11 MUSTER MARK’S QUARKS

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    IN 1911, A British stist named C. T. R. Wilson was studying cloud formations bytramping regularly to the summit of Ben Nevis, a famously damp Scottish mountain, when itoccurred to him that there must be an easier way to study clouds. Ba the dish Labin Cambridge he built an artificial cloud chamber—a simple devi which he could cooland moisten the air, creating a reasonable model of a cloud in laboratory ditions.

    The  device  worked  very  well,  but  had  an additional, ued be. When heaccelerated an alpha particle through the chamber to seed his make-believe clouds, it left avisible trail—like the trails of a passing airliner. He had just ied the particle detector.

    It provided ving evidehat subatomic particles did indeed exist.

    Eventually two other dish stists ied a more powerful proton-beam device,while in California Er Lawre Berkeley produced his famous and impressivecyclotron, or atom smasher, as such devices were loingly known. All of thesetraptions worked—and iill work—on more or less the same principle, the ideabeing to accelerate a proton or other charged particle to aremely high speed along a traetimes circular, sometimes linear), then bang it into another particle and see what fliesoff. That’s why they were called atom smashers. It wasn’t sce at its subtlest, but it wasgenerally effective.

    As physicists built bigger and more ambitious maes, they began to find or postulateparticles or particle families seemingly without number: muons, pions, hyperons, mesons, K-mesons, Higgs bosons, intermediate vector bosons, baryons, tas. Even physicists beganto grow a little unfortable. “Young man,” Enrico Fermi replied when a student asked himthe name of a particular particle, “if I could remember the names of these particles, I wouldhave been a botanist.”

    Today accelerators have hat sound like something Flash Gordon would use inbattle: the Super Proton Synchrotron, the Large Ele-Positron Collider, the Large HadronCollider, the Relativistic Heavy Ion Collider. Using huge amounts of energy (some operateonly at night so that people in neighb towns don’t have to witheir lights fadihe apparatus is fired up), they  whip particles into such a state of livelihat asingle ele  do forty-seven thousand laps around a four-mile tunnel in a sed. Fearshave been raised that in their enthusiasm stists might iently create a black hole oreven something called “strange quarks,” which could, theoretically, i with othersubatomic particles and propagate untrollably. If you are reading this, that hasn’thappened.

    Finding particles takes a certain amount of tration. They are not just tiny and swiftbut also often tantalizingly eva. Particles  e into being and be gone again in aslittle as 0.000000000000000000000001 sed (10-24). Even the most sluggish of unstableparticles hang around for no more than 0.0000001 sed (10-7).

    Some particles are almost ludicrously slippery. Every sed the Earth is visited by 10,000trillion trillion tiny, all but massless rinos (mostly shot out by the nuclear broilings of theSun), and virtually all of them pass right through the pla and everything that is on it,including you and me, as if it weren’t there. To trap just a few of them, stists anksholding up to 12.5 million gallons of heavy water (that is, water with a relative abundance ofdeuterium in it) in underground chambers (old mines usually) where they ’t be interferedwith by other types of radiation.

    Very occasionally, a passirino will bang into one of the atomiuclei ierand produce a little puff of energy. Stists t the puffs and by such means take us veryslightly closer to uanding the fual properties of the universe. In 1998, Japaneseobservers reported that rinos do have mass, but not a great deal—about oen-millionththat of aron.

    What it really takes to find particles these days is money and lots of it. There is a curiousinverse relationship in modern physics betweeininess of the thing being sought and thescale of facilities required to do the searg. , the European anization for NuclearResearch, is like a little city. Straddling the border of Frand Switzerland, it employsthree thousand people and occupies a site that is measured in square miles.  boasts astring of maghat weigh more than the Eiffel Tower and an underground tunnel oversixteen miles around.

    Breaking up atoms, as James Trefil has noted, is easy; you do it each time you swit afluorest light. Breaking up atomiuclei, however, requires quite a lot of money and agenerous supply of electricity. Getting down to the level of quarks—the particles that make upparticles—requires still more: trillions of volts of electricity and the budget of a small tralAmeriation. ’s new Large Hadron Collider, scheduled to begiions in 2005,will achieve fourteen trillion volts of energy and cost something over $1.5 billion tostruct.

