Are you reading this page because you decided to or because you were destined to from the start of time? Plus shares Mick's sentiment that we are free to do what we want, any old time. But what does physics and mathematics have to say about free will?

What's that we hear? Sleigh bells! What's that we smell? Chestnuts roasting on an open fire! What can that mean? Christmas is coming! Celebrate the countdown with the Plus advent calendar featuring our favourite mathematical moments from 2012. Now, what's behind today's door...?