ashes, the residual ashes and the gaseous products weigh one gram less than 3,000 tons; that is, one three-billionth part of the original mass will have been converted into energy. The same is true with the liberation of nuclear energy by the splitting or fusing (as will be explained later) of the nuclei of certain elements. The difference is merely that of magnitude. In the liberation of chemical energy by the burning of coal, the energy comes from a very small loss of mass resulting from the rearrangement of electrons on the surface of the atoms. The nucleus of the coal atoms is not involved in any way, remaining exactly the same as before. The amount of mass lost by the surfaceelectrons is one thirtieth of one millionth of one per cent.
On the other hand, nuclear energy involves vital changes in the atomic nucleus itself, with a consequent loss of as high as one tenth to nearly eight tenths of one per cent in the original mass of the nuclei. This means that from one to nearly eight grams per thousand grams are liberated in the form of energy, as compared with only one gram in three billion grams liberated in the burning of coal. In other words, the amount of nuclear energy liberated in the transmutation of atomic nuclei is from 3,000,000 to 24,000,000 times as great as the chemical energy released by the burning of an equal amount of coal. In terms of TNT the figure is seven times greater than for coal, as the energy from TNT, while liberated at an explosive rate, is about one seventh the total energy content for an equivalent amount of coal. This means that the nuclear energy from one kilogram of uranium 235, or plutonium, when released at an explosive rate, is equal to the explosion of twenty thousand tons of TNT.
Nuclear energy can be utilized by two diametrically opposed methods. One is fission—the splitting of the nuclei of the heaviest chemical elements into two uneven fragments consisting of nuclei of two lighter elements. The other is fusion—combining, or fusing, two nuclei of the lightest elements into one nucleus of a heavier element. Inboth methods the resulting elements are lighter than the original nuclei. The loss of mass in each case manifests itself in the release of enormous amounts of nuclear energy.
When two light atoms are combined to form a heavier atom, the weight of the heavier is less than the total weight of the two light atoms. If the heavier atom could again be split into the two lighter ones, the latter would resume their original weight. As explained before, however, this is true only with the light elements, such as hydrogen, deuterium, and tritium, in the first half of the periodic table of the elements. The opposite is true with the heavier elements of the second half of the periodic table. For example, if krypton and barium, elements 36 and 56, were to be combined to form uranium, element 92, the protons and the neutrons in the uranium nucleus would each weigh about 0.1 per cent more than they weighed in the krypton and barium nuclei. It can thus be seen that energy could be gained either through the loss of mass resulting from the fusion of two light elements, or from the similar loss of mass resulting from the fission of one heavy atom into two lighter ones.
In the fusion of two lighter atoms, the addition of one and one yields less than two, and yet half of two will be more than one. In the case of the heavy elements the addition of one and one yields more than two, yet half of two makes less thanone. This is the seeming paradox of atomic energy.
Three elements are known to be fissionable. Only one of these is found in nature: the uranium isotope 235 (U-235). The other two are man-made. One is plutonium, transmuted by means of neutrons from the nonfissionable U-238, by the addition of one neutron to the 146 present in the nucleus, which leads to the conversion of two of the 147 neutrons into protons, thus creating an element with a nucleus of 94 protons and 145 neutrons. The second man-made element (not yet in wide use, as far as is known) is uranium isotope 233 (92 protons and 141 neutrons), created out of the element thorium (90 protons, 142 neutrons) by the same method used in the production of plutonium.
When the nucleus of any one of these elements is fissioned, each proton and neutron in the two resulting fragments weighs one tenth of one per cent less than it weighed in the original nucleus. For example, if U-235 atoms totaling 1,000 grams in weight are split, the total weight of the fragments will be 999 grams. The one missing gram is liberated in the form of 25,000,000 kilowatt-hours of energy, equivalent in explosive terms to 20,000 tons of TNT. But the original number of protons and neutrons in the 1,000 grams does not change.
The fission process, the equivalent of the “burning” of nuclear fuels, is maintained by what is known as a chain reaction. The bullets used forsplitting are neutrons, which, because they do not have an electric charge, can penetrate the heavily fortified electrical wall surrounding the positively charged nuclei. Just as a coal fire needs oxygen to keep it going, a nuclear fire needs the neutrons to maintain it.
