Found a neat article today about an artist called Alejandro Guijarro has collected images of blackboards that have been graced by the thoughts of some of the most brilliant people in the world. His photos capture the temporary state of a thought expressed in chalk and I just love the ghosty feeling I get from these pictures. This one in particular is interesting to me. Even if I could have seen what it said before being erased it would be strange to me!
See more in an article from The Atlantic.