The Impact Theory in relation to the foregoing Theories of the Pre-nebular Condition of Matter.
The Impact Theory in relation to the foregoing Theories of the Pre-nebular Condition of Matter.
The Impact Theory in relation to the foregoing Theories of the Pre-nebular Condition of Matter.
In all these theories, as has already been observed, the primitive condition of the universe was that of matter in a state of extreme tenuity, while by aggregation the materials became successively larger and larger until they assumed the magnitude of suns and planets. For example, according to the meteoric theory, meteorites are formed out of “cosmical dust,” “fire-mist,” or condensed vapour, and then sunsand planets are formed by aggregation from these meteorites. Facts seem, however, to point to the very reverse as being the true course of events.
Meteorites are undoubtedly the fragments of larger masses. It looks more likely that they are, as has already been stated, fragments of stellar masses which have been shattered to pieces by collision, and that this “cosmical dust,” from which the meteorites are alleged to have been formed, are simply the dust arising out of the destruction of the masses. After the two bodies had collided and been shattered to pieces, some of the fragments would undoubtedly be projected with a velocity that would carry them beyond the attractive power of the general mass, and thus they would escape being volatilised. These fragments would continue their wanderings through space as meteorites.
I cannot but think that the number, as well as the importance, of these wanderers has been greatly over-estimated. Mr. Lockyer states that Dr. Schmidt, of Athens, found that the mean hourly number of luminous meteors visible on a clear moonless night by one observer was fourteen. Certainly no such quantity is visible in this country. In Scotland, at least, one may often watch night after night under the most favourable conditions without having the good fortune to see a single meteor.
It is, of course, true that the immediately prior condition of a sun or a planet was that of matter in an extremely attenuated or dissociated state. This is essential to the nebular, as well as to the meteoric,hypothesis. But it is not with the immediately prior condition that we are at present concerned, but with the primitive, or pre-nebular, condition. Take, for example, the case of the solar nebula, out of which our sun and planets were formed. Was this nebulous mass formed from matter in a state of extreme tenuity, scattered through space and collected together by gravity? Or did it result from two solid globes shattered to pieces by collision, which were then converted into the nebulous condition by the heat generated from the collision? It is no doubt true that the analogies of nature would, at first sight, be apt to lead us to the conclusion that the former theory was the more likely of the two, as the larger is generally made by aggregation from the smaller. But a little consideration will show that, in the present case, the weight of this analogy is more apparent than real. The impact theory does not rest upon a purely hypothetical basis. The cause to which it appeals has a real existence. The point of uncertainty is whether the cause actually produces the effect which is attributed to it. We know from observation that there are stellar masses, some of them probably larger than our sun, moving through space with enormous velocities in all directions.[77]According to the ordinary laws of chance, collision at times would be an inevitable result, and when such an event did take place the destruction of the colliding bodies, and their consequent transformation into anebulous mass, would, at least in many cases, be anecessaryresult. In fact, we have, in the case of these vast stellar masses, what we know occurs among the invisible molecules of a gas. So far as mere analogy is concerned, the impact theory is just about as probable as the other.
From what has been stated it would follow that in most cases the stellar masses have been formed out of the destruction of pre-existing masses, like the geological formations out of the destruction of prior formations.
The theories do not account for the motion of the stars.—According to all the foregoing theories aggregation and condensation are produced by gravity. The materials dispersed throughout space are drawn together by their mutual attraction, and aggregated round a centre of gravity. Gravitation, although it imparts motion to the materials, can impart no motion of translation to the mass itself. Gravitation cannot, therefore, be the cause of the motion of translation of the mass. The stars are not supposed to be gravitating towards, or around, a great centre of attraction, for they are found moving in straight lines in all directions, which could not be the case if gravity were the cause of their motion. To what cause is their motion, therefore, to be attributed? A meteorite or other small body might be ejected from any system, by the explosive force of heat or some other cause, with a velocity which might carry it into boundless space; but such could not be the case in regard to a body of the magnitude of a star. No one for a momentcould suppose that 1830 Groombridge, for example, moving at the rate of 200 miles a second, is an eject from any system.
