During the San Francisco earthquake of 1906, a statue of Louis Agassiz fell off the front of a building at Stanford University and landed just as neatly as could be, but upside down--feet in the air and head buried in the pavement. Agassiz had been both the greatest ichthyologist of his day and the last serious creationist holdout against evolution when he died in 1873. David Starr Jordan, the president of Stanford, was the greatest ichthyologist of the generation after Agassiz and an early and fervent Darwinian as well. Thus, the two men shared a similar passion for the same group of organisms, but couldn't have disagreed more on theoretical issues.
According to legend, Jordan delivered one of history's greatest quips when he went out to survey the damage and saw the inverted statue: "Oh well, I always thought better of Agassiz in the concrete than in the abstract." A lovely story that surely deserves to be true. But, alas, it is not. In his own autobiography, The Days of a Man, written in 1922, David Starr Jordan felt duty bound to debunk this tale and admit that he had never uttered the famous line, while the originator had used a less quotable and opposite version. Jordan wrote:
About the quadrangle the only touch of humor was furnished by the large marble statue of Agassiz, which had plunged from its place headfirst and waist-deep into the concrete pavement. Somebody--Dr. Argyll, perhaps--remarked that "Agassiz was great in the abstract but not in the concrete."
People are clever, but almost no one ever devises an optimal quip precisely at the needed moment. Therefore, virtually all great one-liners are later inventions--words that people wished they had spouted, but failed to manufacture at the truly opportune instant. Thus, the most famous scientific epithet of all is also, and alas, surely embellished if not downright phony.
We have all heard the story of Napoleon's meeting with the great astronomer Pierre-Simon Laplace (1749-1827), identified in the Dictionary of Scientific Biography as "among the most influential scientists in all history." Laplace, or so the story goes, gave Napoleon a copy of his multivolume Mecanique celeste (Celestial Mechanics). Napoleon perused the tomes and asked Laplace how he could write so much about the workings of the heavens without once mentioning God, the author of the universe. Laplace replied: "Sire, I have no need of that hypothesis."
The actual quip, well attested in a surviving letter, is mildly clever, but pretty insipid compared with the legend, and made by the general rather than the scientist. Laplace had first met Napoleon in 1785 when he examined the future emperor, then an artillery cadet, in mathematics at the Ecole Militaire in Paris. In October 1799, three weeks before the coup d'etat that brought Napoleon to power, Laplace did present the very weighty first two volumes of his work to his former student. Napoleon hefted them and then promised to read them "in the first six months I have free." He then invited Laplace to dinner the next day "if you have nothing better to do."
I suspect that this legend attached itself to Laplace because he does represent the best candidate for such a tale. Laplace is science's chief apostle of strict determinism and heavenly stability based on obedience of all bodies to laws of nature that damp out any perturbation to restore regularity of motion and position (Laplace coined the term "celestial mechanics").
Even Isaac Newton, so often cited as the apostle of such a view, happily invoked a little help from divine intervention either to get things going or to restore regularity at any time in subsequent celestial history when nature's usual laws could not rein in a perturbation. Newton, for example, sought to reconcile geological evidence for the earth's antiquity with the Genesis story of creation in six days by arguing that the earth then rotated very slowly, thus producing "days" of any desired length. But Newton could not then fathom how an acceleration of rotation to days of twenty-four hours could be accomplished under nature's laws, so he invoked a positive spin from God himself. He wrote to Thomas Burnet (a colleague who upheld universal constancy and sufficiency of nature's laws and who therefore favored an allegorical interpretation of biblical language about "days"):
Where natural causes are at hand God uses them as instruments in his works, but I do not think them alone sufficient for the creation and therefore may be allowed to suppose that amongst other things God gave the earth its motion by such degrees and at such times as was most suitable to the creatures.
