1 The Birth of Science - MSRI

264 10. Lost Science
earth, of course, but toward their own center. We do not know who the
first person to draw this conclusion was. It is reasonable to think that it
was Archimedes himself, since he was very interested in astronomy and
took Aristarchus’ heliocentric hypothesis as a possibility at least, and so
had no reason to restrict to the earth alone the causal relationship, which
he so clearly pointed out, between sphericity and gravity. What cannot be
doubted is that the conclusion was drawn by someone, since Plutarch says
explicitly:
Just as the sun attracts to itself the parts of which it consists, so does
the earth. . . 111
After the theoretical reason for the spherical shape of the earth, sun and
moon was understood, the same shape was also ascribed to other heav-
enly bodies, though it cannot be observed directly in that case. 112
At this point the Aristotelian picture (which later became the Ptolemaic
one) crumbled from inside. The universe no longer has a hierarchical
structure, centered on the earth and based on a distinction between earthly
and celestial bodies; it is made up of so many worlds, equivalent in important
ways to one another. The multiplicity of worlds is closely linked
with the rejection of the sky of fixed stars, with the notion of an infinite
universe and with the relativity of movement. 113 These ideas, too, whose
memory was to play such an important role in the early modern age, seem
to have had (apparently prescientific) forerunners among the pre-Socratic
philosophers. 114
To return to gravity, the train of thought outlined above allows two possibilities:
either one thinks that gravity has so many independent centers,
one for each heavenly body, each capable of attracting things that belong
to it and no others; or one thinks that there is also an attraction between
different heavenly bodies. The first possibility was certainly mooted, since
it is explicitly advanced in the De facie by Lamprias, to whom belongs the
line of the dialog quoted just above. 115
The idea of so many gravity centers, each associated with one world and
not interacting with the others, while it may explain the shape of heavenly
bodies, does not solve the problem of what motions may be hypothesized
theoretically. One can ask, in fact: How would a mass move that is far
111 (Plutarch, De facie quae
in orbe lunae apparet, 924E).
112
Compare Cicero, De natura deorum, II, xlvi, 117; Diogenes Laertius, Vitae philosophorum, VII, 145.
We will return to this question in the next section.
113
See Section 3.7.
114
See, in particular, the testimonia about Anaximander collected in [Diels: FV] under B11.
115
Plutarch, De facie. . . , 924D–F. Compare Plutarch, De defectu oraculorum, 424E–425C.
Revision: 1.11 Date: 2003/01/06 02:20:46
page 330