Humans have had quite a ride in the 500 years since Copernicus. We've built and tested a rational vision of the universe in which our circumstances, and those of the Earth, are unexceptional and insignificant in the grand scheme of things. We are fleeting specks on a crumb of cosmic dust, among countless other crumbs in the briefest sliver of a far bigger story.
This perspective has guided us to the innermost sanctums of matter and to the origins and nature of space and time itself — an expanding fabric that has no spatial center, in which all places are shining examples of unimportance.
Except our great hominid egos have always nagged at us, resisting the soothing embrace of cosmic mediocrity, looking for excuses to be special. Surprisingly, science has now come across reasons to think that life, and life on Earth in particular, may not be quite so ordinary after all. It might be a rare albeit accidental gem. Its presence could even offer clues to the deeper functioning of the universe.
There is now a burgeoning, supremely ambitious scientific endeavor to answer the gem-versus-common speck question by seeking life elsewhere in the cosmos. The outcome of this quest will influence not just our perception of the nature of existence but also the way in which our species chooses to make use of its time.
A piece of the puzzle emerged in the 1970s, when physicists pointed out the apparently coincidental alignment of fundamental properties of the universe and the requirements of living organisms. We live, for example, in a cosmos that makes and disperses plenty of the element carbon, the central piece of known biochemistry. We also live in a galactic landscape of stars that's neither too sparse nor too crowded, and we live at a time when the universe has cooled but not yet succumbed to thermodynamic extinction. If nature's forces were tuned just a little differently, all these things would change, and life might not have ever occurred.
If the universe is the one and only such reality, it's disquieting that it would be tuned this way, because life — even if there is only a single instance — is also providing predictive information about physics. In other words, "anthropic" reasoning leads to a suspicion that there is indeed something special about us.
However, theoretical physics and cosmology have come up with a possible answer to that. If our reality is merely one of a vast number of universe-like phenomena — part of a multiverse — we naturally find ourselves in a type of universe that allows for life. The catch is that no multiverse theory can yet tell us how much life there should be in a given cosmos — how exceptional life on Earth is.
Clues may be emerging from more parochial directions. The remarkable new science of exoplanets — worlds orbiting other stars — is at this frontline. On the face of it, the discovery of a wealth of exoplanets simply verifies the doctrine of mediocrity that Copernicus helped seed. We're surrounded by billions of planetary systems that could, in principle, play host to life.
But exoplanets are incredibly diverse, ranging from giant balls of gas to small rocky worlds and large super-Earths, the likes of which don't exist around the Sun. Their configurations also come in an unanticipated range: from tightly packed clusters of planets to systems with highly elliptical orbits and histories of playing gravitational dodgem. And the types of stars that harbor planets include those that are far more numerous than the family the Sun belongs to.
By these measures, in very crude terms, our solar system is somewhat unusual. Is there a connection to the presence of life here? Is this a clue to the fertility of the cosmos? It could be.
The story of biological evolution on Earth may also hold important lessons about what we can expect elsewhere. A seemingly improbable merger of two single-celled organisms here gave rise to complex cells containing the marvelous little power generators, mitochondria. Otherwise there would be no animals, no insects, birds, fish, reptiles, fungi, sponges or celebrities. Some biologists argue that the low likelihood of this microbial tango implies that a similar step could happen only in very, very few life-bearing planets across the universe. Once again, life that is like us could be the exception rather than the rule.
Yet this might be just a cautionary tale of how we make inferences. Events can take on new meanings after the fact. For example, when something lucky takes place — a winning lottery ticket, for instance — we can always trace the history of small choices leading to that point. Except that history becomes relevant only in retrospect — the snap decision to play, a number that sticks in your head — regardless of whether the end product is actually rare or common.
Speculation has almost had its day, though. The solution to understanding life's cosmic status is at hand. Whether it's through the eyes of a robot on Mars, the probing of a dark ocean on the moon Europa, or in the telltale chemical imbalances seen on a distant exoplanet, the hunt is afoot. The challenges are extreme, but scientists' efforts to count the instances of biological origins across the galaxy will yield an empirical — not philosophical — answer. It will let us crack the puzzle open.
Discovering that cosmic context is an old ambition made new. It comes as we find ourselves living in our own planetary filth. It has the potential to teach us much about our future prospects. Being exceptional would have little value if we choose to remain carelessly and perilously locked to the Earth. Whatever else we are, we are the first arrivals at this particular horizon — whether or not we cross it is entirely up to us.
Caleb Scharf is director of astrobiology at Columbia University and author of "The Copernicus Complex" and "Gravity's Engines."