IN 1911, A Britisist named C. t. R. ilson udying cloud formations bytramping regularly to t of Ben Nevis, a famously damp Scottisain, o  t be an easier o study clouds. Back in t an artificial cloud cen ting a reasonable model of a cloud in laboratory conditions.

    t  ional, unexpected benefit. ed an alpicle to seed  left avisible trail—like trails of a passing airliner.  invented ticle detector.

    It provided convincing evidence t subatomic particles did indeed exist.

    Eventually tists invented a more poon-beam device, Berkeley produced ron, or atom smasingly knoraptions ill o accelerate a proton or oticle to an extremely rack(sometimes circular, sometimes linear), t into anoticle and see ’s  science at its subtlest, but it ive.

    As ps built bigger and more ambitious maco find or postulateparticles or particle families seemingly  number: muons, pions, ermediate vector bosons, baryons, tacs beganto grotle uncomfortable. “Young man,” Enrico Fermi replied  asked icular particle, “if I could remember ticles, I .”

    today accelerators  sound like somettle: ton Syncron, tron-Positron Collider, tivistic s of energy (some operateonly at nig people in neigo o ness ts fadingicles into sucate of liveliness t asingle electron can do forty-seven tunnel in a second. Fears in tists migently create a black range quarks,” eract omic particles and propagate uncontrollably. If you are reading t happened.

    Finding particles takes a certain amount of concentration. t just tiny and sbut also often tantalizingly evanescent. Particles can come into being and be gone again in aslittle as 0.000000000000000000000001 second (10-24). Even t sluggisableparticles han 0.0000001 second (10-7).

    Some particles are almost ludicrously slippery. Every second ted by 10,000trillion trillion tiny, all but massless neutrinos (mostly s out by tually all of t t and everyt is on it,including you and me, as if it  to trap just a feists need tankso 12.5 million gallons of er (t is, er ive abundance ofdeuterium in it) in underground c be interferedypes of radiation.

    Very occasionally, a passing neutrino o one of tomic nuclei in terand produce a little puff of energy. Scientists count take us verysligo understanding tal properties of ted t neutrinos do  not a great deal—about one ten-milliont of an electron.

    it really takes to find particles ts of it. tionsininess of t and ties required to do tion for NuclearResearctle city. Straddling tzerland, it employste t is measured in square miles. CERN boasts astring of magnets t unnel oversixteen miles around.

    Breaking up atoms, as James trefil ed, is easy; you do it eacime you sc ligomic nuclei, e a lot of money and agenerous supply of electricity. Getting doo ticles t make upparticles—requires still more: trillions of volts of electricity and t of a small CentralAmerican nation. CERN’s neions in 2005,rillion volts of energy and cost sometoconstruct.

    1But t could  upon, t and nounately never-to-be Superconducting Supercollider, ed near axaexas, in ts oed States Congress. tention of tolet scientists probe “timate nature of matter,” as it is al, by re-creating as nearlyas possible tions in ts first ten ths of a second.

    to fling particles tunnel fifty-taggering ninety-nine trillion volts of energy. It o build (a figure t eventually rose to $10 billion) and o run.

    In per example in ory of pouring money into a  $2 billion on t, t in 1993 after fourteen miles oftunnel exas nos t expensive eis, I am told by my friend Jeff Guinn of t ortar-telegram, “essentially a vast,cleared field dotted along ted small towns.”

    1tical side effects to all tly effort. t. It ed by a CERN scientist, tim Berners-Lee, in 1989.

    Since ticle ps  ts a little loeven comparatively modest projects can be quite breatly rino observatory at take Mine in Lead,Souta,  $500 million to build—t is already dug—beforeyou even look at ts. ts.” A particle accelerator at Fermilab in Illinois, meano refit.

    Particle p, is a erprise—but it is a productive one.

    today ticle count is ed, butunfortunately, in t is very difficult to understand tionsicles, and ure s t tionsare from one to anotably eacime o unlock a box,  ticles called tacravel faster t. Oto find gravitons—t of gravity. At om is not easy to say. Carl Sagan in Cosmos raised ty t if you traveled doo an electron, you mig it contained auniverse of its oion stories of ties. “it,organized into t of galaxies and smaller structures, are an immense numberof otinier elementary particles,  leveland so on forever—an infinite dohin universes, endlessly.

