The past through tomorrow

I'm not sure how many times I've re-read this book since I got it in 1974 or 1975. My copy looks a bit better than the photo here except for the missing first 125 pages.
I loved this book along with "Time Enough for Love". It must be time to add these back to my want to read list here.
/had to chuckle when it tried to input a 1974 date in the Add Read Dates section. didn't like it/