Post on 27-Feb-2018
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ST A N F O RD L I N EA R A C C EL ERA T O R C EN T ER
Fall 1997, Vol. 27, No.3
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FEATU RES
2 INN ER SPAC E & OU TER SPAC ECosmol ogy is in th e m id st of a Golden A ge
tr iggered i n part by ideas about th e early
m om ent s of the U niv erse based upon th e uni -
ficati on of t he forces and part icl es of N atu re.
Mi chael S. Turner
14 WAS CO SMIC INFLATION THE BANG OFTHE BIG BANG ?
Tw o thousand years after Lucreti us
proclaim ed t hat n othi ng can be created
fr om not hi ng, inflat i onar y cosmol ogy assert s
that he was wrong.
Alan H. G u th
22 Th e Sloan D igi t al Sk y Surv eyPI ON THE SKY
Heidi Jo New berg
29 The D eep Extragalacti c Evolut ionary ProbePRO BING THE EVOLVING U N IVERSEAndrew Phillips and Nicole Vogt
36 THE FATE OF TH E U N IVERSEWi th the i r d iscovery of t he most d is tant
supernov as ever observed, an i nt ern ati onal
scient ific t eam led b y r esearchers from
Law rence Berk eley Nat ional L aboratory hope
to learn the ult i m ate fate of our U ni verse.
G erson G oldhaber and Judith G oldhaber
A PERIOD ICAL OF PARTICLE PH YSIC S
FALL 1997 VOL. 27, N U M BER 3
Editors
REN E D ONALDSON , BILL KIRK
Contributing Editor
M ICHAEL R IORDAN
Editorial Advisory BoardJAMES BJORKEN , G EORGE BROWN ,
ROBERT N . C AH N , D AVID H ITLIN ,
JOEL PRIMACK , N ATALIE ROE,
ROBERT SIEMANN
Illustrat ions
TERRY ANDERSON
Distribut ion
C RYSTAL TILGHMAN
The Beam Li neis published qua rterly bythe Sta nford Linear Accelerator Cent er,P O Box 4349, Stanford, C A 94309.Telephone: (415) 926-2585INTERNET: beam line@slac.stanford.eduFAX : (415) 926-4500Issues of the Beam Li neare accessible electronically onth e World Wide Web at ht tp://w w w.sl ac.st an ford.edu/pubs/beam line. SLAC is operated by Stanford Universityunder contract wit h the U .S. D epartment of Energy. Theopinions of the authors do not necessarily refl ect thepolicy of the St anford Linear Accelerator C enter.
C over: Electronic p hoto m ontag e d esigned by Beam Linegrap hic artist Terry A nd erson. The Einstein im ag e is cour-tesy of the A rchives, C alifornia Institute of Technology. Thephotograph of the K eck telescop es w as taken by A ndyPerala. The H ubble D eep Field im ag e is courtesy ofA U R A /STS ci.
C
opyright1997
N
ationalG
eographic
Society.A
llrightsreserved.)
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CONTENTS
43 SEARC HIN G FOR D ARK MATTER AXIONSThe search is on for one of t he dark m att er
candi dat es so eagerly sought by
astr ophysici st sa conjectu red relic parti cle
from th e ti m e of the Big Bang cal led the axion.
Leslie J Rosenberg and Karl A. Van Bibber
49 ASTRO N OM Y & THE IN TERN ETThe aut hor toured the H arvard-Sm it hsoni an
Center for A strophysics for OMNI Online i n
November 1996. Th is piece led t he series
and is reprint ed from O M N I Online.
Fred Hapgood
DEPARTMENTS
52 TH E U N IVERSE AT LARG ECosmology: Where in the $**%Universe
Are You?
Virginia Trimble
61 CONTRIBUTORS
DATES TO REMEMBER
A
U
R
A
/STScI
D
an
Long
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CO S M O L O G IS TS TA C K LE th e big quest i ons. What
is the size and shape of the U niverse? What is it m ade
of? How did it all begin? How w ill it all end? Not sur-
prisingly, progress has com e in f i t s an d sta r ts . Sometim es i t
is a key event th at advances our understan ding. For exam pleEdw in H ubbles discovery of t he expansion of t he U niverse in
1929 w as the f i rs t ind ica t ion t ha t i t began f rom a B ig Bang
and Arno P enzias an d Robert Wilsons happening upon the m i
crow ave echo of the big bang in 1964 established t hat the be-
ginning w as very hot and dense. Other t im es conceptual break
throughs have advanced cosmology, such as Albert Einsteins
introduction of the G eneral Theory of Relativit y in 1916 which
allow ed the fi rst m athem atical description of the U niverse, and
G e or ge G a m o w s l a t e 1940s sugges t ion th a t t he ea rly U ni-
verse w as a nuclear furnace tha t cooked th e periodic table oelements, w hich w as the fi rst application of physics to the study
of its origin an d evolution.
G olden ages usually com e at t he conjunction of conceptual
and observational adva nces. C osmology is in the m idst of such
an age today. The conceptual breakth rough ca m e in t he 1980s
w i th t he rea l iza t ion t ha t uni f ied par t ic le theories have im-
por tant consequences for the earl ies t m oment s and m ay be
IN N E R
b y M I C H A E L S . T U R N E R
Cosm ology i s in th e
m id st of a Gol den A get ri ggered i n part by i deas
about t he earl i est
m oment s of the
U ni verse based upon
th e uni ficat i on of t he
forces and part i cles
of Nature.
SPACE
&O U T E RSPACE
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BEAM LIN E 3
crucial to answ ering some of t he m ost pressing ques-
tion s in cosmology. And furthermo re, part icle ac-
ce lera tors a re a new k ind o f t e lescope tha t a l low
the recreation of t he earliest m oments in t he colli-
sions of very high-energy part ic les . The inner
space/outer space connection has led t o a remarkable
extension of the Big Bang model w hich, if correct ,
w il l extend our understanding of the Un iverse to
w i t h i n 1032 sec of the beginnin g. This paradigm ,
know n as infl ation and cold dark matt er, holds that
the bulk of the ma tter in the U niverse exists in theform of slow ly m oving elem entary particlescold dark m att erthat
rem ain from the earl iest m om ents and tha t a l l the st ructures w e
see in th e U niversegalaxies, clust ers of galaxies, superclusters,
voids, great w alls and so ongrew from quantum mechanical fl uc-
tuations occurring on the subatomic scales.
On t he observation al side, w e are in the m idst
of a t echnologica l revolut ion t ha t can be t raced
back to the comm issioning of the 200-inch Hale
telescope on Mt. Palom ar in 1948, w hich a l low ed
cosmological pioneers Hubble, Milton H um ason,
and Allan Sandage to begin the serious study of th eU niv erse. The int roduct ion of cha rge-coupled de-
vices in astronomy in the 1970s increased th e light-
gathering pow er of photon detectors a hun dred-
fold, m aking the Hale the equivalent of a 2000-inch
telescope. The increase in com puter pow er over
the past forty years by truly astronomical factors
w as equa l ly c ruc ia l . New w indows on the Uni-
verse w ere opened w ith space-based telescopes for
the ul t raviolet , in frared, X-ray, and gam m a-ray
bands as w ell as the fi rst optical t elescope above
Earths blurring at m osphere. Other new instrum ents w ere developed:long-baseline radio interferom eters w ith m illiarcsecond resolution,
the 10-m eter Keck telescopes w ith their advanced instrum ents, and
sensitive receivers using high electron m obility transist ors and bolome-
ters to study the microw ave rem nant of t he Big Bang.
This issue of t he Beam Li neillustrat es w ell the close relationship
betw een particle physics and cosmology t hat has developed over the
pas t tw o decades . Al l the a r t ic les rela te to t es t ing in f la t ion an d
cold dark ma tt er. Man y of the protagonist s (and aut hors) start ed their
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4 FA LL 1997
careers as high-energy physicists. Alan G uth
author of the art icle on infl ation and inventor
of infl ation, w as trained as a high-energy t he
orist and w as a SLAC visitor w hen he did his
seminal w ork. Indeed, much of in f la t ionary
cosmology w as developed by high-energy t he
orists w ho have become part-tim e or full-tim e
cosmologists like G uth a nd I (m y graduate ca
reer began at SLAC ). The art icle on th e search
for axionsone of th e leading candidates for
the constituents of cold dark mat teris w ritten by tw o experiment alists, Leslie Rosenberg
and Karl van Bibber, w ho began th eir careers
in high-energy and m edium -energy physics respectiv ely. The Fate
of the U niverse w hich describes the quest t o measure its geom e
try and is w ritten by G erson G oldhaber, know n for his role in the dis
covery of charm, and his w ife Judith . Pi on the Sky, w ri t ten by
Heidi N ew berg, is about m apping the large-scale structure of the U ni
verse by determin ing th e three-dimensional posit ions of a m illion
galaxies. One of the ma jor partners in this collaborat ive effort, know n
of f icia l ly a s t he S loan D ig i t a l Sky Survey or S D S S , is the Ferm i
N ation al Accelerator Laboratory in Illinois. While the article w hichconcerns the study o f the origin and evolution of galaxies by bring
ing to bear tw o of the m ost powerful astronomical instrumentsthe
Hubble Space Telescope and the twin Keck 10-m eter telescopesis
w rit ten by t w o astronomers, Andrew Phillips and N icole Vogt , one
of th e key participants in this project is high-energy t heorist turn ed
astronomer and form er SLAC graduate student P rofessor Joel Prim ack
of the U niversity of C alifornia, Santa C ruz. Finally, Virginia Trimble
a frequent Beam Li necontributor and bicoastal astronom er, has con
tributed an overview of the U niverse, from t he sma llest to t he bigges
and th e shortest to t he longest , to put cosm ology in to i t s proper
perspective.
