Transcript Big Bang II: The inflationary universe Dr Cormac O’Raifeartaigh (WIT) Cosmology The study of the cosmos How big is the universe? How old is.

Big Bang II: The inflationary universe
Dr Cormac O’Raifeartaigh (WIT)
Cosmology
The study of the cosmos
How big is the universe?
How old is it?
How did it begin?
How will it end?
Overview
Part I
The expanding universe
The Big Bang model
Other evidence: the cosmic microwave background
Part II
Limitations of the Big Bang model
The theory of inflation
Evidence for inflation
Future work
I The expanding universe (1929)
Edwin Hubble (1889-1958)
Far-away galaxies rushing away
at a speed proportional to distance
v = Ho d
The expanding universe: origin
Rewind Hubble graph
Universe converges
Infinitely hot, infinitely dense
Big Bang
expanding and cooling ever since
Georges Lemaitre
The expanding universe: age
How long since BB?
v = distance / time
v = Ho d here
→ Ho = 1 / t
t
v = Ho d
= 14 billion yr!
Big Bang model
14 billion years ago, U
concentrated in tiny region
Primordial explosion of space,
time, matter and radiation
Universe expanding and
cooling ever since
Misnomer: singularity problem
The expanding universe and gravity
The forces of nature
Strong nuclear force (short-range)
Weak nuclear force (short-range)
Electromagnetic force - attractive or repulsive
Gravitational force - attractive only
At the largest scales, gravity dominates
Why is universe expanding?
Compatible with modern theory of gravity (General Relativity)
Unified field theory:
gauge theory of interactions
Electromagnetic + weak = electro-weak interaction (W,Z bosons)
Electro-weak + strong = grand unification theory (incomplete)
Electro-weak + strong+ gravity = super-unification (quantum gravity?)
Most promising candidate: supersymmetry
Modern theory of gravity
General theory of relativity (Einstein, 1916)
• space+time = space-time
• space-time dynamic
• distorted by mass
• causes other mass to move
gravity = distortion of space-time
Gμν + λgμν= -kTμν
Evidence for general relativity
• bending of light in grav. field
• time dilation in grav. field
• warping of space-time in grav. field
• black holes
General relativity and cosmology
Apply general relativity to entire U
Predicts dynamic U
U expanding or contracting
Depends on density of matter
Friedmann: 3 possibilities Ω =d/dc
Snag: singularity at origin
∞ density, ∞ curvature
quantum gravity?
Evidence for Big Bang
1.
The expansion of universe
(the age of the universe)
2.
The composition of the elements
3.
The cosmic background radiation
2. Composition of the elements
Nucleosynthesis after BB:
neutrons, protons→ light nuceli
Predicts U of 75% H, 25% He
observed
Heavier elements formed in dying stars
Confirmed by Hoyle
Georges Gamow (1906 –1968)
3. Cosmic background radiation
BB model also predicts
U transparent at recombination
Afterglow radiation in U
Image of U at 380,000 yr
Characteristics of radiation
Alpher, Gamow and Herman
Long wavelength
Blackbody spectrum
Low temp
Discovery of cosmic background radiation
Radio-astronomy
Background radiation
Isotropic
Microwave wavelength
Temperature 3 K
Penzias and Wilson (1964)
Big Bang afterglow measured!
Part II
Big Bang puzzles
BB model requires special initial conditions
CMB: Why does the U appear flat, homogeneous & isotropic?
horizon problem
flatness problem
galaxy problem
(why so homogeneous?)
(why so finely balanced?)
(how did they form?)
singularity problem (what banged? quantum gravity)
The horizon problem
•Two distant regions of microwave
background have similar temps
Why?
•Finite speed of light
• Finite age of U
Too far apart to be causally connected
The flatness problem
Expansion finely balanced
Slightest deviation from flatness
→
runaway expansion or crunch
(at t = 1 s, W = 1 to within 1:1015)
Why so finely balanced?
Galaxy formation problem
Microwave background
smooth on large scale
No deviations from
homogeneity obvious
(1 in 1000)
How do galaxies form?
Inflation (Guth 1981)
Initial exponential expansion of U
Driven by negative pressure
Caused by quantum vacuum field
Repulsive gravity (GR)
Expansion of 1026 in 10-32 s
Energy scale ~ 1016 GeV
Smooths out inhomogeneities
Smooths out curvature
‘No-hair’ universe
The inflationary universe
Solves horizon problem
Early U incredibly small
Time to reach equilibrium
Solves flatness problem
Geometry driven towards flatness (balloon)
Mechanism for galaxy formation
Quantum fluctuations inflated to galactic size
Predicts spectrum of T inhomogeneity
0.92 < ns < 0.98
Inflation and particle physics
Arose from Grand Unified Theory (quantum field theory)
GUT = unification of electro-weak/strong interaction at high E
Inflation = symmetry breaking of Higgs field?
Higgs boson responsible for inflation field?
Today
Inflation ≠ symmetry breaking of Higgs field
Super-symmetry (SUSY) = unification of all 4 interactions at high E
Inflation = symmetry breaking of SUSY field?
Super-symmetric particle responsible for inflation field?
Mechanism for inflation (Guth)
Initial condition (t = 10-34 s)


zero scalar field, non-zero potential
unstable equilibrium (false vacuum)
Negative pressure causes inflation
Quantum fluctuations perturb field
toward true vacuum
Snag; perturbations too large!
Old inflation (tunnelling)
5.8 The inflationary Universe and clues from particle physics
Standard Big Bang
Figure 5.7. Comparison of the
evolution of the scale factor and
temperature in the standard Big Bang
19
10 GeV
and inflationary cosmologies.
Scale factor A
The scale factor can be thought of
as the distance between any two
points which partake in the
Factor of
103110
R
uniform expansion of the
Universe.
3K
10 -43 S 10.34 S
Today
Inflationary Scenario
Scale factor R
3K
Today
New inflation (Linde, Steinhardt)
Evidence for inflation? COBE (1992)
• Accurate measurements of
cosmic background radiation
• Perfect blackbody spectrum
• Not quite uniform
• T anisotropy (1 in 105)
• Galaxy formation
COBE Satellite (1992)
Smoot and Mather: Nobel Prize (2007)
Cosmic background radiation: COBE
•Perfect blackbody spectrum
•Not combination of sources
•Extra-galactic origin
•Slight anisotropies in T
•Galaxy formation
•Angular peaks not resolved
Evidence for inflation? WMAP (2002)
Wilkinson Microwave Anisotropy Probe
WMAP satellite (2002)
•Details of T anisotropy
•Details of flatness of U
•Details of galaxy formation
WMAP results (2005)
Flat to 1%
Homogeneous to 1/105
T measurements
Polarization measurements
Spectrum of T anisotropy
Spectral index
ns = 0.951 ± 0.016
2-parameter fit
Confirmation of dark energy
Inflation: observational status
1. Spectrum of T anisotropy
WMAP: very good fit to predicted fluctuations
2. Flatness of U
WMAP: Flat to 1% as predicted
3.
(Ω = ~ 1)
Mass density of U
Supernova data (acceleration of U)
Ωmat(0.3) + Ωvac(0.7) = 1
(Ω ≠ 0.3)
Summary: history of the universe
Future work
Particle responsible for inflation field?
Nature of symmetry breaking? (supersymmetry breaking?)
Successful description of singularity? (quantum gravity)
Detection of gravitational waves? (Planck satellite)
Alternatives to inflation
• Time-varing constants of nature (Barrow, Mageuijo)
• Colliding branes and the cyclic universe (Turok, Steinhardt)
Summary