Neutrons do not exist free in nature, all being tightly locked up within the nuclei of atoms. They are liberated, however, from the nuclei of the three fissionable elements by a self-multiplication process in the chain reaction. The process begins when a cosmic ray from outer space, or a stray neutron, strikes one nucleus and splits it. The first atom thus split releases an average of two neutrons, which split two more nuclei, which in turn liberate four more neutrons, and so on. The reaction is so fast that in a short time trillions of neutrons are thus liberated to split trillions of nuclei. As each nucleus is split, it loses mass, which is converted into great energy.
There are two types of chain reactions: controlled and uncontrolled. The controlled reaction is analogous to the burning of gasoline in an automobile engine. The atom-splitting bullets—the neutrons—are first slowed down from speeds of more than ten thousand miles per second to less than one mile per second by being made to pass through a moderator before they reach the atoms at which they are aimed. Neutron-“killers”—materials absorbing neutrons in great numbers—keepthe neutrons liberated at any given time under complete control in a slow but steady nuclear fire.
The uncontrolled chain reaction is one in which there is no moderator—and no neutron-absorbers. It is analogous to the dropping of a match in a gasoline tank. In the uncontrolled chain reaction the fast neutrons, with nothing to slow them down or to devour them, build up by the trillion and quadrillion in a fraction of a millionth of a second. This leads to the splitting of a corresponding number of atoms, resulting in the release of unbelievable quantities of nuclear energy at a tremendously explosive rate. One kilogram of atoms split releases energy equivalent to that of 20,000,000 kilograms (20,000 metric tons) of TNT.
It is the uncontrolled reaction that is employed in the explosion of the atomic bomb. The controlled reaction is expected to be used in the production of vast quantities of industrial power. It is now being employed in the creation of radioactive isotopes, for use in medicine and as the most powerful research tool since the invention of the microscope for probing into the mysteries of nature, living and non-living.
In the controlled reaction the material used is natural uranium, which consists of a mixture of 99.3 per cent U-238 and 0.7 of the fissionable U-235. The neutrons from the U-235 are made to enter the nuclei of U-238 and convert them to the fissionable element plutonium, for use in atomicbombs. The large quantities of energy liberated by the split U-235 nuclei in the form of heat is at too low a temperature for efficient utilization as power, and is at present wasted. To be used for power, nuclear reactors capable of operating at high temperatures are now being designed.
In the atomic bomb only pure U-235, or plutonium, is used.
In both the controlled and the uncontrolled reactions a minimum amount of material, known as the “critical mass,” must be used, as otherwise too many neutrons would escape and the nuclear fire would thus be extinguished, as would an ordinary fire for lack of oxygen. In the atomic bomb two masses, each less than a critical mass, which together equal or exceed it, are brought in contact at a predetermined instant. The uncontrolled reaction then comes automatically, since, in the absence of any control, the neutrons, which cannot escape to the outside, build up at an unbelievable rate.
Whereas the fission process for the release of nuclear energy entails making little ones out of big ones, the fusion process involves making big ones out of little ones. In both processes the products weigh less than the original materials, the loss of mass coming out in the form of energy. According to the generally accepted hypothesis, the fusion process is the one operating in the sun and the stars of the same family. The radiant energy givenoff by them, it is believed, is the result of the fusion of four hydrogen atoms into one atom of helium, two of the protons losing their positive charge, thus becoming neutrons. Since a helium atom weighs nearly eight tenths of one per cent less than the total weight of the four hydrogen atoms, the loss of mass is thus nearly eight times that produced by fission, with a corresponding eightfold increase in the amount of energy liberated. This process, using light hydrogen, is not feasible on earth.
The nuclei of all atoms are thus vast storage depots of cosmic energy. We must think of them as cosmic safe-deposit vaults, in which the Creator of the universe, if you will, deposited at the time of creation most of the energy in the universe for safekeeping. The sun and the other giant stars that give light have, as it were, drawing accounts in this “First National Bank and Trust Company of the Universe,” whereas we on this little planet of ours in the cosmic hinterland are much too poor to have such a bank account. So we have been forced all these years we have been on earth to subsist on small handouts from our close neighbor the sun, which squanders millions all over space, but can spare us only nickels, dimes, and quarters (depending on the seasons of the year) for a cup of coffee and a sandwich. We are thus in the true sense of the word cosmic beggars, living off the bounty of a distant relative.
The discovery of fission in 1939 meant that after a million years of exclusive dependence on the sun we had suddenly managed to open a modest drawing account of our own in this bank of the cosmos. We were enabled to do it by stumbling upon two special master keys to five of the cosmic vaults. One of these keys we call fission; the other, which allows us entry into a much richer chamber of the vault, we call fusion. We can get a lot of the stored-up cosmic treasure by using the key to the fission vaults alone, but, as with our terrestrial bank vaults, which generally require two keys before they can be opened, it is not possible to use the key to the fusion vault unless we first use the fission key.
