Change
Earth and the changes that take place during the centuries shown in the novel are symbolic of the adaptable nature of human. In a sense, the novel praises the humans who are as much as troublemakers who bring themselves to the brink of extinction as adaptive creatures who create ingenious solutions. To resolve the famine, food-currency is created, to resolve conflicts a homogenous society is enforced, and finally, to resolve overpopulation, heterosexuality is banned and homosexuality enforced, the problematic aspects of these being obvious.
Alien life
The novel shows the idea of possibility of alien life and the human reaction to it. It is introduced as a grave threat to humanity from the very start that need capable individuals to sacrifice themselves to eradicate it. It is also insinuated from the very start, that things might not be the way they were presented to these individuals, and that there is a different reality behind the Taurans, as revealed in the plot twist at the end.
Time
The novel goes into detailed physics about time and space travel, light-years and the way time passes on the Earth compared to somewhere else in space. William is dazed by the effects of the time passing differently on Earth compared to his time in space, he is but a twenty-something-year-old while on Earth he is considered double that upon his first return.
Man
The species that is revealed at the end of the novel, is titled “Man”. They come as the final rescuers and bringers of the truth. They could be interpreted as a symbolic representation of humanity evolved beyond the need for corruption and destruction.
