I haven't seen the movie, but I have a possible explanation for the seemingly long period of time that has past on Earth. If humans have been traveling through space for a long distances at very high speeds, then time dilation would occur. A common example of this is the "twin paradox". Basically, if one twin left Earth on a spaceship that could travel at very near the speed of light, he could go to Alpha-Centari (the closest star system to our own) and back in just days or weeks from his point of view. But to his twin on Earth, over 8 years would have went by. This very real effect is ignored in most science-fiction, so I would actually be impressed if this was the intended explanation.
Did they ever state in the movie how far away (in light years) Nova Prime is from Earth?