Except for the payment of our heat and light bill, the sun gives us nothing directly in cash. Instead it deposits a very small pittance in the plants, which serve as its major terrestrial banks. The animals then rob the plants and we rob them both. When we eat the food we live by we thus actually eat sunshine.
The sun makes its deposits in the plant through an agent named chlorophyll, the stuff that makes the grass green. Chlorophyll has the uncanny ability to catch sunbeams and to hand them over to the plant. A chemical supergenius inside the plant changes the sunlight energy into chemical energy, just as a bank teller changes bills into silver. With this chemical energy at their disposal, a greatnumber of devilishly clever chemists in the plants’ chemical factory go to work building up many substances to serve as vaults in which to store up a large part of the energy, using only part of it for their own subsistence.
The building materials used by these chemists inside the plants consist mainly of carbon-dioxide gas from the atmosphere, and water from the soil, plus small amounts of minerals either supplied by the good earth or by fertilizers. Carbon dioxide, by the way, composed of one atom of carbon and two atoms of oxygen, is the stuff you exhale. In solid form it is what we know as dry ice, used in efforts to make rain. It is present in the atmosphere in large amounts.
Out of the carbon dioxide and water the chemists in the plants build cellulose, starch, sugar, fat, proteins, vitamins, and scores of other substances, all of which serve as vaults for the sun’s rays caught by the chlorophyll. The biggest vaults of all, storing most of the energy, are the cellulose, sugars and starches, fats and proteins. There the stored energy remains until it is released by processes we call burning or digestion, both of which, as we shall see, are different terms for the same chemical reaction. When we burn wood, or the petrified ancient wood we know as coal, we burn largely the cellulose, the chief component of the solid part of plants. When we eat the plants, or the animals in whom the plant tissues are transformedinto flesh by the solar energy stored within them, it is the sugars, starches, fats, and proteins that give us the energy we live by.
In the process of burning wood or coal the large cellulose vaults, composed of carbon, hydrogen, and oxygen, are broken up, thus allowing the original solar energy, stored up within them as chemical energy, to escape in the form of heat and light. This is the same heat and light deposited there by the sun many years before—in the case of coal, some two hundred million years back. The process of burning thus transforms the chemical energy in the plants back to its original form of light and radiant heat energy. The complex carbon and hydrogen units in the cellulose are broken up, each freed carbon atom uniting within two oxygen atoms in the air to form carbon dioxide again, while two hydrogen atoms unite with one of oxygen to form water. Thus we see that the cellulose vaults are broken up once more into the original building bricks out of which the chemists in the plants had fashioned them.
When we eat plant or animal food to get the energy to live by, exactly the same process takes place except at a lower temperature. The sunlight deposit vaults of sugar, starch, and fat, also composed, like cellulose, of carbon, hydrogen, and oxygen, are broken up by the digestive system into their component parts, thus allowing the original solar energy stored within them to get free in theform of chemical energy, which our body uses in its essential processes. Here, too, the end products are carbon dioxide, which we exhale, and water. About half the energy we thus obtain is used by us for the work we do. The other half is used by the body for building up the tissues burned up as part of the regular wear and tear of life.
We thus burn food for our internal energy as we burn cellulose for our external energy. The interesting thing here is that, in both types of burning, fission as well as fusion processes take place. The fission is the splitting of the cellulose, sugar, fats, starches, and proteins into carbon and hydrogen atoms. The fusion part is the union of the carbon and the hydrogen with oxygen to form carbon dioxide and water. The fusion part is just as necessary to release the stored-up solar energy in the wood or coal as is the fission part, for, as everyone knows, unless there is oxygen for the carbon to fuse with, no combustion (burning) can take place and hence no release of energy. The plant vaults would remain closed absolutely tight.
At this point two things become clear. We see, in the first place, that whenever we get any kind of energy in any form we do not in any way create any of it. All we do is merely draw on something that is already stored up; in the case of coal and wood by the sun, in the case of uranium and hydrogen by the same power that created the sun and all energy. We draw water from the spring,but we do not make the water. On the other hand, we cannot draw the water unless we first find the spring, and even then we cannot draw it unless we have a pitcher.
