Here's a nice, simple topic for first thing on a Friday morning: do numbers really exist? Well, do they?
As Mark Jago from the University of Nottingham explains in this video, it's really quite hard to find out about what numbers really, truly are because they're not physical, tangible things. Prepare to have your mind melted as he explains some of the ways people have tried to think about the very existence of numbers in the past.
Image by Håkan Dahlström under Creative Commons licence