Tau Zero

I am reading this 1970 Poul Anderson novel.  You doubtless remember from high school physics how relativistic effects of velocity are calculated using (v**2)/(c**2) for increases in mass, reductions in length, and time dilation relative to restcatch him.

 The curious effects on time dilation were well used in Larry Niven's A World Out of Time where a revived corpsicle is sent on a mission in a Bussard ramjet mission.  Once he is far enough away that they cannot catch him, he goes rogue and goes to the galactic core, returning three million years later to a dramatically changed Earth. 

Tau Zero starts as a generation ship to a nearby star.  An accident en route soon sends on a much longer mission with tau dropping to absurdly low levels as they look for somewhere to find a new Earth.  I am not done yet but like all Anderson novels it is scientifically rich with clear explanation of Doppler shift effect on the view fore and after.  The problems of humans confronting the problem of probably reaching end of like while 100 million Earth years pass is thoughtful and compassionate.