    1But these numbers are as nothing pared with what could have been achieved by, a upon, the vast and now unfortunately o-be Superdug Supercollider, whichbegan being structed near Waxahachie, Texas, in the 1980s, before experieng asupercollision of its own with the Uates gress. The iion of the collider was tolet stists probe “the ultimate nature of matter,” as it is alut, by re-creating as nearlyas possible the ditions in the universe during its first ten thousand billionths of a sed.

    The plan was to fling particles through a tunnel fifty-two miles long, achieving a trulystaggering y-rillion volts of energy. It was a grand scheme, but would also havecost $8 billion to build (a figure that eventually rose to $10 billion) and hundreds of millionsof dollars a year to run.

    In perhaps the fi example in history of p money into a hole in the ground,gress spent $2 billion on the project, then celed it in 1993 after fourteen miles oftunnel had been dug. So Texas now boasts the most expensive hole in the universe. The siteis, I am told by my friend Jeff Guinn of the Fort Worth Star-Telegram, “essentially a vast,cleared field dotted along the circumference by a series of disappointed small towns.”

    1There are practical side effects to all this costly effort. The World Wide Web is a  offshoot. It wasied by a  stist, Tim Berners-Lee, in 1989.

    Sihe supercollider debacle particle physicists have set their sights a little lower, buteven paratively modest projects  be quite breathtakingly costly when pared with,well, almost anything. A proposed rino observatory at the old Homestake Mine in Lead,South Dakota, would cost $500 million to build—this in a mihat is already dug—beforeyou even look at the annual running costs. There would also be $281 million of “generalversion costs.” A particle accelerator at Fermilab in Illinois, meanwhile, cost $260 millioo refit.

    Particle physics, in short, is a hugely expeerprise—but it is a productive one.

    Today the particle t is well over 150, with a further 100 or so suspected, butunfortunately, in the words of Richard Feynman, “it is very difficult to uand therelationships of all these particles, and what nature wants them for, or what the esare from oo another.” Iably each time we mao unlock a box, we find that thereis another locked box inside. Some people think there are particles called tas, which travel faster than the speed of light. Others long to find gravitons—the seat of gravity. Atoint we reach the irreducible bottom is not easy to say. Carl Sagan in os raised thepossibility that if you traveled downward into aron, you might find that it tained auniverse of its own, recalling all those sce fi stories of the fifties. “Within it,anized into the local equivalent of galaxies and smaller structures, are an immense numberof other, much tinier elementary particles, which are themselves universes at the  leveland so on forever—an infinite downward r<tt></tt>egression, universes within universes, endlessly.

    And upward as well.”

    For most of us it is a world that surpasses uanding. To read even aary guideto particle physiowadays you must now find your way through lexical thickets such asthis: “The charged pion and antipion decay respectively into a muon plus arino and anantimuon plus rino with an average lifetime of 2.603 x 10-8seds, the ral piondecays into two photons with an average lifetime of about 0.8 x 10-16seds, and the muonand antimuon decay respectively into . . .” And so it runs on—and this from a book for thegeneral reader by one of the (normally) most lucid of interpreters, Steven Weinberg.

    In the 1960s, in an attempt t just a little simplicity to matters, the Caltech physicistMurray Gell-Mann ied a new class of particles, essentially, in the words of StevenWeinberg, “to restore some ey to the multitude of hadrons”—a collective term used byphysicists for protons, rons, and other particles governed by the strong nuclear force.

    Gell-Mann’s theory was that all hadrons were made up of still smaller, even morefual particles. His colleague Richard Feynman wao call these nearticles partons, as in Dolly, but was overruled. Ihey became known as quarks.

    Gell-Mann took the name from a line in Finnegans Wake: “Three quarks for MusterMark!” (Discriminating physicists rhyme the word with storks, not larks, even though thelatter is almost certainly the pronunciation Joyce had in mind.) The fual simplicity ofquarks was not long lived. As they became better uood it was necessary to introducesubdivisions. Although quarks are muall to have color or taste or any other physicalcharacteristics we would reize, they became clumped into six categories—up, down,strange, charm, top, and bottom—which physicists oddly refer to as their “flavors,” and theseare further divided into the colors red, green, and blue. (One suspects that it was not altogethertal that these terms were first applied in California during the age of psychedelia.)Eventually out of all this emerged what is called the Standard Model, which is essentially asort of parts kit for the subatomic world. The Standard Model sists of six quarks, sixleptons, five known bosons and a postulated sixth, the Higgs boson (named for a Scottishstist, Peter Higgs), plus three of the four physical forces: the strong and weak nuclearforces aromagism.