And we also see, in the second place, that fission and fusion are common everyday phenomena that occur any time you burn anything. Both are essential whenever energy is released, whether it is the chemical energy from coal or the atomic energy from the nuclei of uranium, deuterium, or tritium. When you light a cigarette you employ both fission and fusion or you don’t smoke. The first fission and fusion take place in the lighting of the match, the cellulose in the match (whether it is wood or paper) being fissioned (that is, split into its component atoms of carbon and hydrogen). These atoms are then fusioned with the oxygen in the air. The same thing happens when the tobacco catches fire. In each case the fusion with the oxygen makes possible the fission of the cellulose. When we burn U-235, or plutonium, we again get both fission and fusion, except that, instead of oxygen, the nuclei of these elements first fuse with a neutron before they are split apart. Thus we see that the process of burning U-235, or plutonium, requires not only fission but fusion as well, without which they could not burn. This is true also in hydrogen fusion. When you burn deuterium by fusing two deuterons (nuclei of deuterium) to form helium of atomic weight three,plus a neutron, one of the two deuterons is split in half in the process. Similarly, when you burn tritium by fusion two tritons (nuclei of tritium), one of the tritons splits into two neutrons and a proton, the one proton joining the other triton to form helium of atomic weight four.
Thus we see that fission and fusion are the cosmic firebrands that are always present whenever a fire is lighted, chemical or atomic, whether the fuel is wood, coal, or oil, or uranium, plutonium, deuterium, or tritium. Both, with some variations, are essential for opening the cosmic safe where the energy of the universe is kept in storage. The only reason you get much more energy in the fission and fusion of atomic nuclei is that so much more had been stored in them than in the cellulose vaults on this planet.
The same reason that limits our ability to obtain stored chemical energy to a few fuels also limits our ability to obtain atomic energy. Coal, oil, and wood are the only dividend-paying chemical-energy stocks. Similarly only five elements, uranium 233 and 235, plutonium, deuterium, and tritium are the only dividend-paying atomic-energy stocks, and of these only two (U-235 and deuterium) exist in nature. The other three are re-created from other elements by modern alchemical legerdemain. What is more, we know for a certainty that it will never be possible to obtain atomic energy from any other element, by either fission or fusion.
This should put to rest once and for all the notion of many, including some self-styled scientists, that the explosion of a hydrogen bomb would set the hydrogen in the waters, and the oxygen and the nitrogen in the air, on fire and thus blow up the earth. The energy in common hydrogen is locked up in one of those cosmic vaults which only the sun and the stars that shine can open and which no number of H-bombs could blow apart. Oxygen and nitrogen are locked even for the sun. As for the deuterium in the water, it cannot catch fire unless it is highly concentrated, condensed to its liquid form, and heated to a temperature of several hundred million degrees. Hence all this talk about blowing up the earth is pure moonshine.
But while we know that we have reached the limit of what can be achieved either by fission or by fusion, that by no means justifies the conclusion that we have reached the ultimate in discovery and that fission and fusion are the only possible methods for tapping the energy locked up in matter. We must remember that fifty years ago we did not even suspect that nuclear energy existed and that until 1939 no one, including Dr. Einstein, believed that it would ever become possible to use it on a practical scale. We simply stumbled upon the phenomenon of fission, which in its turn opened the way to fusion.
If science tells us anything at all, it tells us that nature is infinite and that the human mind, drivenby insatiable curiosity and probing ever deeper into nature’s mysteries, will inevitably find ever greater treasures, treasures that are at present beyond the utmost stretches of the imagination—as far beyond fission and fusion as these are beyond man’s first discovery of how to make a fire by striking a spark with a laboriously made flint. The day may yet come, and past history makes it practically certain that it will come, when man will look upon the discovery of fission and fusion as we look today upon the crudest tools made by primitive man.
A great measure of man’s progress has been the result of serendipity, the faculty of making discoveries, by chance or sagacity, of things not sought for. Many an adventure has led man to stumble upon something much better than he originally set out to find. Like Columbus, many an explorer into the realms of the unknown has set his sights on a shorter route to the spices of India only to stumble upon a new continent. Unlike Columbus, however, the explorers in the field of science, instead of being confined to this tiny little earth of ours, have the whole infinite universe as the domain of their adventures, and many a virgin continent, richer by far than any yet discovered, still awaits its Columbus.
