From the 1960s to the 1980s, Carl Sagan (1934-1996) was US science's greatest communicator: a toothy, tanned, polo-necked, clubbable (in every sense of the word) egghead, whose vivid, hyperbolic prose and TV persona somehow enabled people to gawp at the vast, bizarre universe. At public lectures, crowds would beg him to say "BILLions and BILLions" - which he loathed, but it eventually became the title of his last book. And while many scientists dismissed his wild theorising and lifelong obsession with extraterrestrial intelligence, he was also science's ideal salesman.
In this bulky, journalistic biography, Davidson, a science writer with the San Francisco Examiner, traces Sagan from poor, Brooklyn, Jewish roots to New Jersey, where the family moved after his granduncle's New York Girl Coat Company made a fortune from the second World War and where Sagan had the best of everything.
Unsurprisingly, Sagan's main teenage enthusiasm, apart from chemistry sets, was Edgar Rice Burroughs's Mars sci-fi books. At 18, he even wrote to the Secretary of State about the likely extraterrestrial origin of UFOs. Yet he won Class Brain at high school, and before studying theoretical astrophysics at Berkeley and Harvard, received his degree at the University of Chicago, reading Mendel, Darwin and Newton in the original - and the humanities.
Chicago was also the campus where the famous Miller-Urey experiment had demonstrated that a hydrogen-rich atmosphere (methane, ammonia, water), when electrified, could form amino acids in abundance - implying that life was less miraculous than inevitable under certain conditions, and neatly cementing Sagan's peculiar brand of atheism.
The young Sagan went out of his way to "glad-hand" Nobel laureates such as H.J Muller, Joshua Lederberg and Harold Urey, and once marched unannounced into Linus Pauling's office in Pasadena. He even landed a job working for the pioneering astronomer, Gerard Kuiper.
His disillusionment with UFOs led him to become an oddly manic critic of pseudoscientists such as Velikovsy or the Scientologists. But his celebrity really began with best-sellers such as Cosmic Connection (1973), and Dragons of Eden, his 1977 book on human intelligence (it won a Pulitzer). His blockbuster 1979 TV series, Cosmos, won him global fame.
In the 1980s, he returned to science-fiction with a novel, Contact (later an awful movie, starring Jodie Foster), about an atheistic scientist whose interstellar journey to meet aliens was ultimately portrayed as a search for love. Although it was howled down as sexist, Davidson reveals this as a feminised, allegorical version of Sagan's idea of himself.
By now, Sagan was also politicised, influenced by his third wife, Ann Druyan. Despite his own early, classified, nuclear-related contracts, he made enemies in the Reagan White House for his promotion of the "nuclear winter" hypothesis.
THE blistering running commentary from other scientists is the most interesting sideshow in the book. Indeed, Sagan was refused tenure at Harvard, and indeed right up to his death (from myelodysplasia) refused admission to the National Academy of Sciences.
Perhaps Sagan's most quixotic exercise was the graphic greeting to extraterrestrials on the Pioneer 10 and 11 space probes, and phonogram discs on Voyagers 1 and 2, carrying images and sounds of earth (Beethoven, Chuck Berry, spoken greetings in many languages) - optimistic space-junk now drifting towards the edge of our galaxy.
With his distaste for lab graft, Sagan was always an ideas man, from his early involvement in a "Mars jar" experiment - irradiating a "primordial atmosphere" in an attempt to produce ATP (the energy-storing molecule inside living cells); to his lifelong collaborations with reputable scientists Jim Pollack, George Mullen and Bishun Khare on planetary atmospheres.
Sagan correctly predicted organic molecules in the atmosphere of Saturn's moon, Titan, but other predictions fared worse: organic matter on the Moon, life-traces on Mars and Jupiter, where he envisaged great Jovian gasbags, grazing the upper atmosphere. His theories of super-intelligent, benevolent, extraterrestrial races are now derided by his first son, a science-writer, as a "replacement for religion".
As such, it comes as no shock, or indeed horror, that Sagan was an enthusiastic marijuana-smoker since the early 1960s, finding it particularly useful when writing. Davidson has an ambiguous relationship with his subject. He does backflips to point up Sagan's acts of generosity, but it's hard to ignore the endless testimonies to Sagan's brashness, arrogance, ruthlessness, sexism and bloated ego - from a raft of former friends, colleagues, two wives, and indeed his first two sons, whose childhoods he largely ignored.
Despite this immediacy, Davidson never gets under the skin of Sagan, a brilliant, multi-millionaire showman who successfully popularised science, yet remained fixated on many wild ideas - in contravention of his own Popperian dictum that no theory can be considered "scientific" unless one can conceive of a way, in principle, to disprove it.
Mic Moroney is a writer, critic and journalist based in Dublin