TALL SH OU LD ERSTH E H O T BIG -BANG (stan dard) cosmology w ill likely be view edas one of the intellectual t riumphs of the tw entieth century. It pro
vides a tested account of the U niverse from a fraction of a second af
ter the beginning until the present 10 t o 15 billion years later, as w el
The m ain ring of the w orlds m ost pow er-
ful accelerator, Ferm ilabs Tevatron. C ol-
lisions recreate conditions that last
existed 1012 seconds after the B ig Bang.
(C ourtesy Ferm ilab Visual M ed ia S ervices)
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as a fi rm base for speculations about m uch earlier tim es. According
to t h is cosmology, the U niverse began as a hot , very dense form-
less soup of the fundam enta l part iclesqua rks, leptons, gauge bosons,
and possibly oth er elem entary particles. As it expanded and cooled,
layer upon layer of structu re built up. At around 105 sec, neutrons an d
proton s formed from q uarks. In a series of w ell understood nu clear re-
actions t hat t ook place betw een a fraction of a second and several hun-
dred seconds, the nuclei of th e light elements D , 3He, 4He and 7Li were
form ed. (The element s beyond 7Li w ere formed much lat er by nuclear
reactions w ithin st ars.) By a few hu ndred th ousand years the Un iverse
had cooled suf f icient ly so tha t a t oms could form from t he nucleiand free electrons present . Over t he next 10 t o 15 billion years all
the cosmic st ructure seen to-
day, from individual stars to su-
perclusters and great wal ls ,
developed th rough t he at t rac-
tive action of gravit y.
There is a w eal th of obser-
vational data th at support the
standard cosm ology; four ob-
servations provide the corner-
ston es. They a re the expansionof the U niverse; the microw ave
echo of the Big Bang (know n as
the cosm ic background radia-
tion or C BR ); the abun dance of
D , 3He, and 4He and 7Li; and
the t iny variat ions (about one
part in 105) in th e intensit y of
the C BR betw een different di-
rections on the sky.
Hubble present ed the first
evidence for a l inear rela t ionbetw een th e distances and the
veloci t ies of ga laxies . Now
know n as H ubbles Law, t his relation is w ell established (see sidebar
on page 30). The n otorious proportiona lity constan tHubbles con-
stant or H0, w hose reciprocal sets t he t im e back to th e bangis fi -
nally being pinned dow n to a precision of around 10 percent, thank s
to observat ions being m ade by t he H ubble Space Telescope and clever
techniques t hat exploit X-ray an d m icrow ave observat ions. Hubbles
B ig-bang prod uction of the light elem ents
dep ends up on the density of ordinary
m atter and agrees w ith the m easured
ab undances for densities ind icated by thew hite band, w hich falls far short of the critical
density. (C ourtesy K enneth N ollett)
101
103
105
107
109
1032
1031
1030
1029
Abundan
ceRelativetoHydrogen
Density of Ordinary Matter
(bar yo ns) (g/cc)
ConsistencyInterval C
riticalDensityfor
H 0 =70km/s/Mpc
4H e
3H e
7Li
D
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Law supports t he idea of an expanding universe and
provides the fundamenta l m eans of determining dis
tances to ga laxies: the m easured redshif t t imes c/H0is the distance to t he ga laxy .
U n a w a r e o f G a m ow s pr ed ic t i on o f a m ic r ow a v e
afterglow of the Big Bang, Penzia s and Wilson discovered th is ra-
diat ion serendipit iously. The Far Infrared Absolute Spectropho-
tom eter on the C O B E sa tel l i te , launched in 1989, has shown t ha t
the cosmic background radia t ion is black
b od y r a d i a t i on t o ex t r a o rd in a r y pr ec i
s ion , b et t e r t h a n 0.01 p er c en t , w i t h atem perature of 2.7277 0.002K. (All o b-
jects emit radia t ion charac t erist ic
o f the i r t empera ture ; for a fea-
tureless black body t he spectrum
only depends upon th e temperature and
is of a form first described by Pla nck.)
Since the C BR provides a snapshot of t he U niverse
at the t ime t hese photons last scat t ered, around 300,000
years after the bang w hen the Un iverse was about one thou-
sandth i t s present s ize; i t has been scrut inized for in tensi ty
(tem perature) variat ions t hat can reveal the distribution of m at-ter a t th is early t ime. In the 1970s a dipolar variat ion of about
3 m K w as d iscovered ; i t s s implest in t erpre t a t ion i s t ha t our
G alaxy m oves a t a veloci ty of 620 km /sec w ith respect t o the
cosmic rest f rame. In 1992 the Dif ferent ia l Microwave Radiome-
ter (D M R ) on t he C O B E sa tel l i te d iscovered much sm aller var ia
t ion s in the temperat ure: 30 m icroKelvin tem perature differences
betw een directions separated by an gles of around 10 degrees on th e
sky. This discovery tells us tw o thin gs: the early U niverse w as very
smoot h , and there were sm a l l va r ia t ions in the dens i t y o f m a t -
ter, about one part in 105.
The t iny varia t ions in t he C BR tem perature validat e a key ele-m en t o f t h e B ig B a n g t h eor y , t h e id ea t h a t a l l t h e s t r u c t u r e w e
see arose from small var ia t ions in t he mat ter densi ty w hich grew
under the influence of gravit y over th e past t en billion or so years
Fu r t h er , t h ey a l l ow u s t o b eg in t o q u a n t i f y t h e n a t u r e o f t h e
prim eva l lum piness and tes t ideas (inc lud ing G uth s and m ine
about t heir origin.
C O BE D M R m ap of the C B R (bright band across
m iddle is em ission from our ow n galaxy). The tw o
blow -up s show a sim ulation of the ne detail that
exists w ithin the C O B E 7 beam w hich the M A P
and Planck satellites should reveal. The d if-
ference betw een an open universe m odel
( = 0.1) on the left and a at universe m od el
( = 1) on the right is very striking.
(C ourtesy M artin W hite)
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Finally, the abundan ce patt ern of the light elem ents D , 3He, 4H e
and 7Li seen in the m ost prim itive sam ples of the cosmos conform t o
the predictions of big-bang nucleosynt hesis. This tests t he Big Bang
theory t o w ithin a f rac t ion of a second of the beginning, and pro-
vides tw o bonuses: the yields of these elements depend upon t he m ass
density cont ributed by ordinary m att er (baryons) and t he num ber of
light n eutrino species. Since the early 1980s it has been known t hat
thi s agreement holds only i f the num ber of neutrino species is less
tha n four and the baryon density is betw een about 1 percent an d 10
percent of t he critical density. The cosmological prediction of the
num ber of neutr ino species m ade by D avid Schram m and his col-laborators was confi rmed in 1989 by precision m easurements of t he
properties of th e Zboson w ith the SLC at SLAC and w ith LEP at CERN ,
the European particle physics laboratory. This determin ation of th e
baryon dens i t y i s the l inchpin in the a rgument tha t most o f the
m ass in the U niverse exists in the form of elementa ry particles left
over from earliest m om ents.
The hot big-bang cosmology is not complete, nor is it likely to be
the w hole story. There are importan t properties of the Un iverse yet t o
be determ ined: the precise value of the expansion rate and t im e back
to t he bang, the fract ion of th e crit ical density contributed by m at-
ter, the geometric shape of the U niverse (fl at , curved like th e surfaceof a ball , or curved like th e surface of a saddle), th e value of Ein-
steins cosmological constant, a better understanding of how galax-
ies form and evolv e, a m ore precise description of t he large-scale
distribution of m att er, and the nat ure of the ubiquitous dark m att er.
(While the tota l am ount of m att er is not know n precisely, only a sm all
fraction of it exists in the form of stars and sim ilar visible m att er.)
And, fundam ental questions remain unansw ered. Why is t he U niverse
m ade of mat ter and not equal amount s of matt er and antim att er? What
is the origin of the m att er lumpiness that seeded all structure in the
U niverse? Why w as the early U niverse so smooth? What w ent bang?
Thanks t o the current explosion in observational cosm ology, w e arerapidly c losing in on m any of the f irst set of quest ions. The m ea-
surem ents being ma de can strengthen the case for the sta ndard cos-
m ology as w ell as help to t est ideas put forth to extend it. And, of course,
they could bring some surprises. The second set of questi ons points t o
th e existence of a grander theory, w hich is w here the inner space/out er
space connection comes in.
The LE P tunnel atC E R N w hich houses
the m ost pow erful electron/positron
collider and w ill eventually house the
Large H adron C ollider, w hich w ill be
able to recreate conditions that last
existed 1015 second s after the B ig
B ang. (C ourtesy C E R N )
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The B aB ar detector w ill be used to
stud y the m atter-antim atter asym m etry
puzzle and could help cosm olog ists to
understand better the origin of ordinary
m atter in the U niverse.
TH E IN N ER SPAC E/OU TER SPAC E C ONN EC TIONIN ITS IN FAN C Y TH E U NIVERSE w as a hot soup of the fundam ental part iclesquarks, leptons, and gauge bosons. The further
back in ti m e, the higher th e tem perature and energy per partic le. Par
ticle accelerators creat e a soup of high-energy q uarks, leptons, an d
related particles w hen they collide proton s and antiprotons, electron
and positrons, or positrons and protons. Therefore, like telescopes
they are cosm ic t im e machines that a llow cosmologists to explore
the earliest m om ents. C onversely, the early U niverse is a very powerful cosm ic accelerator t hat allow s particle physicists to probe deepe
into inner space than they can with terrestrial accelerators.