By contrast, the most famous quote genuinely attributed to Laplace vigorously defends a strict determinism that does make a conventional view of God's continuous role both irrelevant and unnecessary. (God may still be a clockwinder, an instigator of nature's immutable laws at the outset, but he has no need ever to intervene in subsequent history; after all, a truly omnipotent God can surely establish optimal laws right at the start, thus avoiding any necessity for direct miraculous correction should imperfect laws cause the heavens to go awry.) In an epigram that has defined strict determinism ever since, Laplace boasted: If anyone could provide a complete account of the position and motion of evely particle in the universe at any single moment, then total knowledge of nature's laws would permit a full determination of all future history. Laplace's boast is usually cited from the introduction to his Analytical Theory of Probabilities (1812), but the Dictionary of Scientific Biography cites a much earlier and crisper version from a youthful article written in the seminal year of 1776:
The present state of the system of nature is evidently a consequence of what it was in the preceding moment, and if we conceive of an intelligence which at a given instant comprehends all the relations of the entities of this universe, it could state the respective position, motions, and general affects of all these entities at any time in the past or future.
After his work in celestial mechanics, Laplace won most renown for his pioneering studies of probability. One might ask why the prophet of determinism and heavenly constancy should have focused upon probability, now so strongly associated with opposing ideas of randomness, but the solution is not far to seek. Laplace firmly believed that, in reality, every event is fully determined by general laws of the universe. But nature is complex and we are woefully ignorant of her ways; we must therefore calculate probabilities to compensate for our limitations. Events, in other words, are probable only relative to our knowledge.
Celestial mechanics is the most triumphant realm of deterministic predictability because our instruments are precise and the laws relatively simple (primarily Newton's principle of universal gravitation). But more complex terrestrial events are just as determined if only we knew the laws and conditions as well--as one day, perhaps, we will. Laplace wrote in his popular book of 1796, the one that shall be the focus of this essay:
Everything in nature obeys these general laws; everything derives from them by necessity and with as much regularity as the cycle of seasons. The path followed by a light atom [atome leger] that the winds seem to transport at random, is ruled in as certain a manner as the planetary orbits [my translation--by "atom," Laplace only means a tiny particle, not the invisible and chemically indivisible building block that later theory would identify].
Later in the book, he explicitly states that we will eventually learn the more complex laws for smaller terrestrial objects, and that earthly physics will then be as deterministic as celestial mechanics:
Several experiments already made give us reason to hope that, one day, these laws will be perfectly known; then, by applying mathematics, we will be able to raise the physics of the earth to the same level that the discovery of universal gravitation has given to celestial physics:
In his 1776 article, Laplace explicitly links the need for a theory of probability to human ignorance of nature's deterministic ways, and he makes the same comparison between a simpler and well-known celestial mechanics and a much more difficult earthly physics:
Man owes that advantage [in celestial mechanics] to the power of the instrument he employs, and to the small number of relations that [this field] embraces in its calculations. But ignorance of the different causes involved in the production of events, as well as their complexity, taken together with the imperfection of analysis, prevents our reaching the same certainty about the vast majority of phenomena. Thus there are things that are uncertain for us, things more or less probable, and we seek to compensate for the impossibility of knowing them by determining their different degrees of likelihood. So it is that we owe to the weakness of the human mind one of the most delicate and ingenious of mathematical theories, the science of chance or probability.
(I think that Laplace's view of probability is still commonly held by some scientists and, more widely, by well-educated people in general. Such is the allure of physical determinism, and our hope for a simple order of things--although I fear that nature contains much truly intrinsic randomness at all levels.)
In his study of celestial mechanics, the primary focus of his career, Laplace emphasized one theme above all others: the laws of nature, with Newton's principle of universal gravitation in the lead, decree a permanent stability that could only be disturbed by foreign causes (like God's miraculous hand--the unneeded hypothesis!). Laplace attacked this issue by studying all the classical and apparent exceptions that studies of planetary motion had accumulated over the centuries. These exceptions all took the same form: measurement of planetary orbits had detected a slight, but accumulating, irregularity, which if continued over eons, would destabilize the solar system. In each case, Laplace devised the same style of solution: these irregularities are not cumulative, but self-correcting. They are cycling oscillations that maintain the broader and permanent stability of the heavens. For this brilliant work, Laplace justly earned his common epithet as the Newton of France.
