ces that you would be on or near a planet would be less than one in a billiontrillion trillion。鈥潯。╰hat鈥檚 1033； or a one followed by thirty…three zeroes。） 鈥渨orlds are precious。鈥�
which is why perhaps it is good news that in february 1999 the international astronomicalunion ruled officially that pluto is a planet。 the universe is a big and lonely place。 we can dowith all the neighbors we can get。
xi锛shuotx锛础锛辑
3 THE REVEREND EVANS鈥橲 UNIVERSE
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when the skies are clear and the moon is not too bright； the reverend robert evans； aquiet and cheerful man； lugs a bulky telescope onto the back deck of his home in the bluemountains of australia； about fifty miles west of sydney； and does an extraordinary thing。 helooks deep into the past and finds dying stars。
looking into the past is of course the easy part。 glance at the night sky and what you see ishistory and lots of it鈥攖he stars not as they are now but as they were when their light leftthem。 for all we know； the north star； our faithful panion； might actually have burnedout last january or in 1854 or at any time since the early fourteenth century and news of it justhasn鈥檛 reached us yet。 the best we can say鈥攃an ever say鈥攊s that it was still burning on thisdate 680 years ago。 stars die all the time。 what bob evans does better than anyone else whohas ever tried is spot these moments of celestial farewell。
by day； evans is a kindly and now semiretired minister in the uniting church in australia；who does a bit of freelance work and researches the history of nineteenth…century religiousmovements。 but by night he is； in his unassuming way； a titan of the skies。 he huntssupernovae。
supernovae occur when a giant star； one much bigger than our own sun； collapses and thenspectacularly explodes； releasing in an instant the energy of a hundred billion suns； burningfor a time brighter than all the stars in its galaxy。 鈥渋t鈥檚 like a trillion hydrogen bombs going offat once；鈥潯ays evans。 if a supernova explosion happened within five hundred light…years of us；we would be goners； according to evans鈥斺�渋t would wreck the show；鈥潯s he cheerfully puts it。
but the universe is vast； and supernovae are normally much too far away to harm us。 in fact；most are so unimaginably distant that their light reaches us as no more than the faintesttwinkle。 for the month or so that they are visible； all that distinguishes them from the otherstars in the sky is that they occupy a point of space that wasn鈥檛 filled before。 it is theseanomalous； very occasional pricks in the crowded dome of the night sky that the reverendevans finds。
to understand what a feat this is； imagine a standard dining room table covered in a blacktablecloth and someone throwing a handful of salt across it。 the scattered grains can bethought of as a galaxy。 now imagine fifteen hundred more tables like the first one鈥攅nough tofill a wal…mart parking lot； say； or to make a single line two miles long鈥攅ach with a randomarray of salt across it。 now add one grain of salt to any table and let bob evans walk amongthem。 at a glance he will spot it。 that grain of salt is the supernova。
evans鈥檚 is a talent so exceptional that oliver sacks； in an anthropologist on mars； devotesa passage to him in a chapter on autistic savants鈥攓uickly adding that 鈥渢here is no suggestionthat he is autistic。鈥潯vans； who has not met sacks； laughs at the suggestion that he might beeither autistic or a savant； but he is powerless to explain quite where his talent es from。
鈥渋 just seem to have a knack for memorizing star fields；鈥潯e told me； with a franklyapologetic look； when i visited him and his wife； elaine； in their picture…book bungalow on atranquil edge of the village of hazelbrook； out where sydney finally ends and the boundlessaustralian bush begins。 鈥渋鈥檓 not particularly good at other things；鈥潯e added。 鈥渋 don鈥檛remember names well。鈥�
鈥渙r where he鈥檚 put things；鈥潯alled elaine from the kitchen。
he nodded frankly again and grinned； then asked me if i鈥檇 like to see his telescope。 i hadimagined that evans would have a proper observatory in his backyard鈥攁 scaled…downversion of a mount wilson or palomar； with a sliding domed roof and a mechanized chair thatwould be a pleasure to maneuver。 in fact； he led me not outside but to a crowded storeroomoff the kitchen where he keeps his books and papers and where his telescope鈥攁 whitecylinder that is about the size and shape of a household hot…water tank鈥攔ests in a homemade；swiveling plywood mount。 when he wishes to observe； he carries them in two trips to a smalldeck off the kitchen。 between the overhang of the roof and the feathery tops of eucalyptustrees growing up from the slope below； he has only a letter…box view of the sky； but he says itis more than good enough for his purposes。 and there； when the skies are clear and the moonnot too bright； he finds his supernovae。
