1. 1 The Accelerating Universe: Why you should worry… 2006 Hoxton Lecture Christopher Stubbs Department of Physics Departme nt of Astronomy Harvard University 2006 Hoxton Lecture Christopher Stubbs Department of Physics Departme nt of Astronomy Harvard University

2. This is a remarkable time Our view of the Universe is shifting, yet again Our view of the Universe is shifting, yet again Sun-centered solar system Galactic structure Recognition of external galaxies Discovery of Expansion of the Universe Big Bang paradigm, inflation Dark Matter >> Luminous matter Discovery that the rate of cosmic expansion is increasing: The “Accelerating” Universe Our view of the Universe is shifting, yet again Our view of the Universe is shifting, yet again Sun-centered solar system Galactic structure Recognition of external galaxies Discovery of Expansion of the Universe Big Bang paradigm, inflation Dark Matter >> Luminous matter Discovery that the rate of cosmic expansion is increasing: The “Accelerating” Universe

3. 3 Emergence of a Standard Cosmology Our geometrically flat Universe started in a hot big bang 13.7 billion yrs ago. The evolution of the Universe is increasingly dominated by the phenomenology of the vacuum, the “Dark Energy”. Our geometrically flat Universe started in a hot big bang 13.7 billion yrs ago. The evolution of the Universe is increasingly dominated by the phenomenology of the vacuum, the “Dark Energy”. Matter, mostly non-baryonic, is a minor component. “Dark matter” matters most. Luminous matter comprises a very small fraction of the mass of the Universe. Matter, mostly non-baryonic, is a minor component. “Dark matter” matters most. Luminous matter comprises a very small fraction of the mass of the Universe. preposterous

4. It’s like living through a bad episode of Star Trek! Empty regions of space (vacuum) interact via a repulsive gravitational force. This effect will increasingly dominate, leading to all unbound galaxies eventually being unobservable Scientists at the interface between particle physics and gravity are in a more sophisticated state of confusion than ever before… Empty regions of space (vacuum) interact via a repulsive gravitational force. This effect will increasingly dominate, leading to all unbound galaxies eventually being unobservable Scientists at the interface between particle physics and gravity are in a more sophisticated state of confusion than ever before…

5. An accelerating Universe: some things to worry about... Worry #1: What if the observations are wrong or misinterpreted? What if the observations are wrong or misinterpreted? Worry #2: What if the observations are right!? What if the observations are right!? Worry #3: What are the implications? What are the implications? Worry #4: Prospects for understanding the underlying physics? Worry #1: What if the observations are wrong or misinterpreted? What if the observations are wrong or misinterpreted? Worry #2: What if the observations are right!? What if the observations are right!? Worry #3: What are the implications? What are the implications? Worry #4: Prospects for understanding the underlying physics?

6. 6 Reason to Worry #1: What if the observations are wrong?! “Cosmologists are often in error, but seldom in doubt” Need a way to gauge our level of concern… “Cosmologists are often in error, but seldom in doubt” Need a way to gauge our level of concern…

7. 7 Close, Far, Recent Ancient Expansion history can be mapped by measuring both distances and redshifts Our View of the Expanding Universe Expansion causes stretching of light, “redshift”

8. 8 A Cosmic Sum Rule General Relativity + isotropy and homogeneity require that (in the relevant units)  geometry +  matter +     nergy = 1 If the underlying geometry is flat, and if  m <1 then the cosmological constant term must be non-zero. So it would seem…….. General Relativity + isotropy and homogeneity require that (in the relevant units)  geometry +  matter +     nergy = 1 If the underlying geometry is flat, and if  m <1 then the cosmological constant term must be non-zero. So it would seem……..

9. 9 (Hubble Space Telescope, NASA) Supernovae are powerful cosmological probes Distances to ~6% from brightness Redshifts from features in spectra

10. 10 Schmidt et al, High-z SN Team

11. 11 Extinction by “gray” dust? Careful multicolor measurements, esp. in IR Exploit different z-dependence Look at SNe behind clusters of galaxies “Evolutionary” Effects? Use stellar populations of different ages as a proxy Selection differences in nearby vs. distant samples? Increase the sample of well-monitored Sne Calibrate detection efficiencies K-corrections, Galactic extinction, photometric zeropoints.... See Leibundgut, astro-ph/0003326

