Seeing Dark Energy 10 Years Later Space Telescope Science Institute Johns Hopkins University

g MODELS OF EXPANDING UNIVERSE - 10 YRS AGO

High-Z Supernovae Team In 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… Negative Mass? This is the first moment when I had indication of discovery. This sign is really saying negative deceleration which means acceleration! Adam’s Lab book, Key Page, Fall 1997: testing… precision… accuracy answer This negative sign represents 70% of Universe!

Days later … What does this mean? Instead of negative mass, would Einstein’s Cosmological Constant explain apparent acceleration? The Cosmological Constant (Dark Energy) Enters… Odds are… Yes!!! At least 99.73% sure that Einstein’s Cosmological Constant is needed ! After cross-checks, time to publish this!

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

z=redshift Could 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. Fainter Brighter Relative Brightness average supernova IS THIS THE RIGHT INTERPRETATION?

z=1.34 HST is uniquely able to measure Supernovae at z>1 From we measured 25 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, 2007 average supernova Era of Dark Energy Era of Dark Matter CONFIRMATION COMES AT HIGH-REDSHIFT Fainter Brighter Relative Brightness

A NEW CLUE: DARK ENERGY IN YOUNG UNIVERSE Hubble detects presence of Dark Energy 9 billion years ago, when Universe was still losing tug of war (via gravity) with dark matter Supportive of stable, Einstein-type of Dark Energy

SN Ia from Ground z<0.8 SN Ia from Space z>0.8 Hubble Constant SDSS BAO Large-scale Structure WMAP Weak Lensing X-ray Clusters High-z BAO Now, to lock down hub, we need to tighten the spokes… Wheel of Dark Energy-related Measurements SZ-effect, strong lensing, velocity fields, age tests, ISW effect, etc Present/Future CONCORDANCE! Dark* Energy *w(z)=p/c 2 , F  (  +3p)

Eliminating noisy steps: 1) no change in telescope; 2) no change in Cepheid type; 3) more precise anchor HUBBLE CONSTANT: REBUILD DISTANCE LADDER 3% Anchor: NGC4258 Hubble Flow 4% error ____ 3% 0% NEW LADDER (100 Mpc) Hubble Flow 5% Anchor: LMC 4% SN Ia hosts, Metal poor to Metal rich 11% error ____ 3% 5% Fast to Slow Cepheids 4% Ground to HST OLD DISTANCE LADDER (100 Mpc)

first light June 2007 Gigapixel Camera Largest 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 Pan-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<z<2 to its natural limit (whole sky) ADEPT will collect 1000 SNe Ia z>0.8 from space to connect to ground (Pan-STARRS) * ADEPT provides 10 8 spectroscopic redshifts to enable LSST and Pan-STARRS lensing measurements JDEM FINALIST: ADEPT

Fluctuations on all scales, but characteristic scale provides a measuring rod BAO: smallest systematic errors, simplest physics, angles easier to measure than fluxes, shapes 0.3 Myr 5 Gyr 10 Gyr 12 Gyr WMAP ADEPT Fluctuation Spectrum (SDSS), of Baryons via galaxies Fluctuation Spectrum (WMAP). of Baryons+photons via CMB T 1 deg 500 Mly NEW TOOL: BARYON ACOUSTIC OSCILLATIONS

The Quest w(z) For Dark energy equation of state: P = w  c 2 (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 Current Future Ground Space SNe ADEPT

» 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 expensive SUMMARY

Communications with the Team A. Filippenko, Berkeley, CA, 1/10/ :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: 4:19am “Concerning 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 perplexing…Let’s 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/ :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 don’t care and you’re just reporting the observations…It 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 at least 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 it…The 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 explanation…well 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 ourselves…If you are really sure that the [cosmological constant] is not zero—my god, get it out! I mean this seriously—you 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.”

g Universe now expanding ~20% faster than 5 billion years ago THE ACCELERATING UNIVERSE Universe now expanding ~20% faster than 5 billion years ago XX