Well, even if our position, our epoch, our motion, and our world are not unique, maybe we are. We're different from the other animals. We're specially created. The particular devotion of the Creator of the Universe is evident in us. This position was passionately defended on religious and other grounds. But in the middle nineteenth century Charles Darwin showed convincingly how one species can evolve into another by entirely natural processes, which come down to the heartless business of Nature saving the heredities that work and rejecting those that don't. "Man in his arrogance thinks himself a great work worthy [of] the interposition of a deity," Darwin wrote telegraphically in his notebook. "More humble and I think truer to consider him created from animals." The profound and intimate connections of humans with the other life forms, on Earth have been compellingly demonstrated in the late twentieth century by the new science of molecular biology.
IN EACH AGE the self-congratulatory chauvinisms are challenged in yet another arena of scientific debate—in this century, for example, in attempts to understand the nature of human sexuality, the existence of the unconscious mind, and the fact that many psychiatric illnesses and character "defects" have a molecular origin. But also:
Well, even if we're closely related to some of the other animals, we're different—not just in degree, but in kind—on what really matters: reasoning, selfconsciousness, tool making, ethics, altruism, religion, language, nobility of character. While humans, like all animals, have traits that set them apart—otherwise, how could we distinguish one species from another?—human uniqueness has been exaggerated, sometimes grossly so. Chimps reason, are self-conscious, make tools, show devotion, and so on. Chimps and humans have 99.6 percent of their active genes in common. (Ann Druyan and I run through the evidence in our book Shadows of Forgotten Ancestors.)
In popular culture, the very opposite position is also embraced, although it too is driven by human chauvinism (plus a failure of the imagination): Children's stories and cartoons make animals dress in clothes, live in houses, use knives and forks, and speak. The three bears sleep in beds. The owl and the pussycat go to sea in a beautiful pea-green boat. Dinosaur mothers cuddle their young. Pelicans deliver the mail. Dogs drive cars. A worm catches a thief. Pets have human names. Dolls, nutcrackers, cups, and saucers dance and have opinions. The dish runs away with the spoon. In the Thomas the Tank Engine series, we even have anthropomorphic locomotives and railway cars, charmingly portrayed. No matter what we're thinking about, animate or inanimate, we tend to invest it with human traits. We can't help ourselves. The images come readily to mind. Children are clearly fond of them.
When we talk about a "threatening" sky, a "troubled" sea diamonds "resisting" being scratched, the Earth "attracting" passing asteroid, or an atom being "excited," we are again drawn to a kind of animist worldview. We reify. Some ancient level of our thinking endows inanimate Nature with life, passions, and forethought.
The notion that the Earth is self-aware has lately been growing at the fringes of the "Gaia" hypothesis. But this was commonplace belief of both the ancient Greeks and the earl Christians. Origen wondered whether "the earth also, according to its own nature, is accountable for some sin." A host of ancient scholars thought the stars alive. This was also the position of Origen, of St. Ambrose (the mentor of St. Augustine), and even, in a more qualified form, of St. Thomas Aquinas. The Stoic philosophical position on the Sun's nature was stated by Cicero, in the first century B.C.: "Since the Sun resembles those fires which are contained in the bodies of living creatures, the Sun must also be alive."
Animist attitudes in general seem to have been spreading recently. In a 1954 American survey, 75 percent of people polled were willing to state that the Sun is not alive; in 1989, only 30 percent would support so rash a proposition. On whether an automobile tire can feel anything, 90 percent of respondents denied it emotions in 1954, but only 73 percent in 1989.
We can recognize here a shortcoming—in some circumstances serious—in our ability to understand the world. Characteristically, willy-nilly, we seem compelled to project our own nature onto Nature. Although this may result in a consistently distorted view of the world, it does have one great virtue—projection is the essential precondition for compassion.