12. 12 The accelerating Universe scenario is supported by multiple independent lines of evidence Lower bound on age, from starsLower bound on age, from stars Inventories of cosmic matter contentInventories of cosmic matter content Measurements of expansion history using supernovaeMeasurements of expansion history using supernovae Primordial element abundancesPrimordial element abundances Cosmic Microwave Background provides strong confirmationCosmic Microwave Background provides strong confirmation Lower bound on age, from starsLower bound on age, from stars Inventories of cosmic matter contentInventories of cosmic matter content Measurements of expansion history using supernovaeMeasurements of expansion history using supernovae Primordial element abundancesPrimordial element abundances Cosmic Microwave Background provides strong confirmationCosmic Microwave Background provides strong confirmation

13. 13 WMAP- The Relic Hiss of the Big Bang (NASA)

14. 14 High-z Supernova Search Team Microwave Background Cluster Masses mm  “Best Fit” at  mass ~ 0.3   ~ 0.7 Is the expansion really accelerating? What does this mean? Insufficient mass to halt the expansion Rate of expansion is increasing…

15. 15 So, are the observations are wrong? My assessment: My assessment: Probably not, the effect seems to be real. My assessment: My assessment: Probably not, the effect seems to be real.

16. 16 Reason to Worry #2: What if the observations are right?! What’s responsible for what we see?

17. 17 Three philosophically distinct possibilities... A “classical” cosmological constant, as envisioned by Einstein, residing in the gravitational sector.A “classical” cosmological constant, as envisioned by Einstein, residing in the gravitational sector. A “Vacuum energy” effect, arising from quantum fluctuations in the vacuum, acting as a “source” termA “Vacuum energy” effect, arising from quantum fluctuations in the vacuum, acting as a “source” term Departure from GR on cosmological length scalesDeparture from GR on cosmological length scales A “classical” cosmological constant, as envisioned by Einstein, residing in the gravitational sector.A “classical” cosmological constant, as envisioned by Einstein, residing in the gravitational sector. A “Vacuum energy” effect, arising from quantum fluctuations in the vacuum, acting as a “source” termA “Vacuum energy” effect, arising from quantum fluctuations in the vacuum, acting as a “source” term Departure from GR on cosmological length scalesDeparture from GR on cosmological length scales Regardless, it’s evidence of new fundamental physics!

18. 18 Worry #2: What if the observations are right? It’s good news: It’s good news: Clear evidence for new physics at the interface between gravity and quantum mechanics. Clear evidence for new physics at the interface between gravity and quantum mechanics. It’s good news: It’s good news: Clear evidence for new physics at the interface between gravity and quantum mechanics. Clear evidence for new physics at the interface between gravity and quantum mechanics.

19. 19 Worry #3: What are the implications? If there is some Dark Energy permeating the Universe, what are the implications? If there is some Dark Energy permeating the Universe, what are the implications?

20. 20 Has Dark Energy toppled reductionism!? The reductionist approach to physics has been very successfulThe reductionist approach to physics has been very successful Newton’s Universal law of gravitation Atoms, Electricity & Magnetism Quarks and Leptons Unification of fundamental interactions... The reductionist approach to physics has been very successfulThe reductionist approach to physics has been very successful Newton’s Universal law of gravitation Atoms, Electricity & Magnetism Quarks and Leptons Unification of fundamental interactions... memememe m top    = 0 Elegant TOE equation The goal: Constrained parameters

21. 21 Through some profound but not yet understood mechanism, the vacuum energy must be cancelled to arrive at value of identically zero ummm... Supersymmetry uhhh...Planck Mass...

22. 22 Two possible “natural” values Vacuum energy integrated up to Planck scaleVacuum energy integrated up to Planck scale Cancellation via tooth fairy:Cancellation via tooth fairy: But it’s measured to be around 0.7!But it’s measured to be around 0.7! Vacuum energy integrated up to Planck scaleVacuum energy integrated up to Planck scale Cancellation via tooth fairy:Cancellation via tooth fairy: But it’s measured to be around 0.7!But it’s measured to be around 0.7!

23. 23 From string theory perspective... Constraining   =0 reduces number of candidate vacuum configurations (“landscapes”).Constraining   =0 reduces number of candidate vacuum configurations (“landscapes”). With non-zero  , get of order 10 500 landscapes, each with potentially different kinds of physicsWith non-zero  , get of order 10 500 landscapes, each with potentially different kinds of physics What picks the one we inhabit?What picks the one we inhabit? Constraining   =0 reduces number of candidate vacuum configurations (“landscapes”).Constraining   =0 reduces number of candidate vacuum configurations (“landscapes”). With non-zero  , get of order 10 500 landscapes, each with potentially different kinds of physicsWith non-zero  , get of order 10 500 landscapes, each with potentially different kinds of physics What picks the one we inhabit?What picks the one we inhabit?