In 1773, Laplace took up the long-troubling problem of why Jupiter's orbit seemed to be shrinking while Saturn's expanded (a situation that, if continued, would destroy planetary alignment; the great Newton, in fact, had thrown up his hands and invoked occasional divine intervention to safeguard equilibrium). Laplace showed that these inequalities are periodic (with a cycle of nearly 1,000 years), and not accumulating. In the next phase of the cycle, Jupiter's orbit will expand, and Saturn's will shrink. Then, in 1786, Laplace developed a general proof that eccentricities and inclinations of planetary orbits must remain small and be fully self-correcting, thus maintaining the stability of the solar system.
Finally, in 1787, Laplace resolved the last major anomaly in planetary motion by relating the moon's orbit to changes in eccentricity of the earth's revolution about the sun. The moon's orbit had been expanding and our satellite would eventually escape, should the trend continue. Laplace showed that the moon's mean motion is accelerated when the earth's orbit becomes more circular, but will be retarded when the earth's eccentricity increases. He then argued that the earth's orbital eccentricity cycles with a period measured in millions of years; the lunar orbit will therefore be self-correcting, and the moon will not escape.
In 1788, with the fall of the Bastille and the great secular revolution just one year away, Laplace summarized his views on the fact and meaning of celestial stability:
Thus the system of the world only oscillates around a mean state from which it never departs except by a very small quantity. By virtue of its constitution and the law of gravity, it enjoys a stability that can be destroyed only by foreign causes, and we are certain that their action is undetectable from the time of the most ancient observations until our own day. This stability in the system of the world, which assures its duration, is one of the most notable among all phenomena, in that it exhibits in the heavens the same intention to maintain order in the universe that nature has so admirably observed on earth for the sake of preserving individuals and perpetuating species.
All this quotation and argument properly leads us to view Laplace as the archetypal defender of a certain view of science, all too commonly equated with the entire varied enterprise: stability in the heavens, determinism of all events under the aegis of natural laws with clean, mathematical formulation--an almost antihistorical view that we might contrast with alternative models of complex unpredictability and dynamic change, often in accumulating and directional modes.
Fair enough, but we now encounter the anomaly that inspired this essay. Laplace is also the author of the first widely-credited historical theory for the origin of the solar system--the so-called nebular hypothesis of Kant and Laplace, first enunciated in 1796. (The great philosopher Immanuel Kant published a similar theory in the same year as Laplace; the two men were not in contact and surely developed their ideas independently.) How could the apostle of nonchange and antihistory also devise a theory that, according to the Dictionary of Scientific Biography, "has conventionally been cited as an early instance, perhaps as marking the introduction, of a historical dimension into physical science. That attribution, indeed, has been its chief attraction."
In 1796, Laplace published a wonderful book, honored and regarded as a prototype ever since, in a tradition that the French call haute vulgarisation, or high-class popularization (not at all an oxymoron, but the worthiest of all goals for scientific writers). The work, titled Exposition du systeme du monde (Exposition of the System of the World), is suffused with the rationalistic spirit of a revolutionary France that had thrown off the shackles of past history. The title page, in fact, does not say 1796, but only "L'an IV de la Republique Francaise," since the revolutionary government had started time all over again on September 22, 1792, the day after the founding of the French republic.
In the opening avertissement, Laplace states that he will divide the circle into 400 degrees (100 for each quadrant), the day into ten hours, the hour into 100 minutes, the minute into 100 seconds, and temperature into 100 degrees from freezing to boiling of water (the only survivor, as the centigrade scale). (Do not infer that Laplace was a revolutionary zealot. Quite the contrary. He was shrewd and basically unpolitical. His major accomplishment, as the old quip goes about Talleyrand, was to serve every government from revolution to restoration, and die in bed. Laplace flourished by supporting any group in power, while not alienating the probable successors. His written dedication to Napoleon in his Theorie analytique des probabilites  seemed so embarrassingly sycophantic to later editors that the semiofficial Oeuvres completes, published after Laplace's death, left it out).
The Exposition is a two-volume work in five books--the first, on what may be seen by observing the heavens on a clear night; the second, on the "real" motion of planets, moons, and comets; the third, on laws of motion; the fourth, on Laplace's own work in celestial mechanics and gravity; and the fifth, on the history of astronomy. Laplace shows his distrust and discomfort for real history with all its messiness, its backings and forthings, by stating that he will not discuss astronomy as people actually developed the ideas, but will instead provide a rationally ordered chronological account of successes:
The order in which I am about to discuss the principal results of the system of the world is not that which the human mind followed in its research. The march of the mind has been encumbered and uncertain; often it only reached the true cause of phenomena after having exhausted all the false hypotheses that imagination had suggested; and discovered truths have almost always been allied to errors that time and observation finally separated out. I will offer in a few words the tableau of attempts, and of successes.
