How many songs are there?  "Assuming the world doesn't end, will
there come a day when all the music it's possible to write has
been written? It's finite isn't it?" - Claire W, via Twitter.
Excellent question. Yes, there are a finite number of songs in
the universe - with the one condition that no song can last
forever. Let's make it more restrictive and say no song can last
for more than 5 minutes (though we could choose 20 or 30 mins
and come to the same conclusions.)  Given that, though, it turns
out it might not make very much difference that its a finite
number...  All of these 5 minute songs could be played on a
digital player. So we know all songs can be represented
digitally: the waveform can be encoded in numbers. This is jolly
helpful for answering this question. Digital encoding is
ultimately bits: ones and zeros. So each bit can only be in one
of two states, like a lightswitch. 1 - 0. If you have two bits,
there are more options: 1/1 - 1/0 - 0/1 - 0/0. You have four
options for how to arrange two