Cities In Flight, Volume IV

James Blish wrote The Triumph Of Time (alternative title: A Clash Of Cymbals) specifically to complete and conclude his Okie series, collected as Earthman, Come Home, making it impossible to write another sequel about this set of characters. Because the characters are physically unaging, Blish shows them surviving until the end of the universe. However, for story purposes, he brings this end much closer to the present than we would have expected.

This end of the universe is not its heat death but its mutually annihilating collision with its anti-matter counterpart. Thus, all cosmic matter is transformed into energy but the energy remains active - it does not become quiescent. Some of it will be transformed back into matter and will then continue on its way towards a heat death at a much later date. For this reason, one character, a philosopher, refers to " '...the period of Interdestruction...' "(Cities In Flight, London, 1981, p. 515)

However, he also refers to a number of dissimilar myths and philosophies that had allowed for:

" '...a break or discontinuity right in the middle of the span of existence...' " (p. 515)

Blish in conversation once applied the term "Interdestruction" not to a discontinuity midway between the monobloc and the heat death but to the period between cosmic collapse and a new monobloc as presented in Poul Anderson's Tau Zero - so the term "Interdestruction" does not seem to have one unambiguous meaning.

The Triumph Of Time is a good novel of endings and new beginnings after the endings. It begins:

"In these later years..." (p. 472)

- and ends:

"Creation began." (p. 596)

The characters hold a farewell dinner and walk for the last time through the city that they had flown between the stars. Every single physical action is eventually performed for the last time. The "...epitaph for Man..." is:

"We did not have time to learn everything that we wanted to know." (p. 596)

At the very end, a philosopher says, "I think-," but is interrupted by the end of the universe (p. 595).

Making it impossible to write another sequel does not rule out adding yet another prequel or earlier episode and Blish did this in A Life For The Stars, which is why the concluding novel is Volume IV, not III.