Cosmology 101 2

Home , Big Bang nucleosynthesis, Cosmological horizon, Inflationary epoch, Reionization, Structure formation

Chris Pearson : RAL Space July 2015 COSMOLOGY 1 How did the Universe Begin ? 1 How old is the Universe ? 1 How big is the Universe ? 1 Where are we in the Universe ? 1 What is the Universe made of ? 1 Will the Universe end ?

2 COSMOLOGY

1 Our Universe is flat and infinite 1 The expansion of the Universe is expanding 1 The Universe began in a hot Big Bang

Ho = 67.3 ± 0.012 km/s/Mpc

τage = 13.81 ± 0.05 Gyr

ΩΛ,o = 0.685 ± 0.017

Ωm,o = 0.315 ± 0.016

ΩDM,o = 0.2662 ± 0.016

Ωb,o = 0.0487 ± 0.00027

3 A Very Brief History of Time

4 The Redshift

Frequency increasing Frequency decreasing Wavelength decreasing Wavelength increasing Wave crests get closer together Wave crests get further apart Colour gets BLUER = BLUESHIFT Colour gets REDDER = REDSHIFT

5 The Redshift

! Δν Δλ ν −ν λ − λ v z = = = e o = o e ≈ υ << c ν λ ν λ c ! o e o e for! λe λo ! νe λo -0.2 + z = ≡ The Redshift νo λe -0.4 ! 1 -0.6 )) ν !

(F -0.8

(Flux -1 lg

-1.2

Cirrus Spectrum -1.4

-1.6 6 8 10 12 14 16 wavelength (µm) 6 The Redshift

Δν Δλ ν ❍ Doppler Redshift z = = = e − ν λ ν ! o e o 1 ! ! ! ! ν + v c c + v v ❍ Special Relativistic Redshift + z = e = ! = ! ≈ υ << c ν − v c c − v c ! o 1 / 1 for! 1 / ! ! ❍ Cosmological Redshift v = cz = H d Hubble’s Law ! o

§. Correct interpretation of Cosmological Redshift of galaxies is NOT a Doppler shift. §. Wave fronts expand with the expanding Universe, stretching the photon wavelength.

7 The Redshift Cosmological Redshift

λ R t + z ≡ = ( o ) λ0 R t ! e ( e ) 1Cosmological explanation: Redshift - natural consequence since R(t) is an increasing function of time !Wavefronts expand with the expanding Universe, stretching the photon wavelength.

R(to) λo λe R(te) 8 A Very Brief History of Time

THE HOT BIG BANG: How does the temperature of the early Universe evolve ?

Redshift Wiens Law λ o Ro λ T = constant RoTo = RT λ = = (1+ z) max R Energy density of radiation 4 2 ε = aT = ρc 2 ρ Friedmann Equation R 8πG 2 = R 3 ! $ -1/4 32πGa -1/2 10 -1/2 T = # 2 & t ≈1.5x10 t " 3c %

= Radiation constant a = Newton’s Gravitational Constant G = speed of light c Temperature evolution in early Universe depends ONLY on Nature’s fundamental constants! 9 A Very Brief History of Time

t=0 10-43s 10-35s 10-12s 10-6s 10-4s 0.01s 1s 4s 3mins 3x105yrs 107yrs 109yrs 1010yrs T=∞ 1031K 1027K 1015K 1013K 1012K 1011K 1010K 5x109K 109K 3000K 300K 30K 2.73K

Dark Ages q+ He W± µ+ ν ? o Z q- µ-‐ ν

ν Matter

ν Atoms Clumping Initial Singularity

+ annihila�on µ -‐ decouple μ e Planck Time Inﬂa�on E-‐W Phase Transi�on quark -‐ an�quark annihila�on Hadron-‐Lepton Reac�ons ν shi� -‐> Proton n-‐p ra�o freezes Primordial NucleosynthesisEpoch of Recombina�on First Stars and Galaxies Epoch (re-‐ioniza�on) of Galaxy Forma�on Forma�on of Solar System and Birth of Life 10 It All Started with a Big Bang

11 It All Started with a Big Bang In the Beginning…… Planck Era = 10-43 s 1031 K

# → ' % t 0 % % → % Running Time backwards $ R 0 ( Initial singularity - The Creation Event %T → ∞% % % &ρ → ∞)

-43 O t < 10 s known as the Planck Era O Quantum Effects become important O Einstein’s Theory of gravity breaks down

12 It All Started with a Big Bang In the Beginning…… Planck Era = 10-43 s 1031 K

Quantum fluctuations of spacetime ~ Planck length, are of cosmic magnitude

For a particle of mass, m, λ h Scale at which quantum effects become important : Compton Wavelength c = mc Scale at which self gravity becomes important : Schwarzchild Radius 2Gm RS = 2 c

λC

For a particle of mass, mP = the Planck mass λ c ≈RS Compton Wavelength & Schwarzchild Radius are comparable 13 It All Started with a Big Bang In the Beginning…… Planck Era = 10-43 s 1031 K

Did the Big Bang …….. Bang?!? Or was it a Quantum Theory of Gravity ?

