The Big Bang Big Bang Big Bang IIII Theory Big Bang IIor Fact? The inflationary universe Dr Cormac O’Raifeartaigh (WIT)
Download ReportTranscript The Big Bang Big Bang Big Bang IIII Theory Big Bang IIor Fact? The inflationary universe Dr Cormac O’Raifeartaigh (WIT)
The Big Bang
The inflationary universe
Dr Cormac O’Raifeartaigh (WIT)
Overview
Part I
Cosmology vs astronomy The expanding universe and the Big Bang The expanding universe and relativity More evidence for the Big Bang
Part II
Limitations of the model The theory of inflation Recent observations The standard model
Einstein’s blunder
I Cosmology
The study of the cosmos
Is it finite?
How big is it?
Is it eternal?
How old is it?
How did it begin?
How will it end?
The galaxies
20 th cent astronomy
powerful telescopes photography
other galaxies?
Cepheid variables stellar distance
1929: many galaxies
Edwin Hubble (1889-1958
)
The expanding universe
1929: galaxies moving apart
Edwin Hubble (1889-1958
) Far-away galaxies rushing away at a speed proportional to distance
v =
H o
d
Doppler Effect
frequency
of light depends on relative motion of observers stars moving away look redder than if stationary
Redshift
The origin of the universe rewind Hubble graph universe converges extremely dense, extremely hot?
primeaval atom?
Expanding and cooling ever since
Georges Lemaitre
Age of the universe
How long since origin?
velocity = distance / time but
→
t v
= H
= 1 /
o H d o
t~ 14 billion yr
agrees with astrophysics √
Note: initially wrong age due to distance measurements
The Big Bang model 14 billion years ago,
U
concentrated in tiny volume primordial explosion of matter, energy, space and time
U
expanding and cooling ever since
Misnomer: singularity problem
III The theory of the Big Bang
Newton
• gravity pulls in not out • space is fixed • time has no beginning
How can space be expanding?
What is pushing out?
What happened at time zero?
Isaac Newton
The general theory of relativity
Modern theory of gravity (1916)
• space and time = space-time • space-time affected by mass • gravity = distortion of spacetime • causes other mass to move
Planetary motion due to spacetime curvature
Einstein (1916)
Evidence for general relativity • bending of starlight by gravity (1919) • expanding universe • time stretching by gravity
(GPS)
• black holes
Relativity and the Big Bang
Apply Einstein’s gravity to the cosmos Ω > 1: big crunch Ω < 1: runaway universe Ω = 1: exact balance
dynamic universe?
space-time expanding?
Einstein:
static universe
G
μν +
λg
μν = -k
T
μν
Friedmann: expanding U
gravity vs expansion
Ω =d/d c
Other evidence for Big Bang
√
1.
The expansion of the
U
2.
The composition of the
U
3.
The cosmic background radiation
2. Big Bang nucleosynthesis baryonic plasma formation of atoms
U
cools too quickly for metals predicts
U
= 75%
H
, 25%
He
observed in astronomy
how do heavier elements form?
formed in the stars (0.1%) supernovas confirmed by Hoyle
Georges Gamow (1906 –1968)
3. Cosmic microwave background
Alpher, Gamow and Herman
BB prediction
radiation from hot origin released at
recombination
300,000 years
afterglow still observable?
low temp microwave frequency blackbody spectrum
Cosmic microwave background
Observed: 1965
radio-astronomy ubiquitous interference
Penzias and Wilson
microwave frequency temperature 3 K
Dicke: Echo of Big Bang!
Modern measurements of CMB
COBE satellite (1992)
• balloon measurements • COBE: differential radiometer • full spectrum
Cosmic background radiation • expected temperature • expected frequency • perfect blackbody spectrum
not from galaxy scattering
COBE (1992)
Nobel Prize 2006
•
radiation not quite uniform?
•
less than 1 in 10 4
•
hints of flatness?
Part II Big Bang puzzles
CMB raised new questions
horizon problem
why so homogeneous?
galaxy problem
how did galaxies form?
flatness problem
fine balance?
singularity problem
(what banged?)
∞ density, ∞ curvature at
t
= 0
GR: expanding U must begin in singularity: Hawking quantum gravity?
The horizon problem •Two distant regions of microwave background have similar temps
Why?