    And upward as well.”

    For most of us it is a  surpasses understanding. to read even an elementary guideto particle p nos sucipion decay respectively into a muon plus antineutrino and anantimuon plus neutrino ime of 2.603 x 10-8seconds, tral piondecays into time of about 0.8 x 10-16seconds, and timuon decay respectively into . . .” And so it runs on—and t lucid of interpreters, Steven einberg.

    In ttempt to bring just a little simplicity to matters, tecMurray Gell-Mann invented a neicles, essentially, in teveneinberg, “to restore some economy to titude of ive term used byps for protons, neutrons, and oticles governed by trong nuclear force.

    Gell-Mann’s t all ill smaller, even morefundamental particles. ed to call ticles partons, as in Dolly, but ead they became known as quarks.

    Gell-Mann took terMark!” (Discriminating ps rorks, not larks, even tter is almost certainly tion Joyce al simplicity ofquarks  long lived. As tter understood it o introducesubdivisions. Altoo small to aste or any oteristics o six categories—up, dorange, cop, and bottom—o as to ts t it  altogetal t terms  applied in California during tually out of all t is called tandard Model,  of parts kit for tomic andard Model consists of six quarks, sixleptons, five knoulated sixttisist, Peter rong and romagnetism.

    t essentially is t among tter are quarks;togeticles called gluons; and togetons and neutrons, tuff of tom’s nucleus. Leptons are trons andneutrinos. Quarks and leptons toget S. N. Bose) are particles t produce and carry forces, and include pons andgluons. t actually exist; it ed simply as a icles h mass.

    It is all, as you can see, just a little un it is t model t can explainall t icles. Most particle ps feel, as Leon Ledermanremarked in a 1985 PBS documentary, t tandard Model lacks elegance and simplicity.

    “It is too complicated. It oo many arbitrary parameters,” Lederman said. “e don’t reallysee tor ty knobs to set ty parameters to create t.” Pimate simplicity, but so far all  it: “t ture is not beautiful.”

    tandard Model is not only ungainly but incomplete. For one t  allto say about gravity. Searcandard Model as you  findanyto explain able it doesn’t float up to t noted, can it explain mass. In order to give particles any mass at all roduce tional  actually exists is a matter for ty-first-century puck  kno it is a little  leastincomplete.”

    In an attempt to draogets ring tulates t all ttle tons t icles are actually “strings”—vibrating strands of energy toscillate in eleven dimensions, consisting of time and sevenot are, o us. trings are very tiny—tiny enougopass for point particles.

    By introducing extra dimensions, superstring ts to pull togetum laational ones into one comparatively tidy package, but it also meanst anytists say about to sound  ofts t o you by a stranger on a park bench.

    Micructure of tring perspective: “terotic string consists of a closed string t ypes ofvibrations, clockerclocked differently. tions live in a ten-dimensional space. terclocky-six-dimensional space, of  inKaluza’s original five-dimensional, tified by being o a circle.)” And so it goes, for some 350 pages.

    String tessurfaces knoo top on t of us must get off.

    ence from times, explaining to a generalaudience: “tic process begins far in te past  emptybranes sitting parallel to eacum fluctuation in tant past and ted apart.” No arguing . No understanding it eitic, incidentally, comes from tion.”

    Matters in pc, as Paul Davies noted in Nature, it is“almost impossible for tist to discriminate betimately rig.” tion came interestingly to a iousdensity involving sucs as “imaginary time” and tincondition,” and purporting to describe t  o be unkno predated ts properties).

    Almost at once ted debate among ps as to ’s clearly more or less completenonsense,” Columbia University p Peter oit told times, “but t doesn’t mucinguis from a lot of t of terature.”

    Karl Popper,  t be an ultimate t, ration may require a furtion, producing “an infinite cal principles.” A rival possibility is t sucunately,” es einberg in Dreams of a Final tseem to be coming to tellectual resources.”

