Where Is Everybody?
Perhaps my favorite essay in Aliens: The World’s Leading Scientists on the Search for Extraterrestrial Life is by the astrobiologist Lewis Dartnell, who patiently explains why aliens would not come here to have sex with us or eat us for supper.
I can only assume that he gets these questions a lot.
Here are the answers, should you find these possibilities concerning: The likelihood that we’d be genetically compatible with aliens is terribly remote, which means that they’d almost certainly be immune to our sexual charms. For similar reasons, having to do with biochemistry, we’d be lousy refreshments for them—they would almost certainly lack the proper enzymes to digest us.
As a bonus, Dartnell goes on to reassure us why aliens wouldn’t be especially interested in raiding our planet for raw materials, either (asteroids are a far easier source to mine); and if it were water they were after, they’d be far better off going to Europa, one of Jupiter’s largest moons, which contains more water beneath its icy shell than all the oceans on Earth combined.
If you’re interested in non-Earthly life, don’t look to the movies, is his point.
You could argue that that’s the general point of this modest, eccentric collection. Jim Al-Khalili, a quantum physicist and the editor of Aliens, opens with a question asked by Enrico Fermi in 1950: If the universe is so vast, and its age so old, and its stars so plentiful, where is everybody?
I’m no marketing expert, but “Where Is Everybody?” strikes me as a far catchier title for this book than the one it has, and it’s definitely more accurate. There really is nobody—so far—to write about. (Fighting words, I know. My hands hovered, spaceshiplike, for several minutes over the keyboard before committing that sentence to print.) This doesn’t mean that life elsewhere doesn’t exist. But it probably corresponds very little to what most of us have in mind, and not at all to the ooze-covered beasts of Ridley Scott’s electric dreams.
One of the most consistent takeaways from this anthology is just how banal extraterrestrial life might be. Often, when entertaining the possibility of aliens, what we’re really entertaining is the possibility of hardy microbes that can withstand extreme conditions, whether they’re thermophiles (heat lovers), psychrophiles (cold lovers) or halophiles (salt lovers). Read enough of Aliens, and you realize that the search for life is just as much about the most mundane aspects of biology as about the trippier questions of cosmology.
But it is also about philosophy. In this search, it helps to know what life is. Yet there’s no consensus about how to answer this question, strangely. (At the risk of being too Clintonian, it depends on what your definition of “is” is.)
Nor do we know how life began. At some point, the Earth made the transition from chemistry to biology, yes, but we cannot “agree on a definition that separates the nonliving chemistry from life,” as the geneticist Johnjoe McFadden puts it. (He then paraphrases the astronomer Fred Hoyle, who famously said that the odds of assembling something like a bacterium out of the primordial ooze were akin to the odds of a tornado’s assembling a jumbo jet out of a junkyard heap as it sweeps through.)
There are scientists who will go so far as to say that life is a spectacular fluke. Not everyone, mind you: Researchers now estimate that there are one billion Earthlike exoplanets in the Milky Way. “To my mathematical brain, the numbers alone make thinking about aliens perfectly rational,” Stephen Hawking has said.
But a powerful essay by the evolutionary biologist Matthew Cobb will make you wonder whether any form of multicellular life is far less likely than one in a billion. He points out that “there are more single-celled organisms alive on Earth than there are Earthlike planets in the observable universe”; that the number of single-celled organisms that have lived on this planet over the course of 3.8 billion years is beyond calculation; that these organisms have interacted “gazillions” of times (I love it when words of the appropriate magnitude desert even the experts). Yet we’ve never had a second instance of eukaryogenesis—that remarkable moment when one unicellular life form lodged inside another, forming something much more complex—in all this time.
Of course, there are researchers who dispute this theory and Cobb’s reasoning. But you get the idea.
The experience of reading almost any anthology is a bit like traveling across the country in a rental car with only an FM radio for company. Sometimes you get Sinatra; other times you get Nickelback.
This collection has its share of Nickelback. One of its most disappointing essays is about aliens in science fiction, which manages, against stupefying odds, to contain just one interesting insight: that authors tend to be more concerned with physics than with biology. (How did those gigantic sandworms evolve on the desert planet in Dune?)
But the best of these essays are far out in more ways than one. The very first, by the cosmologist Martin Rees, notes that our best hope for interstellar travel isn’t as humans, who don’t live very long and require far too much fuel to get very far, but as post-humans, who will have made the Kurzweilian transition from organic to inorganic, from decaying mortals to silicon-based, eminently portable machines. He adds that alien intelligence, if we ever detect it, will also be in this form.
The final essay, by Seth Shostak, a senior astronomer at the SETI institute (short for Search for Extraterrestrial Intelligence), goes even further, saying that if we really want to be attuned to alien life in the cosmos, it’s so likely to be in the form of machine intelligence that we ought to “be alert to apparent violations of physics.”
These forms of life may well be speaking to us even now. It’s just that our radio telescopes, which listen to the skies for signals from alien beings, can’t understand what they’re hearing. “Even if the search succeeded,” Rees writes, “it would still in my view be unlikely that the ‘signal’ would be a decodable message.”
It’s a whole new twist on George Berkeley’s question. The tree would fall in the forest. We’d hear it. But it would sound nothing like a tree.
 See Jennifer Senior, “‘Aliens’ Asks: If the Universe Is So Vast, Where Is Everybody?”, New York Times (May 24, 2017). This article is review of the book: Al-Khalili, Jim(2007). ALIENS :The World’s Leading Scientists on the Search for Extraterrestrial Life. New York: Picador. Follow Jennifer Senior on Twitter: @jenseniorny. A version of this review appears in print on May 25, 2017, on Page C2 of the New York edition with the headline: “I Think It’s Gonna Be a Long, Long Time.” Downloaded May 26, 2017
 Scott is a South African born movie director of sci-fi films, including Alien, and The Martian.