The unificat ion of the forces and part icles of Nat ure is the holy
gra i l of part ic le physics . There is a genera l bel ief and som e evi
dence (for example, the uni f ica t ion of the
w eak and electromagnetic forces) tha t t he ful
simplicity of N ature is only m anifest at high
energies and tem perat ures. This m akes th e
early U niverse a testing ground for th e grand
est ideas of particle physics, including uni-
f ica t ion o f t he s t rong , w eak , and e lec t rom agnetic forces, supersym m etry, and super-
strings. C onversely, the unifi cation of the par
ticles and forces certainly has consequences
for the earliest evolution of the U niverse.
The 1980s w ere the go-go days of early U ni
verse cosmology. Ma ny excit ing ideas about
the earl iest m om ents based upon specula
tions about the unifi cation of the forces w ere
put forth. An at tract ive explanation for the
origin of the asym metry betw een m atter and
ant im at ter know n as baryogenesis developed. Baryogenesis holdsthat a slight excess of matterquarks and leptonsarose early on
due to the sam e force that leads to t he instability of the proton and
the sl ight preference for m at t er in the law s of physics (C P v io la
tion). (See the article, The Myst ery of the Ma tt er Asymm etry by
Eric Sather in t he Spring/ Sum m er 1996 issue of the Beam L i ne
Vol. 26, No. 1.) After all the an tim att er annihilated w ith m att er (around
105 sec) only th e mat ter w e see today rem ained. The m ajor scien-
t i f ic goa l o f the SLAC B Factory is a bet ter understanding of C P
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BEAM LIN E 9
violation and possibly of baryogenesis (see the article by N ata lie Roe
and M ichael Riordan, Why Are We Building B Factories? in t heSpring/Sum m er 1996 issue, Vol. 26, No. 1.)
As the U niverse evolved it sho uld have gone through a series of
phase transit ions a s th e different forces of Nat ure developed their
ow n charact er and the forces became less unifi ed. These phase tran-
sit ions, not unlike the m ore fam iliar phase transit ion from steam
to w ater, could w ell have left t heir imprint on the future evolution
of the U niverse. If a phase transition did not proceed smoot hly an d
uniformly, topological defects m ay have been formed that could
still be w ith u s today. They include superheavy m agnetic m onopoles
and cosmic strings, w hich are very thin con centration s of false vac-
uum energy. These defects could act as t he seeds for the form ationof s t ructure or have ot her in terest ing consequences such as pro-
ducing extremely high-energy cosm ic rays. Som e theorists ha ve spec-
ula ted tha t even t he m ost w ell understood phase t ransi t ion , f rom
quark-gluon plasm a to ordinary ha drons, may h ave left macroscop-
ic nuggets of quark m att er.
B
EYO N D TH E STANDARD C O S M O L O G Y:
IN FLATION AN D C O LD D AR K M ATTER
THE MO S T CO M P ELLING and expansive idea to come from th einner space/outer space connection is infl ation and cold dark m att er.
It addresses essentially all of th e fundam ental q uestions being asked
by cosm ologists and has m oved a generat ion of observers and ex-
periment ers to go out an d disprove it! As G uth describes, the smoot h-
ness and f la t ness of the observed Un iverse ar ises because of an
enorm ous burst of expansion ca used by false-vacuu m energy. The
eventual decay of this energy produced all the heat of the Big Bang
PaulJ.Stom
ski,Jr.
The tw in 10-m eter K eck telescopes on
M auna K ea in H aw aii.
(C ourtesy Paul Stom ski)
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10 FA LL 1997
and eventually all t he
mat ter w e see today
The m ost st riking pre
d ic t i on i s t h a t t h e
primeval lumpiness
arises due to quant um
mechan ica l f luc tua-
t ions on suba tomic
sca les , wh ich were
s t re t ched to cosmic
size by the enormousburst of expansion.
A f la t universe
has t he critical density and expands forever. Big-Bang nucleosynt hesi
tells us that ordinary m att er accounts for slightly less than 10 per-
cent of the crit ical density; this m eans that something m ore exotic
m ust t ake up the slack. Pa rticle physics provides several prom ising
particle candidates: the axion, a hypoth etical particle that is supposed
to w eigh a million, m illion t im es less than the electron (discussed
in t he art icle by va n Bibber and Rosen berg on page 43 of th is issue)
the neutralino, a h ypothetical part icle predicted to exist if N ature
is supersym m etric and is supposed to be betw een ten and fi ve hundred t im es heavier than the proton; and ordinary neutrinos if they
have m ass, as most u nified theories predict . All th ree candida tes
should have been present during the earliest fi ery m om ents in great
abundan ce and according to calculat ions should be present t oday
in about t he right n um bers to account for the critical density. Axion
and neut ra l inos m ove s lowly and for th is reason a re ca l led co ld
dark matt er; neutrinos move fast and are known as hot dark mat ter
Hav ing th e bu lk o f the ma t ter in the form of re l ic elementa ry
pa r t i c le s fi t s n i c ely w i t h t h e f a c t t h a t m os t o f t h e m a t t e r in t h e
U niverse is know n to be dark. C osmologists are more interested in
cold dark m at t er tha n neutr inos because they a re conf ident tha tthe developm ent of s t ructure in a hot dark ma t t er universe leads
to a universe radically different from ours.
The idea that t he bulk of the dark mat ter is cold dark ma tt er par
t ic les and tha t the pr imeva l lumpiness a rose f rom quan tum
m echanical fl uctua tions provide the basis for a com prehensive theory
for how cosmic structure formed and thereby a powerful w ay of test
ing inf la t ion i t sel f . The cold dark m at ter (or C D M ) th eory hol ds
tha t C D M part icles provide the cosmic infrastructure as it is th eir
The H ubble Space Telescop e, w hich
has prod uced the highest resolution and
deepest im ag es of the U niverse.
(C opyright1997 N ational G eograp hic
Society. A ll rights reserved.)
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BEA M LIN E 1
gravity t hat h olds all cosmic struct ures from galaxies to superclusters
together; and that structure forms from the bottom up. G alaxies form
fi rst w hen the U niverse was one-third t o one-half its present size; clus-
ters of galaxies form n ext ; and fina lly superclusters are just form -
ing today. The bringing together of m att er leaves voids. This picture
is generally consistent w ith a broad base of observations, from m ea-
surem ents of t iny variat ions in
the C BR tem perat ure to the deep-
est im ages of the Un iverse from
th e H ubble Space Telescope.
The C D M theory is being fur-th er tested by a f lood of obser-
vat ions and experiment s ; four
key t ests are described in thi s is-
sue of the Beam Li ne. New berg
describes how the SDSS w ill map
cosmic structure by determinin g
the positions of a m illion galax-
ies. Phillips and Vogt discuss th e
DEEP Projec t w hose sc ien t i f ic
goal is the study of t he origin and
evolution of galaxies. Van Bibberand Rosenberg tel l about their
search for the axions, w hich m ay be th e C D M that holds our G alaxy
together. Finally, the G oldhabers discuss the quest for om ega an d the
test ing of the infl ationary predict ion of a fl at universe.
Many other important t ests are underw ay; som e a t part ic le ac-
celerators. While too m uch hot da rk mat ter is a bad thing, a little bit
may be just w hat the C D M theory needs to agree w ith exist ing ob-
servations. Neut rino experiments at Fermilab and CERN are test-
ing this possibility. The neutralino, t he other prom ising C D M can-
d ida te , i s be ing hunted a round the wor ld , both w i th par t ic le
accelerators and w ith cryogenic detectors designed to detect the neu-tralinos that m ay be the dark m atter in our ow n galaxy.
Finally, let m e mention w hat I believe is the most pow erful test
o f infl a t ion + C D M as w ell as a precision probe of the stan dard cos-
m ology it self . Encoded in t he t iny variat ions of the t emperature of
the C BR across the sky a re both th e va lues o f the cosmologica l
parameters and th e deta ils of infl ation . A precision, high-resolution
ma p of the C BR has the potential to determine accurately the Hub-
ble constant , baryon density, tot al density (om ega), the value of the
r < 17.55, d > 2, 6Slice
Redshift Space
62295 G alaxies
200 h1
M pc
400 h1
M pc
A sim ulation of the galaxy distribution
that the S loan Survey m ight nd . W e sit
at the ap ex of the w ed ge.
(C ourtesy D avid W einberg)
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12 FA LL 1997
cosmological constant , the value of the vacuum energy t hat drove
inflat ion, the spectrum a nd am plitude of the prim eval lumpiness
that arose from q uantum m echanica l f luctuat ions, and other im-portant cosmological parameters.
The C O B E satellite m apped the full C BR sky w ith angular reso
lution of seven degrees. G round-based and balloon-borne instrum ents
are mapping sm all patches w ith resolution of bett er than one degree
NASA plans to launch t he Microw ave Anisotropy P robe in August
2000 w hich wil l map the C BR sky w ith a beam of 0.2 degree. In 2005
the European Space Agency plans to la unch t he Plan ck sa t el l i te
w hich wil l map w ith a beam of less than 0.1 degree. Over the next
decade, ground-based, balloon-borne, an d satellit e-borne inst rum ents
should reap the full scient ifi c potent ial of this snapshot of th e ado
lescent U niverse. In process, in f la t ion + C D M w il l be pu t to thetest an d the details of infl ation m ay be revealed. In addition, preci-
sion checks of the st andard cosm ology w ill be made.
