CELESTIAL MECHANICS
A GREAT landmark was reached when Pierre Laplace, in 1796, published his Systeme du Monde. In this he set forth his famous nebular hypothesis, in which the birth of stars and planets was traced to a rotating nebula -- an hypothesis, by the way, which entirely dispensed with God.
The nebular hypothesis of Laplace has been largely augmented or modified, rather than entirely superseded, by subsequent observation; yet to the great French astronomer is due the formation of a theory which still holds good in part, and which accounts for the formation of stars. "Apart from minor details," writes Jeans, [The Universe Around Us. p. 231.] "the process imagined by Laplace explains the birth of suns out of nebulae; it cannot explain the birth of planets out of suns." This is because the sequence of events in the development of planets is distinct from that formulated by Laplace in respect to suns. Nevertheless, he was the Darwin of the skies, who first, in a masterly way and with a grasp of mathematics which far transcended that of many of his contemporaries, traced the evolution of heavenly bodies from a simple and widely-diffused mist, or nebula, in a state of rotation, up to the giant constellations and colossal star systems we see today. His theory, which still forms the basic outline of present- day cosmological development, falls short of explaining the origin of planets from a sun, and here we come to the tidal theory postulated by Jeans, which will be considered in due course.
Whatever particular process heavenly bodies pursued in their evolution from nebulae up to mighty constellations, one thing is tolerably certain. Stars came into existence, not at the command of a ghost, nor by a few words spoken in Hebrew, but by a process of slow condensation in the primeval chaos, consuming many billions of years. The same process may be witnessed today in what are called rotating nebulae, of which many millions exist, and is recorded on photographic plates. "These photographs," says Jeans, [The Universe Around Us, p. 230.] "exhibit a process taking place before our eyes, which is essentially identical with that imagined by Laplace, except for a colossal difference of scale. Everything happens qualitatively as Laplace imagined, but on a scale incomparably grander than he ever dreamed of. In these photographs the primitive nebula is not a single sun in the making; it contains substance sufficient to form hundreds of millions of suns; the condensations do not form puny planets the size of our earth, but are themselves suns." This is what we witness today, and it is in deadly conflict with the theory of creation as pictured in the Bible.
Nor is there, in any concept of cosmic evolution, any need of postulating a ghostly finger twirling the stars, or starting them spinning in their orbits. No initial push, no divine "shove" is required even in the earliest stages of stellar evolution. As Jeans points out, [The Universe Around Us, p. 214.] "Stars, as soon as they come into being, are endowed with rotations transmitted to them by their parent nebula, in addition to the rotations resulting from the currents set up in the process of condensation."
From chaos to nebulae, from nebulae to stars, and from stars to planets and satellites, a steady procession of natural events occurs, unattended by deities or demons. Stars move, not because of some heavenly hand, but because of what is known as the "conservation of angular momentum." This means, as Jeans explains, [Ibid., p. 214.] that "rotation, like energy, cannot entirely disappear. Its total amount is conserved, so that when a nebulae breaks up into stars, the original rotation of the nebula must be conserved in the rotations of the stars." And this rotary movement is traceable to nothing more supernatural than "the existence of currents in the primordial medium" which "endow the resulting nebulae with varying amounts of rotation." Hence, by the inherent properties of motion, with which matter is endowed, the entire fabric of the universe is woven, and continues in a state of motion. There is no time thinkable when matter was at rest, or without the property of motion or of changing its position in space, whether in the form of giant stars whirling through space at a thousand times the speed of an express train or of a molecule of air traversing a tiny space at 500 yards a second, the approximate speed of a rifle bullet. Matter in motion is eternal: the vision of "dead," inert, or motionless matter stirred to sudden activity by a ghost belongs to the age of fables.