This track from the Interstellar soundtrack is seriously genius.

The tempo changes over the course of the song, 48 bpm for the first minute, 50 bpm for 2nd minute, and then it ends up at exactly 60 bpm to coincide with the sound of the ticking second hand of a watch, which is a major part of the movie. Zimmer is always building intricacies like this into soundtracks for Nolan's movies, like little easter eggs for those with an eye for detail.

This track starts playing when the crew lands on Miller's water planet, where time dilation takes effect because of the proximity to a singularity, and time runs slower for those on the planet than those on earth.

For every 60 seconds of the track there are 48 ticks of the second hand sound. So, each 'tick' interval is 1.25 seconds.

According to the movie, every hour on the water planet equals about 7 years on Earth. There are 3600 seconds in an hour, and (86400 x 365.25 x 7) or roughly 221,000,000 seconds in 7 years, giving us a conversion factor of 221,000,000/3600 ≈ 61400 seconds which pass on Earth for every second spent on the water planet.

Multiply this by the interval between each 'tick', and you get 77000 Earth-seconds, about 21 hours.

So, *each 'tick' you hear is a whole day passing on Earth.*

It's a beautiful score, but it also highlights Zimmer's brilliance.