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cutaway diagram showing the earths interior as it would look if you cut intothe planet with a large knife and carefully withdrew a wedge representing about a quarter ofits bulk。
its hard to believe that there was ever a time when i had not seen such an illustrationbefore； but evidently i had not for i clearly remember being transfixed。 i suspect； in honesty；my initial interest was based on a private image of streams of unsuspecting eastboundmotorists in the american plains states plunging over the edge of a sudden 4；000…mile…highcliff running between central america and the north pole； but gradually my attention did turnin a more scholarly manner to the scientific import of the drawing and the realization that theearth consisted of discrete layers； ending in the center with a glowing sphere of iron andnickel； which was as hot as the surface of the sun； according to the caption； and i rememberthinking with real wonder： 〃how do they know that？〃i didnt doubt the correctness of the information for an instant…i still tend to trust thepronouncements of scientists in the way i trust those of surgeons； plumbers； and otherpossessors of arcane and privileged information…but i couldnt for the life of me conceive how any human mind could work out what spaces thousands of miles below us； that no eye hadever seen and no x ray could penetrate； could look like and be made of。 to me that was just amiracle。 that has been my position with science ever since。
excited； i took the book home that night and opened it before dinner…an action that i expectprompted my mother to feel my forehead and ask if i was all right…and； starting with the firstpage； i read。
and heres the thing。 it wasnt exciting at all。 it wasnt actually altogether prehensible。
above all； it didnt answer any of the questions that the illustration stirred up in a normalinquiring mind： how did we end up with a sun in the middle of our planet？ and if it isburning away down there； why isnt the ground under our feet hot to the touch？ and why isntthe rest of the interior melting…or is it？ and when the core at last burns itself out； will some ofthe earth slump into the void； leaving a giant sinkhole on the surface？ and how do you knowthis？ how did you figure it out？
but the author was strangely silent on such details…indeed； silent on everything butanticlines； synclines； axial faults； and the like。 it was as if he wanted to keep the good stuffsecret by making all of it soberly unfathomable。 as the years passed； i began to suspect thatthis was not altogether a private impulse。 there seemed to be a mystifying universalconspiracy among textbook authors to make certain the material they dealt with never strayedtoo near the realm of the mildly interesting and was always at least a longdistance phone callfrom the frankly interesting。
i now know that there is a happy abundance of science writers who pen the most lucid andthrilling prose…timothy ferris； richard fortey； and tim flannery are three that jump out froma single station of the alphabet （and thats not even to mention the late but godlike richardfeynman）…but sadly none of them wrote any textbook i ever used。 all mine were written bymen （it was always men） who held the interesting notion that everything became clear whenexpressed as a formula and the amusingly deluded belief that the children of america wouldappreciate having chapters end with a section of questions they could mull over in their owntime。 so i grew up convinced that science was supremely dull； but suspecting that it needntbe； and not really thinking about it at all if i could help it。 this； too； became my position for along time。
then much later…about four or five years ago…i was on a long flight across the pacific；staring idly out the window at moonlit ocean； when it occurred to me with a certainunfortable forcefulness that i didnt know the first thing about the only planet i was evergoing to live on。 i had no idea； for example； why the oceans were salty but the great lakeswerent。 didnt have the faintest idea。 i didnt know if the oceans were growing more saltywith time or less； and whether ocean salinity levels was something i should be concernedabout or not。 （i am very pleased to tell you that until the late 1970s scientists didnt know theanswers to these questions either。 they just didnt talk about it very audibly。）and ocean salinity of course represented only the merest sliver of my ignorance。 i didntknow what a proton was； or a protein； didnt know a quark from a quasar； didnt understandhow geologists could look at a layer of rock on a canyon wall and tell you how old it was；didnt know anything really。 i became gripped by a quiet； unwonted urge to know a littleabout these matters and to understand how people figured them out。 that to me remained thegreatest of all amazements…how scientists work things out。 how does anybody know howmuch the earth weighs or how old its rocks are or what really is way down there in thecenter？ how can they know how and when the universe started and what it was like when itdid？ how do they know what goes on inside an atom？ and how； e to that…or perhapsabove all…can scientists so often seem to know nearly everything but then still cant predict anearthquake or even tell us whether we should take an umbrella with us to the races nextwednesday？
so i decided that i would devote a portion of my life…three years； as it now turns out…toreading books and journals and finding saintly； patient experts prepared to answer a lot ofoutstandingly dumb questions。 the idea was to see if it isnt possible to understand andappreciate…marvel at； enjoy even…the wonder and acplishments of science at a level thatisnt too technical or demanding； but isnt entirely superficial either。
that was my idea and my hope； and that is what the book that follows is intended to be。
anyway； we have a great deal of ground to cover and much less than 650；000 hours in whichto do it； so lets begin。
PART I LOST IN THE COSMOS
？灏忚/t锛竧｜澶╁爞
they鈥檙e all in the same plane。
they鈥檙e all going around in the same direction。 。 。 。
