jectories 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 achieve respectable universehood。 They are so far away from us； though—much farther than the 15 billion light…years that is the conventional scale of our universe—that； if they exist； they appear to be wholly inaccessible and undetectable。
Most of these other universes reach a maximum size and then collapse； contract to a point； and disappear forever。 Others may oscillate。 Still others may expand without limit。 In different universes there will be different laws of nature。 We live； Linde argues； in one such universe—one in which the physics is congenial for growth； inflation； expansion； galaxies； stars； worlds； life。 We imagine our universe to be unique； but it is one of an immense number—perhaps an infinite number—of equally valid； equally independent； equally isolated universes。 There will be life in some； and not in others。 In this view the observable Universe is just a newly formed backwater of a much vaster； infinitely old； and wholly unobservable Cosmos。 If something like this is right； even our residual pride； pallid as it must be； of living in the only universe is denied to us。
Maybe someday； despite current evidence； a means will be devised to peer into adjacent universes； sporting very different laws of nature； and we will see what else is possible。 Or perhaps inhabitants of adjacent universes can peer into ours。 Of course； in such speculations we have far exceeded the bounds of knowledge。 But if something like Linde's Cosmos is true； there is—amazingly—still another devastating deprovincialization awaiting us。*
For such ideas； words tend to fail us。 A German locution for Universe is ＇dad 911which makes the inclusiveness quite unmistakable。 We might say that our universe is but one in a 〃Multiverse；〃 but I prefer to use 〃Cosmos〃 for everything and 〃Universe〃 for the only one we can know about。
Our powers are far from adequate to be creating universes anytime soon。 Strong Anthropic Principle ideas are not amenable to proof （although Linde's cosmology does have some testable features）。 Extraterrestrial life aside； if self…congratulatory pretensions to centrality have now retreated to such bastions impervious to experiment； then the sequence of scientific battles with human chauvinism would seem to have been； at least largely； won。
THE LONG…STANDING VIEW； as summarized by the philosopher Immanuel Kant； that 〃without man 。 。 。 the whole of creation would be a mere wilderness； a thing in vain； and have no final end〃 is revealed to be self…indulgent folly。 A Principle of Mediocrity seems to apply to all our circumstances。 We could not have known beforehand that the evidence would be； so repeatedly and thoroughly； inpatible with the proposition that human beings are at center stage in the Universe。 But most of the debates have now been settled decisively in favor of a position that； however painful； can be encapsulated in a single sentence： We have not been given the lead in the cosmic drama。
Perhaps someone else has。 Perhaps no one else has。 In either case； we have good reason for humility。
CHAPTER 4 A UNIVERSE NOT MADE FOR US
The Sea of Faith
Was once； too； at the full； and round earth's shore
Lay like the folds of a bright girdle furl'd。
But now I only hear
Its melancholy； long； withdrawing roar；
Retreating； to the breath
Of the night…wind； down the vast edges drear
And naked shingles of the world。
—MATTHEW ARNOLD； 〃DOVER BEACH〃 （1867）
What a beautiful sunset；〃 we say； or 〃I'm up before sunrise。〃 No matter what the scientists allege； in everyday speech we often ignore their findings。 We don't talk about the Earth turning； but about the Sun rising and setting。 Try formulating it in Copernican language。 Would you say； 〃Billy； be home by the time the Earth has rotated enough so as to occult the Sun below the local horizon〃？ Billy would be long gone before you're finished。 We haven't been able even to find a graceful locution that accurately the Heliocentric insight。 We at the center and everything else circling us is built into our la