According to the impact theory the whole is plain; for this 200 miles per second is simply a part of the untransformed motion of translation which the materials composing the star had from the beginning. In other words, the matter and the motion were eternal, or, what is more probable, as will afterwards be seen, co-existed from creation—not, however, as molecular motion, but as motion of the mass.
The theories do not account for the amount of heat required.—It has been shown that, although the materials of our solar system had fallen together from an infinite distance, it could not have generated heat sufficient to have formed a gaseous nebula extending to the distance of the planet Neptune. Gravitation alone could not, therefore, have been the source from which the nebula obtained its heat. The solar nebula, however, must originally have extended far beyond the orbit of Neptune.
But supposing it could be demonstrated that the heat thus generated was sufficient to have formed a nebula extending to even twice the distance of Neptune, this would not remove the fatal objection to the gravitation theory of the origin of the solar nebula. For the facts, both of geology and of biology, equally show that the sun has been radiating his heat at the present rate for more than twice the length of time that it could possibly have done had gravitation been the source from which the energy was derived.This objection is alike fatal to the meteoric theory as it is to all other theories which attribute the origin and source of the heat to gravitation.
Evolution of matter.—Our inquiries into stellar evolution do not, however, begin with the consideration of a gaseous nebula, or with swarms of meteorites. There was a pre-nebular evolution. The researches of Prout, Newlands, Mendelejeff, Meyer, Dumas, Clarke, Lockyer, Crookes, Brodie, Hunt, Graham, Deville, Berthelot, Stoney, Reynolds, Carnelley, Mills, and others, clearly show, I think, that the very matter forming this nebulous mass passed through a long anterior process of evolution. And not only the matter, but the very elements themselves constituting the matter, were evolved out of some prior condition of substance.
I have already given at some length the views which have been advanced by several of our leading physicists and chemists on the evolution of the chemical elements, and on some of the bearings which these views have on stellar evolution. I shall now briefly refer to a point on which I venture to think the theory discussed in this volume seems to cast some additional light.
If the elements were evolved out of a common source, there is, in order to this, one necessary condition, viz. an excessively high temperature; for the temperature must be above the point of the dissociation of all the chemical elements. “In the primal stage of the universe,” says Mr. Crookes, “before matter, as we now find it, was formed from the protyle,all was in an ultra-gaseous state, at a temperature inconceivably hotter than anything now existing in the visible universe; so high, indeed, that the chemical atoms could not yet have been formed, being still far above their dissociation point.”
What, then, produced this excessive temperature in this supposed ultra-gaseous protyle? It could not have resulted from condensation by gravity. In condensation the heat increases as the condensation proceeds, because it is the condensation which produces the heat. But here the reverse must have been the case, for the ultra-gaseous mass was much hotter than the sun which was afterwards formed out of it. It was, according to Mr. Crookes, when this gaseous mass cooled down, so as to permit of its becoming converted into solid matter, that condensation into a sun could take place. Besides, was it not the excessive heat which produced the assumed ultra-gaseous condition?
There is another difficulty besetting the theory that the primitive heat was derived from condensation by gravitation. Supposing we should assume it possible that the protyle could exist in this ultra-gaseous state without possessing temperature, and that it obtained its heat from condensation by gravity, then the fact of condensation taking place shows that the gas was not in a state of equilibrium. But the gas could not have remained stationary for a single moment without beginning to condense while in a condition of unstable equilibrium. We must therefore conclude that the gas must have been in some other condition than the gaseous state prior to condensation.
The impact theory seems to remove all these difficulties. It is just as likelyà priori, if not more so, that the primitive form of the protyle should have been that of large cold masses moving through space in all directions, with excessive velocities, as that it should have been that of a gaseous mass in a state of unstable equilibrium. If we assume the former condition, then the colliding of these masses would account not only for the ultra-gaseous state, but also for its inconceivably high temperature. Besides, in this case we are not called upon to account for any other antecedent state of the masses before collision, for they may have existed from the beginning of creation in the form of masses in motion through space.