1. Quantum Gravity 2. Super Gravity 3. Superstrings 4. M-Theory

14 Problems with the Big Bang ? The Inflationary Era = 10-35 s 1027 K

1. THE HORIZON PROBLEM the isotropy of apparent causally disconnected regions of the CMB

2. THE FLATNESS PROBLEM the apparent remarkable closeness of Omega to 1

3. THE RELIC PROBLEM the apparent absence of relics from the Big Bang in our Universe

15 Problems with the Big Bang ? The Inflationary Era = 10-35 s 1027 K

1. THE HORIZON PROBLEM the isotropy of apparent causally disconnected regions of the CMB

2. THE FLATNESS PROBLEM the apparent remarkable closeness of Omega to 1

3. THE RELIC PROBLEM the apparent absence of relics from the Big Bang in our Universe

16 The Horizon Problem The Inflationary Era = 10-35 s 1027 K

Cosmological Horizon: measure of distance at a given time from which information can be retrieved into the past: Defines the Observable Universe.

y 17 The Horizon Problem The Inflationary Era = 10-35 s 1027 K

Cosmological Horizon: measure of distance at a given time from which information can be retrieved into the past: Defines the Observable Universe.

Cosmic distance from # 2 & 2 2 2 2 % dr 2 θ 2 2θ φ 2 ( Robertson Walker metric dS = c dt -R (t)% 2 + r (d +sin d )( $1-kr '

The Horizon Scale: ∫ tH c d H = R(tH)r = R(tH) 0 dt ≈ 3ctH R(t)

Horizon size today: ~ 46 Billion light years

18 The Horizon Problem The Inflationary Era = 10-35 s 1027 K

Horizon size today: ~ 46 Billion light years

5 13 Horizon on microwave background: t ~ 3x10 yrs 10 s : 1 million light years ~ 1.3 degrees on the sky

180 degrees

O CMB isotropic To is identical to 1 part in 10,000 O Opposite regions appear never to have been in causal contact O But opposite points in CMB are ~ 90 horizon distances apart !! O So how do they know that they should be at the same temperature?? 19 Problems with the Big Bang ? The Inflationary Era = 10-35 s 1027 K

1. THE HORIZON PROBLEM the isotropy of apparent causally disconnected regions of the CMB

2. THE FLATNESS PROBLEM the apparent remarkable closeness of Omega to 1

3. THE RELIC PROBLEM the apparent absence of relics from the Big Bang in our Universe

20 The Flatness Problem The Inflationary Era = 10-35 s 1027 K

Planck satellite Observations: The Universe is almost flat today: Ωo~1± 0.02 How about in the past ?

2 ! 2 ρ 2 2 k c R 2 8πG kc Ω 2 kc Ω 2 = H = - 2 = H - 2 -1 = 2 2 !R 3 R R ! R H 2 2 Ω -1 (R H ) t to Evolution of Ω with time = 2 2 Ω -1 (R H ) t t ! o

Matter dominated Era:

2/3 ∝ 2/3 ⇒ 2 2 ! 2 ∝ -2/3 Ω ! $ ! $ R t R H = R t -1 t t t = # & = # & Radiation dominated Era: Ω " % " % -1 to matter to radiation to 1/2 2 2 ! 2 -1 ! R∝t ⇒ R H = R ∝t 21 The Flatness Problem The Inflationary Era = 10-35 s 1027 K

Planck satellite Observations: The Universe is almost flat today: Ωo~1± 0.02 How about in the past ?

