Big Bang

CONTENTS

Introduction History Time line FLRW Metric Horizons Observational evidence Features & problems The Future

INTRODUCTION

“Big-bang is the cosmological model of universe whose primary assertion is that the universe has expanded into its current state

from primordial condition of enormous density and

temperature.”

PREREQUISITIES

Elementary particles – Lepton( not subjected to strong interaction)

- Hadrons( subjected to strong interaction)

Hadrons-

Quarks

Baryons {eg.: nucleons}

Mesons {eg.: Pi mesons}

Fundamental building blocks of matter

HISTORY

1912- Vesto Slipher- measured Doppler Shift of a spiral nebulae-found nebulae recedes from earth.

10yrs after –Alexander Fredman - Fredman equation- 1st suggested the expansion of universe.

1924 – Edwin Hubble measured distance to the nearest nebulae - Hubble’s Law.

1929- Lemaitre confirmed the expansion of the universe-father of Big Bang.

HISTORY After 2nd world war, two possibilities:

Later one is supported by George Gamow & Ralph Alpher.

George Gamow – nucleosynthesis.

Ralph Alpher – microwave background.

Fred Hoyle’s steady state model. Lemaitre’s Big Bang model.

TIME LINE

Extrapolating universe backwards using general relativity. Birth of universe-hot dense fire ball - Big Bang. Age of universe = 13.7±0.2 billion yrs. The expansion passes through three stages:

Very early universe.

Early universe.

Structure formation.

VERY EARLY UNIVERSE

Its about 1st split second. It was so hot – energy is higher than that can be

achieved using particle accelerators. A little is known about it. Many theories to explain. Hartle- Hawkin initial state, string landscape, brane

inflation etc.. Many epochs.

PLANK EPOCH {up to 10-43 after big bang}

Four fundamental forces - Electromagnetism, Weak nuclear force, Strong nuclear force, Gravitational force

-all have same strength.

Possibly they unified into one fundamental force.

Universe cooled from1028 to 1023 eV.

Gravity begins to separate from fundamental forces.

GRAND UNIFICATION EPOCH {b/w10-43 &10-35 sec}

THE INFLATIONARY EPOCH {b/w10-35 &10-32}

Universe is flattened and it enters a homogeneous, isotropic, rapidly expanding phase.

Exponential growth:

Reheating Exponential expansion ceases. Potential energy decays to hot relativistic plasma of particles. Universe dominated by radiations. (Pair formation, destruction)

Baryogenesis Unknown process which violated the baryon number. Predominance of matter over anti-matter.

EARLY UNIVERSE

After inflation universe is filled with quark gluon plasma

This stage can be predicted by high energy physics

First protons, neutrons, electrons formed, there after nuclei and atoms

Formation of neutral Hydrogen- CMB emitted

ELECTRO WEAK EPOCH{ b/w

Temp. is high enough to merge electromagnetic and weak interaction into single electroweak interaction

Particle interactions are energetic enough to create large no of exotic particle (w and z bosons, Higg’s boson)

Super symmetry breaks at energy as low as 1 TeV Masses of particles and their super partners are no

longer equal Super partners of known particles have ever been

observed

10-32 &10-12 }

Super symmetry braking

QUARK EPOCH{ b/w 10-12 & 10-06 }

By electroweak symmetry breaking all fundamental particle are believed to acquire mass mass by Higgs mechanism

Fundamental interaction – present form

Quark gluon plasma cools – hadrons form ( protons neutrons)

At 1s neutrinos decouple and began to travel freely through space - Cosmic Neutrino Background

( analogous to CMB)

HADRON EPOCH { b/w 10-06 & 1 sec }

LEPTON EPOCH { 1sec to 3 min } At end of hadron epoch hadrons and anti- hadrons

annihilate each other. Leptons and anti- leptons dominating mass of universe. At 3sec small residue of leptons.

Energy dominated by Photon. Photons interacted frequently with charged prtons,

electrons for the next 300000 yrs. Universe was opaque to light.

PHOTON EPOCH { 3min to 3800 yrs }

NUCLEOSYNTHESIS {3 min to 20 min }

Temp fall to a point where atomic nuclei can begin to form.

Pn & Nn combined to form nuclei by fusion lasting 17min.

After 17 min temp falls to a point at which fusion cannot continue.

Hydrogen 3 times more than Helium.

MATTER DOMINATION { 70000 yrs }

More matter created by high energy radiation. When universe cools matter looses less energy than

radiation. Energy density of matter > energy density of radiation.

H & He atoms forms. Density of universe falls. Photons evolve independently from matter during

recombination decoupling- CMB.

RECOMBIATION { 38000 yrs }

STRUCTURE FORMATION First structure to be formed are Quasars, early active

galaxies, population III stars. Non-linear structure begins to form.

REIONIZATION

Quasars form from gravitational collapse.

The intense radiation they emit re-ionize the surrounding universe.

1st stars are population III stars.

Light elements heavier elements.

FORMATION OF STARS

FORMATION OF GALAXIES

Large volume of matter collapse to form galaxy. Population II star are formed early than population I. July 11 2007 , California Institute of Tech found 6 stars

forming galaxy about 13.2 billion light yrs away (created when universe was 500 million yrs only!).