24. 24

25. 25 The “selection effect” viewpoint From all possible (presumably equally likely) sets of parameters and interaction strengths, only a small subset could produce heavy elements and evolve life.From all possible (presumably equally likely) sets of parameters and interaction strengths, only a small subset could produce heavy elements and evolve life. This selection effect is what determines observables, such as m e /m p, coupling strengths, etc, and not something deep and fundamental!This selection effect is what determines observables, such as m e /m p, coupling strengths, etc, and not something deep and fundamental! Ouch. Ouch. From all possible (presumably equally likely) sets of parameters and interaction strengths, only a small subset could produce heavy elements and evolve life.From all possible (presumably equally likely) sets of parameters and interaction strengths, only a small subset could produce heavy elements and evolve life. This selection effect is what determines observables, such as m e /m p, coupling strengths, etc, and not something deep and fundamental!This selection effect is what determines observables, such as m e /m p, coupling strengths, etc, and not something deep and fundamental! Ouch. Ouch.

26. 26 Worry #3: What are the implications? It is entirely possible that astrophysical observations of non-zero vacuum energy have killed the reductionist approach to physics. It is entirely possible that astrophysical observations of non-zero vacuum energy have killed the reductionist approach to physics.

27. 27 Worry #4: What are the prospects for figuring this out? Given the confusion over what’s going on here, how likely are we to figure it out? Given the confusion over what’s going on here, how likely are we to figure it out?

28. 28 Dark Energy’s Equation of State w = 0, matter P = w  w = 1/3,radiation w =  1,  w =  N/3, topological defects Our current challenge is measuring the value of w. w = 0, matter P = w  w = 1/3,radiation w =  1,  w =  N/3, topological defects Our current challenge is measuring the value of w.

29. Probing the nature of Dark Energy SN cosmology tests SN cosmology tests Gravitational lensing Gravitational lensing Galaxy cluster abundances Galaxy cluster abundances Baryon oscillations Baryon oscillations Particle physics experiments Particle physics experiments Tests of gravity on all scales Tests of gravity on all scales SN cosmology tests SN cosmology tests Gravitational lensing Gravitational lensing Galaxy cluster abundances Galaxy cluster abundances Baryon oscillations Baryon oscillations Particle physics experiments Particle physics experiments Tests of gravity on all scales Tests of gravity on all scales signal!signal!

30. 30 The ESSENCE Survey Our goal is to determine the equation of state parameter to 10%Our goal is to determine the equation of state parameter to 10% This should help determine whether  belongs on the left or right side of the Einstein equations…This should help determine whether  belongs on the left or right side of the Einstein equations… w =  1 or any variation over cosmic time favors QMw =  1 or any variation over cosmic time favors QM Supernovae are well suited to this task – they probe directly the epoch of accelerating expansion.Supernovae are well suited to this task – they probe directly the epoch of accelerating expansion. Our goal is to determine the equation of state parameter to 10%Our goal is to determine the equation of state parameter to 10% This should help determine whether  belongs on the left or right side of the Einstein equations…This should help determine whether  belongs on the left or right side of the Einstein equations… w =  1 or any variation over cosmic time favors QMw =  1 or any variation over cosmic time favors QM Supernovae are well suited to this task – they probe directly the epoch of accelerating expansion.Supernovae are well suited to this task – they probe directly the epoch of accelerating expansion.