Ω ! $2/3 ! $ -1 t t t Evolution of with time # & # & Ω Ω = = "to % "to % -1 t matter radiation ! o

6 13 ➠ -7 Ma�er Radia�on Equality teq~ 10 yr = 10 s |1-Ω| < 10

➠ -18 Big Bang Nucleosynthesis tBBN~ 3mins = 180s |1-Ω| < 10

-43 ➠ -63 Planck Time tP ~ 10 s |1-Ω| < 10

Why is the Universe so FLAT ….. fine Tuning FLATNESSto > 1 part in 1060 Why did the Universe not expand - contract back to a big crunch very quickly Why did the Universe not expand so quickly that galaxies and life were unable to form PROBLEM22 Problems with the Big Bang ? The Inflationary Era = 10-35 s 1027 K

1. THE HORIZON PROBLEM the isotropy of apparent causally disconnected regions of the CMB

2. THE FLATNESS PROBLEM the apparent remarkable closeness of Omega to 1

3. THE RELIC PROBLEM the apparent absence of relics from the Big Bang in our Universe

23 The Relic Problem The Inflationary Era = 10-35 s 1027 K PHASE TRANSITION Strong Nuclear

Electromagnetic GUT STRENGTH ELECTROWEAK t=10-‐35s T=1027K TOE -‐12 t=10 s E=1015GeV T=1015K Weak Nuclear E=102GeV t=10-‐43s T=1031K E=1019GeV Gravity

O At high energies the forces of nature unify O Symmetry ➡ Forces become indistinguishable from each other O Universe cools ➡ temperature drops ➡ symmetry breaks ➡ phase transition O Like water freezing into ice ➡ defects appear on cooling 24 The Relic Problem The Inflationary Era = 10-35 s 1027 K PHASE TRANSITION Strong Nuclear

Electromagnetic GUT STRENGTH ELECTROWEAK t=10-‐35s T=1027K TOE -‐12 t=10 s E=1015GeV T=1015K Weak Nuclear E=102GeV t=10-‐43s T=1031K E=1019GeV Gravity

O Phase transition ➡ loss of symmetry ➡ topological defects O Predicted for GUT (strong/electroweak unification) t=10-35s, T=1027K, E=1015GeV O Compare with freezing water O different ice nucleation sites O different axes (domains) of symmetry ➡ topological defects 25 The Relic Problem The Inflationary Era = 10-35 s 1027 K PHASE TRANSITION Strong Nuclear

Electromagnetic GUT STRENGTH ELECTROWEAK t=10-‐35s T=1027K TOE -‐12 t=10 s E=1015GeV T=1015K Weak Nuclear E=102GeV t=10-‐43s T=1031K E=1019GeV Gravity

O 0D point like defects = Magnetic Monopoles (isolated North/South poles) O 1D linear defects = Cosmic Strings O 2D sheet like defects = Textures

26 The Relic Problem The Inflationary Era = 10-35 s 1027 K

Magnetic Monopole rest energy ~ 1015GeV ➡ E=mc2 ➡ mass ≡ bacterium

O Phase Transition ➡ symmetry breaking ➡ topological defects O Expect one topological defect / horizon distance

Horizon distance at t GUT d = 2ct H GUT Number density of Monopoles 1 146 -3 3 ≈10 Mpc d H 2 with energy density mc 161 -3 3 ≈10 GeVMpc d H Monopoles would dominate the energy density and close the Universe by 10-12 s

However…… we are here …… so where are the monopoles ????

27 Problems with the Big Bang ? The Inflationary Era = 10-35 s 1027 K

1. THE HORIZON PROBLEM

2. THE FLATNESS PROBLEM

3. THE RELIC PROBLEM

Solution ? : Inflation

Inflationary Epoch

1 1980s, Alan Guth - Inflation Theory - 1 Period between 10-36 and 10-34 s 1 Small portion of Universe balloons to become today’s visible Universe. 1 Can solve horizon, flatness, relic problems !!

28 Inflation The Inflationary Era = 10-35 s 1027 K

During inflation the Universe accelerates Negative pressure, or large, positive Λ

Friedmann Equations become

4πGρ ΛR ΛR R = - R + ⇒ 3 3 3 Λ1/2 t 2 ρ 2 Λ Λ ∝ 3 Ht R 2 8πG kc ⇒ R e = e 2 = H = - 2 + R 3 R 3 3

Hubble Parameter during inflation is constant = 1/2 (Λ / 3) Universe expands exponentially 29 Inflation The Inflationary Era = 10-35 s 1027 K

