CosmologyCosmology
Physics CSG Day at Southampton University 5/6/7 13.7Gyr ABB
Steve King
Revolutionaries
Copernicus Kepler Galileo Newton
These men taught us that the Earth is not the centre of the Universe
Newfangled CosmologyHubble Space Telescope
The Universe Age 700 million years
Cosmological PrincipleCosmological Principle
Our position in the Universe is not special
-all points in the Universe are equivalent just as all points on the surface of the Earth are equivalent
-the Universe looks the same wherever you are
- cosmological principle is an approximate property of the global Universe, which only applies on the largest distance scales
The Milky Way Spiral Galaxy You are here
The Milky Way Local Group: satellites
You are here
The Milky Way Local Group: including Andromeda galaxy
N.B. Large galaxies separated by about 1,000,000 pc = 1 Mpc
You are here
The Virgo Supercluster: containing Virgo Cluster and our Local Group
Each dot is a bright galaxy. Milky Way is dot in the exact centre.
You are here
Our Neighbouring Superclusters: Virgo Supercluster at the centre
Note the presence of filaments and voids in an irregular cellular pattern.
50Mpc
You are here
On the largest distance scales the Universe appears smooth, with no further structures
You are here
Homogeneity and IsotropyHomogeneity and Isotropy
The fact that the Universe is smooth on the largest distance scales (bigger than a billion light years) supports the cosmological principle.
In fact the Universe appears to have two separate features:
HomogeneousHomogeneous – the same at each point (c.f. homogenised milk)
IsotropicIsotropic – the same in all directions
Very small departures from homogeneity are clearly present due to the irregular cellular large scale structure of the Universe.
Hubble’s Law: all galaxies are moving away from us with a speed of recession v proportional to the distance of the galaxy d
0v H d
Hubble’s constant
The Expansion of the Universe
How is the galactic speed v measured?
– from redshift z of absorption and emission lines (Doppler effect)
How is galactic distance d measured?
– from the apparent luminosity of “standard candles” in the galaxy (e.g. Cepheid variables, type Ia supernovae,…)
What is the interpretation of Hubble’s law?
– the Universe is expanding at a constant rate
obs em
em
z
v
zc
If the Universe is expanding at a constant rate then every galaxy will be moving away from every other galaxy in accordance with Hubble’s law
Mod
ern
Cos
mol
ogy
This implies that in the distant past the Universe would have been much smaller than now. We infer that the Universe started from a small, dense, hot region from some initial explosion called the Big Bang.
History of the Universe\_PC START.exe
_PC START.exe
The Universe Age 380,000 years just after the atoms were formed and the Universe becomes transparent -- henceforth these Big Bang photons travel unhindered through the Universe
H
H
H
HH
H
H
H
H
H
H
HH
H
He
e
e
e
ee
e
e
e
??
?
?
As the Universe expands, the Big Bang photons in the visible spectrum get redshifted into microwave photons
The Big Bang photons from the time of atom formation (380,000 yrs) are observed as microwave background radiation, with a Black Body spectrum corresponding to a temperature of about 3 K = -270o C (redshifted from a temperature of about 3,000 K )
Cosmic microwave background
Penzias & WilsonIn 1965 Penzias and Wilson discovered the CMB as an irremovable background hiss in their antenna
Nobel Prize 1978
About 1% of TV White Noise is due to CMB
These days more sophisticated equipment is used to make temperature maps of the sky
George Smoot, Berkley PI of DMR
John Mather, NASA GSFCOverall PI of COBE and PI of FIRAS
COBE Nobel Prize 2006
The first people to make a temperature map of the sky
Temperature Maps
Earth
Universe
COBE 1992
WMAP 2006
We can learn a lot from these temperature maps
Requirements:• Flat Universe• Dark Energy • Dark Matter
WOW!!
The Standard Cosmological Model
1 …means the Universe is flat
Why did nature choose this one?
This could be due to an exponential inflation
Atoms only make up 4% of the mass of the Universe
The rest is unknown Dark Energy (fluid like) and Dark Matter (particle like)
A Final Word on Dark EnergyCould the Dark Energy be Einstein’s Cosmological Constant?
``My biggest blunder…”
Dark Matter has been ``seen’’Do you believe in Dark Matter? Seeing is believing!
The Bullet Cluster of Galaxies
How Dark Matter Evolves
This computer simulation takes the CMB temperature fluctuations as seeds of density fluctuations which evolve in time to give long filaments of dark matter
By the time the Universe is 100 million years old it is dominated by filaments of dark matter around which the galaxy clusters and superclusters will form
Who is the dark matter particle?Who is the dark matter particle?
An excellent candidate for dark matter is the spin ½ partner to the photon called the photino
The photino could be discovered at the CERN Large Hadron Collider which starts later this year
Atlas
particle_event_full_ns.mov
. .
E t h
How Did it All Begin? Some
believe it was a vacuum quantum fluctuation quickly
followed by inflation
Conclusion
• Cosmology has now entered a precision era• Landau’s adage that cosmologists are “often in error
never in doubt” is undoubtedly no longer true!• There is now a Standard Model of the Universe
consisting of 74% Dark Energy which looks like Einstein’s Cosmological Constant
• But only 4% is atoms • The remaining 22% is Dark Matter consisting of
particles which could be discovered soon at CERN (with the help of Southampton students!)
Appendices
• Parsecs
• Spherical Harmonics
• Angular Power Spectrum
• Fluids in the Early Universe
• Sound Waves
• First Peak = Geometry
• Second Peak = Baryons
• Third Peak = Dark Matter
Stars: main source of visible light from nuclear fusion in stars
Sun is typical: 302 10M kg
Sun Earth
1 Parsec ~ 3.26 light years ~ 3 × 1016 meters
11. . 1.5 10AU metres
1
, ,,
( , ) ( , )l m l ml m
Ta Y
T
We want to understand this
Position of First Peak Measures the Geometry
of the Universe
The Relative Height of Second Peak Measures the Density of Baryons
The Relative Height of Third Peak Measures the Density of Dark Matter
Dark Matter Domination (later times – lower peaks)
Photon Domination (earlier times – higher peaks)