Seeing Dark Energy 10 Years LaterSpace Telescope Science InstituteJohns Hopkins University

gMODELS OF EXPANDING UNIVERSE - 10 YRS AGO

High-Z Supernovae TeamIn 1995 the High-z Team was formed: To Measure the Cosmic Deceleration of the Universe with Type Ia Supernovae

It was expected that the degree of deceleration would reveal mass & fate of Universe

To measure changes in the expansion rate, we sought the highest-redshift supernovae to compare to their nearby brethren we had already collected

I was leading a study of all supernova data to date.

Eureka Moment from 10 yrs ago came when calculating the mass of Universe causing the deceleration I assumed was present in the data.EUREKA! It was the Fall of 1997

Days later What does this mean?Instead of negative mass, would Einsteins Cosmological Constant explain apparent acceleration?The Cosmological Constant (Dark Energy) EntersAfter cross-checks, time to publish this!

High-z,1998SCP, 1999SNe Ia near and far indicate level of acceleration equating to ~70% dark energy in Universe!THE ACCELERATING UNIVERSE

z=redshiftCould supernova just be fainter in past or obscured by dust? Need SNe at z>1. In 2002, I formed a new team (Higher-z Team) to use ACS on HST to find out.average supernovaIS THIS THE RIGHT INTERPRETATION?

z=1.34HST is uniquely able to measure Supernovae at z>1From 2002-2007we measured25 new SNe Ia at z>1

Yes, supernovae were right! First detection of turn-over i.e., transition of dark matter to dark energy dominance . Riess et al. 2004, 2007 Riess et al. 2004, 2007average supernovaCONFIRMATION COMES AT HIGH-REDSHIFT

A NEW CLUE: DARK ENERGY IN YOUNGUNIVERSEHubble detectspresence of Dark Energy 9 billion yearsago, when Universewas still losingtug of war (via gravity) with dark matter

Supportive of stable,Einstein-type of DarkEnergy

SN Ia from Ground z0.8Hubble ConstantSDSS BAOLarge-scale StructureWMAPWeak LensingX-ray Clusters High-z BAONow, to lock down hub, we need to tighten the spokes

Wheel of Dark Energy-related MeasurementsSZ-effect, strong lensing, velocity fields, age tests, ISW effect, etcPresent/FutureCONCORDANCE!Dark*Energy*w(z)=p/c2, F (+3p)

Eliminating noisy steps: 1) no change in telescope; 2) no change in Cepheid type; 3) more precise anchorHUBBLE CONSTANT: REBUILD DISTANCE LADDER

Telescope@Haleakulafirst light June 2007Gigapixel CameraLargest digital camera

1.4 gigapixels over 7 square degree field of view

Can survey 3/4ths of sky every week

Expect ~10,000 SNe Ia in 3 years

first light August 20072008-2011Pan-STARRS: Largest Search for NEOs and SNe

BAO + SNe + Lensing*ADEPT is the sequel to WMAP, for dark energy

ADEPT collects 3D positions for 100 million galaxies to measure BAO from 1

Fluctuations on all scales, but characteristic scale provides a measuring rodBAO: smallest systematic errors, simplest physics, angles easier to measure than fluxes, shapes0.3 Myr5 Gyr10 Gyr12 GyrWMAPADEPTFluctuation Spectrum (SDSS),of Baryons via galaxiesFluctuation Spectrum (WMAP).of Baryons+photons via CMB T1 deg500 MlyNEW TOOL: BARYON ACOUSTIC OSCILLATIONS

The Quest w(z) For Dark energy equation of state: P = w r c2(a) Is w = constant? (b) Changing with time/redshift?(c) Or is w irrelevant, because GR is wrong?Options have HUGE implications for fundamental physics

We discovered accelerating expansion and dark energy 10 years ago. SNe Ia at z>1 from HST confirmed we are on the right track.We will better constrain dark energy by tightening a spate of different measurements Most promising include: Hubble constant from 11% to 4%, Pan-STARRS ADEPT, a JDEM enabled by WMAP, measures BAO over the whole sky + Space SNe is very competitive, least expensiveSUMMARY

Communications with the TeamA. Filippenko, Berkeley, CA, 1/10/1998 10:11am:Adam showed me fantastic plots a few days before he left for his wedding. For right now, our data imply a non-zero cosmological constant at the 95% confidence level. Who knows? This might be the right answer. And I would hate to see the other group publish it first. [He advocates for a rapid, short publication]

B. Leibundgut Garching, Germany, 1/11/1998: 4:19amConcerning a fast-track article on a cosmological constant I'd like to ask Adam or anybody else in the group, if they feel prepared enough to defend the answer we get. There is no point in writing an article, if we are not very sure we are getting the right answer.

