The biochemist Leslie Orgel once remarked that “we have no way of knowing anything about the possibility of life in the Cosmos. It could be everywhere, or we could be alone.” But physicist Enrico Fermi put the question more colorfully. If aliens had visited the Earth, he asked, then “Where is everybody?”

In fact, however, American scientists via the government agency NASA spent decades and considerable funds creating spacecraft (probes) to seek out imagined distant civilizations. The project intended to reveal information about Earth and elicit reciprocity. These enthusiasts created the SETI project, abetted by science fiction and UFO interests. The famous Carl Sagan helped develop the now self-deprecating Pioneer plaque, wherein was revealed the DNA of Earthlings, their solar address, and an etching showing that Adam and Eve were astrophysicists. A few years later, on a Voyager probe, grainy and unimpressive (by modern standards) images of plants, animals, and earth objects were added, plus the famous Golden Record, a long play record complete with stylus and phonograph, containing representative Earth music: Beethoven, Mozart, Chuck Berry. In space, we are frozen in time, and any recipient extraterrestrial will wonder what, really, we were thinking as a civilization.

John Gribbin’s book Alone in the Universe is not about philosophy but astronomy, and the quotes of Orgel and Fermi (but not the details about Sagan’s NASA input) are his. The book neatly refutes the cherished late 20th-century myth about extraterrestrial intelligence and the ambitious projects it spawned. Converted to more powerful telescopes, a fraction of that money would have yielded information about gases, liquids, metals, temperatures — the real foundation of information about life. The 1970s-80s obsession with extraterritoriality was the zeitgeist of the Cold War.

Gribbin’s telling evidence starts with the Milky Way, where, in fact, only about 10% of the stars are in the Galactic Habitable Zone, that Goldilocks region of favorable safety (from shooting objects), metals, and evolutionary space and time. Everywhere else in the known universe are fainter stars, hence lower metalicities for sustaining life.

Then one moves to the Solar Habitable Zone, finding liquid water, essential to life as we know it. Here temperatures must be just right (zero to 50 Celsius) — Venus is too hot and Mars too cold. Next comes the Continuously Habitable Zone of Earth, where circular versus elliptical orbit turns out to be crucial. The Sun is 95% less massive and more bright (hence more stable) than 75% of the other stars we know of in the Milky Way, which are red dwarfs already dying, or unstable binaries.

The relationship between Earth and moon is critical because it further stabilizes orbit and gravity, while the Earth itself comprises a magnetosphere via plate tectonics, something absent from virtually all the potential planets of the galaxy. Earth has a strong metallic core, which is hot but both sustains the spectrum of temperatures on its surface and maintains the Earth’s favorable tilt. This balance of elements further includes a cycle of greenhouses gases that sustains the environment that evolved life and human beings on its surface.

Thus the Gaia theory of scientist James Lovelock posited that life on the planet sustains the ongoing cycle, and the ongoing cycle sustains life. Disruptions like the Cambrian Explosion, however, show that this precarious balance is easily disrupted even on Earth, a process which never even evolves (let alone gets disrupted) on other galactic bodies. Life itself is, as Grbbfin puts it, an “extraordinarily rare event.” We are the interplay of extinction and balance, having evolved as the result of a “string of coincidences.” We have been on the planet a short time under the most favorable conditions, conditions never likely to evolve again. Our own doing, as technological civilization threatens the precious balance.

“The biggest threat to technological civilization,” notes Gribbin, “seems to be technological civilization …” assuming that global war does not do us in first. The next biggest long-term threat is an impact from space (Gribbin discussed what past and possible impacts these are or may be). Volcanism is another threat. One may add that with Fukushima, one can see a convergence of such threats quite possible, if not probable. With global climate change, the threat now gives decades left to the fast-receding balance.

So the conclusion that the stars are silent and that we are alone in the universe is not a difficult one to make. This conclusion only makes the book’s subtitle (“Why Our Planet is Unique”) a more urgent notion to reflect upon, for the reasons we are here, says Gribbin, “form a chain so improbable” that the chance of another civilization anywhere in the Milky Way or beyond is “vanishingly small.”

In both Hinduism and Buddhism, a kalpa is an eon of time — 4 billion years or 16 billion years, depending on the tradition. We now know that that is long time, enjoying a better sense of time from modern physics and astronomy. But even the traditional calculation could not fathom the complexity of the universe except to say — as says the Dalai Lama among others — that to be born a human being is the rarest event in the universe. And so it is. Thus realization that we are “alone in the universe” becomes a mirror to our solitary lives in society, culture, and what was called “the world.” And so we are.