it鈥檚 perfect； you know。
it鈥檚 gorgeous。
it鈥檚 almost uncanny。
…astronomer geoffrey marcy
describing the solar system
w锛穡銆倄iaoshuo txt锛�
1 HOW TO BUILD A UNIVERSENO MATTER
灏忥紲璇达紲t锛渪t锛炲ぉ锛煛峰爞
how hard you try you will never be able to grasp just how tiny； how spatiallyunassuming； is a proton。 it is just way too small。
a proton is an infinitesimal part of an atom； which is itself of course an insubstantial thing。
protons are so small that a little dib of ink like the dot on this i can hold something in theregion of 500；000；000；000 of them； rather more than the number of seconds contained in halfa million years。 so protons are exceedingly microscopic； to say the very least。
now imagine if you can （and of course you can鈥檛） shrinking one of those protons down to abillionth of its normal size into a space so small that it would make a proton look enormous。
now pack into that tiny； tiny space about an ounce of matter。 excellent。 you are ready to starta universe。
i鈥檓 assuming of course that you wish to build an inflationary universe。 if you鈥檇 preferinstead to build a more old…fashioned； standard big bang universe； you鈥檒l need additionalmaterials。 in fact； you will need to gather up everything there is every last mote and particle ofmatter between here and the edge of creation and squeeze it into a spot so infinitesimallypact that it has no dimensions at all。 it is known as a singularity。
in either case； get ready for a really big bang。 naturally； you will wish to retire to a safeplace to observe the spectacle。 unfortunately； there is nowhere to retire to because outside thesingularity there is no where。 when the universe begins to expand； it won鈥檛 be spreading outto fill a larger emptiness。 the only space that exists is the space it creates as it goes。
it is natural but wrong to visualize the singularity as a kind of pregnant dot hanging in adark； boundless void。 but there is no space； no darkness。 the singularity has no 鈥渁round鈥�
around it。 there is no space for it to occupy； no place for it to be。 we can鈥檛 even ask how longit has been there鈥攚hether it has just lately popped into being； like a good idea； or whether ithas been there forever； quietly awaiting the right moment。 time doesn鈥檛 exist。 there is no pastfor it to emerge from。
and so； from nothing； our universe begins。
in a single blinding pulse； a moment of glory much too swift and expansive for any form ofwords； the singularity assumes heavenly dimensions； space beyond conception。 in the firstlively second （a second that many cosmologists will devote careers to shaving into ever…finerwafers） is produced gravity and the other forces that govern physics。 in less than a minute theuniverse is a million billion miles across and growing fast。 there is a lot of heat now； tenbillion degrees of it； enough to begin the nuclear reactions that create the lighter elements鈥攑rincipally hydrogen and helium； with a dash （about one atom in a hundred million） oflithium。 in three minutes； 98 percent of all the matter there is or will ever be has beenproduced。 we have a universe。 it is a place of the most wondrous and gratifying possibility；and beautiful； too。 and it was all done in about the time it takes to make a sandwich。
when this moment happened is a matter of some debate。 cosmologists have long arguedover whether the moment of creation was 10 billion years ago or twice that or something inbetween。 the consensus seems to be heading for a figure of about 13。7 billion years； but thesethings are notoriously difficult to measure； as we shall see further on。 all that can really besaid is that at some indeterminate point in the very distant past； for reasons unknown； therecame the moment known to science as t = 0。 we were on our way。
there is of course a great deal we don鈥檛 know； and much of what we think we know wehaven鈥檛 known； or thought we鈥檝e known； for long。 even the notion of the big bang is quite arecent one。 the idea had been kicking around since the 1920s； when georges lema？tre； abelgian priest…scholar； first tentatively proposed it； but it didn鈥檛 really bee an activenotion in cosmology until the mid…1960s when two young radio astronomers made anextraordinary and inadvertent discovery。
their names were arno penzias and robert wilson。 in 1965； they were trying to make useof a large munications antenna owned by bell laboratories at holmdel； new jersey； butthey were troubled by a persistent background noise鈥攁 steady； steamy hiss that made anyexperimental work impossible。 the noise was unrelenting and unfocused。 it came from everypoint in the sky； day and night； through every season。 for a year the young astronomers dideverything they could think of to track down and eliminate the noise。 they tested everyelectrical system。 they rebuilt instruments； checked circuits； wiggled wires； dusted plugs。
they climbed into the dish and placed duct tape over every seam and rivet。 they climbedback into the dish with brooms and scrubbing brushes and carefully swept it clean of whatthey referred to in a later paper as 鈥渨hite dielectric material；鈥潯r what is known moremonly as bird shit。 nothing they tried worked。
unknown to them； just thirty miles away at princeton university； a team of scientists led byrobert dicke was working on how to find the very thing they were trying so diligently to getrid of。 the princeton researchers were pursuing an idea that had been suggested in the 1940sby the russian…born astrophysicist george gamow that if you looked deep enough into spaceyou should find some cosmic background radiation left over from the big bang。 gamowcalculated that by the time it crossed the vastness of the cosmos； the radiation would reachearth in the form of microwaves。 in a more recent paper he had even suggested an instrumentthat might do the job： the bell antenna at holmdel。 unfortunately； neither penzias andwilson； nor any of the princeton team； had read gamow鈥檚 paper。
the noise that penzias and wilson were hearing was； of course； the noise that gamow hadpostulated。 they had found the edge of the universe； or at least the visible part of it； 90 billi