The nebular hypothesis is undoubtedly the most famous legacy of Laplace's Exposition, but it appears only as an afterthought in a few pages of a final chapter appended to the end of book 5--Considerations sur le systeme du monde, et sur les progres futurs de l'astronomie (Considerations on the Sysrem of the World and on the Future Progress of Astronomy). This remarkable chapter also features a correct hypothesis that many "nebulae" (resolved in the best telescopes of the time as diffuse clouds) are actually distant galaxies of stars (with the Milky Way as an arm of our own galaxy), and that the universe is therefore vaster than we have ever conceived. In this section, Laplace even recognizes that some stars may be so dense that gravity precludes the escape of their own light--the phenomenon now recognized (in different form) as black holes. Thus Laplace argues (wrongly this time) that much apparent darkness in the night sky may really be occupied by enormous, dense stars. His figures and sizes are wrong by irrelevant modern standards, but his conjecture is fascinating:
A luminous star of the same density as the earth, but with a diameter 250 times greater than that of the sun, would not allow any of its light to reach us, by virtue of its own gravitational attraction. It is therefore possible that the largest luminous bodies in the universe are, for this reason, invisible.
According to the nebular hypothesis, the sun, early in its history, was surrounded by an atmosphere that extended well beyond the current planetary orits. This atmosphere rotated with the sun. At successive intervals, large segments of this atmosphere broke off and coalesced in an equatorial plane at the periphery of this contracting mass; these segments also began to rotate on their own behalf and formed the planets at their centers. Satellites formed by a similar process, one fractal level down, of atmospheric rotation and spalling off around planetary cores. Laplace argued that no other mechanism could account for all the primary regularities of motion in the solar system--particularly, the revolution of all planets in the same direction and virtually in the same plane, the revolution of satellites in the same direction, and the rotation of all planets and satellites (not true, but Laplace didn't know) in the same direction.
How then can we resolve the paradox that the scientific apostle of stability, a man who seemed to distrust and reject any real history either for celestial objects or for his own profession, should also be godfather to the first important theory for the origin of the solar system? Part of the answer may simply be that Laplace only dedicated a few pages to the nebular hypothesis--and anyone might allow himself an uncharacteristic speculation, or a flight into a field usually considered alien, for such little dedicated space. (Until I read the Exposition after buying a copy last week, I had never realized how few pages the nebular hypothesis occupied, so the anomaly seemed greater to me. We so often make the silly mistake of equating later importance with length of original effort. Many of the most famous ideas in science began as paragraphs or footnotes in weighty tomes otherwise entirely forgotten. Have we not all been surprised and amused to find that some of the best known biblical stories only occupy a line or two among pages of begats and other dull lists?)
But the main reason is far more interesting and entirely conceptual, rather than practical. Most intellectuals never abandon their motivating belief; if they seem to write about something contrary, more careful reading usually reveals the passage as a form of support for the familiar central doctrine. Of course, the nebular hypothesis is a historical statement about the origin of planets, but as I read Laplace's conjecture and came to the last paragraph, I saw the evident solution and chuckled. Laplace invoked the nebular hypothesis in his customary interest of bolstering stability in the solar system! Planets must have some origin after all, and Laplace argues that this particular style of formation best guarantees permanence thereafter. The striking last paragraph, virtually cribbed from his 1788 article, triumphantly proclaims:
Whatever one makes of this origin for the planetary system...it is certain these elements are ordered in such a manner that they must enjoy the greatest stability, if foreign causes never trouble them. Only by this means [formation by the nebular hypothesis] are the movements of planets and satellites almost circular, and directed in the same sense and almost in the same plane. This system can only oscillate about a mean state, from which it can only deviate by very tiny amounts. The average movements of rotation and revolution of these different bodies are uniform....It seems that nature arranged all bodies in the heavens in order to assure the duration of the system, and by means similar to those so admirably followed on earth for the conservation of individuals and the perpetuation of species.