31. 31 Claudio Aguilera --- CTIO/NOAO Claudio Aguilera --- CTIO/NOAO Brian Barris --- Univ of Hawaii Brian Barris --- Univ of Hawaii Andy Becker --- Bell Labs/Univ. of Washington Andy Becker --- Bell Labs/Univ. of Washington Peter Challis --- Harvard-Smithsonian CfA Peter Challis --- Harvard-Smithsonian CfA Ryan Chornock --- UC Berkeley Ryan Chornock --- UC Berkeley Alejandro Clocchiatti --- Univ Catolica de Chile Alejandro Clocchiatti --- Univ Catolica de Chile Ricardo Covarrubias --- Univ of Washington Ricardo Covarrubias --- Univ of Washington Alex V. Filippenko --- Univ of Ca, Berkeley Alex V. Filippenko --- Univ of Ca, Berkeley Arti Garg --- Harvard University Arti Garg --- Harvard University Peter M. Garnavich --- Notre Dame University Peter M. Garnavich --- Notre Dame University Malcolm Hicken --- Harvard University Malcolm Hicken --- Harvard University Saurabh Jha --- UC Berkeley Saurabh Jha --- UC Berkeley Robert Kirshner --- Harvard-Smithsonian CfA Robert Kirshner --- Harvard-Smithsonian CfA Kevin Krisciunas --- Notre Dame Univ. Kevin Krisciunas --- Notre Dame Univ. Bruno Leibundgut --- European Southern Observatory Bruno Leibundgut --- European Southern Observatory Weidong D. Li --- Univ of California, Berkeley Weidong D. Li --- Univ of California, Berkeley Thomas Matheson --- Harvard-Smithsonian CfA Thomas Matheson --- Harvard-Smithsonian CfA Gajus Miknaitis --- Fermilab Gajus Miknaitis --- Fermilab Jose Prieto --- The Ohio State University Jose Prieto --- The Ohio State University Armin Rest --- NOAO/CTIO Armin Rest --- NOAO/CTIO Adam G. Reiss --- Space Telescope Science Institute Adam G. Reiss --- Space Telescope Science Institute Brian P. Schmidt --- Mt. Stromlo Siding Springs Observatories Brian P. Schmidt --- Mt. Stromlo Siding Springs Observatories Chris Smith --- CTIO/NOAO Chris Smith --- CTIO/NOAO Jesper Sollerman --- Stockholm Observatory Jesper Sollerman --- Stockholm Observatory Jason Spyromilio --- European Southern Observatory Jason Spyromilio --- European Southern Observatory Christopher Stubbs --- Harvard University Christopher Stubbs --- Harvard University Nicholas B. Suntzeff --- CTIO/NOAO Nicholas B. Suntzeff --- CTIO/NOAO John L. Tonry --- Univ of Hawaii John L. Tonry --- Univ of Hawaii Michael Wood-Vasey --- Harvard University Michael Wood-Vasey --- Harvard University ESSENCE Survey Team

32. 32ImplementationImplementation 5 year project on 4m telescope at CTIO in Chile5 year project on 4m telescope at CTIO in Chile Wide field images in 2 bandsWide field images in 2 bands Same-night detection of SNeSame-night detection of SNe SpectroscopySpectroscopy  Magellan, Keck, Gemini telescopes Near-IR from HubbleNear-IR from Hubble Goal is ~200 SNe, 0.2<z<0.8Goal is ~200 SNe, 0.2<z<0.8 5 year project on 4m telescope at CTIO in Chile5 year project on 4m telescope at CTIO in Chile Wide field images in 2 bandsWide field images in 2 bands Same-night detection of SNeSame-night detection of SNe SpectroscopySpectroscopy  Magellan, Keck, Gemini telescopes Near-IR from HubbleNear-IR from Hubble Goal is ~200 SNe, 0.2<z<0.8Goal is ~200 SNe, 0.2<z<0.8

33. 33

34. 34

38. 38 ESSENCE Survey Progress to date – 3 of 5 seasons completed

39. 39 (High-z Supernova Team) Image Subtraction

40. 40 Preliminary ESSENCE constraints on w Essence supernovae plus nearby sample jointly constrain w and  m.Essence supernovae plus nearby sample jointly constrain w and  m. Adding other data sets collapses contours.Adding other data sets collapses contours. Essence supernovae plus nearby sample jointly constrain w and  m.Essence supernovae plus nearby sample jointly constrain w and  m. Adding other data sets collapses contours.Adding other data sets collapses contours.