Okay, maybe we're not much, maybe we're humiliatingly related t0 apes, but at least we're the best there is. God and angels aside, we're the only intelligent beings in the Universe. One correspondent writes to me, "I am as sure of this as anything in my experience. There is no conscious life anywhere else in the Universe. Mankind thus returns to its rightful position as center of the universe." However, partly through the influence of science acid science fiction, most people today, in the United States at least, reject this proposition—for reasons essentially stated by the ancient Greek philosopher Chrysippus: "For any human being in existence to think that there is nothing in the whole world superior to himself would be an insane piece of arrogance."
But the simple fact is that we have not yet found extraterrestrial life. We are in the earliest stages of looking. The question is wide open. If I had to guess—especially considering our long sequence of failed I would guess that the Universe is filled with beings far more intelligent, tar more advanced than we are. But of course I might be wrong. Such a conclusion is at best based on a plausibility argument, derived from the numbers of planets, the ubiquity of organic matter, the immense timescales available for evolution, and so on. It is not a scientific demonstration. The question is among the most fascinating in all of science. As described in this book, we are just developing the tools to treat it seriously.
What about the related matter of whether we are capable of creating intelligences smarter than ourselves? Computers routinely do mathematics that no unaided human can manage, outperform world champions in checkers and grand masters in chess, speak and understand English and other languages, write presentable short stories and musical compositions, learn from their mistakes, and competently pilot ships, airplanes, and spacecraft. Their abilities steadily improve. They're getting smaller, faster, and cheaper. Each year, the tide of scientific advance laps a little further ashore on the island of human intellectual uniqueness with its embattled castaways. If, at so early a stage in our technological evolution, we have been able to go so far in creating intelligence out of silicon and metal, what will be possible in the following decades and centuries? What happens when smart machines are able to manufacture smarter machines?
PERHAPS THE CLEAREST INDICATION that the search for an unmerited privileged position for humans will never be wholly abandoned is what in physics and astronomy is called the Anthropic Principle. It would be better named the Anthropocentric Principle. It comes in various forms. The "Weak" Anthropic Principle merely notes that if the laws of Nature and the physical constants—such as the speed of light, the electrical charge of the electron, the Newtonian gravitational constant, or Planck's quantum mechanical constant had been different, the course of events leading to the origin of humans would never have transpired. Under other laws and constants, atoms would not hold together, stars would evolve too quickly to leave sufficient time for life to evolve on nearby planets, the chemical elements of which life is made would never have been generated, and so on. Different laws, no humans.
There is no controversy about the Weak Anthropic Principle: Change the laws and constants of Nature, if you could, and a very different universe may emerge—in many cases, a universe incompatible with life.* The mere fact that we exist implies (but does not impose) constraints on the laws of Nature. In contrast, the various "Strong" Anthropic Principles go much farther; some of their advocates come close to deducing that the laws of Nature and the values of the physical constants were established (don't ask how or by Whom) so that humans would eventually come to be. Almost all of the other possible universes, they say, are inhospitable. In this way, the ancient conceit that the Universe was made for us is resuscitated.
* Our universe is almost incompatible with life—or at least what we understand as necessary for life: Even if every star in a hundred billion galaxies had an Earthlike planet, without heroic technological measures life could prosper in only about 10-37 the volume of the Universe. For clarity, let's write it out: only 0.000 000 000 000 000 000 000 000 000 000 000 000 1 of our universe is hospitable to life. Thirty-six zeroes before the one. The rest is cold, radiation-riddled black vacuum.
To me it echoes Dr. Pangloss in Voltaire's Candide, convinced that this world, with all its imperfections, is the best possible. It sounds like playing my first hand of bridge, winning, knowing that there are 54 billion billion billion (5.4 X 1028) possible other hands that I was equally likely to have been dealt . . . and then foolishly concluding that a god of bridge exists and favors me, a god who arranged the cards and the shuffle with my victory foreordained from The Beginning. We do not know how many other winning hands there are in the cosmic deck, how many other kinds of universes, laws of Nature, and physical constants: that could also lead to life and Intelligence and perhaps even delusions of self-importance. Since we know next to nothing about how the Universe was made—or even if it was made—it's difficult to pursue these notions productively.
