Gas: then solid

Read More

Building on ideas advanced earlier in the 18th century by Emanuel Swedenborg and Immanuel Kant, French astrophysicist Pierre-Simon Laplace reasoned from Newtonian principles that gravity could cause the gas in interstellar clouds ("nebulae") eventually to collapse into hot spheres, forming young stars and planets. In his Exposition du Système du Monde (1796), Laplace conjectured that our sun was born from a "fiery mist" and at one time was surrounded by a vast atmosphere of hot gas and dust that flattened into a disk and produced planets as it rotated, contracted, and cooled. As telescopes revealed nebulae that seemed to be forming stars, just as predicted, 19th century intellectuals wrestled with the theory's implications. By the end of the century its explanatory power was widely acknowledged, though scientists by then knew that high temperature need not be attributed to the original nebula, since gravitational contraction would itself produce great heat. (Understanding of nuclear fusion in stars would come later still.)

Robert Stawell Ball's The Story of the Heavens (1886), which sits on Bloom's bookshelf, acknowledges that Laplace offered his model only as a conjecture but suggests that it fits the known facts well: "Such is, in fact, the doctrine of the origin of our system which has been advanced in that celebrated speculation known as the nebular theory of Laplace....It is merely a conjecture, more or less plausible, but perhaps in some degree necessarily true, if our present laws of heat, as we understand them, admit of the extreme application here required" (526). Ball focuses on Laplace's idea of progressive cooling, noting that it accounts not only for our hot sun but also for the formation of planets and moons: "Precisely similar reasoning may be extended to the individual planets: the farther we look back, the hotter and the hotter does the whole system become. It has been thought that if we could look far enough back, we should see the earth too hot for life; back further still, we should find the earth and all the planets red-hot; and back further still, to an exceedingly remote epoch, when the planets would be heated just as much as our sun is now. In a still earlier stage the whole solar system is thought to have been one vast mass of glowing gas, from which the present forms of the sun, with the planets and their satellites, have been gradually evolved" (526).

As Ball observes, the hypothesis arose in response to three remarkable physical coincidences: the planets in our solar system occupy the same plane, they revolve around the sun in the same direction, and they rotate on their axes in the same direction. "Suppose that countless ages ago a mighty nebula was slowly rotating and slowly contracting. In the process of contraction, portions of the condensed matter of the nebula would be left behind. These portions would still revolve around the central mass, and each portion would rotate on its axis in the same direction. As the process of contraction proceeded, it would follow from dynamical principles that the velocity of rotation would increase; and thus at length these portions would consolidate into planets, while the central mass would gradually contract to form the sun. By a similar process on a smaller scale the systems of satellites were evolved" (527).

Our lifetimes are far too short to observe these processes, which take place over tens or hundreds of millions of years, but the temporal progression can be read in space, as one does with trees of different ages in a forest, or as geologists do with rocks and fossils: "The nebular origin of the solar system receives considerable countenance from the study of the sidereal heavens. We have already dwelt upon the resemblance between the sun and the stars. If, then, our sun has passed through such changes as the nebular theory requires, may we not anticipate that similar phenomena should be met with in other stars? If this be so, it is reasonable to suppose that the evolution of some of the stars may not have progressed so far as has that of the sun, and thus we may be able actually to witness stars in the earlier phases of their development" (527). Such an inference was made, Ball observes, by the great astronomer William Herschel (1738-1822), who catalogued thousands of nebulae in 1802 and again in 1820: "by looking at one nebula after another, the astronomer thinks he is able to detect the various stages which connect the nebula in its original form with the final form. He is thus led to believe that each of the nebulæ passes, in the course of ages, through these stages. And thus Herschel adopted the opinion that stars—some, many, or all—have each originated from what was once a glowing nebula" (529).