Had space and time permitted, it might have been shown that there are other obscure points on which the theory seems to shed additional light. I shall now, in conclusion, refer to a point wherein the theory differs radically from that of all other theories of stellar evolution. But before doing so I may briefly refer to an objection which has been frequently urged against the theory.
Objection considered.—The objection to which I refer is this, that, had the nebulæ been produced by impact in the way implied in the theory, then we ought to have had some historical record of such an event. I can perceive no force in such an objection. Our historical records, I presume, do not extend much farther back than about 3,000 years, and we have no evidence to conclude that a new nebula makes its appearance in the visible firmament with such frequency;and supposing it did, we have no grounds for assuming that its production by impact in the way supposed by the theory would attract general notice. It is doubtful if the nebula produced would, in the first instance, be actually visible. I have shown that the temperature of the nebula could not have been less than about 300,000,000° C., and it is very doubtful if the gaseous mass enveloping all that was solid in the nebula would, at such a temperature, be self-luminous. The probability is that all the chemical elements composing it would be in a state of utter dissociation, and converted back into the original protyle from which they were derived, again to be slowly reconverted into their former atomic condition as the temperature fell.
Can we on scientific grounds trace back the evolution of the universe to an absolute first condition?—As has been repeatedly stated, all inquiries into the evolutionary history of the stellar universe begin in the middle of a process. Evolution is a process. The changes that now occur arose out of preceding changes, and these, preceding changes out of changes still prior, and so on indefinitely back into the unknown past. This chain of causation—this succession of change—of consequent and antecedent—could not in this manner have extended back to infinity, or else the present stage of the universe’s evolution ought to have been reached infinite ages ago. The evolution of things must therefore have had a beginning in time. Professor Winchell, in his final generalisation to his work, “World Life,” has stated this matter soclearly and forcibly that I cannot do better than here quote his words on the subject.
“We have not,” says Professor Winchell, “the slightest scientific grounds for assuming that matter existed in a certain condition from all eternity, and only began undergoing its changes a few millions or billions of years ago. The essential activity of the powers ascribed to it forbids the thought. For all that we know—and, indeed, as theconclusionfrom all that we know—primal matter began its progressive changes on the morning of its existence. As, therefore, the series of changes is demonstrably finite, the lifetime of matter itself is necessarily finite. There is no real refuge from this conclusion; for, if we suppose the beginning of the present cycle to have been only a restitution of an older order effected by the operations of natural causes, and suppose—what science is unable to comprehend—that older order to be a similar re-inauguration, and so on indefinitely through the past, we only postpone the predication of an absolute beginning, since, by all the admissions of modern scientific philosophy, it is a necessity of nature to run down.”
These are consequences which necessarily follow from every theory of stellar evolution which has hitherto been advanced. The impact theory, however, completely removes the difficulty, for according to it the evolutionary process can, on purely scientific grounds, be traced back to an absolute beginning in time. If huge solid masses moving through space were the original condition of the universe, then, in so far as either philosophy or science can demonstrate to thecontrary, it might have been in this condition from all eternity. We are therefore not called upon to account for this primitive condition of things. Now it is evident, unless a collision should take place, the universe would remain in this condition for ever: without a collision there could be no change, no work performed, and absolutely no loss or gain of energy, and therefore no process of evolution. The first collision would be the absolute commencement of evolution—the beginning of the process of the development of the universe. Evolution would, in this case, have its absolute beginning in time, and consequently was not eternal. If, on the other hand, we assume, what is far more in harmony with physics, metaphysics, and common sense, that the universe was created in time, we are still led to the same result as to an absolute commencement of evolution. In both cases we reach a point beyond which there can be no legitimate inquiry; no further question which the scientists can reasonably ask.
We have no grounds to conclude that there is anything eternal, except God, Time, and Space. But if time and space be subjective, as Kant supposes, and not modes pertaining to the existence of things in themselves, then God alone was uncreated, andofHim andtoHim are all things.