41. 41 Next-Generation Facilities Microwave background - Better angular resolution CMB maps Detection of clusters of galaxies vs. z Supernovae – Dedicated Dark Energy satellite mission Large Synoptic Survey Telescope (LSST) Weak Gravitational Lensing Both ground-based and space based Probing the foundations of gravity Equivalence principle Inverse square law SNAP, Lawrence Berkeley Laboratory LSST Corporation

42. 42 What would an optimized ground-based facility look like? Large collecting areaLarge collecting area Wide field of viewWide field of view Real-time analysis of dataReal-time analysis of data Significant leap in figure-of-meritSignificant leap in figure-of-merit Area x Field of View Large collecting areaLarge collecting area Wide field of viewWide field of view Real-time analysis of dataReal-time analysis of data Significant leap in figure-of-meritSignificant leap in figure-of-merit Area x Field of View

43. 43 Large Synoptic Survey Telescope Highly ranked in Decadal Survey Optimized for time domain scan mode deep mode 10 square degree field 6.5m effective aperture 24th mag in 20 sec >20 Tbyte/night Real-time analysis Simultaneous multiple science goals Simultaneous multiple science goals

44. 44 LSST Merges 3 Enabling Technologies Large Aperture OpticsLarge Aperture Optics Computing and Data StorageComputing and Data Storage High Efficiency DetectorsHigh Efficiency Detectors Large Aperture OpticsLarge Aperture Optics Computing and Data StorageComputing and Data Storage High Efficiency DetectorsHigh Efficiency Detectors

45. 45 Large Mirror Fabrication University of Arizona

46. 46 Cost per Gigabyte

47. 47 Large Format CCD Mosaics Megacam, CfA/Harvard

48. Unobscured Aperture, sq meters Field of View, sq degrees 100 m 2 deg 2 500 m 2 deg 2 300 m 2 deg 2 LSST PS1 PS4 Keck Subaru SDSS DES Magellan CTIO CFHT

49. 49

50. 50 Near Earth Asteroids Inventory of solar system is incompleteInventory of solar system is incomplete R=1 km asteroids are dinosaur killersR=1 km asteroids are dinosaur killers R=300m asteroids in ocean wipe out a coastlineR=300m asteroids in ocean wipe out a coastline Demanding project: requires mapping the sky down to 24 th every few days, individual exposures not to exceed ~20 sec.Demanding project: requires mapping the sky down to 24 th every few days, individual exposures not to exceed ~20 sec. LSST will detect NEAs to 300mLSST will detect NEAs to 300m Inventory of solar system is incompleteInventory of solar system is incomplete R=1 km asteroids are dinosaur killersR=1 km asteroids are dinosaur killers R=300m asteroids in ocean wipe out a coastlineR=300m asteroids in ocean wipe out a coastline Demanding project: requires mapping the sky down to 24 th every few days, individual exposures not to exceed ~20 sec.Demanding project: requires mapping the sky down to 24 th every few days, individual exposures not to exceed ~20 sec. LSST will detect NEAs to 300mLSST will detect NEAs to 300m

51. 51 LSST Challenges Large effective aperture wide field telescopeLarge effective aperture wide field telescope 3 Gpix focal plane3 Gpix focal plane Analysis pipelineAnalysis pipeline Automated Variability ClassificationAutomated Variability Classification Database schema/structure and indexingDatabase schema/structure and indexing $$$$ Large effective aperture wide field telescopeLarge effective aperture wide field telescope 3 Gpix focal plane3 Gpix focal plane Analysis pipelineAnalysis pipeline Automated Variability ClassificationAutomated Variability Classification Database schema/structure and indexingDatabase schema/structure and indexing $$$$

52. 52 Worry #4: What are the prospects for deeper understanding? Next steps are fairly clear: precision cosmology. Next steps are fairly clear: precision cosmology. What if w=  1.000? We’ll need more clues: particle physics particle physics expt’l gravity expt’l gravity ….?… ….?… Next steps are fairly clear: precision cosmology. Next steps are fairly clear: precision cosmology. What if w=  1.000? We’ll need more clues: particle physics particle physics expt’l gravity expt’l gravity ….?… ….?…

53. A summary of where we stand.. 1.Maybe it’s not right? 2.Maybe it is right? 3.Implications? 4.Prospects? 1.Maybe it’s not right? 2.Maybe it is right? 3.Implications? 4.Prospects?

54. 54 Closing thoughts The Accelerating Universe poses a challenge to both theory and experiment/observation This problem sits squarely at an interface we don’t understand: the intersection between gravity and quantum mechanics Look for upcoming new results from Supernova and galaxy cluster cosmology Gravitational lensing Large Hadron Collider (LHC) Tests of gravitation, on all scales The Accelerating Universe poses a challenge to both theory and experiment/observation This problem sits squarely at an interface we don’t understand: the intersection between gravity and quantum mechanics Look for upcoming new results from Supernova and galaxy cluster cosmology Gravitational lensing Large Hadron Collider (LHC) Tests of gravitation, on all scales