In @johncarlosbaez talk on the #TenfoldWay https://math.ucr.edu/home/baez/tenfold.html I am failing to understand what it means, physically or intuitively, that an #antiunitary (#time reversal #symmetry) operator T squares to 1 or -1. What is the difference between those two cases?

There it is! The video recording of @johncarlosbaez' talk from Feb 6! That was quick! I couldn't attend, but I'm looking forward to watch it soon!

In the description he says:

> The importance of the tenfold way in physics was only recognized in this century. Simply put, it implies that there are ten fundamentally different kinds of matter...

https://www.youtube.com/watch?v=CgaMMjC3rnM

#tenfoldWay