The Life of the Universe

From Beginning to End

• Early Universe is extremely hot and dense

• All 4 forces were merged• As Universe cooled,

forces became unique• Energy of photons high

enough to create matter and vice versa

• GUT – strong and electroweak forces united

• SuSy – GUT and Gravity united

The Big Bang Theory

• The early Universe was exceedingly hot and dense

• Big Bang theory explains how the early Universe cooled and evolved into the Universe we observe today

• Relies on Theoretical and Observational data

Planck Era

• t < 10-43 s

• T > 1032 K

• Current physics is unable to understand times before the Planck era– Need to unite physics of large

scales (general relativity) with physics of small scales (quantum mechanics)

GUT Era

• 10-43 s < t < 10-38 s

• 1029 K < T < 1032 K

• Supersymmetry force splits into GUT force and gravity

Electroweak Era• 10-38 s < t < 10-10 s

• 1015 K < T < 1029 K

• GUT force splits into strong and electroweak forces– Huge release of energy

Inflation

• Inflation expands Universe at exponential rate

Particle Era• 10-10 s < t < 10-3 s• 1012 K < T < 1015 K• Electroweak splits into weak

force and electromagnetism– All four forces distinct

• T too low for spontaneous conversion of photons to particles

• Photons became quarks, which merge into protons and neutrons

Era of Nucleosynthesis• 0.001 s < t < 5 min

• 109 K < T < 1012 K

• Fusion begins– T still so high that most He

nuclei will break apart again

• Expansion reduces density so fusion ceases despite T being so high

• 75% H, 25% He, trace others

Era of Nuclei• 5 min < t < 380,000 years

• 3000 K < T < 109 K

• Photons still hot enough to ionize, so electrons and nuclei stay separated

• Photons cannot travel far because they are scattered by electrons

Era of Atoms• 380,000 yrs < t < ~109 yrs

• T < 3,000 K

• T drops low enough for atoms to form

• With electrons bound to nuclei, photons can travel long distances– Cosmic Microwave

Background

Era of Galaxies• t > 109 years

• Universe filled with nearly homogeneous distribution of matter and dark matter after era of atoms

• Slightly overdense regions collapse to form first stars and galaxies

• Gravity dominates on large scales

A Few Questions

• Where did the large scale structure come from?

• Why is the Universe so uniform?

• Why is the density of the Universe so close to the critical density?

Inflation

• Separation of strong force from GUT force would release enormous amount of energy

• Energy would cause the Universe to expand by factor of 1030 in 10-36 sec

Inflation and Structure

• Huge expansion would make tiny quantum fluctuations in density large ripples

• A ripple the size of a nucleus would become the size of our solar system

• Creates density enhancements that give rise to the structure we observe today

Inflation and Uniformity

• No reason why things so far away should be similar

• Things close by should be

• Inflation takes things that were very close together and spreads them out a lot– Universe was all close together, so everything

was uniform, then inflation spread it out

Inflation and Density

• Density implies curvature of spacetime– Think general relativity– Critical density has flat

geometry

• If Universe started somewhat curved, inflation would make it seem much flatter

Evidence for the Big Bang

The Cosmic Microwave Background

The CMB

• Line – a theoretically calculated thermal radiation spectrum based on the Big Bang Theory

• Dots – Observed data

• They match!

The Fate of the Universe

Two Things to Consider

• Expansion of the Universe

• Gravity – makes things collapse

• Critical density – the density required to balance gravitational attraction and expansion

• Dark energy – a repulsive force opposite of gravity

An Accelerating Universe

• SN Ia data show that we most likely live in an accelerating universe

• Acceleration is driven by some force that is not well-understood– Dark energy

The Big Rip

The End