Inflation mechanism: symmetry breaking

O Ordinary vacuum, Higgs field is non-zero known as TRUE VACUUM O Phase transition is slow compared to cooling of Universe O Regions of Universe supercool without breaking symmetry O Like water super cooling 253K without turning to ice O Supercooled regions in a state known as FALSE VACUUM O False Vacuum acts like a Cosmological Constant Λ O Higgs field finally reaches lowest state- symmetry breaks. O Latent heat stored in Higgs Field released and re-heats the Universe - inflation ends Inflation can provide the BANG in the Big Bang ? 30 Inflation The Inflationary Era = 10-35 s 1027 K

1. THE HORIZON PROBLEM The isotropy of apparent causally disconnected regions of the CMB

O Inflate from a small sub horizon region O Seemingly causally disconnected points today were in causal contact before inflation O Inflation creates bubble Universes separated by domain walls of order of Horizon

Horizon t>tinflation Universe

Horizon t

our domain

31 Inflation The Inflationary Era = 10-35 s 1027 K

2. THE FLATNESS PROBLEM the apparent remarkable closeness of Omega to 1

Inflation can make Universe arbitrarily flat During inflation, H is constant: Ω is driven relentlessly towards unity

2 Ω k c → -1 = 2 2 0 ! R H

O Require flatness to ~10-63 O ➠ need >1031 inflation folds

32 Inflation The Inflationary Era = 10-35 s 1027 K

3. THE RELIC PROBLEM the apparent absence of relics from the Big Bang in our Universe

Inflation pushes domain boundaries beyond our horizon distance

The density of relics is diluted

33 Inflation 1/2 -35 27 Λ The Inflationary Era = 10 s 10 K t ∝ 3 Ht O Require Flatness 1031 R e = e O Require Horizon ~100 O For Relics depends on details of the physics -36 -34 O For inflation from t1=10 (1/H1) to t2=10 s ➡ 100 e foldings !

40 During the inflationary era 20 Standard big bang t2-t1 t 99 43 0 R /R = e 1 = e = 10 2 1 lg(R) {m} -20 -43 -40 T /T = 10 2 1 -60 inﬂa�on But energy in Higgs Field reheats -40 -30 -20 -10 0 10 lg(t) {s} Inflation of quantum fluctuations ➡ macroscopic scales ➡ seeds of Structure Formation 34 Inflation The Inflationary Era = 10-35 s 1027 K

Inflation of quantum fluctuations ➡ macroscopic scales ➡ seeds of Structure Formation

Structure of the Cosmic Microwave Background can constrain inflation 35 Post Inflation Universe Post Inflationary Era = 10-34 s

Thermal Equilibrium in the Early Universe O For any particle X of mass, m, there will be an epoch where kT~mc2

O Creation of particle anti-particle pair creation becomes favourableγ + γ ⇔ X + X O For kT>mc2 : number of particles ~ number of photons O For kT

e-‐ -‐ e+ e LEPTONS ν

ν ν

GUT γ (Higgs) q q q QUARKS q q

36 The Quark Era The Quark Era = 10-34 – 10-23 s 1022 K

O 10-34s inflationary period ends O Energy in inflation field released O Universe reheats to 1022 K

The primordial soup in thermal equilibrium O photons + free quarks, antiquarks, exchange particles

!q+ q ↔γ +γ

37 The Hadron Era Electroweak symmetry breaking= 10-12 s 1015 K

O 10-12 s ElectroWeak Symmetry breaking (g, W±, Z0) ➡ E-M and Weak Nuclear Force

O 4 fundamental forces of nature now distinct

O Expansion of Universe cools Big Bang Fireball ~1013K (10-6s) ≡ 1GeV

O Quarks bond to form individual Baryons ➡ Quark Confinement ➡ Baryogenesis

1) Why are there so many photons in the Universe ? 2) Why is there no antimatter in the Universe ?

1) Photon Background produced from matter/antimatter annihilation 38 The Hadron Era Matter Antimatter Asymetry = 10--4 s 1012 K

Assume some tiny tiny asymmetry between quarks & anti quarks (matter & antimatter)

n - n n δ q q After matter & antimatter anihilation: δ q q = small excess of quarks remain q ≈ nq + nq ng

Baryons CMB

O How large is δq ? -10 O From CMB and Ωbaryon estimate Baryon to photon ratio = ~10

39 The Lepton Era Neutrino Decoupling = 1s 1010 K

O ~ equal numbers of γ, e, n in thermal equilibrium

O For every 109 photons, electrons, or neutrinos, ~ 1 proton or neutron exists

O T<~1010K neutrinos decouple forming their own ‘ghost Universe’

O T~109K electrons and positrons annihilate

O Universe gets extra source of photons (heating) which neutrinos never “see” ➠ neutrino background colder Neutrino background ~ 1.4 Photon background