    The arra essentially is that among the basic building bloatter are quarks;these are held together by particles called gluons; and together quarks and gluons formprotons arons, the stuff of the atom’s nucleus. Leptons are the source of eles arinos. Quarks aons together are called fermions. Bosons (named for the Indianphysicist S. N. Bose) are particles that produd carry forces, and include photons andgluons. The Higgs boson may or may not actually exist; it was ied simply as a way ofendowing particles with mass.

    It is all, as you  see, just a little unwieldy, but it is the simplest model that  explainall that happens in the world of particles. Most particle physicists feel, as Leon Ledermanremarked in a 1985 PBS dotary, that the Standard Model lacks elegand simplicity.

    “It is too plicated. It has too many arbitrary parameters,” Lederman said. “We don’t reallysee the creator twiddling twenty knobs to set twenty parameters to create the universe as weknow it.” Physics is really nothing more than a search for ultimate simplicity, but so far all wehave is a kind of elegant messiness—or as Lederman put it: “There is a deep feeling that thepicture is not beautiful.”

    The Standard Model is not only ungainly but inplete. For ohing, it has nothing at allto say about gravity. Search through the Standard Model as you will, and you won’t findanything to explain why when you place a hat on a table it doesn’t float up to the ceiling. Nor,as we’ve just noted,  it explain mass. In order to give particles any mass at all we have tointroduce the notional Higgs boson; whether it actually exists is a matter for twenty-first-tury physics. As Feynman cheerfully observed: “So we are stuck with a theory, and we donot know whether it is right , but we do know that it is a little wrong, or at leastinplete.”

    In an attempt to draw everything together, physicists have e up with something calledsuperstring theory. This postulates that all those little things like quarks aons that reviously thought of as particles are actually “strings”—vibrating strands of energy thatoscillate in eleven dimensions, sisting of the three we know already plus time and sevenother dimensions that are, well, unknowable to us. The strings are very tiny—tiny enough topass for point particles.

    By introdug extra dimensions, superstring theory enables physicists to pull togetherquantum laws and gravitational ones into one paratively tidy package, but it also meansthat anything stists say about the theory begins to sound wly like the sort ofthoughts that would make you edge away if veyed to you by a stranger on a park bench.

    Here, for example, is the physicist Michio Kaku explaining the structure of the universe froma superstring perspective: “The heterotic string sists of a closed string that has two types ofvibrations, clockwise and terclockwise, which are treated differently. The clockwisevibrations live in a ten-dimensional space. The terclockwise live in a twenty-six-dimensional space, of which sixteen dimensions have been pactified. (We recall that inKaluza’s inal five-dimensional, the fifth dimension was pactified by being edup into a circle.)” And so it goes, for some 350 pages.

    String theory has further spawned something called “M theory,” whicorporatessurfaces known as membranes—or simply “brao the hipper souls of the world ofphysics. I’m afraid this is the stop on the knowledge highway where most of us must get off.

    Here is a sentence from the New York Times, explaining this as simply as possible to a generalaudiehe ekpyrotic process begins far in the indefinite past with a pair of flat emptybranes sitting parallel to each other in a ed five-dimensional space. . . . The two branes,whi the walls of the fifth dimension, could have popped out of nothingness as aquantum fluctuation in the even more distant past and then drifted apart.” Nuing withthat. No uanding it either. Ekpyrotitally, es from the Greek word for“flagration.”

    Matters in physics have now reached<s>.９9lｉb?</s> such a pitch that, as Paul Davies noted in Nature, it is“almost impossible for the non-stist to discrimiween the legitimately weird aright crackpot.” The question came iingly to a head in the fall of 2002 when twoFrench physicists, twin bror and Grickha Bogdanov, produced a theory of ambitiousdensity involving such cepts as “imaginary time” and the “Kubo-Sger-Martindition,” and purp to describe the nothihat was the universe before the BigBang—a period that was always assumed to be unknowable (si predated the birth ofphysid its properties).

