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

Summary