Table of Contents
Read the Preface
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From Chapter 1:
This is a book about possibilities. It is about the possibility that, within a decade or two, robotic or human explorers will drill into the Martian surface and discover microscopic life in subterranean pockets of liquid water. It is about the possibility of landing spaceborne submarines on Jupiter's moon Europa, where they might melt their way through miles of ice and observe life swimming in a volcanically heated ocean. It is about the possibility of strange, cold-adapted life forms on Saturn's moon Titan, a world on which we have already landed a robotic emissary, despite its being located nearly a billion miles away. It is about the possibility of SETI researchers detecting an unmistakable signal coming to us from a civilization that has grown up around a faraway star. It is about the possibility that we may already be surrounded by a galactic civilization, populated by beings who surpassed our own current level of development millions or even billions of years ago. Most of all, it is about the possibilities that await us, if and when we learn that we are not alone in the universe.
From Chapter 2:
...Let's start with the first [key aspect of science], which happens to lie at the root of the current debate about whether "intelligent design" should be taught in science classes. Proponents of intelligent design claim that life is so intricate and complex that it could not have arisen naturally, and they therefore claim that life must have been deliberately designed by an intelligent Designer. Personally, I find their evidence of design far less than compelling, but that's really beside the point. The real question is whether their idea should qualify as a competing scientific model that could then be taught as an alternative to the theory of evolution. If you accept the usual definition of science, then intelligent design clearly does not qualify, because it violates the first hallmark: Rather than seeking natural causes for life, intelligent design posits that life is the work of a supernatural Designer who is beyond our scientific comprehension. That is why those who want to teach "ID" in science classes (such as the Kansas Board of Education in 2005) have attempted to redefine science so that it does not have to be solely about natural causes.
The trouble with these attempts to redefine the first hallmark is that they would render science pointless. As a simple analogy, consider the collapse of a bridge. If you choose to believe that the collapse was an act of God, you might well be right-but this belief won't help you design a better bridge. We learn to build better bridges only by assuming that collapses happen through natural causes that we can understand and learn from. In precisely the same way, it is the scientific quest for a natural understanding of life that has led to the discovery of relationships between species, genetics, DNA, and virtually all modern medicine. Many of the scientists who made these discoveries, including Charles Darwin himself, believed deeply that they could see God's hand in creation. But if they had let their belief stop them from seeking natural explanations, they would have discovered nothing. Intelligent design may or may not be true, and it may be worth discussing in philosophy classes. But if we allow science to be redefined to accommodate it, we will undermine everything that makes science so successful in advancing human knowledge.
From Chapter 3:
...My knowledge of alien visitors to Earth is actually quite limited. I cannot tell you what they look like, or whether they have arms, legs, and eyes. I cannot tell you what their biochemistry is like, or whether their cells use DNA as genetic material. I don't know what they eat or breathe, or why they might be coming here, if indeed they are. But there's one thing that I can tell you: Technologically speaking, at least, they are very, very smart. If aliens really are visiting Earth and if they are drawing their plans against us-as in the excerpt from The War of the Worlds that opens this chapter-we don't stand a chance.
Now, I can cut a break here for H. G. Wells. The invaders of his novel came from Mars, a planetary neighbor that we ourselves can already reach with robotic spaceships. If there really were intelligent Martians, they wouldn't need to be much more technologically advanced than we are to plot their war against Earth. We'd presumably stand a fighting chance in such an invasion, especially if they had been lax enough in their study of biology to neglect the danger that earthly germs could cause them.
Hollywood doesn't deserve quite so much slack. The recent movie version of The War of the Worlds was vague about where the invaders came from, presumably since we now know that Mars is not home to an advanced civilization. Other movies with Earth invasions have been more direct in showing us fighting for survival against beings from the stars. Sorry, but we'd be squashed like bugs in any such battle, and that's not just my opinion. Rather, it's a conclusion that we can reach by scientifically examining the case for alien visitors, whom we may hope to be much less malicious than Hollywood usually thinks.
From Chapter 4:
You might think that it would be easy to define life, but it's not. Consider a cat and a car, which turn out to have a lot in common. Both require energy to function-the cat gets energy from food, and the car gets energy from gasoline. Both can move at varying speeds and can turn corners. Both expel waste products. But a cat clearly is alive, while a car clearly is not. What's the difference?
