Transcript The Big Bang Is it true? The Big Bang: Fact or Fiction? Dr Cormac O’Raifeartaigh.

The Big Bang
Is it true?
The Big Bang: Fact or Fiction?
Dr Cormac O’Raifeartaigh
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?
Not science?
20th cent astronomy
Powerful telescopes
Photography
Cepheid variables
The great debate (1920)
Spiral nebulae
Harlow Shapley vs Heber Curtis
Part of our galaxy?
Distinct galaxies?
How big is the Universe?
The galaxies (1925)
Edwin Hubble
resolved Cepheids in nebulae
stars at huge distance
distinct galaxies
Hooker 100-inch reflector
U is very large
Bonus: the expanding universe
Hubble: distribution of galaxies
Investigated relation between
distance and motion (redshift)
Linear relation (1929)
Hubble’s Law
Far-away galaxies rushing away
at a speed proportional to distance
v = Hod
Motion of galaxies: redshift
frequency of light depends on
relative motion of observers
Doppler Effect
Vesto Slipher
measure motion of galaxies from
light emitted (Vesto Slipher)
Origin of the universe
rewind Hubble graph
U smaller in the past
extremely dense, extremely hot
Expanding and cooling ever since
t~ 4 billion yr
χ
Fr Georges Lemaitre
The Big Bang model (1931)
U originally concentrated in
tiny volume
primordial explosion of matter,
energy, space and time
U expanding and cooling ever
since
Density = clock
What happened at time zero?
II
Explanation ?
Newton
• gravity pulls in not out
• space is fixed
Isaac Newton
• time has no beginning
How can galaxies be receding?
What is pushing out?
The general theory of relativity
Modern theory of gravity (1915)
• space and time = space-time
• space-time affected by mass (and motion)
• gravity = distortion of spacetime
• causes other mass to move
Planetary motion due to spacetime curvature
Einstein (1915)
Evidence for general relativity
• special relativity well-established
• orbit
of mercury
• bending
of starlight by gravity (1919)
Very mathematical
Relativity and the universe
Apply Einstein’s gravity to the cosmos
Alexander Friedmann (1917)
galaxies not moving
space-time expands or contracts
depends on mass
gravity vs expansion
Ω > 1: big crunch
Ω < 1: runaway universe
Ω = 1: exact balance
Einstein: static universe
Gμν + λgμν= -kTμν
The big bang: is it true?
χ
1930-50
1. Situated in general relativity
Small mathematical community
2. Relativity attacked 1925-45
Hitler, Stalin
3. Age of U problem
4. Singularity problem
Singularity problem
Science a conservative activity
Quantum gravity?
III
New predictions
Nuclear physics (1940s)
Apply to Big Bang model
H, He nuclei (1 s)
Atoms (300,000 yr)
U = 75% H, 25% He
Heavier atoms formed in stars
Georges Gamow
BB prediction 3: microwave background
BB : superhot superdense beginning
radiation from hot origin
released when atoms form
recombination (300,000 yr)
radiation still observable?
low temp, microwave frequency
No-one looked (1940s)
Alpher, Gamow and Herman
Steady-state model (1950s)
Rival model
Expanding universe
BUT
No beginning
Fred Hoyle
Matter continuously created
Density of matter constant
Large impact
Steady-State prediction: eternal U
 Continuous creation
 Density of matter constant
 U unchanging, eternal
 Distant galaxies similar to present?
 Youngest galaxies similar to present?
Falsification possible
Radio-astronomy (1960s)
Study most distant galaxies
Study density and intensity
Cambridge
3C survey
Density the same at all times? (SS)
Or different? (BB)
Answer: different
PULSARS!
End of steady-state model
Martin Ryle
Bonus: background radiation (1965)
CMB observed accidentally
background radiation
microwave frequency
temperature 3 K
Penzias and Wilson
Echo of Big Bang!
BB model goes mainstream
Modern measurements of CMB
• accurate measurements
• full spectrum
• fit with theory
COBE satellite (1992)
Cosmic background radiation
• expected temperature
• expected frequency
• perfect blackbody spectrum
• radiation quite uniform?
•1 in 10,000
COBE (1992)
Nobel Prize 2006
• galaxy formation?
IV
Is it true? New puzzles
CMB raised new questions
horizon problem
galaxy problem
flatness problem
why so homogeneous?
how did galaxies form?
fine balance?
singularity problem (what banged?)
∞ density, ∞ curvature at t = 0
GR: strong observational evidence
Expanding U must begin in singularity?
Stephen 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
Slightest deviation from flatness
→
runaway expansion or crunch
Not observed
Why so finely balanced initially?
Ω = 1?
At t = 1 s, W = 1 to within 1:1015)
Astrophysics: Ω= 0.3 ?
Dark Matter
First suggested in 1930s
Stellar motion
normal gravitational effect but
weak electromagnetic coupling
Explains motion of stars
Explains motion of galaxies
Explains gravitational lensing
Matter = OM (30%) + DM (70%)
Also suggested by nucleosynthesis
Ω = 0.3
Explanation: Inflation (Guth, 1981)
Initial exponential expansion of U ?
Driven by phase transition
Repulsive force
Expansion of 1026 in 10-32 s
Energy scale ~ 1016 GeV
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 < ns < 0.98
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 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 1/105
Spectrum of T anisotropy
Acoustic peaks
Scale invariant
ns = 0.951 ± 0.016
• Also: U flat to 1%
• CDM problem: dark energy?
2-parameter fit
Confirmation of Dark Energy
WMAP: flatness
Fit parameters: Ωλ = 0.73, Ωm = 0.24
Ωλ = dark energy ?
Type Ia supernova measurements (1998)
Accelerating universe
Caused by dark energy
Confirmation of dark energy
Compatible with inflation
ΛCDM model
How can universe be flat?
1.
2.
Ordinary matter: 4% (astrophysics)
Dark matter:
22% (astrophysics)
3.
Dark energy Λ: 74% (supernova, CMB)
Ωm(0.04) + Ωdm(0.22) + Ωvac(0.74) = 1
Dark energy = zero-point fluctuations ?
Theory:
λ = 1069 m2
CMB:
λ = 10-52 m2
ΛCDM
The big bang: is it true? (2011 )
Three planks of evidence for BB
The expanding universe, nucelosynthesis, CMB
General relativity
Strong observational evidence
The theory of inflation
Horizon, galaxy and flatness problems
A flat, accelerating universe containing
matter, dark matter and dark energy
Remaining puzzles
Nature of dark energy?
Nature of dark matter?
What model of inflation?
Eternal inflation and the multiverse
Singularity at time zero?
Slides: ANTIMATTER blog
Something from nothing?
Quantum gravity?
Summary
Summary
Evidence for BB model (expanding U 1929)
Accepted by relativists (1933)
Resisted by physics community
New avenues of evidence for BB (1948,49)
Ignored by physics community
Rise of rival SS model (1950)
Defeat of SS model (radiogalaxies, 1960)
New evidence for BB (CMB 1965)
Latest: cyclic universe?
Model gradually accepted (1968..)
New inflation (Linde, Steinhardt)
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
4.
(Ω = ~ 1)
Scale invariant spectrum
Predicted by most inflationary models