B EYOND IN FLATION AND C OLD D AR K M ATTER
The arcs seen in the left panel are
produced by gravitational lensing of
distant galaxies by a closer cluster of
galaxies. Analysis of the gravitational
lensing led to the m ap of the cluster
m ass d istribution show n on the right.
Such m aps have helped to establish the
existence of large am ounts of dark
m atter in the U niverse.
(C ourtesy Tony Tyson)
IF IN FLATIO N AN D C O L D D A RK M ATTER prove correct, itw ill be a great trium ph for the in ner space/outer space connection
The know n h is tory o f t he U niverse w i l l be extended to t imes a s
early as 1032
sec and a w indow t o the unifi cation of the fundamental forces and part icles of Na ture w ill have been opened. Our con-
ception of t he U niverse and our place in it w ill have been changed
profoundly. As G uth describes, infl ation a nsw ers w hat ban ged: Wha
w e refer to as the Big Bang and beginning of the U niverse w as sim-
ply the inflat ionary event that w as our beginning. Andrei Linde o
Stanford U niversi ty has em phasized, i f in f la t ion h as occurred a t
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all, it ha s occurred countless times
in the past and w ill continue to oc-
cur forever. Each infl ationa ry event
spaw ns a region large enough so tha t
it never comm unicates with others
and can be rightfully called a sub-
universe. Sub-universes m ay be very
dif ferent as the rea l iza t ion of t he
law s of physics, including the num-
ber of spatial dimensions, may de-
pend upon historical accidents as-sociated w ith th e loss of symm etry
betw een the forces.
These are excitin g tim es in cos-
m ology. We should f ind out soon
w hether or not our most promising
and expansive ideas about the ori-
gin of t he U niverse are correct. Even
if current t hinkin g proves w rong, or
only partially correct, there are in-
teresting tim es ahead as w e search
for new ideas. They w ill alm ost cer-tain ly involve t he inn er space/outer
space connection.
BEA M LIN E 13
The cosm ic p icture. H ere and now is at the bottom ; as w e look
out into space w e look back in tim e.(C ourtesy Scott D od elson)
High-Energy
Physics Era
Radiat ion Era
Matt er Era
Here
Looking Out into th e Universe,
Back in Time
Age of Univ erse Increasing,
Temperature of
CMBR Decreasing
N o w t= 15 billion years, T= 2.73 K
G alaxies and Large-
Scale Structure
Un seen U niverse
Our Causal Horizon
Inflat ion
Helium Forms
D ecoupling Occurs
Atoms Form
Matt er Clumping Begins
First Stars and G alaxies Form
t = 1 billion years,
T= 16 K
t = 15 million years,
T= 300 K
t = 150,000 years,
T= 4,000 K
t= 100 seconds,
T= 1 billion K
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WH EN AN O BSC U R E RU SSIAN METEOROLOG IST namedAlexander Friedman n proposed, in 1922, th at th e U niversem ight be expanding, Albert Einstein w as sure that he w aswrong. Five years earlier Einstein had published a static model of the Universe,
and he w as still convinced that it w as correct. In a rare but drama tic blunder,
Einstein bolstered his unfounded beliefs w ith an erroneous calculation, and
fi red off a note to the Z eit schri f t fr Physikclaim ing that Friedm anns theory
violated th e conservation of energy. Eight m onth s later, how ever, after a visit
from a colleague of Friedmann s, Einstein a dmit ted his m istake an d published
a retraction. The equat ions of general relativity do, he conceded, allow for the
possibility of an expand ing univ erse.
Today t he Big Bang th eory, w hich began w ith Friedm anns calculations
in 1922, has become th e accepted view of cosm ology. The expansion of th e
U niv erse w as fi rst observed in t he early 1920s by Vesto Melvi n Slipher, and in
1929 w as codifi ed by Edw in Hubble into w hat w e now know as Hubbles
Law : on average, each distan t galaxy is receding from us w ith a velocity t hat
is proportional t o it s distance. In 1965 Arno Penzias a nd R obert Wilson detect-
ed a background of m icrowa ve radiation arriving at Earth from all directions
the aft erglow of the prim ordial hot , dense fi reball. Today w e know, based on
Wa s C o sm i c In f l a t i on t hTwo th ousand years after Lucret iu s proclai m ed
th at n othi ng can be created from nothi ng,
i nflat i onar y cosm ology assert s th at he was w rong.
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BEA M LIN E 15
data from the Cosmi c Background Explorer (COBE) satellite (see Beam Line,
Vol. 23, N o. 3, Fall/Wint er 1993), th at t he spectrum of t his ba ckgroun d radia -
tion agrees w ith exquisit e precisionto 1/30 of 1 percent w ith th e therm al
spectrum expected for the glow of hot m att er in t he early U niverse. In addi-
tion, calculations of nucleosynt hesis in th e early universe show tha t t he Big
Bang theory can correctly account for the cosmic abun dance of the light nu-
clear isotopes: hydrogen, deuterium, h elium -3, helium -4, and lit hium -7.
(Heavier elem ents, w e believe, w ere synt hesized m uch lat er, in the in terior of
sta rs, and w ere th en explosively ejected in to int erstellar space.)
D espite t he strikin g successes of the Big Ban g theory, there is good
reason to believe th at t he theory in it s traditional form is incomplete.
Although it is called the Big Bang theory, it is not really the th eory of a bang
at all . It is only th e theory of the af termath of a ban g. It elegant ly describes
how th e early U niverse expanded and cooled, and how m att er clumped to form
galaxies and sta rs. But t he theory says n othin g about t he underlying physics of
the prim ordial explosion. It gives not even a clue about w hat banged, w hat
caused it to bang, or w hat happened before it ban ged. The infl ationa ry univ erse
th eory, on t he oth er han d, is a description of the ban g itself, and provides plau-
sible answ ers to t hese questions and m ore.
B a n g o f t h e B ig B a n g?
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16 FA LL 1997
To see how diffi cult it is to explain
th is un i fo rmi ty a s the resu l t o f an
ordinary explosion, w e need to kn ow
a lit t le about t he history of the cos-
m ic background radiati on. The early
U niverse w as so hot tha t e lectrons
w ould have been ripped aw ay from
a toms, resu l t ing in a p la sma tha t
f i l led space. Such a plasm a is very
opaque , so the pho tons tha t now
ma ke up the cosmic background ra-
diation w ere constantly absorbed and
re-emit ted. After about 300,000 years,
how ever, the U niverse cooled enough
for the plasma to form a gas of neu-
tra l a tom s, which is very t ranspar-
ent. The photons of the cosm ic back-
ground rad ia t ion have t rave led on
straight lines ever since, so they pro-
vide today an im age of the U niverse
at an age of 300,000 years, just as t he
pho tons reach ing your eye a t t h ism oment provide an im age of the page
in front o f y ou. Thus, th e observa-
t ions of th e cosmic background ra-
dia t ion show tha t t he Universe w as
uniform in temperature, to one part
in 100,000, a t an age of several hun-
dred thousand years.
U nder m any circumstan ces such
uniformity w ould be easy to under-
A VERY SPEC IAL BANG
C ould the Big Bang have been caused
by a colossal stick of TNT, or perhaps
a therm onuclear explosion? Or may -
be a gigantic ball of ma tt er collided
w ith a gigantic ball of antimatt er, re-
leasing an untold am ount of energy
in a pow erful cosmic blast .
In fact, none of t hese scenarios can
plausibly account for the Big Bang
that started our Universe, w hich hadtw o very specia l fea tures dist in-
guishing it from any t ypical explosion.
First , the Big Bang wa s far more
hom ogeneous, on large scales, th an
can be exp la ined by an o rd ina ry
explosion. In discussin g hom ogene-
ity, how ever, I must fi rst clarify that
the Universe i s in m any w ays con-
sp icuously inhomogeneous . Pa lo
Alto is very different from San Fran-
c isco , and th e s t a rs , ga lax ies , and
clusters o f ga laxies are sca t teredthrough space in a lum py, complex
pat tern . Cosmologica l ly speaking,
how ever, all this structure is small-
sca le . We can focus on the large
scales, for exam ple, by dividi ng space
into cubes of 300 m illion light-years
or more on a side. We w ould fi nd that
each such cube closely resembles th e
others in a ll it s average properties,
such as m ass density, galaxy density,
and l igh t ou tpu t . This l a rge-sca le
uniformit y can be seen in galaxy sur-
v e ys , b u t t h e m o s t d r a m a t i c e v i -
dence com es from t he cosmic back-
g ro u n d r a d i a t i o n . D a t a f ro m t h e
C OB E satellite, confi rmed by subse-
quent ground-based observat ions,
show t hat this radiation has the same
tem perat ure in all directions (after
correc t ing fo r the mot ion o f the
Earth) to an accuracy of one part in
100,000.
s t and , s ince anyth ing w i l l come to
a uniform temperature if left undis
turbed for a long enough tim e. In th e
standard Big Bang theory, how ever
the U niverse evolves so quickly that
there is no t ime for the uniformity
to be established. One ca n pretend
for the sake of discussion, tha t the
U niverse is populated by lit t le pur
ple creatures, each equipped w ith a
furnace and a refrigerator, and each
dedicated to th e cause of creating auniform tem peratu re . Those l i t t le
crea tures, how ever, w ould have to
communica te a t roughly 100 t imes
the speed o f l igh t i f they a re to
achieve their goal of creating a uni
form temperature across the v isible
U niverse by 300,000 years a f ter the
Big Bang. Since neither st icks of
d yn a m i t e n o r b a ll s o f m a t t e r a n d
antim atter can t ransmit their energy
faster than light, they cann ot accoun
for the uniform ity. The classical formof the B ig Bang th eory requ ires us
to pos tu la te , w i thou t exp lana t ion
tha t the pr imord ia l f i reba l l f i l led
space from the beginning. The tem
perature was t he same everyw here
by assum ption, not as a consequence
of any physical process. This short-
comin g i s know n as the horizon
problem, since cosmologists use t he
w o rd h o r iz o n t o in d ic a t e t h e
largest distance that informat ion or
energy could ha ve traversed since the
ins t an t o f the B ig Bang , g iven th e
restriction of t he speed of light.
