During my lifetime, as the author himself says, the pendulum has swung from the confidence that there are no aliens to the conviction that there certainly are. In the meantime, though, the science hasn’t fundamentally changed, and we just don’t know:
http://blogs.scientificamerican.com/guest-blog/maybe-life-in-the-cosmos-is-rare-after-all/
Paul Davies, a physicist, cosmologist, and astrobiologist, is an exceptionally interesting thinker. I’ve read several of his books.