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？ puters 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 positions； learn from their mistakes； and petently 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 es 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 inpatible 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 e 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 e 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 inpatible 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 enpassing 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 monsense 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 patible 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 es； if it ever does； it seems to me premature to put faith in the Anthropic Principle as an argument for human centrality or uniqueness。
Finally； even if the Universe were intentionally created to allow for the emergence of life or intelligence； other beings may exist on countless worlds。 If so； it would be cold fort to anthropocentrists that we inhabit one of the few universes that allow life and intelligence。
There is something stunningly narrow about how the Anthropic Principle is phrased。 Yes； only certain laws and constants of nature are consistent with our kind of life。 But essentially the same laws and constants are required to make a rock。 So why not talk about a Universe designed so rocks could one day e to be； and strong and weak Lithic Principles？ If stones could philosophize； I imagine Lithic Principles would be at the intellectual frontiers。
There are cosmological models being formulated today in which even the entire Universe is nothing special。 Andrei Linde； formerly of the Lebedev Physical Institute in Moscow and now at Stanford University； has incorporated current understanding of the strong and weak nuclear forces and quantum physics into a new cosmological model。 Linde envisions a vast Cosmos； much larger than our Universe—perhaps extending to infinity both in space and time—not the paltry 15 billion light…years or so in radius and 15 billion years in age which are the usual understanding。 In this Cosmos there is； as here； a kind of quantum fluff in which tiny structures— much smaller than an electron—are everywhere forming； reshaping； and dissipating； in which； as here； fluctuations in absolutely empty space create pairs of elementary particles—an electron and a positron； for example。 In the froth of quantum bubbles； the vast majority remain submicroscopic。 But a tiny fraction inflate； grow； and