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.