Roentgen and Becquerel were exploring what they thought was an untrodden path in the forest and came upon a new road that led their successors to the very citadel of the material universe. YoungEnrico Fermi was curious to find out what would happen if he fired a neutron into the nucleus of uranium, hoping only to create a heavier isotope of uranium, or at best a new element. His rather modest goal led five years later to the fission of uranium, and in another six years to the atomic bomb.
Yet, as we have seen, in both fission and fusion only a very small fraction of the mass of the protons and neutrons in the nuclei of the elements used is liberated in the form of energy, while 99.3 to 99.9 per cent of their substance remains in the form of matter. We know of no process in nature which converts 100 per cent of the matter in protons and neutrons into energy, but scientists are already talking about finding means for bringing about such a conversion. They are seeking clues for such a process in the mysterious cosmic rays that bombard the earth from outer space with energies billions of times greater than those released by fission or fusion, great enough to smash atoms of oxygen or nitrogen, or whatever other atoms they happen to hit in the upper atmosphere, into their component protons and neutrons. Luckily, their number is small and most of their energy is spent long before they reach sea level.
But we have already learned how to create secondary cosmic-ray particles of relatively low energies (350,000,000 electron-volts) with our giant cyclotrons. The creation of these particles, known as mesons, which are believed to be the cosmiccement responsible for the nuclear forces, represents the actual conversion of energy into matter. This is the exact reverse of the process taking place in fission and fusion, in which, as we have seen, matter is converted into energy. And we are now about to complete multibillion-volt atom-smashers that will hurl atomic bullets of energies of from three to ten billion volts at the nuclei of atoms. With these gigantic machines, known as the cosmotron (at the Brookhaven National Laboratory of the Atomic Energy Commission) and the bevatron (at the University of California), we shall be able to smash nuclei into their individual component protons and neutrons and thus get a much more intimate glimpse of the forces that hold the nuclei together. What is more, instead of creating only mesons, particles with only 300 electron masses, we shall be able for the first time to convert energy into protons and neutrons, duplicating, as far as is known, an act of creation that has not taken place since the beginning of the universe. Man at last will be creating the very building blocks out of which the universe is made, as well as the cosmic cement that holds them together.
What new continents will our first glimpse into the mechanism of the very act of creation of matter out of energy reveal? What new secrets will be uncovered before the dazzled eyes and mind of man when he takes the nucleus of the atom completely apart at last? Not even Einstein could tellus. But, as Omar Khayyám divined, “a single Alif” may provide “the clue” that, could we but find it, leads “to the Treasure-House, and peradventure to the Master too.” The fact is that we already have opened the door to the anteroom of the treasure-house, and we are about to unlock the door to one of its inner chambers. What shall we find there? No one as yet knows. But we do know that every door man has opened so far has led to riches beyond his wildest dreams, each new door bringing greater rewards than the one before. On the other hand, we also know that the treasure-house has many mansions, and that no matter how many chambers he may enter, he will always find new doors to unlock. For we have learned that the solution of any one secret always opens up a thousand new mysteries.
We also have learned, to our sorrow, that any new insight gained into nature’s laws and forces can be used for great good and for equally great evil. The greater the insight, the greater the potentialities for good or evil. The new knowledge he is about to gain by his deeper insight into the heart of matter, and by his ability to create it out of energy, may offer man the means to make himself complete master of the world he lives in. It is equally true, alas, that he could use it to destroy that world even more thoroughly than with the hydrogen bomb.
As already stated, scientists are even now discussingthe possibility of finding means for the complete annihilation of matter by the conversion of the entire mass of protons and neutrons into energy, instead of only 0.1 to 0.7 per cent. And while the total annihilation of protons and neutrons still seems highly speculative, we already know that such a process actually does take place in the realm of the electron. This is the phenomenon already achieved numerous times on a small scale in the laboratory, in which a positive electron (positron) and an electron with a negative charge completely destroy each other, their entire mass being converted into energy. Luckily, this is at present only a laboratory experiment, in which each positron must be individually produced, since there are hardly any positive electrons in our part of the universe. But suppose the new knowledge we are about to pry loose from the inner citadel of matter reveals to us a new process, at present not even suspected, that would release positrons in large numbers, just as the fission and fusion processes made possible for the first time the liberation of large quantities of neutrons. Such an eventuality, by no means beyond the realm of the possible, would open potentialities of horror alongside which those of the H-bomb, even the rigged one, would be puny. For any process that would release large numbers of positrons in the atmosphere, in a chain reaction similar to the one now liberating neutrons, may envelop the earth in one deadly flash of radioactivelightning that would instantly kill all sensate things. And although this is admittedly purely speculative, no one dare say that such a discovery will not be made, not when one remembers how remote and unlikely a process such as fission seemed to be just before it was made.
