The Dark Side of the Universe

Transcription

1 The Dark Side of the Universe Logistics An overview A first taste without the sourness of equations! Outline Phys

2 Phys Logistics Basic Information Instructor: Professor Bernard Sadoulet (sadoulet@cfpa.berkeley.edu) Class Time: T/Th 9:40-11:00 Pacific Time Class Location: 501 Campbell Hall UCB and on the Internet Office Hours: Immediately after class in 501 Campbell (Astronomy Dept Coffee) Thursday 2:00-3: LeConte or by phone ( ) Or by appointment Credit (UCB) Requirements regularly attend the lectures and read the assigned preparatory material problem sets approximately every three weeks a final paper on a topical aspect of the dark matter or dark energy problems Outline due end of October Paper due Dec 1 Other students and postdocs are welcomed (and encouraged) to submit problem sets and the final paper. Should only represent medium load! Books: None required (we will use recent articles on the web) P.J.E. Peebles Principles of Physical Cosmology (Princeton University Press, 1993) E.W. Kolb and M.S. Turner The Early Universe (Addison-Wesley, 1994)

3 Style As interactive as possible Your own experience Linkages and connections Attempt to go beyond The standard lore and current fashion The maths or the complexity Spirit of Awe Looking beyond: Camille Flammarion Phys

4 The Big Bang Initial explosion! <= Expansion of the universe Since Hubble (1925) we know that distant galaxies are receding from each other <= Universe was hot in the early times We detect the glow in cosmic microwave background Initially at 3000K, now at 2.73K The formation of deuterium, helium and lithium requires a hot furnace Phys

5 Galaxies as Tracers of Space Hubble Space Telescope Deep Field 5 million galaxies/squared degree 200 billion galaxies over whole sky Phys

6 COBE Cosmic Microwave Background K! Phys

7 Primordial Nucleosynthesis Not enough 4 He produced to account for observed 23% in mass => hot early universe (Gamov) Phys

8 From Quarks to the Cosmos Big Bang enables influence of infinitely small on infinitely large Phys

9 The Role of Gravity Expansion is governed by gravity Slowed down by gravity At least we thought so, till recently! Define critical density ρ c as the density at which the kinetic energy and potential energy are equal in magnitude > 1 recollapses = closed universe = = 1 expands forever, stops at infinity = flat universe c < 1 expands forever = open universe a(t) = scale parameter (e.g., distance between two distant galaxies) Ω < 1 Ω = 1 Ω > 1 time How can we have gravitational repulsion? Generalization of Newton s law to General Relativity a acceleration { = G r 2 { V mass density { = G 1 u r 2 c 2 { + 3 { p V energy density pressure a acceleration GR gravitational mass V r a Phys If pressure is negative, gravity can become repulsive!

10 Cosmic Microwave Background Boomerang + Maxima: The universe is spatially flat! Phys

11 The Role of Gravity 2 Formation of structure Gravity is unstable! Local increase of density tends to grow: attracts matter around it. This generates velocities on top of expansion. We see these fluctuations in cosmic microwave background. We can follow them as a function of time A quantum origin? Extrapolation flat universe ν only baryonic CDM => We need to do a little bit of General Relativity To describe expansion Understand how we can extract both the energy density and the pressure To understand the growth of structure Very sensitive also to the energy density and the pressure Also a signature of the nature of dark matter Phys CMB at z 1000 Large scale structure

12 The Initial Seeds Seen in Cosmic Microwave Background e.g. Boomerang Phys

13 A Bizarre Universe The Dark Side! Not a mixture of matter and antimatter! The most obvious guess: equal mixture of matter and antimatter We do not see the high energy photons from matter-antimatter annihilation There is more than ordinary matter and photons Ordinary matter = baryons + electrons Primordial abundance of deuterium => Ω baryon 5% In addition: Dark matter Represents 85% of matter = which clumps! => Ω dark matter 30% Dominates gravity and is responsible for the formation of structure Dark energy? Evidence for acceleration of the universe = antigravity! Diffuse and appeared recently => Ω dark energy 65% Phys Cosmic microwave background: universe is flat => SUM 100%

