Cosmology Physics CSG Day at Southampton University 5/6/7 13.7Gyr ABB Steve King

Revolutionaries CopernicusKeplerGalileoNewton These men taught us that the Earth is not the centre of the Universe

Newfangled Cosmology Hubble Space Telescope

The Universe Age 700 million years

Cosmological 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. You are here

On the largest distance scales the Universe appears smooth, with no further structures You are here

Homogeneity 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: Homogeneous Homogeneous – the same at each point (c.f. homogenised milk) Isotropic Isotropic – 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 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

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

Modern Cosmology 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

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 H H H H H H H H H H H He e e e e e 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 = -270 o C (redshifted from a temperature of about 3,000 K ) Cosmic microwave background

Penzias & Wilson In 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 GSFC Overall 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

…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 Energy Could 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? 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

. 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: SunEarth 1 Parsec ~ 3.26 light years ~ 3 × meters

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)