Time Dilation! - Queen sang of it in 1975. Freddie Mercury did background vocals.

Queen's little known song, '39, had words sung which demonstrated time dilation. The song was released in 1975 and was on A Night At The Opera album.

Some info:

The song relates the tale of a group of space explorers who embark on what is, from their perspective, a year-long voyage. Upon their return, however, they realise that a hundred years have passed, because of the time dilation effect in Einstein's special theory of relativity, and the loved ones they left behind are now all dead or aged.

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Time dilation:

In the theory of relativity, time dilation is a difference of elapsed time between two events as measured by observers either moving relative to each other or differently situated from a gravitational mass or masses.

An accurate clock at rest with respect to one observer may be measured to tick at a different rate when compared to a second observer's own equally accurate clock.

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