Too far apart to be causally connected
• Finite speed of light • Finite age of cosmos
Is U too big?
Galaxy formation problem Microwave background smooth on large scale No deviations from homogeneity obvious (1 in 10,000) How did slight perturbations become galaxies?
The flatness problem A
t t = 1 s,
W
= 1 to within 1:10 15 )
Slightest deviation from flatness → runaway expansion or crunch
Not observed
Why so finely balanced initially?
Ω = 1?
Astrophysics: Ω = 0.3
?
Dark Matter: CDM model First suggested in 1930s Stellar motion
normal gravitational effect but weak electromagnetic coupling
Explains motion of stars within galaxies Explains motion of galaxy clusters Explains gravitational lensing
Matter = OM (30%) + DM (70%)
Also suggested by nucleosynthesis
Ω = 0.3
BB II: Inflation (Guth, 1981) Initial
exponential expansion
of
U
Driven by
phase transition
Caused release of vacuum energy
Repulsive force
Expansion of 10 26 in 10 -32 Energy scale ~ 10 16 GeV s Smooths out inhomogeneities Smooths out curvature
‘No-hair’ universe: many models
The inflationary universe Solves horizon problem
Early U incredibly small Time to reach equilibrium
Solves flatness problem
Geometry driven towards flatness (balloon) CDM problems
Mechanism for galaxy formation
Quantum fluctuations inflated to galactic size
Predicts spectrum of
T
inhomogeneity
0.92 < n s < 0.98
5.8 The inflationary Universe and clues from particle physics Figure 5.7. Comparison of the evolution of the scale factor and temperature in the standard Big Bang and inflationary cosmologies. The scale factor can be thought of as the distance between any two points which partake in the uniform expansion of the Universe. 19 10 GeV Standard Big
Bang
Scale factor A Factor of
103110 R
3K 10 -43 S 10.34 S
Inflationary Scenario
Today Scale factor
R
3K Today
New inflation (Linde, Steinhardt)
New evidence? WMAP (2002)
WMAP satellite (2002)
Cosmic microwave background
•Details of
T
anisotropy •Details of galaxy formation •Details of flatness of
U
WMAP results (2005)
Strong support for inflation
Homogeneous to 1/10 5 Spectrum of
T
anisotropy Acoustic peaks Scale invariant
n s = 0.951 ± 0.016
•
Also: U
flat to 1% • CDM problem:
dark energy?
2-parameter fit
Inflation: observational status 1.
Size of T anisotropy
WMAP: very good fit to predicted fluctuations 2.
Power spectrum of T anisotropy
WMAP: very good fit to predicted fluctuations
3.
Flatness of U
WMAP: Flat to 1% as predicted (Ω = ~ 1)
4. Scale invariant spectrum
Predicted by most inflationary models
Confirmation of Dark Energy WMAP: flatness Fit parameters: Ω λ Ω λ = dark energy ?
= 0.73, Ω m = 0.24
Type Ia supernova measurements (1998) Accelerating universe Caused by dark energy
Confirmation of dark energy Compatible with inflation
ΛCDM
model 1.
2.
3.
How can universe be flat?
Ordinary matter: 4% (astrophysics) Dark matter: 22% (astrophysics) Dark energy
Λ
: 74% (supernova, CMB) Ω m (0.04) + Ω dm (0.22) + Ω vac (0.74) = 1
Dark energy = zero-point fluctuations ?
Theory: λ = 10 69 CMB: λ = 10 -52 m 2 m 2
Standard Model (
ΛCDM
)
Three planks of evidence for BB
The expanding universe, nucelosynthesis, CMB
The theory of inflation
Horizon problem, galaxy problem, flatness problem
The accelerating universe
Supernova measurements, CMB
A flat, accelerating universe containing matter, dark matter and dark energy
Revised Friedmann universes
Next: Planck Satellite (ESA)
1. Improved sensitivity
T T
1
x
10 6
2. Full spectrum of T anisotropy
New acoustic peaks Scale invariance?
Non-Gaussianity?
3. Accurate values for cosmological constants 4. Polarization measurements
E mode polarization of fluctuations B-modes: gravity waves?
Remaining puzzles
Nature of dark energy?
Nature of dark matter?
Particle responsible for inflation?
Singularity at time zero?
What happened at BB?
Something from nothing?
Slides: ANTIMATTER blog More on Planck: ESA website