html5-img
1 / 56

The Accelerating Universe: Why you should worry…

The Accelerating Universe: Why you should worry…. 2006 Hoxton Lecture Christopher Stubbs Department of Physics Departme nt of Astronomy Harvard University. This is a remarkable time. Our view of the Universe is shifting, yet again Sun-centered solar system Galactic structure

lars-sutton
Télécharger la présentation

The Accelerating Universe: Why you should worry…

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. This is a remarkable time 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. Emergence of a Standard Cosmology preposterous 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.

  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…

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

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

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

  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……..

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

  10. Schmidt et al, High-z SN Team

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

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

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

  15. So, are the observations are wrong? OK uh-oh Panic Concern-o-meter My assessment: Probably not, the effect seems to be real.

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

  17. Three philosophically distinct possibilities... • 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” term • Departure from GR on cosmological length scales Regardless, it’s evidence of new fundamental physics!

  18. Worry #2: What if the observations are right? OK uh-oh Panic Concern-o-meter It’s good news: Clear evidence for new physics at the interface between gravity and quantum mechanics.

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

  20. Has Dark Energy toppled reductionism!? • The 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 goal: mtop = 0 me  Constrained parameters Elegant TOE equation

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

  23. From string theory perspective... • Constraining  =0 reduces number of candidate vacuum configurations (“landscapes”). • With non-zero , get of order 10500 landscapes, each with potentially different kinds of physics • What picks the one we inhabit?

  24. 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. • This selection effect is what determines observables, such as me/mp, coupling strengths, etc, and not something deep and fundamental! Ouch.

  25. Worry #3: What are the implications? OK uh-oh Panic Concern-o-meter It is entirely possible that astrophysical observations of non-zero vacuum energy have killed the reductionist approach to physics.

  26. 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?

  27. 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.

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

  29. The ESSENCE Survey • 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… • w = -1 or any variation over cosmic time favors QM • Supernovae are well suited to this task – they probe directly the epoch of accelerating expansion.

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

  31. Implementation • 5 year project on 4m telescope at CTIO in Chile • Wide field images in 2 bands • Same-night detection of SNe • Spectroscopy • Magellan, Keck, Gemini telescopes • Near-IR from Hubble • Goal is ~200 SNe, 0.2<z<0.8

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

  33. Image Subtraction (High-z Supernova Team)

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

  35. 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

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

  37. 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

  38. LSST Merges 3 Enabling Technologies • Large Aperture Optics • Computing and Data Storage • High Efficiency Detectors

  39. Large Mirror Fabrication University of Arizona

  40. Cost per Gigabyte

  41. Large Format CCD Mosaics Megacam, CfA/Harvard

  42. 500 m2 deg2 300 m2 deg2 100 m2 deg2 LSST PS1 PS4 Field of View, sq degrees DES CFHT SDSS Magellan Subaru Keck CTIO Unobscured Aperture, sq meters

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

More Related