    Almost certainly t s of t, and almostcertainly ts  of us.

    s in tietury o tronomers ing an incompletenessof understanding in t large.

    met Ed nearly all t tance of treat are neatlyproportional: ter it is moving.  tion, ant, v is ty of a flying galaxy, andd its distance a and ted t t tle ae 1920s it  many t least Eartself—. Refining tion of cosmology.

    Almost tant about tant  ofdisagreement over o give it. In 1956, astronomers discovered t Cep; ties, not one. to reions and come up o 20 billion years—not terribly precise, but at least old enoug last, to embrace tion of th.

    In t folloed a long-running dispute bet ilson, and Gérard de Vaucouleurs, a Frencronomer based atty of texas. Sandage, after years of careful calculations, arrived at a value for tant of 50, giving tain t tant was 100.

    2t t Sandage believed—ten billion years. Matters took a furto uncertainty ories in California,using measures from telescope, suggested t ttleas eigarseam from NASA and tCenter in Maryland, using a neellite called tropy Probe, announced  take a ters rest, at least fort.

    ty in making final determinations is t ten acres of room forinterpretation. Imagine standing in a field at nigrying to decide ant electric ligraigools of astronomy you can easilyenougermine t tness and t one is, say, 50 percent moredistant t  be certain of is  ussay, a 58-t bulb t is 122 feet at lig is 119 feet, 8 incop of t you must make alloortions caused by variations in tmospergalactic dust, contaminating ligars, and many otors. t is t your computations are necessarily based on a series of nestedassumptions, any of ion. taccess to telescopes is al a premium and orically measuring red ss ably costly in telescope time. It could take all nigo get a single exposure. Inconsequence, astronomers imes been compelled (or o base conclusionson notably scanty evidence. In cosmology, as t Geoffrey Carr ed,  on a molein Rees  it:

    “Our present satisfaction [ate of understanding] may reflect ty of taratheory.”

    tainty applies, incidentally, to relatively nearby to tantedges of tes,  t-years a do not often stress to t it is someitled to  exactly by quot;a constant of 50quot; or quot;a constant of 100.quot; tronomical units of measure. Except conversationally, astronomers dont use ligance called traction of parallax and second), based on a universal measure called tellar parallax and equivalent to 3.26 ligant is expressed in terms of kilometers per second per megaparsec.

    tronomers refer to a ant of 50, ;50 kilometers per second permegaparsec.quot; For most of us t is of course an utterly meaningless measure, but tronomicalmeasures most distances are so o be utterly meaningless.

    quite t large, matters are naturally magnified. Bearing allt in mind, t bets to be fixed on a range ofabout 12 billion to 13.5 billion years, but y.

    One interesting recently suggested t t nearly as big as , t ance some of tions, g images created by rebounded light.

    t is, t deal, even at quite a fundamental level, t  knoleast ists calculate t of matter needed toogetely s. It appears t at least 90 percentof t, is composed of Fritz Zter”—stuff t is by its nature invisible to us. It is sligo t , for t part,  even see, but t least ts are entertaining: to be eiteracting Massive Particles, ter left over from t s—really just anotars).

    Particle ps ended to favor ticle explanation of IMPs, astropstellar explanation of MACime MAC not nearlyenougiment so  no IMP eracting, t) very o detect. Cosmic rays oo mucerference. Soscientists must go deep underground. One kilometer underground cosmic bombardments t even ill missing from t,” as one commentator it. For t ectable Objects Somewhere).

    Recent evidence suggests t not only are t t t a rate t is accelerating. ter to all expectations. Itappears t t only be filled ter, but h dark energy.

    Scientists sometimes also call it vacuum energy or, more exotically, quintessence. ever itis, it seems to be driving an expansion t no one can altoget for. t empty space isn’t so empty at all—t ticles of matter and antimatterpopping into existence and popping out again—and t t an accelerating rate. Improbably enoug resolves all tein’s cosmological constant—ttle piece of mato tivity to stop t blunder of mylife.” It no ten t after all.

    t of all t e compute,surrounded by stars  altogetter identify, operating in conformance ies  trulyunderstand.

    And on t rattling note, let’s return to Planet Eartand—t be surprised to  understand it completely and and ood for long.