Physics   

and water: but nothing of the kind is observed.
(b) Nor can fire or any other of the elements be infinite. For
generally, and apart from the question of how any of them could be
infinite, the All, even if it were limited, cannot either be or become
one of them, as Heraclitus says that at some time all things become
fire. (The same argument applies also to the one which the physicists
suppose to exist alongside the elements: for everything changes from
contrary to contrary, e.g. from hot to cold).
The preceding consideration of the various cases serves to show us
whether it is or is not possible that there should be an infinite
sensible body. The following arguments give a general demonstration
that it is not possible.
It is the nature of every kind of sensible body to be somewhere, and
there is a place appropriate to each, the same for the part and for
the whole, e.g. for the whole earth and for a single clod, and for
fire and for a spark.
Suppose (a) that the infinite sensible body is homogeneous. Then each
part will be either immovable or always being carried along. Yet
neither is possible. For why downwards rather than upwards or in any
other direction? I mean, e.g, if you take a clod, where will it be
moved or where will it be at rest? For ex hypothesi the place of the
body akin to it is infinite. Will it occupy the whole place, then? And
how? What then will be the nature of its rest and of its movement, or
where will they be? It will either be at home everywhere-then it will
not be moved; or it will be moved everywhere-then it will not come to
rest.
But if (b) the All has dissimilar parts, the proper places of the
parts will be dissimilar also, and the body of the All will have no
unity except that of contact. Then, further, the parts will be either
finite or infinite in variety of kind. (i) Finite they cannot be, for
if the All is to be infinite, some of them would have to be infinite,
while the others were not, e.g. fire or water will be infinite. But,
as we have seen before, such an element would destroy what is contrary
to it. (This indeed is the reason why none of the physicists made fire
or earth the one infinite body, but either water or air or what is
intermediate between them, because the abode of each of the two was
plainly determinate, while the others have an ambiguous place between
up and down.)
But (ii) if the parts are infinite in number and simple, their proper
places too will be infinite in number, and the same will be true of
the elements themselves. If that is impossible, and the places are
finite, the whole too must be finite; for the place and the body
cannot but fit each other. Neither is the whole place larger than what
can be filled by the body (and then the body would no longer be
infinite), nor is the body larger than the place; for either there
would be an empty space or a body whose nature it is to be nowhere.
Anaxagoras gives an absurd account of why the infinite is at rest. He
says that the infinite itself is the cause of its being fixed. This
because it is in itself, since nothing else contains it-on the
assumption that wherever anything is, it is there by its own nature.
But this is not true: a thing could be somewhere by compulsion, and
not where it is its nature to be.
Even if it is true as true can be that the whole is not moved (for
what is fixed by itself and is in itself must be immovable), yet we
must explain why it is not its nature to be moved. It is not enough
just to make this statement and then decamp. Anything else might be in
a state of rest, but there is no reason why it should not be its
nature to be moved. The earth is not carried along, and would not be
carried along if it were infinite, provided it is held together by the
centre. But it would not be because there was no other region in which
it could be carried along that it would remain at the centre, but
because this is its nature. Yet in this case also we may say that it
fixes itself. If then in the case of the earth, supposed to be
infinite, it is at rest, not because it is infinite, but because it