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sionally unavoidable； not least in a chapter dealing with things on a cosmic scale。
time。” to which adds guth： “although the creation of a universe might be very unlikely；tryon emphasized that no one had counted the failed attempts。”
martin rees； britain’s astronomer royal； believes that there are many universes； possibly aninfinite number； each with different attributes； in different binations； and that we simplylive in one that bines things in the way that allows us to exist。 he makes an analogy witha very large clothing store： “if there is a large stock of clothing； you’re not surprised to find asuit that fits。 if there are many universes； each governed by a differing set of numbers； therewill be one where there is a particular set of numbers suitable to life。 we are in that one。”
rees maintains that six numbers in particular govern our universe； and that if any of thesevalues were changed even very slightly things could not be as they are。 for example； for theuniverse to exist as it does requires that hydrogen be converted to helium in a precise butparatively stately manner—specifically； in a way that converts seven one…thousandths ofits mass to energy。 lower that value very slightly—from 0。007 percent to 0。006 percent；say—and no transformation could take place： the universe would consist of hydrogen andnothing else。 raise the value very slightly—to 0。008 percent—and bonding would be sowildly prolific that the hydrogen would long since have been exhausted。 in either case； withthe slightest tweaking of the numbers the universe as we know and need it would not be here。
i should say that everything is just right so far。 in the long term； gravity may turn out to be alittle too strong； and one day it may halt the expansion of the universe and bring it collapsingin upon itself； till it crushes itself down into another singularity； possibly to start the wholeprocess over again。 on the other hand it may be too weak and the universe will keep racingaway forever until everything is so far apart that there is no chance of material interactions； sothat the universe bees a place that is inert and dead； but very roomy。 the third option isthat gravity is just right—“critical density” is the cosmologists’ term for it—and that it willhold the universe together at just the right dimensions to allow things to go on indefinitely。
cosmologists in their lighter moments sometimes call this the goldilocks effect—thateverything is just right。 （for the record； these three possible universes are known respectivelyas closed； open； and flat。）now the question that has occurred to all of us at some point is： what would happen if youtraveled out to the edge of the universe and； as it were； put your head through the curtains？
where would your head be if it were no longer in the universe？ what would you find beyond？
the answer； disappointingly； is that you can never get to the edge of the universe。 that’s notbecause it would take too long to get there—though of course it would—but because even ifyou traveled outward and outward in a straight line； indefinitely and pugnaciously； you wouldnever arrive at an outer boundary。 instead； you would e back to where you began （atwhich point； presumably； you would rather lose heart in the exercise and give up）。 the reasonfor this is that the universe bends； in a way we can’t adequately imagine； in conformance witheinstein’s theory of relativity （which we will get to in due course）。 for the moment it isenough to know that we are not adrift in some large； ever…expanding bubble。 rather； spacecurves； in a way that allows it to be boundless but finite。 space cannot even properly be saidto be expanding because； as the physicist and nobel laureate steven weinberg notes； “solar systems and galaxies are not expanding； and space itself is not expanding。” rather； thegalaxies are rushing apart。 it is all something of a challenge to intuition。 or as the biologist j。
b。 s。 haldane once famously observed： “the universe is not only queerer than we suppose； itis queerer than we can suppose。”
the analogy that is usually given for explaining the curvature of space is to try to imaginesomeone from a universe of flat surfaces； who had never seen a sphere； being brought toearth。 no matter how far he roamed across the planet’s surface； he would never find an edge。
he might eventually return to the spot where he had started； and would of course be utterlyconfounded to explain how that had happened。 well； we are in the same position in space asour puzzled flatlander； only we are flummoxed by a higher dimension。
just as there is no place where you can find the edge of the universe； so there is no placewhere you can stand at the center and say： “this is where it all began。 this is the centermostpoint of it all。” we are all at the center of it all。 actually； we don’t know that for sure； wecan’t prove it mathematically。 scientists just assume that we can’t really be the center of theuniverse—think what that would imply—but that the phenomenon must be the same for allobservers in all places。 still； we don’t actually know。
for us； the universe goes only as far as light has traveled in the billions of years since theuniverse was formed。 this visible universe—the universe we know and can talk about—is amillion million million million （that’s 1；000；000；000；000；000；000；000；000） miles across。 butaccording to most theories the universe at large—the meta…universe； as it is sometimescalled—is vastly roomier still。 according to rees； the number of light…years to the edge ofthis larger； unseen universe would be written not “with ten zeroes； not even with a hundred；but with millions。” in short； there’s more space than you can imagine already without going tothe trouble of trying to envision some additional beyond。
for a long time the big bang theory had one gaping hole that troubled a lot of people—namely that it couldn’t begin to explain how we got here。 although 98 percent of all thematter that exists was created with the big bang； that matter consisted exclusively of lightgases： the helium； hydrogen； and lithium that we mentioned earlier。 not one particle of theheavy stuff so vital to our own being—carbon； nitrogen； oxygen； and all the rest—emergedfrom the gaseous brew of creation。 but—and here’s the troubling point—to forge these heavyelements； you need the kind of heat and energy of a big bang。 yet there has been only onebig bang and it didn’t produce them。 so where did they e from？
interestingly； the man who found the answer to that question was a cosmologist whoheartily despised the big bang as a theory and coined the term “big bang” sarcastically； as away of mocking it。 we’ll get to him shortly； but before we turn to the question of how we gothere； it might be worth taking a few minutes to consider just where exactly “here” is。
。。
2 WELE TO THE SOLAR SYSTEMAS
tronomers these days can do the most amazing things。 if someone struck a matchon the moon； they could spot the flare。 from the tiniest throbs and wobbles of distant starsthey can infer the size and character and even potential habitability of planets much tooremote to be seen—planets so distant that it would take us half a million years in a spaceshipto get there。 with their radio telescopes they can capture wisps of radiation so preposterouslyfaint that the total amount of energy collected from outside the solar system by all of themtogether since collecting began （in 1951） is “less than the energy of a single snowflakestriking the ground；” in the words of carl sagan。
in short； there isn’t a great deal that goes on in the universe that astronomers can’t findwhen they have a mind to。 which is why it is all the more remarkable to reflect that until 1978no one had ever noticed that pluto has a moon。 in the summer of that year； a youngastronomer named james christy at the u。s。 naval observatory in flagstaff； arizona； wasmaking a routine examination of photographic images of pluto when he saw that there wassomething there—something blurry and uncertain but definitely other than pluto。 consulting acolleague named robert harrington； he concluded that what he was looking at was a moon。