This video outlines Knuth's #1 open GoL problem. Any ideas how to solve it?
https://www.youtube.com/watch?v=AWDCNCszn-U
EDIT by dvgrn: the link is to Tom Rokicki's talk at Gathering for Gardner 15, two years ago.
There's a 2015 discussion thread here on the forums, with a message from Tom at the end that slightly predates the G4G15 talk.