With the verve and accessibility which have made Dr. Sagan one of the most widely known scientists of his time [the essays in "Broca's Brain"] range across such topics as planetary systems (which are his speciality), the search for extraterrestrial intelligence, pseudo-science, science fiction, and religion—something for everybody who is at all interested in science.

Dr. Sagan sees us as living at a "unique transitional moment." He thinks the past 50 years have raised questions that could not even have been asked before and that the next 50 years will have answered most of them…. Agreeing that the next 50 years will answer a vast range of questions, probably including whether we are living in a universe that will expand to cold emptiness or one that will collapse back upon itself, possibly to produce another Big Bang, yet still I believe, and hope, that 50 years from now an aged Dr...