    Almost at ohe Bogdanov paper excited debate among physicists as to whether it wastwaddle, a work of genius, or a hoax. “Stifically, it’s clearly more or less pletenonsense,” bia Uy physicist Peter Woit told the New York Times, “but thesedays that doesn’t much distinguish it from a lot of the rest of the literature.”

    Karl Popper, whom Steven Weinberg has called “the dean of modern philosophers ofsce,” once suggested that there may not be an ultimate theory for physics—that, rather,every explanation may require a further explanation, produg “an infinite  of more andmore fual principles.” A rival possibility is that suowledge may simply bebeyond us. “So far, fortunately,” writes Weinberg in Dreams of a Final Theory, “we do o be ing to the end of our intellectual resources.”

    Almost certainly this is ahat will see further developments of thought, and almostcertainly these thoughts will again be beyond most of us.

    While physicists in the middle decades of the tweh-tury were looking perplexedlyinto the world of the very small, astronomers were finding no less arresting an inpletenessof uanding in the universe at large.

    When we last met Edwin Hubble, he had determihat nearly all the galaxies in our fieldof view are flying away from us, and that the speed and distance of this retreat are lyproportional: the farther away the galaxy, the faster it is moving. Hubble realized that thiscould be expressed with a simple equation, Ho = v/d (where Ho is the stant, v is therecessional velocity of a flying galaxy, andd its distance away from us). Ho has been knownever since as the Hubble stant and the whole as Hubble’s Law. Using his formula, Hubblecalculated that the universe was about two billion years old, which was a little awkwardbecause even by the late 1920s it was fairly obvious that many things within the universe—not least Earth itself—were probably older than that. Refining this figure has been an ongoingpreoccupation of ology.

    Almost<tt>99lｉb?t> the only thing stant about the Hubble stant has been the amount ofdisagreement over what value to give it. In 1956, astronomers discovered that Cepheidvariables were more variable than they had thought; they came in two varieties, not ohisallowed them to rework their calculations and e up with a new age for the universe offrom 7 to 20 billion years—not terribly precise, but at least old enough, at last, to embrace theformation of the Earth.

    In the years that followed there erupted a long-running dispute between Allan Sandage, heirto Hubble at Mount Wilson, and Gérard de Vaucouleurs, a French-born astronomer based atthe Uy of Texas. Sandage, after years of careful calculations, arrived at a value for theHubble stant of 50, giving the universe an age of 20 billion years. De Vaucouleurs wasequally certain that the Hubble stant was 100.

    2This would mean that the universe wasonly half the size and age that Sandage believed—ten billion years. Matters took a furtherlurto uainty when in 1994 a team from the egie Observatories in California,using measures from the Hubble space telescope, suggested that the universe could be as littleas eight billion years old—an age even they ceded was youhan some of the starswithin the universe. In February 2003, a team from NASA and the Goddard Space Flightter in Maryland, using a new, far-reag type of satellite called the WilkinsonMicrowave Anistropy Probe, announced with some fidehat the age of the universe is13.7 billion years, give or take a hundred million years or so. There matters rest, at least forthe moment.

    The difficulty in making final determinations is that there are often acres of room forinterpretation. Imagianding in a field at night and trying to decide how far away twodistaric lights are. Using fairly straightforward tools of astronomy you  easilyenough determihat the bulbs are of equal brightness and that one is, say, 50 pert moredistant thaher. But what you ’t be certain of is whether the nearer light is, let ussay, a 58-watt bulb that is 122 feet away or a 61-watt light that is 119 feet, 8 inches away. Ontop of that you must make allowances for distortions caused by variations in the Earth’satmosphere, by intergalactic dust, inating light from fround stars, and many otherfactors. The upshot is that your putations are necessarily based on a series of edassumptions, any of which could be a source of tention. There is also the problem thataccess to telescopes is always at a premium and historically measuring red shifts has beennotably costly in telescope time. It could take all night to get a single exposure. Insequence, astronomers have sometimes been pelled (or willing) to base clusionson notably sty evidence. In ology, as the journalist Geoffrey Carr has suggested, wehave “a mountain of theory built on a molehill of evidence.” Or as Martin Rees has put it:

    “Our present satisfa [with our state of uanding] may reflect the paucity of the datarather than the excellence of the theory.”

