Our Evolving Universe1 Vital Statistics of the Universe Today… l l Observational evidence for the Big Bang l l Vital statistics of the Universe   Hubble’s Constant (H 0 )   Curvature (k)   Density (  ) l l How will it all end? (Expand forever - or collapse?) Ho K  

Our Evolving Universe2 T = 0Now Very hot ~ 3K Structure formation ‘Inflation’ Particle/photon Soup ‘Nucleosynthesis ’ ‘Recombination’ Matter ‘Freeze-out’ 380,000 years The CMB… The Big Bang so far…

Our Evolving Universe3 Evidence for the Big Bang n Hubble’s Law l V = H 0  D (H 0 =Hubble’s Constant) l Evidence for expanding universe (not specifically for Big Bang) 1996 type 1 SNe n The Cosmic Microwave Background l Photons from ‘recombination’ at T= 380,000 yrs l Evidence for a HOT beginning

Our Evolving Universe4 Evidence for the Big Bang n The evolution of galaxies l Distant (older) galaxies look different from those nearby.  Older galaxies generally smaller, more irregular & more interacting  More active galaxies l Evidence for changing, non- eternal universe. Earlier lecture ‘Evolution of Galaxies’

Our Evolving Universe5 p n 2H 2H p 3 He 4 He n 2H 2H 3 He 6 Li 7 Li 9 Be 1H 1H A=5 A=8 + 3 He (Rare) Theory makes clear predictions based on ‘well understood physics l Relative abundance of 4 Helium to Hydrogen predicted to be 25% (by mass) of total.  Dependent on ratio of proton to neutrons at the time of nucleosynthesis (~7:1) l Levels of 2 H, 3 He and 7 Li also predicted. Evidence for the Big Bang… The abundance of elements

Our Evolving Universe6 Observations… l (Current abundances dependent on density of ordinary matter at nucleosynthesis - & therefore density now). l Observations agree VERY WELL with predictions l More STRONG evidence for Hot Big Bang ‘Allowed’ density (Allowed ‘baryon’ density also of great interest for later studies of ‘Dark Matter’) He D Li Element Abundance (Relative to Hydrogen) Baryon (normal matter) density (% of  c ) ~25% Observed value Predicted values Evidence for the Big Bang… The abundance of elements

Our Evolving Universe7 Overall… Plenty of evidence FOR the Big Bang… Nothing directly AGAINST. Evidence for the Big Bang… Summary…

Our Evolving Universe8 Vital statistics of the universe n Parameters needed to describe the state (& predict the fate) of the Universe : Size of observable universe Time (t) Einstein’s General Relativity says how it all fits together. … Hubble’s Constant Density term Curvature term Cosmological Constant The fate of the universe… Hubble’s constant (H 0 ) Density (  or  )  = density/critical density =  /  c Curvature (k) (For ‘flat’ universe k = 0). Ho  =<1, k=-ve  =1, k=0  >1, k=+ve ? Now… Big Yawn Big Crunch

Vital statistics of the universe… Measurement of Hubble’s constant n Many ways to do this l l redshift easy: distance challenging l l need long distances (>300 Mlyr or so) n Recent results: l l 73±2±4 km s -1 Mpc -1 (compilation, 2010) l l 69.8±1.5 km s -1 Mpc -1 (WMAP + galaxy surveys) Our Evolving Universe9 HST Cepheid Variable study Type 1 Supernovae Study

Our Evolving Universe10 Vital statistics of the universe… Measurements of curvature l Is dependent on total density . l Inflation predicts universe is FLAT! (i.e. k = 0). Curvature (k) Curvature can be determined through analysis of the ripples in the CMB Position gives: k = 0 (Flat!) (Also H = 70±2 km/s/Mpc)

Our Evolving Universe11 Vital statistics of the universe… Measurements of density (1) Density (  ) l  = density/critical density =  /  c l  c ~ kg.m -3 ~ 6 H atoms per m 3 ! 1) Contribution of stars l Add up the masses of all stars… There are many different ways of determining the density of the universe…  stars ~ ~0.5% of what is needed to make a flat universe!

Our Evolving Universe12 Over 90% of the total mass of galaxies is in the form of a ‘Dark Matter’ Halo Luminous matter 2) Contribution of galaxies R Gas Disc Halo NGC6503 ‘Rotation curves’ tell us about distribution & amount of mass in galaxies  galaxies ~ 0.1 < 10% of what is needed to make a flat universe! Vital statistics of the universe… Measurements of density (2) Dark Matter Luminous matter

Our Evolving Universe13 3) Contribution of clusters Mass distribution implied by warping A) Gravitational lensing study… Images of galaxies warped by central mass More dark matter! B) ‘Bulk flow’ study… l Using redshift to look at motion of large scale structures… Large scale structures ‘PSCz’ Infrared Experiment Velocity survey  clusters ~ 0.25  bulkflow  0.25 At largest scales we see ~25% of what is needed to make a flat universe. Vital statistics of the universe… Measurements of density (3)

Our Evolving Universe14 Galaxy: Stars  Scale (Mpc) Galaxy: All Mass Galaxy Clusters Bulk Flow CMB ripples Prediction of Inflation Results so far… Dark Matter Is this enough to understand the fate of the universe? Flat universe Results so far… l Inflation theory and CMB observations indicate:  The universe is FLAT (ie.  total = 1) l ~25% of the mass needed is seen in observations of largest structures l BUT - the majority (>90%) of the mass in the universe is some form(s) of non-luminous and unknown DARK MATTER… Vital statistics of the universe…  - how it all adds up…

Our Evolving Universe15 Vital statistics of the universe… A new twist? n Type 1a supernovae studies of Hubble’s law at large distances…  = 0  = 1  = 2 Expected: The expansion rate to have decreased due to pull of gravity. Found: The expansion rate has increased! The expansion of the Universe is accelerating!

Our Evolving Universe16 n What is causing this accelerating expansion? l Some kind of ‘Vacuum energy’ that OPPOSES pull of gravity? The Cosmological Constant is back!    total =  matter +    total =  matter +   n Also known as: ‘DARK ENERGY’ l Because it is energy it also contributes to the universe’s total mass (or density)  All Matter Stars  Scale (Mpc) Prediction of Inflation Dark Matter Galaxies Vital statistics of the universe… A new twist?

Our Evolving Universe17 Recipe for the Universe n From WMAP data + galaxy clusters, supernovae etc. of which only 1/10 stars!

Our Evolving Universe18 Separation of galaxies (D) Time (t) The fate of the universe… How will it all end? How does  affect the fate of the universe? Without   = 1 (Flat) With  l Even though universe is nearly flat - it will continue to EXPAND FOREVER… l …at an EVER-INCREASING rate What is DARK ENERGY (  )? What is DARK MATTER? n But… And…

Our Evolving Universe19 Summary