sent dozens of ships to more than seventy worlds； and four spacecraft to the stars。 We are right to rejoice in our acplishments； to be proud that our species has been able to see so far； and to judge our merit in part by the very science that has so deflated our pretensions。
To our ancestors there was much in Nature to be afraid of—lightning； storms； earthquakes； volcanos； plagues； drought； long winters。 Religions arose in part as attempts to propitiate and control； if not much to understand； the disorderly aspect of Nature。 The scientific revolution permitted us to glimpse an underlying ordered Universe in which there was a literal harmony of the worlds （Johannes Kepler's phrase）。 If we understand Nature； there is a prospect of controlling it or at least mitigating the harm it may bring。 In this sense； science brought hope。
Most of the great deprovincializing debates were entered into with no thought for their practical implications。 Passionate and curious humans wished to understand their actual circumstances； how unique or pedestrian they and their world are； their ultimate origins and destinies； how the Universe works。 Surprisingly； some of these debates have yielded the most profound practical benefits。 The very method of mathematical reasoning that Isaac Newton introduced to explain the motion of the planets around the Sun has led to most of the technology Of our modern world。 The Industrial Revolution； for all its shortings； is still the global model of how an agricultural nation can emerge from poverty。 These debates have bread…and…butter consequences。
It might have been otherwise。 It might have been that the balance lay elsewhere； that humans by and large did not want to yaw about a disquieting Universe； that we were unwilling to hermit challenges to the prevailing wisdom。 Despite determined resistance in every age； it is very much to our credit that we have allowed ourselves to follow the evidence； to draw conclusions that at first seem daunting： a Universe so much larger and older that our personal and historical experience is dwarfed and humbled； a Universe in which； every day； suns are born and worlds obliterated； a Universe in which humanity； newly arrived； clings to an obscure clod of matter。
How much more satisfying had we been placed in a garden custom…made for us； its other occupants put there for us to use as we saw fit。 There is a celebrated story in the Western tradition like this； except that not quite everything was there for us。 There was one particular tree of which we were not to partake； a tree of knowledge。 Knowledge and understanding and wisdom were forbidden to us in this story。 We were to be kept ignorant。 But we couldn't help ourselves。 We were starving for knowledge—created hungry； you might say。 This was the origin of all our troubles。 In particular； it is why we no longer live in a garden： We found out too much。 So long as we were incurious and obedient； I imagine； we could console ourselves with our importance and centrality； and tell ourselves that we were the reason the Universe was made。 As we began to indulge our curiosity； though； to explore； to learn how the Universe really is； we expelled ourselves from Eden。 Angels with a flaming sword were set as sentries at the gates of Paradise to bar our return。 The gardeners became exiles and wanderers。 Occasionally we mourn that lost world； but that； it seems to me； is maudlin and sentimental。 We could not happily have remained ignorant forever。
There is in this Universe much of what seems to he design。 Every time we e upon it； we breathe a sigh of relief。 We are forever hoping to find； or at least safely deduce； a Designer。 But instead； we repeatedly discover that natural processes—collisional selection of worlds； say； or natural selection of gene pools； or even the convection pattern in a pot of boiling water—can extract order out of chaos； and deceive us into deducing purpose where there is none。 In everyday life； we often sense—in the bedrooms of teenagers； or in national politics—that chaos is natural； and order imposed from above。 While there are deeper regularities in the Universe than the simple circumstances we generally describe as orderly； all that order； simple and plex； seems to derive from laws of Nature established at the Big Bang （or earlier）； rather than as a consequence of belated intervention by an imperfect deity。 〃God is to be found in the details〃 is the famous dictum of the German scholar Abu Warburg。 But； amid much elegance and precision； the details of life and the Universe also exhibit haphazard； jury…rigged arrangements and much poor planning。 What shall we make of this： an edifice abandoned early in construction by the architect？
The evidence； so far at least and laws of Nature aside； does not require a Designer。 Maybe there is one hiding； maddeningly unwilling to be revealed。 Sometimes it seems a very slender hope。
The significance of our lives and our fragile planet is then determined only by our own wisdom and courage。 We are the custodians of life's meaning。 We long for a Parent to care for us； to forgive us our errors； to save us from our childish mistakes。 But knowledge is preferable to ignorance。 Better by far to embrace the hard truth than a reassuring fable。
If we crave some cosmic purpose； then let us find ourselves a worthy goal。
CHAPTER 5 IS THERE INTELLIGENT LIFE ON EARTH？
They journeyed a long time and found nothing。 At length they discerned a small light； which was the Earth 。 。 。 ＇But＇ they could not find the smallest reason to suspect that we and our fellow—citizens of this globe have the honor to exist。
—VOLTAIRE； MICROMEGAS。 A PHILOSOPHICAL HISTORY （1752）
There are places； in and around our great cities； where the natural world has all but disappeared。 You can make out streets and sidewalks； autos； parking garages； advertising billboards； monuments of glass and steel； but not a tree or a blade of grass or any animal—besides； of course； the humans。 There are lots of humans。 Only when you look straight up through the skyscraper canyons can you make out a star or a patch of blue—reminders of what was there long before humans came to be。 But the bright lights of the big cities bleach out the stars； and even that patch of blue is sometimes gone； tinted brown by industrial technology。
It's not hard； going to work every day in such a place； to be impressed with ourselves。 How we've transformed the Earth for our benefit and convenience！ But a few hundred miles up or down there are no humans。 Apart from a thin film of life at the very surface of the Earth； an occasional intrepid spacecraft； and some radio static； our impact on the Universe is nil。 It knows nothing of us。
YOU'RE AN ALIEN EXPLORER entering the Solar System after a long journey through the blackness of interstellar space。 You examine the planets of this humdrum star from afar—a pretty handful； some gray； some blue； some red； some yellow。 You're interested in what kinds of worlds these are； whether their environments are static or changing； and especially whether there are life and intelligence。 You have no prior knowledge of the Earth。 You've just discovered its existence。
There's a galactic ethic； let's imagine： Look but don't touch。 You can fly by these worlds； you can orbit them； but you are strictly forbidden to land。 Under such constraints； could you figure out what the Earth's environment is like and whether anyone lives there？
As you approach； your first impression of the whole Earth is white clouds； white polar caps； brown continents； and some bluish substance that covers two thirds of the surface。 When you take the temperature of this world from the infrared radiation it emits； you find that most latitudes are above the freezing point of water； while the polar caps are below freezing。 Water is a very abundant material in the Universe； polar caps made of solid water would be a reasonable guess； as well as clouds of solid and liquid water。
You might also he tempted by the idea that the blue stuff is enormous quantities—kilometers deep—of liquid water。 The suggestion is bizarre； though； at least as far as this solar system is concerned； because surface oceans