14 Dark Matter Solid evidence that 85% of the mass in the universe is dark rotation curves in spiral galaxies globular clusters / gas around elliptical galaxies velocity dispersion in clusters X-ray gas in clusters gravitational lensing by clusters Large scale flows Phys

15 What is the Nature of Dark Matter A map of the territory dark matter clumped H 2? gas baryonic dust VMO? MACHOs Primordial Black Holes thermal non baryonic exotic particles non-thermal Mirror branes Energy in the bulk Light Neutrinos WIMPs Axions Wimpzillas => systematic effort Phys

16 Baryonic Dark Matter MACHOs Hot/Warm Diffuse Gas Phys

17 Non Baryonic Dark Matter Many hints that the bulk of Dark Matter is non baryonic! Ω eff Tytler et al. Vel Corr. b=1 Voids Baryon Dipole Invent. b=1 Power spectrum Shaya et al. Primordial Nucleosynthesis H o =65km/s/Mpc Potent b=1 Cluster Evol. Cosmological Tests Supernovae + CMBR Candidates Light massive neutrinos Axions Weakly Interactive Massive Particles e+04 1e+05 1e+06 Scale (kpc) Phys

18 CDMS I Active Veto Detectors Pb Shield 20mK View down tunnel (Icebox at far end) Polyethylene Inner Pb shield Icebox inside Pb shielding Phys

19 Recent Controversy DAMA claims to have found WIMPs CDMS has contradictory results Phys

20 The Dark Energy Revolution Supernovae at high redshift Before After Subtraction Phys A HST image

21 Dark Energy One type of supernovae appears to have very constant light curves (once corrected for decay time) Luminosity Distant supernovae appear dimmer than expected in a flat universe Potential problems Are supernova properties really constant? Dust? Thursday 8/31: discussed by Saul Perlmutter Phys Fainter m =1 =0 time Distance

22 Very surprising! What can it be? Vacuum energy <- fluctuation constant Related to the zero point energy of harmonic oscillator Naïve calculation: too small by ! p =-u Einstein s gravitational A new form of matter/energy: Quintessence p =wu w >-1 Tangled topological defects => We have no clue! Why now? Evolution rate depends on w! 3 ( 1+ w) u( t) ( t) a( t) Phys

23 The Grand Synthesis Not incompatible with rest of cosmology! Phys

24 Our territory dark matter and energy clumped H 2? gas baryonic dust VMO? MACHOs Primordial Black Holes thermal nonbaryonic Quintessence exotic particles Other dimensions? non-thermal Light Neutrinos WIMPs Axions Wimpzillas Phys Why b m Do we understand Gravity?

25 Phys Inventories Our Tools Pattern and growth of structure Pattern and growth of velocities Measurement of pressure Because { = G 1 u r 2 c 2 { + 3 { p V energy density pressure acc acceleration GR gravitational mass we can measure both the energy density and the pressure by measuring the expansion as a function of time or the distance vs z ( ) a { t d z expansion ( ) 1+ z = a t o a( t) t = cd Laboratory searches Dark matter Dark energy We will emphasize New probes CMBR, supernovae, weak lensing, Sunyaev-Zel dovich, laboratory detection New tools ( ) large field of view telescopes, adaptive optics, large format arrays, cryogenic detectors

26 Instrumentation Enabling technology e.g. Cryogenic Detectors Phys

27 Outline The Current Paradigm The Big Bang, Inflation and the homogeneity of the universe at large scale. General Relativity tools: Robertson Walker metric, Friedman equation. Spatial geometry and observations of the Cosmic Microwave Background Baryon density: Baryogenesis and nucleosynthesis Dark Matter: astrophysical observations Observational evidence and inventory The pattern and growth of structure and velocities The dark baryons: MACHOs and warm/hot diffuse baryons Non Baryonic Dark Matter: the particle physics connection Evidence for non baryonic nature Theoretical framework (QCD, supersymmetry, extra dimensions) Neutrino mass measurements Axion searches WIMP searches (Direct and indirect detection) Dark Energy Observational evidence: high redshift supernovae Measuring pressure in the universe: distance versus redshift What can be learnt from the growth of structure? Models for dark energy Directions for progress Phys