In the case of a cat and a car, we can find many important differences without looking too far. For example, cats reproduce themselves, while cars must be built in factories. But as we look deeper into the nature of life, it becomes increasingly difficult to decide what characteristics separate living organisms from rocks and other nonliving materials. Indeed, the question can be so difficult to answer that we may be tempted to fall back on the famous words of U.S. Supreme Court Justice Potter Stewart, who, in avoiding the difficulty of defining pornography, wrote: "I shall not today attempt further to define [it]...But I know it when I see it." If living organisms on other worlds turn out to be much like those on Earth, it may prove true that we'll know them when we see them. But if the organisms are fairly different from those on Earth, we'll need clearer guidelines to decide whether or not they are truly "living."
From Chapter 5:
...The topic of mass extinctions also holds a cautionary lesson for us. Human activity is driving numerous species toward extinction. The best-known cases involve relatively large and wide-ranging animals, such as the passenger pigeon (extinct since the early 1900s) and the Siberian tiger (nearing extinction). But most of the estimated 10 million or more plant and animal species on our planet live in localized habitats, and most of these species have not even been cataloged. The destruction of just a few square kilometers of forest may mean the extinction of species that live only in that area. According to some estimates, human activity is driving species to extinction so rapidly that half of today's species could be gone within a few centuries or less. On the scale of geological time, the disappearance of half the world's species in just a few hundred years would certainly qualify as another of the Earth's mass extinctions, potentially changing the global environment in ways that we are unable to predict. During past mass extinctions, the dominant animal species-those at the top of the food chain-have never made it through to the other side. Today, we are the dominant animal species. Perhaps our intelligence would enable us to find a way to survive while other species perish around us, but I wouldn't count on it. Those who ignore history are doomed to repeat it, and geological history tells us that perpetrating a mass extinction is not in our best interest. Unless we want to be replaced soon by the next dominant animal species-some type of insect, perhaps-then we'd be wise to heed the lesson of the past, and start doing a much better job of preserving the remarkable biodiversity upon which our survival depends.
From Chapter 6:
We live on a planet that is an incredible success, with a self-regulating climate mechanism that has made our existence possible. But we are now messing with success in a serious way. If you want to know how serious, forget all the debates about the rapidity of the warming and of the melting of the ice caps and all that other stuff, and just take a look at the graph in figure 6.6. It shows the change in atmospheric carbon dioxide concentration over the past 400,000 years, based primarily on ice core data for most of this period and on direct measurements for the past few decades. More recently acquired data extend the record back to about a million years ago and show the same basic thing: The carbon dioxide concentration has naturally fluctuated, but for at least the past million years it has never reached anywhere near what we have made it today. You'd have to have your head pretty deeply buried in the sand to look at these data and say there's nothing to worry about.
From Chapter 7:
..., but when I really want to be impressed with human ingenuity I think about this: Titan is nearly a billion miles away from Earth, and we've landed there. That's right; Cassini is an orbiter, but it didn't go to Saturn alone. Attached throughout its journey, it carried a European-built probe named Huygens (after the Dutch scientist Christiaan Huygens). On Christmas Day, 2004, Cassini released the probe, which then spent 21 days coasting through the space around Saturn as it approached Titan. On January 14, 2005, Huygens arrived at Titan, where it plunged into the atmosphere, deployed a series of parachutes, and, after a 2 1/2-hour descent, landed on the surface of this distant world. If you like analogies, just hitting a moon the size of Titan from Earth is the equivalent of shooting a gun and hitting a dime from a distance of 2,500 miles away. Hitting it softly enough to land and take pictures of the surface . . . well, I can't think of any words that would do it justice.
So as you gaze at the surface of Titan (color plate 6), I hope you'll take it as a lesson not only about the possibility of life in our solar system, but about what human beings are capable of when we use our creative powers to build rather than to destroy. It may sound corny, but seeing chunks of ice littering the landscape of Titan gives me hope for the human race.
From Chapter 8:
...Of course, plenty of educated people have participated in the atrocities of the past and present, even though they presumably were taught that Earth is a planet orbiting the Sun. But, personally, I suspect that for these people, the lesson never set in, and they suffer from what I call "center of the universe syndrome." They've never grown up, and like young children they still imagine themselves to be the center of everything. Show me a Saddam Hussein or a Kim Jong-Il or any other petty dictator, and I'll show you a person who suffers from center of the universe syndrome. How else to explain their belief in their own self-importance?...
