4 ideas
Lumen dies in Paris in 1864, and his spirit flies to the star Capella in an instant. The light arriving there left Earth roughly seventy years earlier, so through a telescope-like vision he watches Paris during the Revolution of 1793, including scenes from before his own birth. Seeing history this way depends on a single astronomical fact, not on any magic of the afterlife.
Every event on Earth sends out its image as light, and that image keeps travelling through space long after the event has ended. So the past is never erased. It sits in a sphere expanding at light speed, and an observer at the right distance sees it as present. In principle, any moment of history can be recovered by placing an eye at the right distance.
If an observer moves away from Earth faster than light, he overtakes older and older wavefronts, so he sees events in reverse. Battles un-happen, the dead rise, and an old man grows back into a child. Sequence and simultaneity then look like facts about how light reaches the observer, not facts about the events themselves.
Living beings on other worlds are shaped by local gravity, atmospheric density, light, and chemistry, so they need not resemble humans or any terrestrial species. Lumen describes beings built around conditions unknown on Earth, including organisms that feed from their atmosphere and creatures with senses humans lack. The human body is presented as one local answer to Earth's conditions, not a universal template for intelligence.