University of Virginia Library

Time in Classical Science. While the time of the
Aristotelian and medieval cosmology was relational, it
was still uniform and in this sense universal since it
was physically embodied in the uniform rotation of
the sphere of the fixed stars which represented the
absolute cosmic clock. But with the removal of this
privileged cosmic clock by Giordano Bruno, the unity
and uniformity of time was greatly compromised as
long as time was still regarded as inseparable from
motion, in the sense of the relational theory. For what
becomes of the unity and uniformity of time, if there
is no uniform cosmic clock by which time can be
measured? There are only two ways to avoid this
difficulty: either to accept fully the consequence of the
relational theory and to concede that without the
privileged cosmic clock there should be as many times
as there are motions—tot tempora quot motus; or to
give up the relational theory altogether, that is, to
make time completely independent of any concrete
physical motion; only in this way would the unity and
the uniformity of time not be affected by the diversity
and variability of physical motions. It was the second
solution which was gradually adopted by the incipient
modern science. This separation of time from its physi-
cal content was made easier by the fact that doubts
about the uniform cosmic clock began to arise even
prior to the elimination of the last celestial sphere. The
fact of the precessional motion, already known to the
Greek astronomers, made it necessary to postulate an
additional sphere beyond the eighth sphere; only to
this ninth sphere—and not to the sphere of the “fixed
stars”—did the truly uniform revolving motion belong.

Further observations raised the doubt whether any
uniformly running celestial clock exists at all in nature.
Doubts of this kind were expressed by Nicolas Bonnet
and Grazadei d'Ascoli in the fourteenth century; they
nevertheless insisted that the existence of true mathe-
matical time does not depend on the existence of such
a clock. Similarly, Bernardino Telesio in his De rerum
natura... (1565), though he retained the Aristotelian
cosmology, held that time is logically prior to motion
and change; while motion cannot exist without time,
time which, according to him, exists by itself (per se),
can exist without motion. A similar foreshadowing of
Newton's concept of absolute time can be seen in the
thought of Francisco Suárez, even though he too
retained the Aristotelian cosmic clockwork. He distin-
guishes two kinds of duration: “flowing imaginary
extension” (spatium imaginarium fluens), which flows
uniformly (immutabile in suo fluxu), and concrete
change which coexists with it and, so to speak, fills
it (quasi replens). Thus the distinction between time
as a homogeneous container and its concrete changing
content is clearly drawn; the former is intrinsically
irreversible, the latter is not (Disputationes meta-
physicae, C. L. sec. IX, 15).

But even after the definitive removal of the celestial
clockwork, the concept of absolute time was formed
only gradually and after some hesitation. This is clear
in the thought of G. Bruno, in particular in articles
38-40 of his Camoeracensis acrotismus seu rationes
articulorum physicorum adversus Peripateticos (Witten-

berg, 1588). Certain of its passages show that Bruno
was leaning toward the relational theory of time as,
for instance, when he claims that there are as many
times as there are stars (tot tempora quot astra). On
the other hand, guided by the analogy of infinite space
of which particular spaces are mere parts, he speaks
of universal time (tempus universale) of which particu-
lar durations are finite portions. Time would exist even
if all things were at rest and motionless; against
Aristotle, Bruno holds that change is a necessary condi-
tion for the perception of time, but not for its existence.

Similar hesitancies may be traced in the thought of
Pierre Gassendi. In his Philosophiae Epicuri Syntagma
in 1649, only six years before his death, he speaks of
time in the characteristically Epicurean way as an
“accident of accidents,” that is, accidens accidentium.
Against this relational view of time, Gassendi equally
unambiguously insists on its absolute and independent
nature, e.g., when in his polemic with Descartes he
says: “Whether things are or not, whether they move
or rest, time always flows at an equal rate.” This sen-
tence occurs almost verbatim in the passage of Isaac
Barrow, Newton's tutor (Mathematical Works, ed. W.
Whewell [1860], II, 160f.), where it is stated that mo-
tion presupposes time, but not vice versa, and that time
continues to flow even if all things stand still. Gassendi's
influence on Barrow and Newton is also clear in his
view linking the infinity of space and time with the
divine omnipresence and everlasting duration, and his
insistence that both time and space existed prior to
the creation of the world (Syntagma philosophicum,
Opera omnia, Lyons [1658], I, 183, 225). Newton's
characterization of time, in the scholium of his Philos-
ophiae naturalis principia mathematica (1687), was the
culmination of the process by which the concept of
time was separated from that of concrete physical
change:

(Andrew
Motte's translation, revised by Florian Cajori).

For more than two centuries this concept of time
remained practically unchallenged by physicists; James
Clerk Maxwell's definition of time in his Matter and
Motion (1877) is identical both in spirit as well as in
letter with that of Newton.