How many men can live on earth at once, and how long and fully they can live, depend on man's ability to control energy and matter. Those qualities of mind and spirit that give human life its sense and value cannot be developed until each of us has attained a certain minimal material standard of living. Philosophers may differ regarding how adequately a person should be fed, clothed, housed, protected, transported, educated, and entertained for his own best good, but the whole course of evolution shows that increased ability to control energy and matter is what enables any creature to come increasingly alive.
In an economy in which most people are farmers, the energy controlled by humans is stored in food and feed. These consist of complex molecules whose production involves the waste of more than 99 per cent of the solar energy showered on the plants in which they grow, and the.ir use entails much further energy loss. When the United States first became a republic, labor by people furnished about a quarter, and that by animals a half, of all the energy that kept the nation and its inhabitants functioning. In many countries most work is still done by using the human body as a converter of chemical into mechanical energy, with wife and bullock of nearly equal importance. Though in such countries as India more than 90 per cent of human labor is spent in growing and distributing food, not enough can be produced for everyone. As a consequence many starve, and less than one twentieth of human effort is devoted to occupations other than those involving bare subsistence. Storing energy in starches, sugars, and fats to be later released in the sweat of man's brow is expensive, inefficient, and if overdone, in a 70‑hour week, uncomfortable.
Because we in the United States now do most of our work with machines that take energy from simple sources, each citizen can have 2000 times as much energy working for him as was available in 1800. In the last fifty years, we have acquired 4 million farm tractors, and have gotten rid of three fourths of our draft horses and mules, much of whose effort was spent in raising their own feed. A tractor or a bulldozer can do the work of a dozen horses and six men, or of forty men with shovels, on energy costing $1.69 a day. In the United States, productivity per person has been doubling every generation for many years. Now each man, woman, and child has nearly 10 horsepower working for him day and night, instead of the 2 horsepower of 1900. With only 7 per cent of the world's population, we control almost half of its supply of power, and as a result our standard of living is seven times the average of the rest of the world.
Our ability to convert energy efficiently from one form to another continues to increase rapidly. Forty years ago one kilowatt‑hour of electrical energy could be obtained from about 3.5 pounds of coal. Today only one pound is needed, and 12 ounces will soon be enough. The small gasoline engines that have been developed to propel boats, lawn mowers, and snowplows, because they can carry their energy stored in a small tank, are too noisy, dirty, and hard to start to serve the housewife indoors for running her dishwasher, vacuum cleaner, or clothes drier. So electric motors are used, even though they must be fed energy through wires. This motor is a great emancipator of human hands, for it is clean and quiet, can be made to exert any strength desired, is tireless, seldom needs attention, and uses no energy when at rest.
When we buy energy we pay, not for the energy itself, but for the effort that went into gathering it and bringing it to us. One kilowatt‑hour of electric energy costs only a few tenths of a cent to generate with either burning coal or falling water, but ft usually costs ten times as much when delivered to the home. Most of the extra charge is for transmission costs, and for the privilege of turning the power on or off at will.
The cheapest way to carry energy, especially over long distances, at least, until the coming of nuclear power, has been to keep it locked up in molecules of coal or oil, and to carry these in a ship. Overland, when thousands of miles of travel are involved, it is most feasible economically to pump oil or gas through a large pipeline like the Big Inch. This method may also be applied in the future to coal, powdered and floated in water or oil. But even when the cheapest and best of these methods is used, carrying energy to the consumer ordinarily costs from four to ten times as much as getting it out of the ground or scooping it from a waterfall with a hydroelectric plant.
The age of nuclear energy will bring great savings in energy transport, for a pound of uranium carries more releasable energy than 1500 tons of coal. When the new methods of conversion have been better developed, the cost of transferring energy to the power station should become negligible, and power plants to feed big cities should become emancipated from the necessity of being located near the seacoast, or near coal mines, waterfalls, or dam sites.
All of the energy we use, except "atomic energy," has come to us from the sun. Three fourths of it came to earth ages ago, and was stored first in the leaf cells of plants and later in coal, oil, and gas deposits, which we now are rapidly depleting. The other fourth, including water power and the energy stored in the molecules of foodstuffs, made its eight minute journey from the sun only recently. This glowing globe sends us 20,000 times as much energy as we use now for every purpose -‑ energy equal in a single day to that released by 2 million atomic bombs of the Hiroshima variety. But we don't know yet how to capture and store this energy effectively enough to make it worth using in large quantities, except through intermediate concentration and storage by nature in plants and in the clouds. Both of these processes are, of course, very wasteful.
All of the energy the earth gets from the sun goes to keep it warm, but this energy could be used for many purposes first, and later would keep the earth warm anyway, like water, which, after dancing in a fountain, can be piped off to keep the garden green. Neither energy nor matter is ever "used up"; they are only converted and modified until they escape into the basic reservoirs of each, where they get out of reach of mankind.