40 Big Bang Nucleosynthesis The Neutron Proton ratio = 1-4 s 1010 K

O After Hadron era - Neutrons & Protons (nucleons) present in equal numbers 9 2 - + γ γ • T ~ 9x10 K >> mec ⇒ e + e ⇋ + O Nucleons in thermal equilibrium with electrons and photons

− n ↔ p+ e +νe Neutron Decay − n+ν ↔ p+ e Mode (1) e n+ e+ ↔ p+ν !(2) e 10 Q 1.5x10 (3) - - Number! densities of nucleons given Nn kT T by Maxwell-Boltzmann Distribution = e = e Np

Neutron - Proton ratio is decided by the temperature

41 Big Bang Nucleosynthesis The Neutron Proton ratio = 1-4 s 1010 K

O After Hadron era - Neutrons & Protons (nucleons) present in equal numbers O T~1010K neutrinos decouple from nucleons

O T~9x109K electrons and positrons annihilate e- + e+ ➞ γ + γ

O Small neutron mass difference ➡ reactions shift in favour of lighter Proton

10 1.5x10 - 9 Nn 9x10 1 = e ≈ 0.2 Neutron freezeout Np 0.1

Only neutron decay mode remains /N n

N 0.01

-t/τ N (t) = N e 0.001 n no t ~16mins decay time of free neutron 0.0001 1011 1010 109 Neutrons disappearing quickly !!!! Temperature (K) 42 Big Bang Nucleosynthesis Nucleosynthesis = 3 minutes 109 K

Onset of nucleosynthesis locks up all free neutrons in nuclei, halting the neutron decay

O Nucleosynthesis of the elements begins with Deuterium and ends with Helium (+ a little Lithium, Beryllium, Boron) 4 O Number densities too low to directly make 2p + 2n ➞ He O Sequence of 2 body reactions

FIRST STEP: Deuterium 2H = D

2H n +p ⇔ D+γ

Deuterium binding energy low = mn+mp+mD=2.22MeV ➞ Immediately destroyed

8 Stability when ND~Nn ➞ Temperature drops ~ kT~0.07 = 7x10 K (t~200s)

Neutron decay mode ➞Nn/Np~0.16 (nucleosynthesis will be quite an inefficient process) 43 Big Bang Nucleosynthesis Nucleosynthesis = 3 minutes 109 K

Onset of nucleosynthesis locks up all free neutrons in nuclei, halting the neutron decay

O Once significant Deuterium formed the heavier elements form very fast O Reactions proceed quickly to Helium n+p → D+γ 2H D+n → 3H+γ D+p → 3He+γ 3H D+D→ 3H+p D+D→ 3He+n 4 3He !D+D→ He+γ

3 4 H+p → He +γ 3 4 He + n → He +γ 4He 3 4 H+ D→ He + n 3 4 He + D→ He +p 44 Big Bang Nucleosynthesis Nucleosynthesis = 3 minutes 109 K

Most of 3H, 3He gets locked up in 4He - how about heavier elements ?

4He 4 6 56Fe He + D→ Li +γ 4 3 7 He + H→ Li +γ 6Li 4 3 7 He + He → Be +γ 4 4 8 7 → Li He + He Be

8 → 7Be Be (unstable) 5 8 56 → 4 4 -16 He + He (t~ 3x10 s)

1 Decrease in binding energy beyond Iron as the nucleus gets bigger, strong force loses to electrostatic force. 1 Maximum binding energy at iron ➠ means that elements lighter than Iron release energy when fused. 1 Elements heavier than iron only release energy when split 1 Peaks in binding energy at 4,16 & 24 nucleons from the stability of 4He combination of 2 protons/neutrons

O No stable nuclei with atomic number 5 or 8 Universe runs out of steam O Unusually large binding energy of Helium production ceases with Helium 45 Big Bang Nucleosynthesis Nucleosynthesis = 3 minutes 109 K

Only the very lightest elements are synthesized in the Big Bang

Everything Else is made in Stars 107-108 yrs later

46 Big Bang Nucleosynthesis Nucleosynthesis = 3 minutes 109 K

Abundance depends on Baryon photon ratio (η)

• High η ➠ higher density O ➠ nucleosynthesis starts earlier (higher T) O Helium production more efficient O Less D & 3He leftover

