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.

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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

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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

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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

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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.

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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

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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

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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

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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)