the term supernova was coined in the 1930s by a memorably odd astrophysicist namedfritz zwicky。 born in bulgaria and raised in switzerland； zwicky came to the californiainstitute of technology in the 1920s and there at once distinguished himself by his abrasivepersonality and erratic talents。 he didn鈥檛 seem to be outstandingly bright； and many of hiscolleagues considered him little more than 鈥渁n irritating buffoon。鈥潯 fitness buff； he wouldoften drop to the floor of the caltech dining hall or other public areas and do one…armedpushups to demonstrate his virility to anyone who seemed inclined to doubt it。 he wasnotoriously aggressive； his manner eventually being so intimidating that his closestcollaborator； a gentle man named walter baade； refused to be left alone with him。 amongother things； zwicky accused baade； who was german； of being a nazi； which he was not。 onat least one occasion zwicky threatened to kill baade； who worked up the hill at the mountwilson observatory； if he saw him on the caltech campus。
but zwicky was also capable of insights of the most startling brilliance。 in the early 1930s；he turned his attention to a question that had long troubled astronomers： the appearance in thesky of occasional unexplained points of light； new stars。 improbably he wondered if theneutron鈥攖he subatomic particle that had just been discovered in england by jameschadwick； and was thus both novel and rather fashionable鈥攎ight be at the heart of things。 itoccurred to him that if a star collapsed to the sort of densities found in the core of atoms； theresult would be an unimaginably pacted core。 atoms would literally be crushed together；their electrons forced into the nucleus； forming neutrons。 you would have a neutron star。
imagine a million really weighty cannonballs squeezed down to the size of a marble and鈥攚ell； you鈥檙e still not even close。 the core of a neutron star is so dense that a single spoonfulof matter from it would weigh 200 billion pounds。 a spoonful！ but there was more。 zwickyrealized that after the collapse of such a star there would be a huge amount of energy leftover鈥攅nough to make the biggest bang in the universe。 he called these resultant explosionssupernovae。 they would be鈥攖hey are鈥攖he biggest events in creation。
on january 15； 1934； the journal physical review published a very concise abstract of apresentation that had been conducted by zwicky and baade the previous month at stanforduniversity。 despite its extreme brevity鈥攐ne paragraph of twenty…four lines鈥攖he abstractcontained an enormous amount of new science： it provided the first reference to supernovaeand to neutron stars； convincingly explained their method of formation； correctly calculatedthe scale of their explosiveness； and； as a kind of concluding bonus； connected supernovaexplosions to the production of a mysterious new phenomenon called cosmic rays； which hadrecently been found swarming through the universe。 these ideas were revolutionary to say theleast。 neutron stars wouldn鈥檛 be confirmed for thirty…four years。 the cosmic rays notion； though considered plausible； hasn鈥檛 been verified yet。 altogether； the abstract was； in thewords of caltech astrophysicist kip s。 thorne； 鈥渙ne of the most prescient documents in thehistory of physics and astronomy。鈥�
interestingly； zwicky had almost no understanding of why any of this would happen。
according to thorne； 鈥渉e did not understand the laws of physics well enough to be able tosubstantiate his ideas。鈥潯wicky鈥檚 talent was for big ideas。 others鈥攂aade mostly鈥攚ere leftto do the mathematical sweeping up。
zwicky also was the first to recognize that there wasn鈥檛 nearly enough visible mass in theuniverse to hold galaxies together and that there must be some other gravitational influence鈥攚hat we now call dark matter。 one thing he failed to see was that if a neutron star shrankenough it would bee so dense that even light couldn鈥檛 escape its immense gravitationalpull。 you would have a black hole。 unfortunately； zwicky was held in such disdain by mostof his colleagues that his ideas attracted almost no notice。 when； five years later； the greatrobert oppenheimer turned his attention to neutron stars in a landmark paper； he made not asingle reference to any of zwicky鈥檚 work even though zwicky had been working for years onthe same problem in an office just down the hall。 zwicky鈥檚 deductions concerning dark matterwouldn鈥檛 attract serious attention for nearly four decades。 we can only assume that he did alot of pushups in this period。
surprisingly little of the universe is visible to us when we incline our heads to the sky。 onlyabout 6；000 stars are visible to the naked eye from earth； and only about 2；000 can be seenfrom any one spot。 with binoculars the number of stars you can see from a single locationrises to about 50；000； and with a small two…inch telescope it leaps to 300；000。 with a sixteen…inch telescope； such as evans uses； you begin to count not in stars but in galaxies。 from hisdeck； evans supposes he can see between 50；000 and 100；000 galaxies； each containing tensof billions of stars。 these are of course respectable numbers； but even with so much to take in；supernovae are extremely rare。 a star can burn for billions of years； but it dies just once andqui