The second special featu re of the
Big Bang, w hich is very dif f icult to
ima gine arising from a st andard ex
plosion, is a rem arkable coincidence
cal led the fl a tness problem. This
problem concerns the pinpoint
precision w ith w hich the mass den
si t y o f the ea r ly Un iverse must be
I nflat i on
is a w il dfire
tha t w i l l inev i tab l y
t ake over t he forest,
as l ong as
t here is som e
chance th at
i t w i l l sta r t .
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BEA M LIN E 17
specified for the Big Bang t heory to
agree w ith reality.
Fi rs t , w e need to rev iew a l i t t le
vocabulary. If the m ass density of the
Universe exceeds a value called the
criti cal densit y, t hen grav i t y w i l l be
strong enough t o reverse the expan-
sion eventua lly, causing the U niverse
to recollapse into w hat is sometimes
called the bi g crunch. If the mass den-
sity is less than t he critical value, the
U niverse wil l go on expanding for-ever. The ra t io o f th e ac tua l m ass
density t o the critical value is know n
to cosmologists by the G reek letter
omega (). G eneral relativity implies
tha t the geomet ry o f th e Universe
is Eucl idean on ly i f om ega i s one ,
so an = 1 universe is ca l led fl a t
(see box on th e right ).
Om ega is very difficult to deter-
m ine, but it is safe to say t hat it s pre-
sen t va lue l ies somew here in the
range of0.1
t o2
. That seems like abroad range, but consideration of t he
t im e developm ent o f the Universe
leads to a spect acu la r ly d i f fe ren t
po in t o f v iew. = 1 i s an unst ab le
equil ibrium point o f cosmologica l
evo lu t ion , w h ich means tha t i t re-
sembles the situat ion of a pencil bal-
ancing on i t s sharpened t ip . The
phrase equilibrium point im plies that
if omega is ever exactly equal t o one,
i t w i l l rema in exact ly equa l t o one
foreverjust as a pencil bala nced pre-
cisely on end w ill , according to the
law s of classical physics, remain for-
ever ver t ica l . The w ord unst ab le
means tha t any devia t ion f rom t he
equilibrium point, in either direction,
wi l l rap id ly g row. I f the va lue o f
omega in the early U niverse w as just
a l i t t le above one , i t wou ld have
rapidly risen tow ard infinity ; if it w as
just a sm idgen below one, it w ould
Critical Mass Density
and Flatness
THE CRITICAL MASS densityc is related to the Hubble con-stant H by
c= 3H2___
8G
where Gis Newtons gravitation-al constant. The quantity isdefined by /c, where isthe actual mass density. It is of-ten assumed that the cosmolog-ical constant introduced byEinstein is zero, in which casethe Universe will recollapse ifand only if > 1. If is non-zero, the condition for recol-lapse is more complicated, butthe equation above is still takenas the definition of c.
The spatial geometry of the
Universe is determined by thequantity
+ ___3H2
.
If this quantity exceeds one, theUniverse curves back on itselfto form a closed space of finitevolume, but without boundary.In such a space the sum of theangles in a triangle would ex-ceed 180 degrees, and a star-ship traveling on a straight line
would eventually return to itspoint of origin. If the quantityabove is less than one, the Uni-verse is an open space in whichtriangles contain less than 180degrees. If the quantity is exact-ly one, the space is Euclidean,which is also called flat.
hav e rapidly fallen tow ard zero. For
omega to be anyw here nea r one
today, it m ust hav e been extraordi-
narily close to one at early t imes. For
example, consider one second after
the Big Bang, the t im e at w hich the
processes related t o Big Bang nuc leo-
synt hesis w ere just beginning. For
omega to be anyw here in the allowed
range today, at that t ime omega must
have equaled one to an accuracy of
15 decimal places!A sim ple explosion gives no ex-
planation for this razor-sharp fine-
tunin g, and indeed no explanat ion
can be found in the tradit ional ver-
sion of t he Big Bang theory. The ini-
t ia l va lues of the mass density and
expansion rate are not predicted by
the theory, but must be postulated.
U nless w e pos tu la te tha t the ma ss
d e n s i t y a t o n e s e c o n d j u s t h a p -
p en e d t o h a v e a v a l u e b e t w e en
0.999999999999999and
1.000000000000001
t im es the crit ical density, how ever,
the theory w i l l no t describe a un i-
verse tha t resembles the one in
w hich w e l ive .
TH E IN FLATION ARY U N IVERSE
Although t he propert ies o f the Big
Bang are very special, w e now know
tha t the law s o f phys ics provide a
m echan ism th a t p roduces exac t ly
this sort of a bang. The mechanism
is know n as cosmic infl at ion.
The crucial property of physical
law tha t m akes infl at ion possible is
the existence of states of mat ter that
have a high energy density tha t can-
not be rapidly low ered. Such a stat e
is called a false vacuum, w here the
w ord vacuum ind ica tes a s t a te o f
low est possible energy density, an d
t h e w o r d fa ls e i s u se d t o m e a n
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In f la t ion i s a w i ld f i re tha t w i l l in
evitably t ake over the forest , as long
as there is some chance tha t i t w il
start .
Once a patch of t he early U niverse
is in the false vacuum stat e, the re
pulsive gravitational effect drives the
patch int o an inflat ion ary period o
exponenti al expansio n. To produce a
universe w ith the special features o
th e Big Bang discussed abov e, the ex
pansion factor must be at least abou1025. There is no upper limit to t he
am ount of expansion. Eventually the
false vacuum decays, and th e energy
that had been locked in it is released
This energy produces a hot, uniform
soup of particles, w hich is exactly t he
assumed start ing point of the tradi-
t ional Big Bang theory. At this point
the infl ationary th eory joins onto the
older theory, mainta ining all the suc
cesses for w hich t he Big Bang theory
is believed.In the inflat ionary t heory the U ni
verse begins incredibly sm all, perhap
as small as 1024 cm , a hundred bil
lion tim es smaller than a proton. The
expansion ta kes place w hile the false
vacuum m aintains a nearly constant
energy density, which m eans that the
to t a l energy increases by the cube
of the linear expansion factor, or at
least a factor of 1075. Although this
sounds like a blatant violat ion of en
ergy conservat ion, i t is in fact con-
sistent w ith physics as w e know i t .
The resolution t o th e energy para
dox l ies in the subt le behavior o f
g rav i t y . Al though i t ha s no t been
wid e ly a p p re c i a t e d , N e wt o n i a n
physics unambiguously implies tha
the energy o f a g rav i t a t iona l f ie ld
i s a lw a y s n e ga t i v e , a f a c t w h i c h
h o l d s a l s o i n g en e r a l r e l a t i v i t y
Th e N e wt o n i a n a rg u m e n t c lo sel y
temporary . For a period th at can be
long by the s t an dards o f the ea rly
U niverse, the false vacuum acts as if
the energy densi t y canno t be low-
ered, s ince the low ering of the en-
ergy is a slow process. The underly-
ing physics of the false vacuum st ate
is described in t he box on th e left.
The peculiar properties of t he false
vacuum s tem f rom i t s p ressure ,
w hich is large and negative (see box
on the right). Mechanica l ly such anegati ve pressure corresponds to a
suct ion, w hich does not sound l ike
something that w ould drive the U ni-
verse into a period of rapid expansion .
The m echan ical effects of pressure,
how ever, depend on pressure differ-
ences, so they are unimportant if the
pressure is reasonabl y un iform . Ac-
cording to general relat ivity, how ev-
er, there is a gravitat ional effect th at
i s very im port an t under these c ir-
cum stan ces. Pressures, like energydensities, create gravita tional fi elds,
and in part icular a positiv e pressure
crea tes an a t t rac t ive g rav i t a t iona l
field. The negat ive pressure of the
false vacuum , th erefore, creates a re-
pulsive gravitat ional fi eld, w hich is
the driving force behind infl ation.
There a re m any vers ions o f in-
flat ionary theories, but generically
they assume that some small patch
of the early U niverse somehow cam e
to be in a fa lse vacuum sta te . Vari-
ous possibilities have been discussed,
including supercooling during a
phase t rans i t ion in t he ea r ly U ni-
verse, or a purely random fl uctuat ion
of the f ie lds. A chance f luctuat ion
seems reasonable even if the proba-
bil i ty is low , since the inf la t ing re-
gion w ill enlarge by m any orders of
magnitude, wh ile the non-infl at ing
regions w i l l rem a in m icroscopic .
Physics
of the
False Vacuum
THE FALSE VACUUM arises nat-
urally in any theory that containsscalar fields, that is, fields thatresemble electric or magneticfields except that they have nodirection. The Higgs fields of theStandard Model of particlephysics or the more speculativegrand unified theories are exam-ples of scalar fields. It is typical ofHiggs fields that the energy den-sity is minimal not when the fieldvanishes, but instead at some
nonzero value of the field. Forexample, the energy density dia-gram might look like
The energy density is zero if= t, so this condition corre-sponds to the ordinary vacuum ofempty space. In this context it isusually called the true vacuum.The state in which the scalar fieldis near = 0, at the top of theplateau, is called the falsevacuum. If the plateau of theenergy density diagram is flatenough, it can take a very long
time, by early Universe stan-dards, for the scalar field to rolldown the hill of the energy den-sity diagram so that the energycan be lowered. For short timesthe false vacuum acts like a vac-uum in the sense that the energydensity cannot be lowered.