    This uainty applies, ially, to relatively nearby things as much as to the distantedges of the universe. As Donald Goldsmith notes, when astronomers say that the galaxy M87is 60 million light-years away, what they really mean (“but do not often stress to the generalpublic”) is that it is somewhere between 40 million and 90 million light-years away—not2You are of course entitled to wonder what is mealy by &quot;a stant of 50&quot; or &quot;a stant of 100.&quot; Theanswer lies in astronomical units of measure. Except versationally, astronomers dont use light-years. Theyuse a distance called the parsec <tt>藏书网</tt>(a tra of parallax and sed), based on a universal measure called thestellar parallax and equivalent to 3.26 light-years. Really big measures, like the size of a universe, are measuredin megaparsecs: a million parsecs. The stant is expressed in terms of kilometers per sed per megaparsec.

    Thus when astronomers refer to a Hubble stant of 50, what they really mean is &quot;50 kilometers per sed permegaparsec.&quot; For most of us that is of course an utterly meaningless measure, but then with astronomicalmeasures most distances are so huge as to be utterly meaningless.

    quite the same thing. For the universe at large, matters are naturally magnified. Bearing allthat in mind, the best bets these days for the age of the universe seem to be fixed on a range ofabout 12 billion to 13.5 billion years, but we remain a long way from unanimity.

    Oerestily suggested theory is that the universe is not nearly as big as wethought, that when we peer into the distane of the galaxies we see may simply berefles, ghost images created by rebounded light.

    The fact is, there is a great deal, even at quite a fual level, that we don’t know— what the universe is made of. When stists calculate the amount of matter ohold things together, they always e up desperately short. It appears that at least 90 pertof the universe, and perhaps as much as 99 pert, is posed of Fritz Zwicky’s “darkmatter”—stuff that is by its nature invisible to us. It is slightly galling to think that we live ina universe that, for the most part, we ’t even see, but there you are. At least the names forthe tossible culprits are eaining: they are said to be either WIMPs (for WeaklyIing Massive Particles, which is to say specks of invisible matter left over from the BigBang) or MACHOs (for MAssive pact Halo Objects—really just another name for blackholes, brown dwarfs, and other very dim stars).

    Particle physicists have teo favor the particle explanation of WIMPs, astrophysiciststhe stellar explanation of MACHOs. For a time MACHOs had the upper hand, but not nearlyenough of them were found, so se swung back toward WIMPs but with the problemthat no WIMP has ever been found. Because they are weakly iing, they are (assumingthey eve) very hard to detect. ic rays would cause too muterference. Sostists must go deep underground. One kilometer underground ibardmentswould be one millionth what they would be on the surface. But even when all these are addedin, “two-thirds of the universe is still missing from the balance sheet,” as one entatorhas put it. For the moment we might very well call them DUNNOS (for Dark UnknownNonreflective able Objects Somewhere).

    Ret evidence suggests that not only are the galaxies of the universe rag away fromus, but that they are doing so at a rate that is accelerating. This is ter to all expectations. Itappears that the universe may not only be filled with dark matter, but with dark energy.

    Stists sometimes also call it vacuum energy or, more exotically, quintessence. Whatever itis, it seems to be driving an expansion that no one  altogether at for. The theory isthat empty space isn’t so empty at all—that there are particles of matter and antimatterpopping iend popping out again—and that these are pushing the universeoutward at an accelerating rate. Improbably enough, the ohing that resolves all this isEinstein’s ological stant—the little pieath he dropped into the general theoryof relativity to stop the universe’s presumed expansion, and called “the biggest blunder of mylife.” It noears that he may have gotten things right after all.

    The upshot of all this is that we live in a universe whose age we ’t quite pute,surrounded by stars whose distances we don’t altogether know, filled with matter we ’tidentify, operating in ah physical laws whose properties we don’t trulyuand.

    And on that rather uling note, let’s return to Plah and sider something thatwe do uand—though by now you perhaps won’t be surprised to hear that we don’tuand it pletely and what we do uand we haven’t uood for long.

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