The Big Bang

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The Big Bang
The Big Bang
Theory or Fact?
Theory or established fact?
Dr Cormac ORaifeartaigh (WIT)
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Overview

• Part I
• Cosmology and gravity
• The expanding universe and the Big Bang
• The theory of the Big Bang model
• More evidence
• Part II
• Limitations of the model
• The theory of inflation
• Recent observations dark energy
• The standard model of cosmology

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I Cosmology

• How big is the universe?
• How old is it?
• How did it begin?

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The universe

• Everything there is
• Space, time, matter, energy
• Matter planets, stars, galaxies

What are the forces in the universe?
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Early cosmology

• Copernicus (15th cent)
• Sun-centered cosmology
• Galileo (16th cent)
• Astronomical evidence
• Kepler (16th cent)
• Elliptical orbits of the planets
• Newton (17th cent)
• Cause law of gravity

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Newtons gravity
Motion of moon
Motion of apple
Caused by earths gravity
Force causes acceleration - change in motion
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Newton (1642-1727)
The force of gravity

• Planet orbits due to gravity

• Gravity caused by suns mass

• Terrestrial gravity due to earths mass

Unites terrestrial gravity with celestial gravity
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Gravity and the universe

• Gravity long range force
• Attractive (extremely weak)
• Accumulative
• Holds solar system together
• Holds galaxies together

Milky Way
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Other universal forces

• Electromagnetic force
• Holds atoms together
• Neutral at long range
• Strong nuclear force
• Holds nucleus together
• Force between protons
• Weak nuclear force
• Causes radioactivity

Atom
Superforce?
All stronger than gravity not long range
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II The expanding universe (1929)
20th century astronomy

• powerful telescopes
• photography
• milky way galaxy
• many other galaxies

1929 galaxies moving apart
Edwin Hubble
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Doppler Effect
Frequency of light depends on relative motion of
observers

• Stars moving away look
• redder than if stationary

Redshift
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The expanding universe (1929)
Edwin Hubble (1889-1958)
Far-away galaxies rushing away at a speed
proportional to distance
v Hod
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The origin of the universe

• rewind Hubble graph
• universe converges
• primeaval atom?
• extremely hot, extremely dense?
• big bang ?

Georges Lemaitre
Expanding and cooling ever since
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Age of the universe (Lemaitre)
How long since origin?

• velocity distance / time
• but v Ho d
• ? t 1 / Ho

t 14 billion yr
agrees with astrophysics v
Note initially wrong due to distance measurements
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The Big Bang model

• 14 billion years ago, universe concentrated at
  a point
• Primordial explosion of matter, energy, space and
  time
• Universe expanding and cooling ever since

Misnomer singularity problem
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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
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The special theory of relativity
Modification of Newtons Laws for bodies moving
at high speed

• speed of light constant
• space and time space-time

• space-time depends on motion
• 2. mass depends on motion
• 3. mass a form of energy

Albert Einstein (1905)
E mc2
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The general theory of relativity
Modification of Newtons Laws due to mass
1. space-time distorted by mass 2. gravity
distortion of space-time
Gµ? -kTµ?

• causes other mass to move

Einstein (1916)
Planetary motion due to spacetime curvature
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Evidence for general relativity

• bending of starlight by gravity
• time stretching by gravity (GPS)
• black holes
• expanding universe

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Relativity and the Big Bang
Apply Einsteins gravity to the cosmos

• Predicts dynamic universe
• Galaxies not moving
• Spacetime expanding
• Depends on mass

Friedmann gravity vs expansion
O gt 1 big crunch O lt 1 runaway universe O 1
exact balance
Which?
O d/dc
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IV Evidence for Big Bang

• v 1. The expansion of universe
• (the age of the universe)
• 2. The abundance of the elements
• (nucleosynthesis)
• 3. The cosmic background radiation

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2. Nucleosynthesis
BB model

• Formation of atoms at high temp
• Predicts U 75 H, 25 He
• Observed in astronomy
• How do heavier atoms form?
• Failed to explain
• Formed in the stars
• Confirmed by Fred Hoyle

We are made of dead stars
Georges Gamow (1906 1968)
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3. Cosmic microwave background
BB prediction