B. Schmidt, Australia, 1/11/1998: 7:13pm[Advocates for more thorough, comprehensive paper] It is true that the new SNe say that [the cosmological constant] is greater than zero but how confident are we in this result? I find it very perplexingLets put out a paper we can be proud of---quickly.

1/12/1998 [R. Schommer (Chile), M. Philips (Chile), J. Tonry (Hawaii), C. Hogan (Seattle, WA), A. Clochiatti (Chile) ] each write in advocating a comprehensive paper

Kirshner Santa Barbara, CA 1/12/1998 10:18am: I am worried that the first cut looks like you might need [the cosmological constant]. In your heart you know this is wrong, though your head tells you that you dont care and youre just reporting the observationsIt would be silly to say we MUST have a nonzero [cosmological constant] only to retract it next year.

A. Filippenko 1/12/1998, 12:02 pm [Still supports rapid publication] If we are wrong in the end, then so be it. But atleast we ran in the race.

Riess Berkeley, CA 1/12/1998 6:36pm:The results are very surprising, shocking even. I have avoided telling anyone about them for a few reasons. I wanted to do some cross checks (I have) and I wanted to get further into writing the results up before [the other team] got wind of itThe data require a nonzero cosmological constant! Approach these results not with your heart or head but with your eyes. We are observers after all! I think I can answer the group's dilemma about a quick kill paper vs a detailed explanationwell I did it already before the wedding. At this point, a detailed paper is as easy to do (and fast) as a letter so lets do it right.start thinking of reasons that the distant SNe Ia could be dimmer. N. Suntzeff Chile 1/13/1998 1:47pm I really encourage you to work your butt off on this. Everyone is right. We need to be careful and publish good stuff with enough discussion to make it believable to ourselvesIf you are really sure that the [cosmological constant] is not zeromy god, get it out! I mean this seriouslyyou probably never will have another scientific result that is more exciting come your way in your lifetime. Are you up for it? I have no doubt you can be.

XgUniverse now expanding ~20% faster than 5 billion years ago THE ACCELERATING UNIVERSEUniverse now expanding ~20% faster than 5 billion years ago X

I am going to provide an observers view of dark energywith a somewhat different perspective than Dr. PerlmuttersIn 1992, the year I left college and started graduate school, the biggest questionIn cosmology was whether our Universe resembled the model on the left, on the right, or wasA borderline case between the two.The left shows a dense Universe, filled with matter whose gravity is retarding the expansionSo much so that it will stop, contract, and crunch. On the right the Universe is sparsely filledAnd will expand forever. The borderline case is that there is exactly enough matterTo halt the expansion after infinite time. Dr. Perlmutter described one of our best techniques for measuring the type of Universe in which we live.Find a distance supernovae which exploded in the past but whose light has just reached usexplain.In 1992, the year I left college and started graduate school, the biggest questionIn cosmology was whether our Universe resembled the model on the left, on the right, or wasA borderline case between the two.The left shows a dense Universe, filled with matter whose gravity is retarding the expansionSo much so that it will stop, contract, and crunch. On the right the Universe is sparsely filledAnd will expand forever. The borderline case is that there is exactly enough matterTo halt the expansion after infinite time. Dr. Perlmutter described one of our best techniques for measuring the type of Universe in which we live.Find a distance supernovae which exploded in the past but whose light has just reached usexplain.So in 1998 I wrote a paper for the High-z Team with the provocative titleIn 1999 Sauls Team published the same conclusionTogether these became the breakthrough However, we remained concernedThese studies also gave us a new clue about dark energynot only is it winning the battle now, we can seeIt starting the battle at least 9 billion years agoSmallest systematic errors (DETF), simple physics Angles easier to measure than fluxes and source shapes Gives two independent measures, H(z) and D(z), from radial and transverse correlation function Can usefully measure w(z) to z~2