Voltaire asked "Why is there anything?" Einstein's formulation was to ask whether God had any choice in creating the Universe. But if the Universe is infinitely old—if the Big Bang some 15 billion years ago is only the most recent cusp in an infinite series of cosmic contractions and expansions—then it was never created and the question of why it is as it is is rendered meaningless.
If, on the other hand, the Universe has a finite age, why is it the way it is? Why wasn't it given a very different character? Which laws of Nature go with which others? Are there meta-laws specifying the connections? Can we possibly discover them? Of all conceivable laws of gravity, say, which ones can exist simultaneously with which conceivable laws of quantum physics that determine the very existence of macroscopic matter? Are all laws we can think of possible, or is there only a restricted number that can somehow be brought into existence? Clearly we have not a glimmering of how to determine which laws of Nature are "possible" and which are not. Nor do we have more than the most rudimentary notion of what correlations of natural laws are "permitted."
For example, Newton's universal law of gravitation specifies that the mutual gravitational force attracting two bodies towards each other is inversely proportional to the square of how far they are apart. You move twice as far from the center of the Earth and you weigh a quarter as much; ten times farther and you weigh only a hundredth of your ordinary weight; etc. It is this inverse square law that permits the exquisite circular and elliptical orbits of planets around the Sun, and moons around the planets—as well as the precision trajectories of our interplanetary spacecraft. If r is the distance between the centers of two masses, we say that the gravitational force varies as 1/r2.
But if this exponent were different—if the gravitational law were 1/r4, say, rather than 1/r2 —then the orbits would not close; over billions of revolutions, the planets would spiral in and be consumed in the fiery depths of the Sun, or spiral out and be lost to interstellar space. If the Universe were constructed with an inverse fourth power law rather than an inverse square law, soon there would be no planets for living beings to inhabit.
So of all the possible gravitational force laws, why are we so lucky as to live in a universe sporting a law consistent with life? First of course, we're so "lucky," because if we weren't, we wouldn't be here to ask the question. It is no mystery that inquisitive beings who evolve on planets can be found only in universes that admit planets. Second, the inverse square law is not is the only one consistent with stability over billions of years. Any power law less steep than 1/r3 (1/r2.99 or 1/r, for example) will keep a planet in the vicinity of a circular orbit even if it's given a shove. We have a tendency to overlook the possibility that other conceivable laws of Nature might also be consistent with life.
But there's a further point: It's not arbitrary that we have an inverse square law of gravitation. When Newton's theory is understood in terms of the more encompassing general theory of relativity, we recognize that the exponent of the gravity law is 2 because the number of physical dimensions we live in is 3. All gravity laws aren't available, free for a Creator's choosing. Even given an infinite number of three-dimensional universes for some great god to tinker with, the gravity law would always lave to be the law of the inverse square. Newtonian gravity, we might say, is not a contingent facet of our universe, but a necessary one.
In general relativity, gravity is due to the dimensionality and curvature of space. When we talk about gravity we are talking about local dimples in space-time. This is by no means obvious and even affronts commonsense notions. But when examined deeply, the ideas of gravity and mass are not separate matters, but ramifications of the underlying geometry of space-time.
I wonder if something like this doesn't apply generally to all anthropic hypotheses. The laws or physical constants on which our lives depend turn out to be members of a class, perhaps even a vast class, of other laws and other physical constants—but some of these are also compatible with a kind of life. Often we do not (or cannot) work through what those other universes allow. Beyond that, not every arbitrary choice of a law of Nature or a physical constant may be available, even to a maker of universes. Our understanding of which laws of Nature and which physical constants are up for grabs is fragmentary at best.
Moreover, we have no access to any of those putative alternative universes. We have no experimental method by which anthropic hypotheses may be tested. Even if the existence of such universes were to follow firmly from well-established theories—of quantum mechanics or gravitation, say—we could not be sure that there weren't better theories that predict no alternative universes. Until that time comes, if it ever does, it seems to me premature to put faith in the Anthropic Principle as an argument for human centrality or uniqueness.
