There are also indirect resistances, the effects of tidal friction, on all bodies which, like the earth, have portions of their free surfaces covered by liquids, which, so long as these bodies move relatively to neighboring bodies, must keep drawing off energy from their relative motions. "Thus, if we consider the action of the moon on the earth, with its oceans, lakes, and rivers, we perceive that it must tend to equalize the period of the earth's rotation on its axis, and of the revolution of the two bodies about their centre of inertia; because, so long as these periods differ, the tidal action of the earth's surface must keep subtracting energy from their motions."[160] As the tidal wave sweeps over the oceans and rushes into the numerous bays and estuaries, the motions which it produces in the waters necessarily involve an expenditure of power or vis viva in overcoming the resistance from friction. The energy of motion thus expended must be drawn from the set of machinery which produces the motions—that is, from the motion of revolution of the moon, and the motion of rotation of the earth. It can not be returned to the machinery, because all that is not spent in triturating the sand and other materials composing the ocean-bed, is transformed into heat and radiated into space.
It is true that in the present state of science we have not exact data for estimating the relative importance of tidal friction, and of the resistance of the interstellar medium; but, whatever it may be, there can be, says Thomson, "but one ultimate result for such a system as that of sun and planets if continuing long enough under existing laws.... That result is the falling together into one mass, which, although rotating for a time, must in the end come to rest relatively to the surrounding medium."[161]
Another evidence that the solar system is temporal, and that the present cosmical order must come to an end, is found in the fact that the sun is radiating heat into space in quantities incomparably greater than it receives. If it were not so, we should receive, on the average, as much heat from every other quarter of the heavens as from the sun, and no vicissitudes of temperature would ever occur on the earth. Now, from what we know of the nature of heat, it is impossible that the supply contained in the sun should be inexhaustible. There is no apparent reason why the sun should form an exception to the fate of all fires, its only difference being one of size and time. It is larger and hotter than ordinary lamps, but is nevertheless a lamp in which invisible molecular energy is consumed, and consumed, too, at a rate which baffles all conception. From every square foot of its surface the sun gives out energy equal in amount to seven thousand horse-power. The total amount of heat sent off from the sun in one minute is "five thousand millions of millions of units": a unit of heat being the quantity of heat required to raise one kilogramme—or about one quart—of water one Centigrade degree.[162] This enormous consumption of energy must finally exhaust the original stock. Were the sun a solid block of coal, and were it allowed a sufficient quantity of oxygen to enable it to burn at the rate necessary to produce the observed emission of heat, it would be utterly consumed in five thousand years. Or if we suppose, with Thomson, that the initial form of the energy of the universe is the potential energy of gravitation in matter diffused through space, and if this potential energy (energy of position) is transformed into heat (molecular kinetic energy) by condensation or contraction of the sun, and this energy of molecular motion (heat) is again transformed into radiant energy and diffused through infinite space, it is obvious that this condensation can not be continued forever, and Thomson has shown in his article on the "Age of the Sun's Heat" that its power of radiation must come to an end. Various theories have been suggested for replenishing the solar heat, one of the most plausible of which is the falling of meteoric and cometary bodies into the sun. Prof. Thomson, who was one of the first to adopt this view, has now abandoned it, or at least has denied its adequacy to account for the maintenance of solar heat. Even were the hypothesis accepted as valid, the supply of fuel is still finite. Time will drain the entire space inclosed by the orbit of the planet Neptune of all the meteors and comets. Even the planets must at length be ensepulchred in the sun. "As surely," writes Sir William Thomson, "as the weights of the clock run down to the lowest position, from which they can never rise again unless fresh energy is communicated to them from some source not yet exhausted, so surely must every planet creep in, age after age, toward the sun." Not one can escape its fiery end. And, finally, the heat of the sun itself—that is, its molecular energy—must be transformed into radiant energy, and diffused and lost as a working force in infinite space. "Thus do the inexorable laws of mechanics indicate that the sun's store of heat, which can only suffer loss and not gain, must be finally exhausted."[163]
There are thus special geological and astronomical facts which have long been regarded as indicative of the principle that the existing order of the material universe is temporal—it had a beginning, and must have an end. But the modern Theory of Energy,[164] with its three great laws of Conservation, Transformation, and Dissipation, must be regarded as a comprehensive, complete, and final settlement of the question. It has been shown, first, that no system of machinery can create force any more than it can create matter; and that the amount of energy in the universe, or in any limited system which does not receive energy from without, or part with it to external matter, is a constant or invariable quantity. This is the Law of the Conservation of Energy. It has been proved, secondly, as an experimental fact that, in general, one form of energy may, by suitable processes, be transformed wholly or in part to an equivalent amount of another form; and the sole and only function of all possible machines is the conversion or transformation of energy. This is the Law of the Transformation of Energy. This law of Transformation is, however, subject to the limitations which are imposed by the Law of the Dissipation of Energy, the discovery of which is mainly due to Sir William Thomson. He has shown that every machine does its work against friction. "A material system can never be brought through any returning cycle of motions without spending more work against the mutual forces of its parts than it gained from these parts, because no relative motions can take place without meeting with frictional or other forms of resistance." No known process of transformation is exactly reversible. Whenever an attempt is made to transform and retransform energy by an imperfect process, part of the energy is converted into heat, and the heat is dissipated, so as to become useless because incapable of further transformation. It therefore follows that, as energy is constantly in a state of transformation, there is a constant degradation of energy to that final unavailable form of uniformly diffused heat; and this will go on as long as transformations occur, until the whole energy of the universe has taken this form.[165] The reader will find an extended discussion of this great question in Thomson and Tait's "Natural Philosophy," vol. i. pp. 188-304, in which it is shown that the present material system is not a dynamically conservative but a dissipative system, and therefore that in such a system "perpetual motion" is an impossibility.
