[Tau Zero] is the ultimate "hard science-fiction" novel. Everybody else who has been trying to write this kind of thing can now fold up his tent and creep silently away.
The scientific problem is deceptively simple: What happens when an interstellar vessel, accelerating at a steady one gravity, is damaged in such a way that it can't stop doing so?…
The eventual consequences of this seemingly modest and constricting set of assumptions are so staggering as to make the inter-galactic epic of E. E. Smith, Ph.D. (who made up all his "science") seem in retrospect like a trip with mommy to the corner grocer. (p. 14)
[Anderson's book is mind-boggling because when you finish it you realize that:] It is almost all completely possible. Only at the very end does the author pull a rabbit out of his hat, and it seems like a rabbit only because of the scrupulosity of the rest of his argument: He makes two cosmological assumptions, one of which is in good odor among many reputable astrophysicists, the other a conjecture which, to say the worst of it, nobody is ever likely to prove wrong.
Anderson has not failed to populate his starship with interesting people with complex human problems, and the hero … is especially well realized. There are many moments of genuine emotion (as well as a few of facile tear-jerking). But nobody but a Dostoevsky could have given this novel a cast that would not be overshadowed by the grandeur of its events. Its flaws are mostly the consequences of its strengths. Overall, it is a monument to what a born novelist and poet can do with authentic scientific materials. And as is usual with recent Anderson, the poet is as important as the novelist…. (p. 15)
James Blish, "Books: 'Tau Zero'," in The Magazine of Fantasy and Science Fiction (© 1971 by Mercury Press, Inc.; reprinted from The Magazine of Fantasy and Science Fiction), Vol. 40, No. 3, March, 1971, pp. 14-15.