John Gribbin, Astrophysicist. If we destroy ourselves, a grave injustice to the universe

Below are a few paragraphs from Hirshfeld’s excellent book review of:    John Gribbin. 2011. Alone in the Universe: Why Our Planet Is Unique.

Humans are a miracle of blood, bone, and brain, a volatile mixture of compassion and brutality whose most enduring accomplishment is the acquisition of knowledge about our world. We occupy a unique position in the cosmic scheme of things. Having crowned humanity as the apex of galactic intelligence, Mr. Gribbin warns that there is no second chance: If we destroy ourselves, we will have done a grave injustice to the universe, removing perhaps the only means it has to ponder itself.

As John Gribbin points out in his grimly plausible book, “Alone in the Universe,” there is a world of difference between habitable planets and inhabited planets. The author’s conclusion: Earth is the sole abode of intelligent life in the galaxy, the product of a profoundly improbable sequence of cosmic, geologic and climatic events—some thoroughly documented, some inferable from fragmentary evidence—that allowed our planet to become a unique refuge where life could develop to its full potential.

One consequence of Earth’s tumultuous youth was the thinning of its rocky crust. This has provided the planet with a lively tectonic existence, complete with vapor-spewing volcanoes, continents that divide and drift, and an ecologically advantageous global-temperature-regulation system. Earth’s swollen metallic core remained liquid; its constant churning gives rise to electrical currents that generate a far-flung magnetic cocoon that shields us from dangerous solar particles. (The creation of Eden is far more complex than one might have heard.)

Another fortuitous coincidence on Mr. Gribbin’s checklist is the moon’s large size relative to Earth, a ratio unique in the solar system. Without such a gravitational partner to restrain the disrupting tugs of the sun and Jupiter, our planet might suffer paroxysms of axis-tilting. (Try to run a civilization when your once-temperate hemisphere suddenly heels over to an Arctic orientation.)

Mr. Gribbin admits the possibility —even probability—that elementary life forms have arisen elsewhere in the galaxy. But the object of his scientific and statistical scrutiny is intelligent extraterrestrial life. While he cannot prove a galaxy-wide absence of other civilizations, he presents an array of modern, research-based evidence that renders that conclusion eminently reasonable. He even suggests a decades-long survey of infrared emissions around stars (possibly arising from planetary atmospheres, even water vapor). This would yield the true number of “wet-Earth” planets in the galaxy—in his estimation, zero.

One leg of Mr. Gribbin’s argument rests on the theorized life expectancy of advanced civilizations, which he claims is much more fleeting, on a cosmic timescale, than we care to admit. Our species has inhabited this planet for about one hundred-thousandth the age of the galaxy, and it was merely a century ago that we began to transmit radio waves. If technological civilizations did arise before ours, they might have succumbed to war or environmental degradation well before our primate ancestors stood upright.

The rosy alternative—a long-surviving society—seems even less plausible. With millions of years of technological advancement, why haven’t they migrated throughout the galaxy by now? Or why haven’t we picked up the least shred of their radio-wave chatter? Of course, Mr. Gribbin dismisses such questions: These purported civilizations never existed.

Our civilization’s own halting steps into outer space so far suggests an uncertain future for the exploration or colonization of extrasolar worlds. The idea that we—or our robotic avatars—might be the first species to traverse the galaxy presumes a fundamental change in space propulsion, which at present (except in Hollywood) is unsuited to cosmic distances.

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