Indeed, the Law of the Dissipation of Energy is an intelligent and well-supported denial of the chimera of perpetual motion. There is a loose idea that perpetual motion is impossible to us, because we can not avoid friction with its consequent loss of energy, but that nature works without friction, or that, in general, friction entails no loss, and so here perpetual motion is possible; but nature no more works without friction than we do, and friction entails a loss of available power. The supply of invisible molecular energy in the sun is no more infinite than the quantity of matter in the sun is infinite. The sun is daily lifting huge masses of water from the sea to the skies, yearly lifting endless vegetation from the earth, setting breezes and hurricanes in motion, dragging the huge tidal wave round and round the earth; performing, in short, the great bulk of the endless labor of this world and other worlds, so that the energy of the sun is continually being given away without any corresponding restoration. The loss of force in the shape of radiant light and heat can never be weaned back to any other mode of available energy. Carnot, Clausius, Thomson, and Rankine have all from different points of view been led to the same conclusion. We can make no use whatever of the energy represented by equally diffused heat. If one body is hotter than another, as the boiler of a steam-engine is hotter than the condenser, then we can make use of the difference of temperature to convert some of the heat into work; but if two substances are equally hot, even though their particles contain an enormous amount of molecular energy, they will not yield us a single unit of work. Energy is thus of different qualities, mechanical energy being the best, and universal heat the worst; in fact, this latter description of energy may be compared to the waste heap of the universe, in which the effete forms of energy are suffered to accumulate without any further conversion.[166] If, then, when mechanical force passes into heat, some of the heat can never be brought back to be mechanical force, and if the change from mechanical force to heat be ever going on, all the force in the universe must at last take the form of radiant heat. But if that be so, then at last all differences of temperature must disappear, and every thing end in a universal death.
"We are come," says Adolph Fick, "to this alternative: either in our highest, most general, most fundamental abstractions, some great point has been overlooked, or the universe will have an END, and must have had a BEGINNING; it could not have existed from Eternity, but must at some date, not infinitely distant, have arisen from something not forming a part of the natural chain of causes—that is, IT MUST HAVE BEEN CREATED."[167]
So far, then, the deductions of science are found to be in striking harmony with the teaching of revelation—the existing order of the universe had a beginning; the forms, relations, laws, harmonies of the Cosmos had a commencement in time. We may now proceed to the consideration of the second question: Had that which is the ground of all form, the subject of all changes and relations, a beginning? Had the matter of the universe a beginning?
That we may fairly present the answer which modern science offers to this question, we must premise, in general, that it confesses its inability, in the present stage of physical knowledge, to determine what is the ultimate or internal constitution of matter. Many scientists of to-day are of the opinion expressed by Grove[168] that "probably man will never know the ultimate structure of matter." Others, as, for example, Thomson, Bayma, McVicar, and Challis, entertain the opinion that physical science is competent to discover all the minutiæ of molecular actions, and when this has been achieved, the question as to the ultimate constitution of matter can be finally determined. There is one guiding principle, recognized alike by the physicist and the metaphysician, namely, that substances, ultimate entities, are known, and can only be known in and through their respective phenomena. An exact enumeration and careful colligation of all the phenomena are therefore indispensable prerequisites to the solution of the problem.
Meantime nothing is more remarkable, even in the present state of physical science, than the fact that, under the subtile analysis of modern physics, much that we have been accustomed to regard as phenomena of matter dissolves and disappears, surviving only as phenomena of Force. The phenomena of heat, light, color, sound, electricity, and magnetism are now "modes of motion"—manifestations of one and the same omnipresent energy, which is transferred from one portion of matter to another, and modified or transformed simply by the mechanical arrangements and collocations of matter. The opinion is rapidly gaining ground that even chemical action is a mode of motion, and Professor Norton does not hesitate in affirming that "all the phenomena of material nature result from the action of force upon matter."[169] All that we mean by a Material Force "is a force which acts upon matter, and produces in matter its own appropriate effects."[170] It is not an attribute of matter, not a quality inherent in matter, but a mode or state superimposed upon matter.
There is a large, influential, and daily increasing class of scientists, among whom may be named Faraday, Prof. Owen, Dr. Laycock, Wallace, Dr. Winslow, Prof. Huxley, who do not regard matter as an ultimate entity, and who believe that all the phenomena of matter (so called), even extension, resistance, and ultimate incompressibility, may be resolved into phenomena of force. In other words, matter is only phenomenal, and, like all phenomena, demands a cause.[171] These men are perplexed with no difficulties as to the origin of matter. As a phenomenon it must be a product of Creative Efficiency, and therefore had a beginning.