|The Search for Extraterrestrial Life|
The question that won’t go away
It’s the question that will never go away: Are we alone in the universe? These days, when most people ask that question, they’re not asking whether God or angels exists, but whether there is life—intelligent life—on a planet other than Earth.
Just a few decades ago, many scientists believed there was intelligent life on Mars, since it seems so similar to Earth. Scientific discoveries have chastened our expectations, however, so we’re now reduced to looking for evidence of liquid water—merely a necessary condition for life—on the Martian surface.
For decades now, we’ve also been searching the skies beyond our solar system for telltale signals of intelligent life. So far, we haven’t found any.
Nothing special about earth?
Yet the expectation that life is common in the universe lives on. Why? Among scientists, at least, it comes not so much from scientific evidence as from an assumption called the Copernican Principle. From a Christian perspective, of course, God is free to create a universe teeming with life or a universe in which life is rare. So we can just follow the evidence. But the Copernican Principle tends to prejudge the answer. As an offshoot of the materialistic worldview, it assumes that there’s nothing special about Earth. So whatever happened here must have happened countless times elsewhere.
For decades, however, the scientific evidence has stubbornly pointed in the opposite direction. We continue to learn how much must go right to a get just one habitable planet. The list gets longer all the time. Complex life in particular probably needs many of the things that we Earthlings enjoy: a rocky terrestrial planet much like the Earth, with plate tectonics to recycle nutrients and the right kind of atmosphere; a large, well placed moon to contribute to tides and stabilize the tilt of the planet’s axis. The planet needs to be just the right distance from the right kind of single star, in a nearly circular orbit—to maintain liquid water on its surface.
It also needs a home within a stable planetary system that includes some outlying giant planets to protect the inner system from too many deadly comet impacts. That planetary system must be nestled in a safe neighborhood in the right kind of galaxy, with enough heavy elements to build terrestrial planets. And that planet will need to form during the narrow habitable window of cosmic history. (This is to say nothing of having a universe with a fine-tuned set of physical laws and constants to make stars, planets, and people possible in the first place. But that’s another long and complicated story.)
Starting in the mid-1990s, astronomers began detecting planets around other Sun-like stars. And they have taught us an important, if unadvertised, lesson. Planetary systems are not all alike. In fact, mounting evidence suggests that the conditions needed for complex life are exceedingly rare.
Initially, you might think that such a precise configuration of life-friendly factors suggests that Earth is part of some cosmic design. But some scientists familiar with this evidence now argue that while the conditions that allow for complex life may be highly improbable, perhaps even unique to Earth, these conditions are still nothing more than a fluke. The universe, after all, is a big place, with some 1022 stars in the part we can see. With so many opportunities, maybe at least one habitable planet will turn up just by chance.
Notice that even though the evidence contradicts the Copernican Principle, the materialist assumptions that inspired it remain in place.
But what if we’re not merely the winners of a blind cosmic lottery? What if our existence is the result of a conspiracy rather than a coincidence? Is there any way we could tell? In The Privileged Planet, Guillermo Gonzalez and I argue that there is. It turns out that the same rare, finely tuned conditions that allow for intelligent life on Earth also make it strangely well suited for viewing, analyzing and discovering the universe around us.
The fact that we inhabit a terrestrial planet with a clear atmosphere and water on its surface; that our moon is just the right size and distance from Earth to stabilize the tilt of Earth’s rotation axis; that the size and shape of the moon and sun match in our sky; that our position in our large spiral galaxy is just so; that our sun is its precise mass and composition: all of these and many more are not only necessary for Earth’s habitability; they also have been surprisingly crucial for scientists to discover the universe.
Those rare pockets of habitability in our universe are also the best overall places for scientific discovery. This is surprising because there’s no reason to assume that the very same rare properties that allow for observers would also provide the best overall setting for observing the world around them. We think the evidence for this “correlation between life and discovery” forms a pervasive and telling pattern, a pattern that not only contradicts the Copernican Principle, but also suggests that the universe, whatever else it is, is designed for discovery.
Nevertheless, the quixotic search for alien life of any kind goes on despite the sorry showing of the Copernican Principle. I think there are three big reasons for this. First, scientists are now acutely aware of how difficult it would be for life to have emerged spontaneously from a pre-biotic soup on the early Earth. The chasm between early Earth chemistry and a reproducing cell is immensely wide and deep. To get around the harsh improbabilities, many now hope to find evidence that life originally came from elsewhere and simply prospered in Earth’s friendly environment. Any evidence of life-friendly extraterrestrial locations would help support this idea.
Second, there’s an anti-religious motivation. Some prominent advocates of SETI—the Search for Extraterrestrial Intelligence—mistakenly claim that finding life elsewhere will deal a decisive blow to traditional religious belief.
Third, for many of its advocates, the search for advanced alien life serves as a spiritual surrogate. They hope that knowledge, moral guidance, and even immortality may come to us, if not from heaven, then at least from the heavens. Since the search for extraterrestrial life is often motivated, ironically, by both materialist philosophy and a spiritual longing, it’s unlikely to diminish anytime soon.