Emergent Structure: the First Two Centuries of the First Two Eons

Abstract

Scientific recognition of the existence, evolution, and significance of structure within the cosmos developed slowly. We follow the story here from the earliest times to the first systematic redshift surveys and the "Rubin-Ford effect," emphasizing the period beginning with William Herschel and ending about lunch time on Wednesday. The scientific issues cannot be put in any one linear order, because, for instance, some people were studying clusters of galaxies and measuring the mass of M31 while others still denied the existence of external galaxies.The merging of Greek philosophy with medieval church doctrine that was largely the work of Thomas Aquinas imposed this spherical symmetry on European thought after about 1260, along with immutability of the heavens, the four terrestrial elements + quintessence, and much else. Indeed many of the early readers of Copernicus were inclined to think that the most important thing he was saying was the primacy of uniform circular motion, whatever is at the center. But, before this, the 12th century universe of Hildegaard of Bingen had a spherical earth, but a pineapple-shaped lucidus ignis outside it. She also placed the fixed stars close to us, hail and lightening further out beyond the moon, followed by the sun and outer planets (as the stem of the pineapple). Thus she had not yet fully accepted immutability of the heavens as requiring hail, lightning, comets, meteors, and guest stars all to fall within the atmosphere. A Chinese model universe from about the same time is spherical and held up by dragons (Needham 1953). It also has an equatorial mount, rather than an ecliptic one like the European armillary spheres of the time, and the equatorial concept may well be a Chinese inventionThen the spheres and circles close in, first with earth at the center a la Ptolemy (and Martin Luther), then, increasingly, with the sun at the center, a la Copernicus.Next is the question of where to put the stars. Outside the orbit of Saturn, clearly, but how far outside, how many of them, and how far should they extend? Early on, these questions tended to get stirred in with old philosophical considerations of whether voids and infinities were conceivable and hence possible. For some people, they probably still do.Thomas Digges in 1576 extended his "orbe of starres fixed" to infinity (though not in the drawing) and allowed them to have planets and life. He said that the total assemblage though infinite was somehow vaguely spherical, but that it could have neither edges nor a center. Infinite, multiply inhabited, and more or less spherical universes are also to be found in the writings of Nicolas of Cusa (c. 1450), Giordano Bruno (before 1600!), and William Gilbert (d. 1602). Gilbert explicitly allowed the stars in his infinite distribution to be of intrinsically different size (meaning brightness).Kepler (d. 1630) considered the possibility of an infinite, fairly uniform distribution of stars, of which the sun would be merely an undistinguished one, but rejected both this and a "stoic" univ...