Sometimes when I am about to leave the house for some reason, I publish a very short post instead of waiting and publishing a longer one later. Hence, a short objection to Sundaram's thought about annulling the past. His immediately following sentence is:
"Can it be the act of a Providence that nowhere does starfaring go on for very long?" (p. 326)
What does this mean? Interstellar travel, at least with the zero-zero drive, might upset a cosmic energy balance and thus cause the universe to cease to exist? Therefore, it might be providential that such travel never lasts for very long? OK, so far.
But remember that what Sundaram is saying is that, if interstellar travel lasts for too long a time, then the universe will never have existed and therefore interstellar travel will have lasted for zero time! Contradiction.
Jean Kilbirnie reasons:
Tahirian "conservatives" oppose change (so far, that is a tautology);
interstellar travel inevitably brings massive changes;
therefore, the "conservatives" oppose interstellar travel;
therefore, they rationalize their opposition to interstellar travel by convincing themselves that such travel threatens the universe - and even threatens the past!
Yes, conservatives would be horrified by an imagined threat to their past.
Poul Anderson is demonstrating that intelligent beings are capable of rationalizing their defence of the status quo with irrational ideas.