00
ufFalse Vacuum(metastable)
TrueVacuum
EnergyDensity
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BEA M LIN E 19
parallels th e derivat ion of t he ener-
gy density o f an e lectrosta t ic f ie ld ,
except tha t the answ er has the op-
posite sign because the force law has
the opposite sign: tw o positive m ass-
es attract, w hile tw o positive charges
repel. The possibility tha t t he neg-
ativ e energy of gravity could bala nce
the posit ive energy for the ma tt er of
the U niverse was suggested as ear-
l y a s 1932 by Rich ard Tolm an , a l-
though a viable mechanism for theenergy t ransfer was not know n.
D uring in f la t ion , w h i le the en-
ergy of m att er increases by a factor
of 10 75 or more , the energy o f the
gravitat ional fi eld becomes more and
more negative to compensate. The
to t a l energymat t e r p lus g rav i t a -
t ionalremains constan t and very
sma l l , and cou ld even be exac t ly
zero. Con servation of energy places
no l imit on how much the U niverse
can infl ate, as there is no limit t o theam ount of negativ e energy tha t can
be stored in the gravitat ional fi eld.
This borrow ing o f energy f rom
the gravita t ional f ie ld g ives the in-
fl a t ionary paradigm an ent irely di f-
ferent perspective from the classic al
Big Bang theory, in w hich all t he par-
t ic les in t he U niverse (o r a t lea s t
their precursors) w ere assumed to be
in place from t he start . Infl ation pro-
vides a mechanism by w hich the en-
tire U niverse can develop from just
a few ounces of primordia l ma t ter .
Inflat ion is radically at odds w ith the
o ld d ictum o f Dem ocr itus and Lu-
c ret iu s , N o t h in g c a n b e c re a t e d
from nothing. I f in fla t ion is r ight ,
everyt hing can be created from not h-
ing, or at least from v ery lit t le. If in-
f la t ion i s r igh t , the Universe can
properly be called t he ult im ate free
lunch.
Pressure
of the
False Vacuum
THE PRESSURE OF THE FALSE VACUUM can be determinedby a simple energy-conservation argument. Imagine a chamberfilled with false vacuum, as shown in the diagram below.
For simplicity, assume that the chamber is small enough so thatgravitational effects can be ignored. Since the energy density of thefalse vacuum is fixed at some value uf, the energy inside the cham-ber is U= ufV, where Vis the volume. Now suppose the piston is
quickly pulled outward, increasing the volume by dV. If any familiarsubstance were inside the chamber, the energy density woulddecrease. The false vacuum, however, cannot rapidly lower its ener-gy density, so the energy density remains constant and the total en-ergy increases. Since energy is conserved, the extra energy mustbe supplied by the agent that pulled on the piston. A force is re-quired, therefore, to pull the piston outward, implying that the falsevacuum creates a suction, or negative pressure p. Since the changein energy is dU= ufdV, which must equal the work done, dW= pdV,the pressure of the false vacuum is glven by
p = uf .
The pressure is negative, and extremely large. General relativitypredicts that the gravitational field which slows the expansion of theuniverse is proportional to uf+ 3p, so the negative pressure of thefalse vacuum overcomes the positive energy density to produce anet repulsive gravitational field.
Before:
After:
False Vacuumu= uf, p= ?
True Vacuumu= 0, p= 0
dV
dW= p dV= uf dV
F
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20 FA LL 1997
encompass the ent ire observed
Universe . The un i fo rmi ty i s p re-
served by this expansion, because the
law s of physics are (w e assume) the
same everyw here.
The infl ationary model also pro
vides a simple resolution for the fl at
ness problem, the f ine-tuning re-
qu ired o f the mass densi t y o f the
ea r ly U niverse . Reca l l tha t the ra
t io of the actual m ass density t o the
crit ical density is ca lled omega, andtha t t he problem arose because the
condit ion = 1 is unstable: om ega i
a lw ays driven aw ay from one as the
U niverse evolves, m aking it diffi cul
to unders t and how i t s va lue today
can be in the vicinity of one.
D uring the inflat ionary era, how
ever, th e peculiar nat ure of the false
v a c u u m s t a t e resu l t s in so m e im -
portant sign changes in the equa tions
tha t describe the evo lu t ion o f th e
U niverse. D uring this period, as w ehave discussed, the force of gravit y
acts t o accelera te t he expansion of
the U niverse ra ther than t o re t a rd
it . I t turns out that the equation gov
erning the evolution of omega also
has a crucia l chan ge of sign: during
the inflat ionary period the U niverse
is driven very q uickly and very pow
erfully towards a crit ical ma ss den-
sity. This effect can be understood i
one accepts from general relat ivit y
the rela t ionship betw een a cri t ica l
ma ss density and th e geometric fl at
ness of space. The huge expansion
factor of infl ation drives the Un iverse
tow ard fl atness for the same reason
tha t the Ear th appears f l a t , even
though i t i s rea l ly round . A sm a l
piece of any c urved space, i f m ag
nifi ed suffi cient ly, w il l appear fl a t .
Thus, a sh ort period of inflat ion
can drive th e va lue of omega very
INFLATION AND TH E VERY
SPECIAL BANG
Onc e infl ation h as been described, it
is not ha rd to see how it produces just
the special kind of bang that w as dis-
cussed earlier.
Consider first the horizon prob-
lem, the diffi culty of understanding
the large-scale homogeneity of the
U niverse in the context o f the t ra-
ditional Big Bang theory. Suppose w etrace back through tim e the observed
region of the Universe, w hich has a
radius today of about 10 billion light-
years. As w e trace its history back t o
the end of the infl ationary period, our
descr ipt ion i s iden t ica l t o w ha t i t
w ould be in the tradit ional Big Bang
theory, since the tw o th eories agree
exactly for all t im es after the end of
infl at ion. In t he infl at ionary theory,
how ever, th e region undergoes a t re-
mendous spurt of expansion duringthe inf la t ionary era . It fo l low s tha t
the region w as incredibly sm all before
the spurt of expansion began1025 or
more t im es sma ller in radius than in
the traditiona l theory. (N ote that I am
not saying that Universe as a whole
was very sma l l . The in f la t ionary
model makes no statem ent about the
size of the U niverse as a w hole, which
might in fact be infi nite.)
Because the region w as so small,
there was p len ty o f t ime fo r i t t o
come to a uniform tem perature, by
the same mundane processes by
w hich a cup o f ho t co f fee coo ls to
room tem perature as it sits on a table.
So in the infl ationary m odel, the uni-
form tempera ture w as es t ab l i shed
be fore in f la t ion took p lace , in an
ex t remely sm a l l reg ion . The pro-
cess of inflat ion th en stretched this
reg ion to become la rge enough to
1040
1020
100
1020
1040
1060
1040 1020 100 1017.5
Time (seconds)
RadiusofObservedUniverse
(m)
Present
Standard Theory
Inflationary Theory
Inf la tionary Period
10
The solution to the horizon prob lem . The
green line show s the radius of the region
that evolves to b ecom e the presently
ob servab le U niverse, as d escribed by
the traditional B ig B ang theory. The
black line show s the corresponding
curve for the in ationary theory. D ue to
the spectacular grow th spurt duringinfl ation, the infl ationary curve show s a
m uch sm aller U niverse than in the
standard theory for the p eriod before
infl ation. The uniform ity is established at
this early tim e, and the region is then
stretched by infl ation to b ecom e large
enough to encom pass the ob served
U niverse. N ote that the num bers
describing in ation are illustrative, as the
range of possibilities is very large.
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BEA M LIN E 2
accurately to one, no mat ter w here it
start s out. There is no longer any need
to a ssume tha t the in i t i a l va lue o f
omega w as incredibly close to one.
Furtherm ore, there is a predict ion
that arises from this behavior. The
mechanism t hat drives omega to one
a lm o s t a lw a ys o v e rsh o o t s, w h ic h
means that even today the mass den-si ty should be equal t o the cri t ica l
val ue to a h igh degree of accu racy. (If
Einstein s cosmologica l constant
is nonzero, this prediction is m odi-
fi ed to become + /3H2= 1, w here
His H ubbles const ant .) Thus, t he de-
terminat ion of the mass density o f
the U niverse could be a very impor-
tant test o f the infla t ionary m odel.
U nfortunately, it is very difficult to
reliably estimate t he ma ss density of
the U niverse, since most of the m at-te r in the Univ erse i s da rk ,
de tec ted on ly t h rough i t s g rav i t a -
tional pull on visible matt er. C urrent
estim ates of omega range from 0.2 t o
1.1. Nonetheless, it is likely that this
issue can be set t led in t he near fu-
ture . The high precision m easure-
ments of t he microw ave background
rad ia t ion tha t w i l l be made by the
Microw ave Anisotropy Probe, sched-
uled for launch in a bout 2001, are ex-
pected to p in down the va lue o f
omega to about 5 percent accuracy.
THE C U RRENT PICTURE
Wh i l e i t m a y b e t o o e a r l y t o s a y
that inflat ion is proved, I claim tha t
the case for inflat ion is com pelling.
