On The Heavens   

in a certain time, and the part of this infinite, E, cannot be so

modified in the same time, since we assume that a less quantity

makes the movement in a less time. Let E then, when acted upon by A,

complete the movement in the time D. Then, as D is to CD, so is E to

some finite part of B. This part will necessarily be moved by A in the

time CD. For we suppose that the same agent produces a given effect on

a greater and a smaller mass in longer and shorter times, the times

and masses varying proportionately. There is thus no finite time in

which infinites can move one another. Is their time then infinite? No,

for infinite time has no end, but the movement communicated has.

If therefore every perceptible body possesses the power of acting or

of being acted upon, or both of these, it is impossible that an

infinite body should be perceptible. All bodies, however, that

occupy place are perceptible. There is therefore no infinite body

beyond the heaven. Nor again is there anything of limited extent

beyond it. And so beyond the heaven there is no body at all. For if

you suppose it an object of intelligence, it will be in a

place-since place is what 'within' and 'beyond' denote-and therefore

an object of perception. But nothing that is not in a place is

perceptible.

The question may also be examined in the light of more general

considerations as follows. The infinite, considered as a whole of

similar parts, cannot, on the one hand, move in a circle. For there is

no centre of the infinite, and that which moves in a circle moves

about the centre. Nor again can the infinite move in a straight

line. For there would have to be another place infinite like itself to

be the goal of its natural movement and another, equally great, for

the goal of its unnatural movement. Moreover, whether its

rectilinear movement is natural or constrained, in either case the

force which causes its motion will have to be infinite. For infinite

force is force of an infinite body, and of an infinite body the

force is infinite. So the motive body also will be infinite. (The