We use energy in three principal ways. In America, roughly a third is used to help control the environment by heating homes and factories, another third goes to process matter in mining and industry, and the remainder is spent in moving ourselves and our possessions from place to place in ships, airplanes, autos, trains, and streetcars.
Until 1880, most of the energy used by man came from burning wood, which was replaceable. Since then we have relied on irreplaceable coal, oil, and gas, whose great value lies in the concentrated form of the energy they hold and in the ease with which this can be released simply by combining their molecules with oxygen. The energy in a pound of gasoline can push an auto twenty times as far as that in a pound of storage battery fully charged.
Seventy billion barrels of oil have been removed from the earth's crust, and in each generation those who should know predict that the supply will near exhaustion by the time another generation has passed. But the main reason we can seldom see more than twenty‑five years' worth of petroleum resources ahead is that the oil industry becomes less diligent in hunting for more oil when its reserves are built up to that degree. Geophysicists are still able to find oil faster than the world can burn it, but their hunting methods must constantly be made more sensitive, and how long they will be able to keep this up is anybody's guess. When all the oil wells do go dry, oil shale, a mixture of rock and petroleum, of which enough is in sight to keep industry going for a hundred years or so, can be processed for fuel. After this is gone, coal can be hydrogenated, though at some loss in efficiency, to form liquid fuels. In South Africa, where there are no oil wells, but where the concentration of automobiles in some cities is as great as in the United States, 3000 tons of coal are now converted into oil each day by the addition of hydrogen atoms.
Though the coal in sight may last the world for a thousand years, less coal is now being mined in America than in 1910. The coal industry needs a heavy dose of technological salts to bring it back to its proper position as a leading supplier of packaged energy. Coal is harder to get out of the ground than oil; it must be carried on land by rail, which is more expensive than pumping oil through pipes; and it leaves ash. These limitations may well be removed by burning, powdering, or fluidizing coal at the mine, and then piping the resulting products to places where they are needed.
Water power is appealing because it is clean, can readily be converted into electric energy, and is constantly being replenished by the evaporation, caused by solar heat, of water that falls again as rain. It is not cheap to collect, however, and only 5 per cent of the energy now used in the United States comes from this source. If all the potential dam sites were developed, the resulting power would fill only one fourth of our present needs. Yet much more can be done to make hydroelectric power available. In such countries as India, hydroelectric sites lie undeveloped while peasants cook their one hot meal a day on burning dung from holy cows.
Despite the advantages of oil and coal, more wood is cut for fuel today in the world than ever before. In Brazil, 85 per cent of all energy used still comes from wood. However, in forward-looking countries wood is becoming more valuable as matter than as a source of energy. All the cellulose our forests can produce will soon be needed for lumber and paper, and for rayon and other fibers that can be made from cellulose molecules. By A.D. 2000, less than forty‑five years away, our forests should be routinely tidied up to serve as factories that use the energy of sunlight to make complex molecules out of simple carbon dioxide and water from the air.
There are several vast sources of energy that we do not now find it worthwhile to tap. A storm of the sort that passes occasionally, giving the normal rainfall, develops several hundred billion horsepower, and inventors have always dreamed of using the energy of the wind. Even a minor hurricane releases energy as fast as a thousand atomic bombs exploding each second. But this power is hard to harness; and a source of energy, to be industrially useful, must be dependable and not too variable in output. To be effective as a power converter, a windmill must be very large. Calculations show a good diameter to be 225 feet, topping a twenty-story building, and for industrial power, such a windmill should give out at least 2000 kilowatts, no matter how fast the air is moving. However, when a breeze blows up to merely twice its former speed, it does eight times as much work as before. A zephyr blowing at less than 920 miles an hour is too weak to give the needed power; when it rises to a hurricane of 100 miles an hour, five times as fast, it is able to do 125 times as much work but is likely to blow the windmill away. As a consequence, we use more energy to make wind with electric fans and airplane propellers than we take from sails or windmills to operate machinery.
Much energy is stored in the ocean, as temperature difference between the warm surface and cooler depths, in waves, and in the tides. The great size needed and losses from storms have in the past kept installations for collecting energy from the ocean and waves from being successful. Attempts to take energy from the tides ‑‑ which might well succeed in places where a great head of water rushes in and out at every tidal flow and ebb, as in the Bay of Fundy ‑‑ have run up against economic difficulties, because usually such locations are not near enough to cities that need the power, and power transmission costs are high.
Recently we have become increasingly aware of two great sources of energy that appear inexhaustible: the sun and the nuclei of atoms. Will solar nuclear power run the industries of the future? The answer is: Both, plus all the energy sources we exploit at present. Energy is so important to man that his need for it is endless; he uses every new source to supplement rather than to supplant his older supplies.