The Dark Side of the Universe Logistics An overview A first taste without the sourness of equations! Outline Phys 250-1 1
Phys 250-1 2 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 2:00-3:00 301 LeConte or by phone (510 642 5719) 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)
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 250-1 3
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 250-1 4
Galaxies as Tracers of Space Hubble Space Telescope Deep Field 5 million galaxies/squared degree 200 billion galaxies over whole sky Phys 250-1 5
COBE Cosmic Microwave Background 2.726 K! Phys 250-1 6
Primordial Nucleosynthesis Not enough 4 He produced to account for observed 23% in mass => hot early universe (Gamov) Phys 250-1 7
From Quarks to the Cosmos Big Bang enables influence of infinitely small on infinitely large Phys 250-1 8
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 144424443 a acceleration GR gravitational mass V r a Phys 250-1 9 If pressure is negative, gravity can become repulsive!
Cosmic Microwave Background Boomerang + Maxima: The universe is spatially flat! Phys 250-1 10
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 250-1 11 CMB at z 1000 Large scale structure
The Initial Seeds Seen in Cosmic Microwave Background e.g. Boomerang Phys 250-1 12
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 250-1 13 Cosmic microwave background: universe is flat => SUM 100%
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 250-1 14
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 250-1 15
Baryonic Dark Matter MACHOs Hot/Warm Diffuse Gas Phys 250-1 16
Non Baryonic Dark Matter Many hints that the bulk of Dark Matter is non baryonic! Ω eff 1 0.1 0.01 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 0.001 10 100 1000 1e+04 1e+05 1e+06 Scale (kpc) Phys 250-1 17
CDMS I Active Veto Detectors Pb Shield 20mK View down tunnel (Icebox at far end) Polyethylene Inner Pb shield Icebox inside Pb shielding Phys 250-1 18
Recent Controversy DAMA claims to have found WIMPs CDMS has contradictory results Phys 250-1 19
The Dark Energy Revolution Supernovae at high redshift Before After Subtraction Phys 250-1 20 A HST image
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 250-1 21 Fainter m =1 =0 time Distance
Very surprising! What can it be? Vacuum energy <- fluctuation constant Related to the zero point energy of harmonic oscillator Naïve calculation: too small by 10 120! 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 250-1 22
The Grand Synthesis Not incompatible with rest of cosmology! Phys 250-1 23
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 250-1 24 Why b m Do we understand Gravity?
Phys 250-1 25 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 144424443 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
Instrumentation Enabling technology e.g. Cryogenic Detectors Phys 250-1 26
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 250-1 27