I t i s h a rd t o e v e n c o n c e iv e o f a n
a l t e rn a t i v e t h e o ry t h a t c o u ld e x-
p la in the bas ic fea tures o f th e ob-
served U niverse. Not only does in-
f l a t i o n p ro d u c e j u s t t h e k in d o f
specia l bang tha t m a tches the ob-served Univ erse, but quantum fluc-
tuations during inflat ion could have
p ro d u c e d n o n u n i f orm i t i e s w h ic h
served as the seeds of cosmic st ruc-
ture. These nonuniform ities can be
o b se rv e d d i re c t l y in t h e c o sm ic
background rad ia t ion , wi t h an am -
plitude of about one part in 100,000.
S o f a r t h e m e a s u r e m e n t s o f t h e
sp e c t ru m h a v e b e e n b e a u t i f u l l y
consistent w ith t he predictions of in-
f la t ion, a l though it m ust be admit -
ted that nonuniformit ies created by
cosmic s t r ings a re a lso cons is ten t
w ith th e observations. C osmic strings,how ever, cannot expla in t he large-
sca le homogene i t y o r the f l a tness
of the U niverse.
Whi le the ca se fo r in f la t ion i s
strong, it should be stressed that in-
fl ation is really a paradigm a nd not a
theory. The statement th at th e Uni-
verse arose from infl ation, if it is t rue,
i s no t t he end o f the s tudy o f cos-
mic originsit is in fact closer to the
beginning. The deta i ls o f in f la t ion
depend upon the deta i ls o f t he un-
derlying part icle physics, so cos-
mology an d particle physics become
intim ately lin ked together. While I
cannot see any viable alternative to
the genera l idea of in f la t ion, th ere
is st ill much w ork to be done before
a detailed picture is established. And
I suspect that there is room for ma ny
new important ideas.
The expanding sphere illustrates the
solution to the atness problem in
infl ationary cosm olog y. A s the sphere
becom es larger, its surface b ecom es
atter and atter. Sim ilarly the in ation of
space causes it to becom e geom etri-
cally at, and g eneral relativity im pliesthat the m ass density of a at universe
m ust equal the critical value.
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22 FA LL 1997
WH EN TH Eoriginat ors of theSloan D igital SkySurvey (SDSS) m et at O Hare
International a irport in t he fall
of 1988, their intent w as to
form a collaborat ion t hat
w ould measure the size of thelargest st ructures of galaxies in
th e U niverse. Previous galaxy
surveys had show n that the
largest st ructures w ere at least
400 m illion light years in
extent as la rge as t he largest
structures that could have been
found by th ese surveys. In par-
ticular, the results of the C fA
Redshift Survey w ere astound-
ing. From t he spectra of on e
thousand galaxies, the re-
searchers w ere able to depict a
slice of our Un iverse w ith large
voids (w here the galaxy den-
sity w as very low ) surrounded
by dense w alls of galaxies.
heSloa
nDigit
alSk
ySur
vey
Pion th
eSky
y HEIDI
JONE
WBE
RG
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BEA M LIN E 23
C osmology ha d already seen t he demise of the perfect cosmological prin-
ciple in 1929 w ith Edw in Hubbles discovery t hat the U niverse is expanding,
and t herefore chan ges over tim e. We contin ue to believe, how ever, in th e
cosm ological principleth at t he U niv erse is hom ogeneous and isot ropic. To
demonstrat e th e validity of this basic assumption about our U niverse, w e
m ust be able to fi nd some volum e of the U niverse that is representa tive of
the w hole. It is clear that a m uch larger galaxy redshift survey is required to
fi nd a represent ative sam ple of the U niverse.With projects to m easure ten t o one hundred thou sand galaxi es already
plann ed or underw ay, th e early organizers of th e Sloan D igital Sky Survey
(SDSS) proposed a redshift survey of on e milli on galaxies. Rat her tha n look-
ing at a slice of the U niverse, th is new survey w ould measure the position of
every galaxy in a patch of sky steradian s (one qu arter of th e sky) in siz e.
The survey w ould m easure the distan ces to galaxies th ree ma gnitudes
fainter (about four t im es farther aw ay) tha n t hose observed in th e C fA
Redshift Survey. In addition, t hese million galaxies w ould not be chosen
from the photographic sky surveys already in existence. Rather, they w ould
be selected from a new , carefully con trolled survey of th e sky using a largecha rge-coupled dev ice (C C D ) cam era. By im aging th e sky in several optical
passbands, including an ult ra-violet passband, t he data from this sky survey
w ould also be used to select qua si-stellar objects (Q SO s). As the m ost distan t
collapsed objects ever observed in our U niv erse, these w ould give us infor-
m ation about the st ructure of th e U niverse on t he largest possible scales.
The survey w as projected to t ake fi ve years to build, w ith a n additional fi ve
years of operation to complete the scientifi c objectives.
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24 FA LL 1997
and th e budget w ere optim istic. But
i f w e w e re n o t a t t e m p t in g t h e im -poss ib le , we would no t be on the
forefront of research.
THE SLOAN DIG ITAL SKYSurvey has a t t racted the ac
tiv e partic ipation of over one
hundred scient ist s , engineers, and
softw are professionals from eight as
tronomy groups and departm ents, in
cluding: Princeton University, The
U nivers i t y o f C h icago , The JohnsHopkins U niversi ty , th e Japan Par-
t ic ipa t ion G roup (sc ien t is t s a t t he
U niversities of Tokyo a nd Kyot o), the
U nited States Na val Observatory, the
U niversity of Washington, the Insti
tute for Advanced Study, and Ferm
N ationa l Accelerator Laboratory. The
survey is being carried out under
t h e a u spic es o f t h e A st ro ph ys i c a
Research Consortium (AR C ) and h as
received signifi cant funding, totaling
about 54 mil l ion do l la rs , f rom t he
Alfred P. Sloan Foundation (N Y), fro m
the Na t iona l Sc ience Founda t ion
and from each of the mem ber insti
tutions.
The goals a nd sc ope of the projec
have changed on ly s l igh t ly f rom
t h o se pu t f o r t h b y t h e O H a re
group. Since the main surv ey area
is not observable during part of t he
year, three extra st r ips o f sky have
Al though i t may no t have been
recognized at t he t im e, the addit ion
of the ima ging survey t ransformed
the SD SS project from an am bitious
att empt to t race the large scale struc-
tures in the Un iverse into a plan to
stat ist ically sample everything in a
large corner of the visible U niverse.
What these planners had dreamed up
w as an im aging survey covering tenthousa nd squ are degrees of the sky
in four fi lters; a catalog of the 70 mil-
l ion stars , 50 m ill ion ga laxies, and
one million QSO s visible in t he imag-
ing survey; an d a spectroscopic sur-
vey of more than a million of these
objectsall rolled int o one enorm ous
project . This stat ist ical sam ple w ill
have a tremendous impact not only
on our un derstandin g of th e largest
s t ruc tures , bu t on every a spect o f
astronomy.
Any one of th ese three projects
(the im aging survey, the cata log, or
the spectroscopic survey) w ould have
been considered large by the sta n-
dards of ground-based ast ronomy.
Any one of th e three could be sci-
entifi cally justifi ed on its ow n merit .
All together, th e project is a s colos-
sal as its impact w ill be on astrono-
my. Okaythe goals, the t imeline,
A bove: The A pache Point O bservatory
in Sunspot, N ew M exico. The SD SS 2.5
m eter telescope (left) is show n w ith its
protective building rolled aw ay, as for
nightly operation. A lso show n is the
m onitor telescope dom e (top right).
(C ourtesy A pache P oint O bservatory)
M iddle: Prototype ber plug -plate for the
SD SS sp ectrog rap h. D uring op eration,all 640 bers w ill be inserted into the
plug-plates by hand. Several plates w ill
be plug ged during the day in
preparation for a nights observations.
Each ber w ill guide the light from a
galaxy, Q SO , or star into the
spectrog rap h cam era. (C ourtesy
Ferm ilab Visual M ed ia Services)
K
urt
A
nderson
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BEA M LIN E 25
been added to fi ll in t he gap. Also, w e
have added one passband to t he ima g-ing survey, for a tota l of fi ve fi lters.
Most ly, w e have made t remendous
progress designing and bu ilding t he
hardw are and softw are necessary to
assure our success.
The a s t ronomica l da t a fo r the
SDSS w ill be obtained from t w o ded-
icated telescopes located at Apache
Point O bservatory in Sunspot, New
Mexico . The data w il l be part ia l ly
processed at the observatory before
being sent to Fermi N ational Accel-erator Laboratory, w here the m ajor-
i ty o f the da t a processing, s torage,
and distributi on w ill take place. The
m a in SDSS telescope has a prim ary
mirror 2.5 meters in diameter and a
fi eld of view three degrees in diam-
eter. It w ill support tw o instruments:
a photometric camera containing 54
C C D s and a spect rograph w i th 640f ibers . A fu l ly au tom a ted 24-inch
diam eter te lescope w il l opera te si-
m ultaneously. The survey softw are
is designed to opera te these te le-
scopes, p lan imaging and spectro-
scopic observa t ions so a s t o m in i-
miz e th e survey t ime-to-completion,
acquire the data from all survey in-
strum ents, process ima ging data into
catalogs of astronomical objects and
their associated parameters, calibrate
the positions and luminosit ies of the
m easured objec t s , m erge the da t a
from dif ferentC C D
s and dif ferentnights int o one large catalog, select
f rom th is ca t a log the sources fo r
w hich w e w il l obta in spectra , orga-
nize th e targeted objects int o sepa-
rate spectroscopic exposures, reduce
spectroscopic exposures into l is t s
o f objec t s w i th c la ss i f ica t ions and
redshifts, and st ore the results of all
of these steps in a large databa se.
