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（just to put these insights into perspective； it is perhaps worth noting that at the time leavittand cannon were inferring fundamental properties of the cosmos from dim smudges onphotographic plates； the harvard astronomer william h。 pickering； who could of course peerinto a first…class telescope as often as he wanted； was developing his seminal theory that darkpatches on the moon were caused by swarms of seasonally migrating insects。）bining leavitt’s cosmic yardstick with vesto slipher’s handy red shifts； edwin hubblenow began to measure selected points in space with a fresh eye。 in 1923 he showed that a puffof distant gossamer in the andromeda constellation known as m31 wasn’t a gas cloud at allbut a blaze of stars； a galaxy in its own right； a hundred thousand light…years across and atleast nine hundred thousand light…years away。 the universe was vaster—vastly vaster—thananyone had ever supposed。 in 1924 he produced a landmark paper； “cepheids in spiralnebulae” （nebulae；from the latin for “clouds；” was his word for galaxies）； showing that theuniverse consisted not just of the milky way but of lots of independent galaxies—“islanduniverses”—many of them bigger than the milky way and much more distant。
this finding alone would have ensured hubble’s reputation； but he now turned to thequestion of working out just how much vaster the universe was； and made an even morestriking discovery。 hubble began to measure the spectra of distant galaxies—the business thatslipher had begun in arizona。 using mount wilson’s new hundred…inch hooker telescopeand some clever inferences； he worked out that all the galaxies in the sky （except for our ownlocal cluster） are moving away from us。 moreover； their speed and distance were neatlyproportional： the further away the galaxy； the faster it was moving。
this was truly startling。 the universe was expanding； swiftly and evenly in all directions。 itdidn’t take a huge amount of imagination to read backwards from this and realize that it must therefore have started from some central point。 far from being the stable； fixed； eternal voidthat everyone had always assumed； this was a universe that had a beginning。 it mighttherefore also have an end。
the wonder； as stephen hawking has noted； is that no one had hit on the idea of theexpanding universe before。 a static universe； as should have been obvious to newton andevery thinking astronomer since； would collapse in upon itself。 there was also the problemthat if stars had been burning indefinitely in a static universe they’d have made the wholeintolerably hot—certainly much too hot for the likes of us。 an expanding universe resolvedmuch of this at a stroke。
hubble was a much better observer than a thinker and didn’t immediately appreciate thefull implications of what he had found。 partly this was because he was woefully ignorant ofeinstein’s general theory of relativity。 this was quite remarkable because； for one thing；einstein and his theory were world famous by now。 moreover； in 1929 albert michelson—now in his twilight years but still one of the world’s most alert and esteemed scientists—accepted a position at mount wilson to measure the velocity of light with his trustyinterferometer； and must surely have at least mentioned to him the applicability of einstein’stheory to his own findings。
at all events； hubble failed to make theoretical hay when the chance was there。 instead； itwas left to a belgian priest…scholar （with a ph。d。 from mit） named georges lema？tre tobring together the two strands in his own “fireworks theory；” which suggested that theuniverse began as a geometrical point； a “primeval atom；” which burst into glory and hadbeen moving apart ever since。 it was an idea that very neatly anticipated the modernconception of the big bang but was so far ahead of its time that lema？tre seldom gets morethan the sentence or two that we have given him here。 the world would need additionaldecades； and the inadvertent discovery of cosmic background radiation by penzias and wilsonat their hissing antenna in new jersey； before the big bang would begin to move frominteresting idea to established theory。
neither hubble nor einstein would be much of a part of that big story。 though no onewould have guessed it at the time； both men had done about as much as they were ever goingto do。
in 1936 hubble produced a popular book called the realm of the nebulae； whichexplained in flattering style his own considerable achievements。 here at last he showed thathe had acquainted himself with einstein’s theory—up to a point anyway： he gave it four pagesout of about two hundred。
hubble died of a heart attack in 1953。 one last small oddity awaited him。 for reasonscloaked in mystery； his wife declined to have a funeral and never revealed what she did withhis body。 half a century later the whereabouts of the century’s greatest astronomer remainunknown。 for a memorial you must look to the sky and the hubble space telescope；launched in 1990 and named in his honor。
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9THE MIGHTY ATOM
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while einstein and hubble were productively unraveling the large…scale structure ofthe cosmos； others were struggling to understand something closer to hand but in its way justas remote： the tiny and ever… mysterious atom。
the great caltech physicist richard feynman once observed that if you had to reducescientific history to one important statement it would be “all things are made of atoms。” theyare everywhere and they constitute every thing。 look around you。 it is all atoms。 not just thesolid things like walls and tables and sofas； but the air in between。 and they are there innumbers that you really cannot conceive。
the basic working arrangement of atoms is the molecule （from the latin for “little mass”）。
a molecule is simply two or more atoms working together in a more or less stablearrangement： add two atoms of hydrogen to one of oxygen and you have a molecule of water。
chemists tend to think in terms of molecules rather than elements in much the way thatwriters tend to think in terms of words and not letters； so it is molecules they count； and theseare numerous to say the least。 at sea level； at a temperature of 32 degrees fahrenheit； onecubic centimeter of air （that is； a space about the size of a sugar cube） will contain 45 billionbillion molecules。 and they are in every single cubic centimeter you see around you。 thinkhow many cubic centimeters there are in the world outside your window—how many sugarcubes it would take to fill that view。 then think how many it would take to build a universe。
atoms； in short； are very abundant。
they are also fantastically durable。 because they are so long lived； atoms really get around。
every atom you possess has almost certainly passed through several stars and been part ofmillions of organisms on its way to being you。 we are each so atomically numerous andso vigorously recycled at death that a significant number of our atoms—up to a billion foreach of us； it has been suggested—probably once belonged to shakespeare。 a billion moreeach came from buddha and genghis khan and beethoven； and any other historical figureyou care to name。 （the personages have to