Innocence Forever Gone

The theme of innocence lost is perfect for time travel fiction and we have seen that it pervades Poul Anderson's Time Patrol series. See here. The same theme is also relevant to an sf series in which primitive societies are integrated into an interstellar civilization and in which some individuals, benefiting from an advanced education, leave their home planets to visit other planetary systems:

Adzel reflects:

"...now he was so changed that he would never feel at home among the hunters...a certain sense of belonging, an innocence, was forever gone." (David Falkayn: Star Trader, p. 132)

Chee Lan says:

"'We can't go home to what we left when we were young; it may still be, but we aren't, nor is the rest of the cosmos.'" (Rise Of The Terran Empire, p. 290)

The Technic History does to Space what the Time Patrol does to Time. Both series show us distance traveled.