TH E SD SS is aggressivelychar t ing new te rri to ry bo th
in t he design of the telescope
and ins t ruments , and in the pro-
cessing and acq u is i t ion o f th e sc i-
ent i f ic da t a . The spectrograph w il l
be capable of observing m ore objects
a t o n e t im e t h a n a n y o t h e r in t h e
w orld. The photom etric camera w ill
have m ore pixels in the focal plane
t h a n a n y o t h e r C C D c a m e r a i n
Telescope engineer C harlie H ull poses w ith the
skeleton of the Sloan D igital Sky Surveys 2.5
m eter telescope shortly after it w as installed.
D
an
Long
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26 FA LL 1997
tractable. By building a camera wit h
30 la rge C C D s and us ing a dr i f t
scanning technique, w e w ill not only
be able to survey large areas of sky
but also to obtain the im ages simul
taneously in fi ve fi l ters .
In addit ion to the array of 30 pho
tometric C C D s, the focal plane con
ta ins 22 smaller ast rometric C C D s
w hich are used to ca l ibra te the po
sitions of the survey objects. These
C C D s image bo th the a s t romet r icstandard stars (which are saturated
on th e photometric C C D s) and also
some of the brighter stars tha t w il
be unsatura ted on th e photometric
C C D s. This allow s us to t ie our data
to a coordinate system that is fi xed
on the sky. Also, it allow s us to m ea
sure m ore accura te ly t he rela t ive
positions of th e objects found in sep
arate C C D s in the photom etric array
By comparing the same stars as im-
aged at the beginning and end of theC C D array, w e can assess how w el
the telescope is tracking its trajec
tory in th e sky.
The photometric a ccuracy of our
catalogs w ill be limit ed by our abil
ity to characterize the atmospheric
condi t ions dur ing the n igh t . Even
though photom etry w ill be at t empt
ed only on th e clearest , m ost stable
n igh t s , we w i l l measure the t rans
parency of t he atm osphere as a func
t ion of t im e, f i l ter, and posit ion in
the sky . The su i t ab i l i t y o f a g iven
night for photometry will be deter
mined w ith da ta from a w eather sta
t ion w hich logs the t empera ture
w ind speed and direction, hum idity
and dust leve l . In add i t ion , the
w ea ther st a t ion inc ludes a camera
w h ic h im a g es t h e wh o le sk y a t 10
microns every 20 minut es . At th is
w ave leng th , c louds s t and ou t very
existence. Our cat alog of objects w ill
be the largest , and w il l have bet ter
posit ional and photometric accura-
cy th an any other catalog of its kind.
In order to assure th e astromet ric and
photometric uniformity w e require
for describing our statistica l sam ples
of the sky, w e have included in the
des ign severa l nove l ins t rum ents
w hich w il l a l low us to eva luate and
ca l ibra te the da t a be t t e r than any
previous survey. I w ill discuss hereonly a few of the innovat ions w hich
ma ke the survey possible.
The 2. 5 m eter te lescope is spe-
cially designed to reduce dom e see-
ing, the distortion of images caused
by t urbulence in the air very close to
the telescope. To reduce dist ort ion
caused by disruption of th e lamina r
fl ow of air over the observatory, the
SDSS telescope is cant ilevered over
the edge of a cliff in th e direction of
the prevailing wind. In addit ion, w euse a roll-off building w hich elim i-
nat es the telescope building as a po-
tential cause of heat, w hich also con-
tributes to image distort ion. D uring
operation , th e telescope is protected
f rom w ind and s t ray l igh t by a ba f-
f le tha t i s m echan ica l ly separa ted
from the te lescope, but t ha t moves
and t racks w ith i t .
In all areas of optical astronom y
except surveys, data from C C D cam-
eras has supplant ed data from pho-
tographic plates. C C D cameras, un-
like th e plates, have linear response
functions and much higher effi cien-
cy for detecting light , w hich m akes
possible more accura te photomet-
ric (lumin osity) m easurements. U n-
til now , these cam eras w ere not used
for surveys because i t w as not pos-
sible to cover enough sky w ith one
cam era for a large area survey to be
Project Scientist Jim G unn m ounts the
quartz corrector for the SDSS photo-
m etric cam era.
This 24-inch telescope w ill be used to
de ne the SDSS lter system and w ill
also m onitor the atm osphere during
operations.
D
an
Long
M
ike
C
arr
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BEA M LIN E 27
THE SDSS CAMERA will drift-scan the sky, rather thanusing the more common point-and-shoot method, in order
to increase the fraction of the time that the imaging cam-era is integrating light from the sky and to reduce the number ofimages that must be pieced together. Point-and-shoot observa-tions are obtained by tracking the apparent motion of the targetobject in the sky, and opening and closing a shutter to expose thedetector. Drift-scanning is usually done by fixing the position ofthe telescope and moving the photo-sensitive material to trackthe target object. The Sloan Digital Sky Survey will have to moveboth the telescope and the detector to image the survey area.
Before explaining how the SDSS camera works, let me firstdescribe a much simpler drift-scanning camera. Imagine a tele-scope in a fixed position on the Earths equator, and pointingdirectly overhead. The telescope focuses light from the sky
onto a single charged coupled device (CCD) in the focal plane.As the Earth turns, stars will enter the field-of-view of the CCD,travel across it at constant speed, and then disappear fromview. To drift-scan, the two dimensional array of pixel detectorson the CCD must be aligned so that the crossing star travelsexactly along one column. As light from the star moves fromone row of the CCD to the next, all of the accumulated photo-electrons are also moved to the next row. This leaves oneempty row of pixels at the beginning of the CCD, ready to startexposing a new part of the sky. The photoelectrons in the lastrow are read out and digitally stored in a computer. The cam-era accumulates data continuously along one equatorial stripof sky, without stopping to read the data out of the CCD whilethe shutter is closed. The effective exposure time of the data isthe crossing time of a star across the camera.
To scan across the sky in a direction that is not along con-stant latitude or that is far from the equator requires the tele-scope to track and (in most cases) the CCD to rotate. Trackingis also required to drift at arbitrary rate (which sets the expo-sure time) across the sky. The first telescope and CCD combi-nation capable of driven drift scans in arbitrary directions wasthe Fermilab Drift-Scan Camera mounted on the ARC 3.5 metertelescope at Apache Point Observatory, adjacent to the SDSStelescope site. The camera, which was commissioned in 1994,was built as a prototype for testing SDSS data-acquisition
software.The SDSS camera puts 30 large, 20482048 pixel CCDs inthe focal plane of the telescopesix columns of five CCDs. Thesix columns each scan a separate strip of sky while the camerais imaging. Each of the five CCDs in a given column images thesame strip of sky, but using a different filter. The effective expo-sure time in each filter is about 55 seconds. A given object willfirst traverse the CCD with the r filter, then the i , u , z , andg filters, in succession. It takes about 5.8 minutes to traverseall five filters. Each column images a strip of sky 13.7 arc min-utes wide which increases in length by 15 degrees per hour. A
similar camera operated in point-and-shoot mode would spendabout as much time exposing a 55-second image as it did read-ing out the CCD. Also, we would need to piece together 250,000individual images rather than about 1000 long, continuous strips.
In addition to the photometric CCDs, there are 22 astromet-ric chips and two focus chips in the focal plane. Since theseCCDs are the same width and pixel scale as the photometricchips, each row is read out with the same frequencyproducing the same 9.5 megabytes per minute per CCD. Fewerrows in the astrometric and focus CCDs produce shorter expo-sure times rather than lower data rates. The data from thefocus chips will be used to automatically adjust the focus in
real time. Twelve of the astrometric chips, those at the leadingand trailing edge of each column of photometric CCDs, will beused to assure that the rotation of the camera is aligned withthe transit of the sky across the camera and to measure theuniformity of the tracking rate. The ten interleaving astrometricCCDs tie together the positions of the objects found in adjacentcolumns of CCDs.
The SDSS photometric camera will image 164 square de-grees of sky on an average night. Including overhead andoverlaps between strips of sky, we will be able to cover theSDSS survey area in ninety dark, photometric nights.
Drift-Scanning the Sky
The focal plane of the SDSS cam era. The cam era contains 30
photom etric C C D s (shaded squares),22 astrom etric C C D s
(shad ed rectangles), and 2 focus C C D s (topm ost and
bottom m ost shaded rectangles). (C ourtesy M ike C arr)
i'
u'
z'
g'
i'
r' r'
u'
z'
g'
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m onitor t e lescope and reduces the
ima ges; the softw are that selects sev
eral dozen different t ypes of spectroscopic targets w ith th eir individual
selection criteria; and on our ability
to effectively monitor the process.
Building the dat a processing and
storage system s necessary to run the
S D S S requires a higher level o f in-
frastructure than is available at any
of the universities involved w ith t his
project. In im plem enting the dat a ac
quisit ion system , the infrastructure
for the data processing softw are, and
the mechanism s for data storage, w ehave benefi ted from Fermilabs many
years of experience w ith high energy
physics experiment s. Like high en-
ergy phy sics experim ents, t he scien
t i f ic objec t ives , ins t ruments , an d
sof tw are are provided by scient ists
at Fermilab an d at each of the insti
tut ions in the collaboration . The staf
at Ferm ilab supplies the expertise in
m anaging la rge scient i f ic projects
and the accompanyin g infrastructure
that bring the project together
Fermilab staff have been instrumen
ta l in inst i tut ing coding standards
mainta ining code