Getting over center of the universe syndrome is not easy. Some people seem to suffer from it no matter how much they have learned. Incredibly to me, there are even scientists who suffer from it: Apparently, rather than getting a sense of awe and humility from their studies of nature, they become enamored with their own research accomplishments, sometimes to the point of attacking others who may disagree with their conclusions, or denigrating students who they wrongly believe to be intellectually inferior. The syndrome is difficult to beat because we're all born with it, and it's just human nature to want to keep thinking of oneself as somehow special, better, or more important than others. But most of us eventually learn that other people have the same thoughts and feelings as we do, and therefore learn empathy and, with it, the importance of treating our fellow humans with kindness and respect. In other words, most of us eventually grow up.
And that is where the topic of this chapter comes in: The human race is growing up, too. We once thought that this world was all there was, so perhaps it was natural to fight over every piece of it. With the Copernican revolution, we began to realize that there might be more, but how much more remained unknown. Perhaps the first true glimpse of infinity came with Christiaan Huygens, who wrote the passage that I quoted not long after he became the first person to make reasonably accurate estimates of distances to the stars. He was therefore the first to understand, at least with any scientific certainty, that other stars might truly be other suns, orbited by planets and, perhaps, harboring their own life. But this last "perhaps" tells us that we haven't yet matured beyond our adolescence as a species: While we've reached the point where we understand that our world is small and precious to us, we don't yet know if we are members of a larger community. In my opinion, we can't finish growing up unless we continue the effort to find out, one way or the other.
From Chapter 9:
It's true: We cannot hide anymore. For more than seven decades now, we have been broadcasting radio and television transmissions that go beyond Earth's atmosphere and out into space. Once in space, they travel outward at the speed of light. With sufficiently powerful radio telescopes, anyone within about 70 light-years of Earth could now be watching our old TV shows-a somewhat scary thought that might explain why no one wants to visit us. A hundred years from now, our signals will have reached out to 170 light-years from Earth. A hundred thousand years from now, everyone in the galaxy will, at least in principle, have had a chance to learn that we were here, even if we are by then long gone. In that sense, we have already gone beyond making an indelible mark on our planet, for we have made one on the universe.
From Chapter 10:
A couple of chapters back, I offered you words from Christiaan Huygens and Carl Sagan, each explaining how new perspectives on our place in the universe should help us grow up as a civilization. But we have not grown up yet, a sad fact that we are reminded of everyday in the news, as we read about terrorists, hatred, wars, and abject poverty. A grown-up civilization would have learned to do better.
In fact, there's no guarantee that we'll ever grow up. We constantly discover new ideas and develop new technologies that could make the world a better place, but we seem as likely to put them to work for destructive as for constructive ends. Sometimes, when I'm feeling down, I despair that as a species, we just don't care enough to realize our potential, and that centuries from now, archaeologists will sift through the ruins of our civilization and wonder what went wrong. In even deeper moments of angst, I fear that we'll do so much damage to our planet that we'll go the way of the dinosaurs, and it will be millions of years before the Earth sees another set of intelligent beings. In these moments, I think of the art, the music, the dance, the literature, the sports, the science, and the other great things that humans have created...and I'm overcome with sadness at the thought that all would be lost forever.
I share these unhappy thoughts because I think they are important for everyone to contemplate. We need some global guilt. We need for everyone to look at the faces of children, and think about how we'll feel if they grow up in a world in which our civilization is collapsing because we, as individuals and as a society, made the wrong choices. Sometimes, I picture future generations looking back at us, putting us on trial, and judging us for our sins. But then I remember that if we don't change, if we don't learn to grow up, there may be no future generations. There will be no one left to judge us-except perhaps God, who surely would not be pleased-so we must judge ourselves. I think if we all take a hard look at our society today, we'll judge ourselves failures, not because we haven't done a lot of things right, but because we still do too many things wrong. It's only once we recognize our failures that we'll be able to turn them around, and prove ourselves worthy stewards of the incredible good fortune that we have inherited from generations past on this remarkable planet.