The 3 of Brian Greene is sometimes a funny, curly Greek zeta. I haven’t discovered yet the reference frames which determine what the 3 in the end will be.

3's like that because he was writing in an uncomfortable position on the board. He just can't stop writing in the middle, notice how he normally writers 3 on the board when he was in a nice position to write

Study group- I am unsure this fellow follows Prof. Greene s logic, but just to know there are questions about Einstein are important to keep perspective - why can they occur? https://askuswhatever.com/episodes/episode-7-1-how-lorentz-failed-and-physics-took-a-turn-toward-fantasy-land/ Quote- So that should raise your level of skepticism: Einstein synchronization, not nature, causes clocks to be adjusted so that light appears to be moving at a constant speed, and so that the principle of relativity appears symmetric. Without that manual intervention, Einstein’s postulates fall apart. Thank you to Prof. Greene for this course.