In podcast 262 I was going through the ways that Lucretius was proving that the soul cannot be eternal, and came across this section in which Lucretius sets out the logical ways in which something could be eternal. In addition to the soul aspect I think this is helpful in the way it describes (1) the universe as a whole is eternal - by deduction from the fact that there is nothing "outside" the universe, and (2) that the atoms and void are eternal because they are able to "beat back assaults" and suffer nothing from have anything come into contact with them.
In regard to Epicurean gods I find particular interesting the possibility that this section applies: "because it is fortified and protected from things fatal to life, or because things harmful to its life come not at all, or because such as come in some way depart defeated before we can feel what harm they do us..." Of course that's not the case for us as humans, but I would presume that the speculation about the location and makeup of the gods was intended to let them do exactly that.
[800] Nay, indeed, to link the mortal with the everlasting, and to think that they can feel together and act one upon the other, is but foolishness. For what can be pictured more at variance, more estranged within itself and inharmonious, than that what is mortal should be linked in union with the immortal and everlasting to brave raging storms?
[806] Moreover, if ever things abide for everlasting, it must needs be either that, because they are of solid body, they beat back assaults, nor suffer anything to come within them which might unloose the close-locked parts within, such as are the bodies of matter whose nature we have declared before; or that they are able to continue throughout all time, because they are exempt from blows, as is the void, which abides untouched, nor suffers a whit from assault; or else because there is no supply of room all around, into which, as it were, things might part asunder and be broken up—even as the sum of sums is eternal—nor is there any room without into which they may scatter, nor are there bodies which might fall upon them and break them up with stout blow.
[819] But if by chance the soul is rather to be held immortal for this reason, because it is fortified and protected from things fatal to life, or because things harmful to its life come not at all, or because such as come in some way depart defeated before we can feel what harm they do us \[clear facts show us that this is not so\]. For besides that it falls sick along with the diseases of the body, there comes to it that which often torments it about things that are to be, and makes it ill at ease with fear, and wears it out with care; and when its evil deeds are past and gone, yet sin brings remorse. There is too the peculiar frenzy of the mind and forgetfulness of the past, yes, and it is plunged into the dark waters of lethargy.
