But our telescopic survey of the heavens, with the Hubble telescope, the Kepler and numerous ground-based observatories, has failed to detect anything that looks artificial, much less pick up any signals or messages.
Geoff Marcy, the University of California at Berkeley astronomer who has found scores of exoplanets, and who has diligently searched for signs of anything artificial in the data, says the silence is significant: “If our Milky Way Galaxy were teeming with thousands of advanced civilizations, as depicted in science-fiction books and movies, we would already know about them. They would be sending probes to thousands of nearby stars. They would have a galactic Internet composed of laser beams at various wavelengths shooting in all directions, like a museum security system. They would reveal enormous infrared waste heat from their vast energy usage.”
For his part, Tyson says, “I think life may be as plentiful as [Sagan] suggested, but I’m more skeptical about what he’s calling civilizations. But this is a matter of flavor, of how you interpret the data.”
Sagan readily acknowledged that he did not have evidence of extraterrestrial life, much less intelligence. It is a measure of his devotion to scientific reason that he was willing to admit, to the end of his days, that he still didn’t have the goods, that he still hadn’t found what he’d been looking for.
In December I attended the Sagan Lecture at the fall meeting of the American Geophysical Union, in San Francisco. The speaker was the planetary scientist David Grinspoon. He had grown up calling Sagan “Uncle Carl.” His father, Harvard psychiatry professor Lester Grinspoon, was Sagan’s best friend. The younger Grinspoon delivered a fascinating talk that, in the gentlest of ways, demolished one of the central tenets of Sagan’s worldview.
Sagan had talked of the “great demotions.” Humanity had learned, painfully, that it did not live on a planet at the center of the universe, and further demotions followed. We were not (in Sagan’s view) the purpose of the Creation, not specially chosen by a divine authority, and were in fact just one evolutionary twist in a complicated biosphere shaped by the mindless process of natural selection. If we were ever to make contact with another intelligent species, those aliens would in all probability be smarter, because they’d be older, more advanced, just as a statistical likelihood. Sagan’s view of human ordinariness was framed as the “principle of mediocrity.”
But here was the younger Grinspoon talking about the Anthropocene—the idea that human beings are changing the Earth so rapidly and dramatically that our presence is becoming part of the geological record. And we can’t pretend it’s not happening. We have to learn to manage this place. Grinspoon made an analogy: It’s as though we’ve just awoken to the fact that we’re at the wheel of a speeding bus on an unfamiliar road. And we realize we don’t know how to drive.
“We have to figure out how to drive this thing in order to avoid catastrophe,” Grinspoon said. Doesn’t this sound, he said, as if we’re giving ourselves a “great promotion”?
“Yes, kind of, we are, and it is disturbing,” meaning we are not cosmically inconsequential after all—we’re planet-changers. “But really the point of science is not to comfort ourselves with stories that make us feel good,” he said. “Science can’t ignore the Anthropocene because the Earth is becoming unrecognizable from what it was before we became a geological force.”
Would Sagan have been able to square his great demotions with this new Anthropocene concept? Of course. The universe isn’t about us. The Earth is but a grain of sand. But upon this humble rock we will make our stand. It’s a task that will require science and reason—but also courage and far-sightedness. So it is that Grinspoon says of his old “Uncle Carl”: “Lord knows we need him now.”