I was arrogant enough to think that I had made some sort of discovery when I read the Exposition last week and recognized the antihistorical basis for the hypothesis that made Laplace so famous as the first historian for the universe. But I soon discovered that others had followed the same path of argument. C. C. Gillipie, perhaps America's finest senior historian of science, put the point most forcefully in his long article on Laplace in the Dictionary of Scientific Biography:
If the text is allowed to speak for Laplace, it will be altogether evident that evolutionary considerations in the 19th century sense formed no part of his mentality. The conclusions that he had reached concerned stability; the evidence for that he had calculated, many and many a time....He again referred to it as a warranty for the care that nature had taken to ensure the duration of the physical universe, just as it has the conservation of organic species....Clearly, it was not about the development of the solar system that he was thinking. It was about the birth.
We can, I think, best grasp the contrast between Laplace's antihistorical thinking and a truly historical approach by comparing the nebular hypothesis with the only serious contemporary competitor as a theory for planetary origins--the cometary collision hypothesis of the greatest of all eighteenth-century French naturalists, Georges Buffon (1707-1788). Laplace himself admitted Buffon as his only competition, writing in the Exposition: "Buffon is the only one I know who, since the discovery of the true system of the world, has tried to go back to the origin of planets and satellites."
Buffon argued that a comet had struck the sun, knocking out a large plume of solar material that then broke up to form the planets and satellites. Laplace rejected this alternative because Buffon's theory could not, in his view, explain all the regularities of planetary motion. Cometary impact would account for the common direction of planetary revolution with all planets in virtually the same plane (a result of the motion and orientation of the plume knocked from the sun). But Laplace argued that Buffon's theory could not account for the common direction of planetary rotation or for the origin of satellites.
Buffon and Laplace seem so different at first glance. Their generation or two of separation spans a world of change from Buffon's service to the last two King Louis before the revolution, to Laplace's work with various revolutionary governments and Napoleon. But their lives and studies include some striking similarities relevant to their joint interest in theories of planetary origin. Buffon was also a fine mathematician with two special interests that matched Laplace with uncanny precision. He was, first of all, a committed Newtonian who translated The Method of Fluxions into French from an English version of Newton's original Latin. Secondly, his greatest interest lay in probability, and he made a major contribution in first applying integral and differential calculus by extending the theory of probability to surfaces. (Interestingly, both Buffon and Laplace won admission to the French Academy of Sciences for monographs on probability; Buffon in 1734; Laplace in 1773.)
But the two men, in their scientific maturity, occupied opposite ends on the spectrum of professional activity, and the contrasting ethos of these termini set their profoundly differing attitudes to history, making Laplace indifferent and Buffon intrinsically committed. Laplace stuck to the mathematical bent of his youth and became the greatest celestial mechanic of his time. Buffon, on the other hand, changed course and devoted his career to botany and zoology; he became, in short, the greatest earthly naturalist of his day (only Linnaeus himself might have been granted higher rank).
Buffon's magnificent, multivolume Histoire naturelle took a lifetime (Buffon died before its completion) and fills a large library shelf. Students of the heavens may revel in constancy and precision. Students of earthly organisms also search for general patterns and frequently succeed; but naturalists must also take delight in the uniqueness of each creature, and they must be sensitive to the developmental histories of organisms, both in the courses of their lifetimes and (if they study the fossil record, as Buffon did) in the vastly larger domain of geological time. Good naturalists must be historians.
In 1749, Buffon introduced his cometary theory of planetary formation in his first work on geology, Histoire et theorie de la terre (History and Theory of the Earth). Much later, in 1778, Buffon published a much expanded and altered version entitled Epoques de la nature (Epochs of Nature). Most biologists and historians consider the Epoques to be Buffon's masterpiece and one of the finest examples of scientific prose ever written. The Epoques also includes an explicit defense and exposition of historical methodology, thus providing a striking contrast with Laplace and helping us to grasp the criteria of proper history. In particular, two differences between Buffon and Laplace sharpen our understanding of the nature of historical inquiry.