Mass fraction of He

~ Nn/Np~0.16 ➠ ~6 protons for every neutron

So for 2n + 2p ➠ 4He ➠ 10 protons leftover ➠ H (1) 4He+3H 7Be+e-‐

Maximum allowed mass fraction He x( ) = = 28% x + + ! ( 4 number)!He(!nuclei ) 4 4 number!He!nuclei number!H!nuclei 4 10 ! 47 The Radiation Era Recombination = 380,000 years 3000 K

O Temperature 3000o K, electrons captured by protons to form hydrogen atoms O Electrons no longer scatter photons O Radiation decouples from matter O Universe becomes transparent to radiation O Fireball that flooded expanding universe for first 106 years appears as CBR

Before Recombination photon mean free path is very short

Radiation and matter are thermally bound together

48 The Radiation Era Decoupling and Recombination = 380,000 years 3000 K

matter in thermal equilibrium - with the radiation. photons and - e γ e- γ e p electrons to interact via p γ Thompson scattering e- p p γ

Temperature drops

t recombina�on - z p+e H ➠ recombination

γ H ⟹

T γ H R H H γ γ Eventually interactions stop, allowing the photons to decoupling flow freely on scales of H γ the horizon ➠ de-coupling H γ H γ γ H γ

49 The Radiation Era Decoupling and Recombination = 380,000 years 3000 K

Redshift of Recombination / Decoupling ~ z=1089 over redshift shell dz=195 380,000 years after Big Bang over a time scale of ~ 118,000yr

After Recombination and Decoupling O Photons no longer bound to matter and can stream freely O Photons from Big Bang fill the universe observed as the 2.7K microwave background. O The redshifted relic or ashes of the Big Bang O Last time photons interacted ➠ SURFACE OF LAST SCATTERING O Means that we can not observe the Universe when it was younger than ~400,000 years 50 The Radiation Era Decoupling and Recombination = 380,000 years 3000 K

O Before Recombination - Radiation coupled to matter ➠ Matter cannot cluster O After recombination, radiation no longer influences the distribution of matter. O Matter can cluster and collapse around density enhancements O Form the structures of galaxies and clusters of galaxies we observe today

O Universe <106 years old O Universe filled with neutral Hydrogen with density 1 H-atom/cm3 O No galaxies existed prior to 106 years …….. The Dark Ages

Dark Ages Big Bang

52 The Matter Era Reionization = 150 million years 300 K

1 First light in the Universe 1 The first stars and quasars turn on 1 Reionize the neutral Hydrogen 1 Redshifts 10 ~ 6

Dark Ages Reionization Big Bang

53 The Matter Era The formation of structure = 1-11 billion years 30K

1 Galaxies evolving 1 Stars forming

Dark Ages Reionization Galaxy Evolution Big Bang

54 The Matter Era The Present era = 13.8 billion years 2.7K

O 13.8 billion years after big bang O Density 1 H-atom/m3 O ~1080 particles in observable universe O 109 photons and neutrinos for each baryon O Galaxies exist in billions; stars forming everywhere O CBR has redshift of 1000 and temperature of 2.7 K

Dark Ages Reionization Galaxy Evolution Big Bang

55 The Acceleration Era The Universe starts to accelerate = 10 billion years (redshift ~4)

56 The Undiscovered Country The The Fate of the Universe

O STELLAR ERA: O Energy of the Universe from thermonuclear fusion in Stars. O Stellar era lasts until the last stars have used up their fuel. 14 O ~10 yrs for 0.1Mo Red Dwarf

O DEGENERATE ERA: O All stars in the form of stellar remnants O white dwarfs / neutron stars / black holes. O Eventually all stars become black dwarves. Galaxies dissolve

O BLACK HOLE ERA: O Proton decays with lifetime of 1030yrs. O Only organized units are black holes. O Black Holes evaporate via Hawking Radiation over 10100 yr for galactic sized systems. O Universe becomes a cold photon sea Heat Death

O DARK ERA: O Universe consists of leptons + photons - ultimate disorder. O Cools to vacuum energy state 57 The End ?

Followed the evolution of the Universe from the Big Bang to the present and beyond The farthest back we can observe is the surface of last scattering

At times prior to this our evidence is indirect 1 Early Universe must consider Particle Physics 1 T→0 a Quantum Theory of Gravity

1 However the Big Bang Theory has had great success in predicting fine details of 1 The expanding Universe 1 Primordial Nucleosynthesis and the light element abundances 1 The Relic Radiation from the fireball 1 The beginning of structure formation

1 However… there are still many unsolved problems with this Standard Model

58 Just when you thought it was safe ...