• formation of atoms reduces scattering
• radiation released at recombination
• 300,000 years
• afterglow still in todays universe?

low temp microwave frequency blackbody spectrum
Alpher, Gamow and Herman
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Cosmic microwave background
Observed 1965

• Powerful radio-telescope
• Ubiquitous interference
• Microwave region
• Temperature 3 K

Penzias and Wilson
Dicke Echo of Big Bang!
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Modern measurements of CMB

• Accurate measurements
• Full spectrum
• Perfect fit with theory

COBE satellite (1992)
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Cosmic background radiation

• Expected temperature
• Expected frequency
• Perfect blackbody spectrum

Nobel Prize 2006

• Radiation quite uniform?
• 1 in 10,000
• Galaxy formation?

COBE (1992)
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Part II Big Bang puzzles
CMB raised new questions

• horizon problem (why so homogeneous?)
• galaxy problem (how did galaxies form?)
• flatness problem (is cosmos finely
  balanced?)

singularity problem (what banged?) 8 density,
8 curvature at t 0
Hawking expanding U must begin in singularity
quantum gravity?
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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?
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Galaxy formation problem

• Microwave background smooth on large scale
• No deviations from homogeneity obvious
• (1 in 10,000)
• How did slight perturbations become galaxies?

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The flatness problem
Slightest deviation from flatness
? runaway expansion or crunch
Not observed
Why so finely balanced initially?
? 1?
Astrophysics ? 0.3 ?
At t 1 s, W 1 to within 11015)
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Matter and Dark Matter

• DM first suggested in 1930s
• Explained motion of spiral galaxies

DM has normal gravitational effect but couples
weakly with the electromagnetic force

• Explains motion of stars within galaxies
• Explains motion of galaxy clusters
• Explains gravitational lensing

Fritz Zwicky
? 0.3
Matter OM (30) DM (70)
Predicts ?M ?DM 0.3
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The theory of inflation (Guth, 1981)

• Initial exponential expansion of U
• Driven by phase transition
• Caused release of vacuum energy
• Repulsive force
• Expansion of 1026 in 10-32 s
• Energy scale 1016 GeV
• Smooths out inhomogeneities
• Smooths out curvature

No-hair universe
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The inflationary universe

• Solves horizon problem
• Early U incredibly small
• Time to reach equilibrium
• Mechanism for galaxy formation
• Quantum fluctuations inflated to galactic size
• Solves flatness problem
• Geometry driven towards flatness (balloon)
• Predicts spectrum of T inhomogeneity
• 0.92 lt ns lt 0.98

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New inflation (Linde, Steinhardt)
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New evidence? WMAP (2002)
WMAP satellite (2002)

• Details of T anisotropy
• Details of galaxy formation
• Details of flatness of U

Cosmic microwave background
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WMAP results (2005)

• U flat to 1
• Homogeneous to 1/105
• Spectrum of T anisotropy
• Spectral index
• ns 0.951 0.016
• Strong support for inflation

2-parameter fit
Snag Support for Dark Energy
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Dark Energy (1998)

• Type Ia supernova measurements
• Distant supernova too far away

U expansion accelerating!

• Cause of pushout? Dark energy
• Energy of vacuum?

Compatible with inflation
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Cosmological model
How can universe be flat?
Astrophysics
?m ?dm 0.3

• 1. Ordinary matter 4 (astrophysics)
• Dark matter 22 (cosmology)
• Dark energy 74 (supernova, flatness)

?m(0.04) ?dm(0.22) ?vac(0.74) 1
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Summary Standard Model
Three planks of evidence for BB
The expanding universe, nucelosynthesis, CMB
CMB three puzzles
Horizon problem, galaxy problem, flatness problem
The theory of inflation
The accelerating universe
Supernova measurements, CMB

A flat, accelerating universe containing matter,
dark matter and dark energy
SUMM
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Revised Friedmann universes
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Summary
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Remaining puzzles

• Particle responsible for inflation?
• Nature of dark energy?
• Nature of dark matter?
• Missing antimatter?
• Singularity at time zero?

What happened before BB? Something from nothing?
Further reading ANTIMATTER http//coraifeartaigh.
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