Though many of the great discoveries came about as the result of chance, they came because, as Pasteur said, “chance favors the prepared mind.” Actually they came largely through the intellectual synthesis of what had originally appeared as unrelated phenomena or concepts. When Faraday discovered the principle of electromagnetic induction, he established for the first time that electricity and magnetism, looked upon since prehistoric times as two separate and distinct phenomena, were actually only two aspects of one basic natural force, which we know today as electromagnetism. This great intellectual synthesis led directly to the age of electricity and all its wonders. About thirty years later the great Scottish physicist James Clerk Maxwell demonstrated that electromagnetic action traveled through space in the form of transverse waves similar to those of light and having the same velocity. This revealed the existence in nature of electromagnetic waves, better known to us today as radio waves. About a quarter century later the great German-Jewish physicist Heinrich Hertz not only produced these electromagnetic waves but showed that they are propagated just as waves oflight are, possessing all other properties of light, such as reflection, refraction, and polarization. This led directly to wireless telegraphy and telephony, radio and television, radiophotography and radar.
When Einstein, in his special theory of relativity of 1905, united matter and energy in one basic cosmic entity, the road was opened to the atomic age. Yet Einstein was never satisfied and has devoted more than forty-five years of his life to the search for a greater, all-embracing unity underlying the great diversity of natural phenomena. In his general theory of relativity of 1915 he formulated a concept that encompasses the universal law of gravitation in his earlier synthesis of space and time, of which matter and energy were an integral part. This synthesis, wrote Bertrand Russell in 1924, “is probably the greatest synthetic achievement of the human intellect up to the present time. It sums up the mathematical and physical labors of more than two thousand years. Pure geometry from Pythagoras to Riemann, the dynamics and astronomy of Galileo and Newton, the theory of electromagnetism as it resulted from the researches of Faraday, Maxwell, and their successors, all are absorbed, with the necessary modifications, in the theories of Einstein, Weyl, and Eddington.
“So comprehensive a synthesis,” he continued, “might have represented a dead end, leading to no further progress for a long time. Fortunately, atthis moment quantum theory [the theory applying to the forces within the atom] has appeared, with a new set of facts outside the scope of relativity physics [which applies to the forces governing the cosmos at large]. This has saved us, in the nick of time, from the danger of supposing that we know everything.”
Yet Einstein, working away in majestic solitude, has been trying all these years to construct a vast intellectual edifice that would embrace all the laws of the cosmos known so far, including the quantum, in one fundamental concept, which he designates as a “unified field theory.” Early in 1950 he published the results of his arduous labors since 1915. This he regards as the crowning achievement of his life’s work, a unified theory that bridges the vast gulf that had existed between relativity and quantum, between the infinite universe of the stars and galaxies and the equally infinite universe within the nucleus of the atom. If he is right, and he has always been right before, his latest contribution will prove to be a greater synthetic achievement of the human intellect than ever before, embracing space and time, matter and energy, gravitation and electromagnetism, as well as the nuclear forces within the atom, in one all-encompassing concept. In due time this concept should lead to new revelations of nature’s mysteries, and to triumphs even greater than those which followed asa direct consequence of all earlier intellectual syntheses.
If the synthesis of matter and energy led to the atomic age, what may we expect of the latest, all-inclusive synthesis? When Einstein was asked about it he replied: “Come back in twenty years!” which happens to coincide with the end of the hundred-year period recorded by the brothers Goncourt: God swinging a bunch of keys, and saying to humanity: “Closing time, gentlemen!”
The search for new intellectual syntheses goes on, and no doubt new relationships between the diverse phenomena of nature will be found, regardless of whether Einstein’s latest theory stands or falls in the light of further discovery. Physicists, for example, are speculating about a fundamental relationship between time and the electronic charge, one of the most basic units of nature, and there are those who believe that this relationship will turn out to be much more fundamental than that between matter and energy. Should this be found to be true, then the discovery of the relationship between time and charge may lead to finding a way for starting a self-multiplying positron-electron chain reaction, just as the relationship between matter and energy led inevitably to the self-multiplying chain reaction with neutrons. If this comes about, then closing time will come much closer.
Yet the sound of the swinging keys need not necessarily mean closing time for man at the twilight of his day on this planet. It could also mean the opening of gates at a new dawn, to a new earth—and a new heaven.