It’s mildly batty to search for radio signals, sent intentionally or not, from what may be a very advanced civilization, he writes, because even Earth’s own radio output is already beginning to fade. Radio signals are outdated technology, nearly as sun-bleached as an old issue of Omni magazine. (E. T. surely has cable by now.) And because even a nearby alien civilization would probably be some 1,000 light-years away, conversation is just about impossible. Even if this distant civilization could spy on us, here’s what they’d see right now: Earth about 1010, long before the Industrial Revolution.

Image Paul Davies Credit... Dave Tevis/Tevis Photographic

Mr. Davies’s arguments in “The Eerie Silence” are multiple and many-angled, and difficult to summarize here. But among other things, he thinks we need to pay as much attention to Earth as we do to the cosmos. If we can find evidence that life began from scratch more than once on our own planet  a “second genesis”  it would vastly increase the odds that the universe is teeming with life. What’s more, because it’s as likely that alien civilizations visited Earth a million years ago as last month, they might have already been here, and we’ve missed the signs.

When we do look up at the stars, we should squint hard at things that, in Mr. Davies’s words, “look fishy” or out of context. In other words, we should try to “identify signatures of intelligence through the impact that alien technology makes on the astronomical environment.”

Should aliens actually arrive on Earth, forget the whole “take me to your leader” business. Looking at the future of human intelligence, Mr. Davies projects and argues that alien life would probably be postbiological.

“In a million years, if humanity isn’t wiped out before that, biological intelligence will be viewed as merely the midwife of ‘real’ intelligence  the powerful, scalable, adaptable, immortal sort that is characteristic of the machine realm.”

By the same token, he adds, “Should we ever make contact with E. T., we would not be communicating with Mekon-like humanoids, but with a vastly superior, purpose-designed information-processing system.” It’s not that far-fetched, Mr. Davies writes, that E. T. will log on to the Internet. Take me to your WiFi hot spot.

The best sections of “The Eerie Silence” are those that deal with the effect a signal from another civilization would have on humans. About this signal, Mr. Davies asks, “How and by whom would it be evaluated?” and “How would the public get to learn about it?” (From TMZ or WikiLeaks, wouldn’t you think?)