Herschel's observational support of Laplace's theory stirred passionate responses from intellectuals for decades to come. Social reformists were heartened by the notion that the night sky's awe-inspiring displays might have been produced by humanly intelligible forces operating in real time and space. Proponents of the nebular hypothesis, particularly two Scots—publisher Robert Chambers (1802-71) and astronomer and social reformer John Pringle Nichol (1804-59)—saw it as evidence that dynamism and progressive development lay at the heart of the cosmos. In a series of public lectures and books that did much to popularize the theory, Nichol argued that everything in the universe is driven by vital forces of progressive evolution, making social reform seem irresistible. His romantic interpretation of the science inspired thinkers as diverse as John Stuart Mill, George Eliot, and William Thompson, Baron Kelvin.

Although Nichol's progressivist cosmos appealed to Herbert Spencer (for reasons that Nichol would not have approved), most social conservatives abhorred it. The nebular hypothesis also rankled many proponents of traditional religious faith, by doing to the heavens what geology was doing to the physical structures of the earth and evolutionary biology to the understanding of life forms. If Laplace's account of star-formation was even partly true, then the cosmos was no longer a divinely perfect, static creation—the heavens had been regarded as changeless since Aristotle—but a maelstrom of cascading physical forces. People of faith felt their conception of the world to be threatened by these new observations and theory, just as it had been in the 17th century when Galileo saw evidence of celestial change in things like sunspots and supernovae and mounted a heliocentric challenge to the dominant Ptolemaic cosmology.

In the 1840s and 50s two Anglo-Irish astronomers—William Parsons, the 3rd Earl of Rosse (1800-67) and Thomas Romney Robinson (1792-1882), an astrophysicist who was director of the Armagh observatory—joined forces to prove Herschel wrong. Robinson was an ordained Anglican priest who expressed disbelief in "what has been called the Nebular Hypothesis." His friend Lord Rosse built a six-foot reflector telescope ("the Leviathan of Parsonstown," the world's largest by aperture) on his land in King's County (now County Offaly) with the intention of showing that nebulae, rather than being gaseous, were actually composed of countless stars that existing telescopes had failed to resolve. Rosse was partly right: some of the many known "nebulae" turned out actually to be galaxies. He and Robinson published many reports and drawings of the observations made through the huge telescope, but they did not succeed in decisively refuting Herschel's claims. Later, the spectroscopic analysis of William Huggins would demonstrate the gaseous nature of true nebulae.

For people inclined to accept the new model, John Pringle Nichol's exuberant optimism was not the only possible emotional response. Change can be for better or for worse, after all. In life forms it encompasses both growth and decay, and the physics of Laplace's theory implied no less. William Whewell (1794-1866), the Cambridge polymath who coined the phrase "nebular hypothesis" (as well as "scientist," "physicist," "catastrophism," "uniformitarianism," and many other neologisms), was a devout Christian who believed in intelligent design, but he also appreciated the importance of bold theoretical claims. Whewell accepted Laplace's account of the formation of solar systems. In chapter 7 of Astronomy and General Physics he summarized the theory and then, in chapter 8, he imagined its end results. The physics led him to conclude that a system so constituted would continue to lose heat and would also very gradually slow down, leading eventually to cold stasis: "It now appears that the courses of the heavens themselves are not exempt from the universal law of decay; that not only the rocks and the mountains, but the sun and the moon have the sentence 'to end' stamped upon their foreheads. They enjoy no privilege beyond man except a longer respite" (8th ed., 1847, 202).

Whewell was foreseeing the ultimate triumph of entropy. Astrophysicists since his time have predicted many such forms of slow, inevitable winding-down: the finite life-cycles of stars, the collapse of energetic and information-rich systems into black holes, the endless expansion and ultimate heat death of the universe itself. Dénouements like these rebuke the human wish for life to mean something, to be going somewhere. In his brief, bleak recapitulation of the nebular theory, Leopold Bloom appears to understand this entropic principle: first there is hot gas, then a solid planet, then an inhabited world, and then the cooling continues, until all vital heat is lost and the earth goes drifting through the cosmos as a "frozen rock." According to the science that Bloom has absorbed from Ball's book, the cosmos will ultimately disappoint our desire for "happy warmth."

In Joyce and Reality: The Empirical Strikes Back (2004), John Gordon detects various other echoes of the nebular hypothesis in Joyce's fictions, from A Portrait of the Artist through Finnegans Wake.