Criteria of inference. Historians use and cherish the narrative methods of explanation by antecedent events and situations; current results are outcomes of the unique and contingent web of all that came before and all that bears continuity with a present world in need of explanation. Historians also know that records of the past must be imperfect, for many kinds of data are not recorded as material remains, and much that could be preserved in principle has not survived in actuality. We always mourn lost data and hope for greater completion, but we do not apologize for the necessarily fragmentary record of our past, and we may treat spotty information as a delicious puzzle and a challenge. Antihistorians, like Laplace, get very antsy when they must use narrative data; they often become downright apologetic when they base a claim on anything other than a calculation or a direct observation of a present event.
Laplace ended his discussion of the nebular hypothesis with just such an apology, speaking of "this planetary system, which I present with the mistrust that must accompany everything that is not the result of an observation or a calculation." Buffon, on the other hand, begins the Epoques with a paean of praise to the excitement and efficacy of digging into the archives of the past with narrative methods. Consider his opening words:
In civil history, we consult titles, we research medals, we decipher ancient inscriptions in order to determine the time of human revolutions and to fix the dates of events in the moral order. Similarly, in natural history, it is necessary to excavate the archives of the world, to draw old monuments from the entrails of the earth, to collect their debris, and to reassemble into a single body of proof all the indices of physical changes which enable us to go back to the different ages of nature. This is the only way to fix points in the immensity of space, and to place a certain number of milestones on the eternal route of time [my translation].
Character of events. History must respect (and even love) the last two syllables of its name. Narratives must tell a story, a tale that captures our interest as a series of unique events with interesting causal connections. There is no history in Laplace's heavens, only a suite of bodies going nowhere as they cycle endlessly in obedience to simple laws. Any promising hope for directionality or accumulating instability is soon dashed by the self-correcting cyclicity of all perturbations. His nebular hypothesis is history, but only for the geological instant of the solar system's birth; ahistorical timelessness rules forever after. The thing that hath been, it is that which shall be; and that which is done, is that which shall be done; and there is no new thing under the sun.
By contrast, Buffon's Epochs of Nature is premised upon and titled by the opposite conviction that the time of our planet tells an engrossing story of accumulating change through several stages (called epochs by Buffon to set his title). He divided the history of the earth into seven directional epochs: first, the origin of the earth and planets by cometary impact; second, the formation of the solid earth and its mineral deposits; third, the covering of continents by water and the production of marine life; fourth, the retreat of waters and the emergence of new continents by volcanic action; fifth, the appearance of animal life on land; sixth, the fragmentation of continents and formation of the earth's current topography; and seventh, the appearance of humans and our accession to power. Could any contrast with Laplace's ever cycling heavens be more profound?
Buffon explicitly challenged the idea of constancy by noting that the narrative record of geology and paleontology proclaims a story of directional change:
Although it may appear at first sight that the great works [of nature] do not alter and never change, and that its productions, even the most fragile and most evanescent, must be always and constantly the same...nevertheless, in observing more closely, we note that [nature's] course is not absolutely uniform, that it undergoes successive alterations giving rise to new combinations and to mutations of matter and form; and that, finally, however fixed nature may appear in its ensemble, so is it variable in each one of its parts; and if we embrace nature in its full extent, we cannot doubt that it is very different today from what it was at the beginning and from what it has become in the succession of time; it is these changes that we are calling epochs.
Lawful timelessness is awesome, but the pageant of history thrills us too, and in a different way that makes time sensible. Everyone needs a good mechanic, including the heavens, but give me an earthly naturalist any day, for humans are storytellers. In the nearly 250 essays of this series, I have tried to avoid repetition (if only to honor the principles of history cited above). But like a broken record (a metaphor from the last epoch of history, soon to be rendered unintelligible I fear), one quotation keeps recurring. I have used it to end nearly half a dozen essays (shameful in a way, but we all have our Laplacean side). This quotation also includes the masthead for the entire series "This View of Life" (I guess we all need our constancies). I love this quotation because it affirms the power of life and history by making the same contrast between Laplace's ever cycling heavens, always moving yet always the same, and the glorious tale of life, always different, always going somewhere, always telling a story. It is the last paragraph of Darwin's Origin of Species:
There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms more beautiful and most wonderful have been, and are being, evolved.
Stephen Jay Gould teaches biology, geology, and the history of science at Harvard University.…