Queens "39" - from wiki:
The song's lyrics are a science fiction short story which concerns twenty volunteers who leave a dying Earth on a spaceship in search of new worlds to settle. They return to report success, 100 calendar years later, with only a single year passing from the volunteers' perspective (due to time dilation). The lyrics imply that the song's protagonist faces his child upon return to Earth: For so many years have gone/though I'm older but a year/your mother's eyes from your eyes/cry to me. This, and the fact that all his peers and friends have died, are a terrible grief to the protagonist, as the final words insist: For my life/still ahead/pity me!
To provide 100 years' time dilation on Earth in only one year of spaceship time, the velocity of the spaceship must average to 99.995% of the speed of light.
Brian May described the song as follows:
It's a science fiction story. It's the story about someone who goes away and leaves his family and... because of the time dilation effect, when you go away, the people on Earth have aged a lot more than he has when he comes home. He's aged a year and they've aged 100 years. So, instead of coming back to his wife, he comes back to his daughter and he can see his wife in his daughter... a strange story. I think, also, I had in mind a story of Hermann Hesse, which I think is called "The River" [actually "The Poet" [1]]. A man leaves his hometown and has lots of travels and then comes back and observes his hometown from the other side of the river. He sees it in a different light, having been away and experienced all those different things. He sees it in a very illuminating way, 'cause I felt a little bit like that about my home at the time as well, having been away and seen this vastly different world of rock music... totally different from the way I was brought up, and I had those feelings about home.
Rule No. 1 - If it sounds good - it is good!