Gravitational attraction- galaxies to form groups, clusters and super cluster.

Formation of our solar system. (Sun – late generation star)

Today 13.7 billion yrs.

NATURE OF EXPANSION - FLRW Metric

General relativity describes space-time by a metric. Galaxies, stars or other objects are specified using a co-

ordinate chart or “grid” FLRW Metric- homogeneous and isotropic on large scales

(Fried Mann – Lemaitre – Robertson – Warker metric) COMOVING CO- ORDINATE: Grid expands along with universe. Objects moving due to expansion of Universe

remain at fixed point on grid. Co-ordinate distance remain same –physical distance expands proportionally with scale

factor.

Big Bang – Not an expansion of matter moving outward to fill the empty universe.

Space itself expands with time – increases physical distance between two co-moving points.

Local concentration of matter (galaxies) are gravitationally bound – no large scale expansion of space.

Past horizon- events in past whose light did not have time to reach us.

Future horizon – limits event in future that we will be able to influence (if universe is accelerating.)

HORIZON OF UNIVERSE

OBSERVATIONAL EVIDENSE

Hubble’s law- Expansion of space.

Cosmic microwave radiation.

Abundance of primordial elements.

HUBBLE’S LAW & EXPANSION

Observation shows galaxies and other cosmos red shifted. Found from spectroscopic pattern of emission & absorption lines. Red shift interpreted as Doppler shift – the Recessional

velocity can be calculated. Possible to find actual distance for some galaxies . Graph is linear. V = H0 * D

D Dist to the object.V Recessional velocity.H0 Hubble’s const.( 70 + 2.3 / -3.2 Km/Sec)

Hubble’s law

1922 - possibility of Big Bang predicted.

V,H,D – vary as universe expands.

Evidence from cosmological principle.

Corner stone of Big Bang.

Center of explosion.

Center of expansion.

COSMIC MICROWAVE BACKGROUND

First few days of universe- photons emitted & absorbed continuously giving black body spectrum.

During expansion universe cooled- Photons no longer emitted & absorbed .

Temp was high- electrons & nuclei unbound.

Photons reflected from electrons- Thomson scattering. Early universe – opaque to light. Formation of atoms – temp become low – recombination.

Photons scattered infrequently with atoms. This photon make Cosmic Microwave background. Energy of the photon red shifted by expansion causing

tempt fall. Then photons fall on microwave region of EM spectrum.

1964 – Arno Penzias & Robert Wilson found CMB- Nobel Prize.

1989 – NASA – Cosmic Background Explorer satellite (COBE) – John C Mather, George Smooth - Nobel Prize.

2005-06’ – many informations.

Image of the cosmic microwave background radiation

ABUNDANCE OF PREMODIAL ELEMENTS

Concentration of He4 , He3 , Deuterium & Li7 – as ratios of ordinary Hydrogen.

Based on Baryon to photon ratio

Calculated from fluctuations in CMB

Measured abundance agree with this ratio.

Correct for Deuterium – fine for He4 - Not good agreement for Li7 .

GALECTIC EVOLUTION Observations – found evidence for formation of galaxies, clusters,

super clusters etc…

Age of universe - good agreement with radio active dating.

OPPOSING ISSUES

Universe may have +ve , -ve or 0 spatial curvature depending on energy density.

Density < critical density

- Negative.

Density > critical density

- Positive.

Density = critical density

- Flat.

PROBLEM: departure from critical density grows with time but universe is flat!!!!

FLATNESS PROBLEM

BARYON ASSYMETRY

Why matter greater than anti-matter? Early – equal baryon & anti- baryon. Baryogenesis – driving force ? (Asymmetry)

1990 – Age of some cosmological objects revealed. 15 Billion yrs old – contradicts age of universe. 2005 - 06’- It may due to stellar wind.

GLOBULAR CLUSTER AGE

DARK MATTER 1970-80’ – No matter explaining gravitational pull.

Dark matter- 90% in universe – no emission no interaction.

PROBLEM:

No observational

evidence.

DARK ENERGY Expansion – accelerating at half age.

It need negative pressure & energy - dark energy – indicated by other evidence.

PROBLEM: Exact nature of Big Bang energy remains a mystery.

2006 – satellite (WAMP) found dark matter 22%, dark energy 74%, regular matter 4%.

Active area of current research.

MAGNETIC MONOPOLE.

Raised in 1970. Grand unification theory- tells existence of monopole. PROBLEM: no monopole seen.

Speculative driving force.

Quite unknown.

INFLATION PERIOD

EARLY STAGE

ULTIMATE FATE

HEAT DEATH [ Trillion yrs]

Existing stars burn out – Universe goes to dark – high entropy occurs – galaxies collapse to black holes.

BIG CRUNCH

If energy density of dark energy is –ve, universe is closed– expansion reverses– UNIVERSE CONTRACTS- time reversal of Big Bang.

BIG RIP

Energy density increases without limit- Dark energy is called Phantom Energy – Limitless EXPANSION – Cluster galaxies torn off – Solar System too.

“FATE OF UNIVERSE”

REFERENSES

Wikipedia – free encyclopedia

Official website of string theory

Modern physics- Arthur Beiser

Seven wonders of cosmos- Narliker