[Bakkot]

This may have been what you're thinking of. Sadly I lack a source; it's just been kicking around my miscellaneous images folder.

http://i.imgur.com/tBgQkxi.jpg

[friendcomputer]

That's from http://arxiv.org/pdf/gr-qc/9704009.pdf

There's some more from the author here: http://space.mit.edu/home/tegmark/crazy.html

[GuiA]

Thank you! I love the internet :)

[pohl]

So where would categories hang on that graph? Below semigroups?

[igravious]

That's it! Thanks!