Inflation as a solution to the problems of the Big Bang

InﬂationA solution to the problems of the Big Bang Ian Huston Astronomy Unit, Queen Mary, University of London

Big Bang Problems • Flatness Problem • Horizon Problem • Relics Problem

Flatness Problem Universe is poised on knife-edge between collapse and over-expansion

Horizon Problem Why were opposite sides of the universe the same temperature?

Relics Problem Where are the monopoles and other relics?

What is the solution? • Problems solved if the universe expanded rapidly at early times. • Universe then driven towards ﬂatness. • Much smaller universe initially would have time for temperatures to become equal. • Expansion pushes relics outside observable region.

Spectacular Realization Alan Guth’s notebook with his ﬁrst description of inﬂation

Inﬂation Accelerated expansion at very early times ¨ R>0

How to get this acceleration? For inﬂation to happen need universe ﬁlled with substance that has “anti-gravitational” properties. Pressure and density push outwards causing expansion.

Exotic Matter Scalar ﬁelds have the right properties for this expansion. Still haven’t seen one in nature (yet)!

Scalar Fields Scalar ﬁelds have one value at each place in the universe. Similar to a temperature ﬁeld over the surface of Earth.

Physics of Inﬂation Field Need Potential Energy > Kinetic Energy. One way is to have a valley shaped potential well.

Physics of Inﬂation Field When bottom of potential is reached inﬂation ends and normal Big Bang expansion begins.

Potential needs to be flat In order for inflation to last sufficiently long the potential is in reality much flatter. “Slow Roll” conditions impose this flatness on potential.

End Result of Inﬂation Universe increases in 1030 = 10000000000 size by a factor of 0000000000 0000000000 10−33 s = 0.0000000000 in approximately 0000000000 0000000000 001 seconds.

Solution to problems How does inflation solve the Big Bang problems? • Flatness Problem: Inflation pushes universe towards flatness. Longer Inflation ⇒ Flatter Universe • Horizon Problem: Observable universe was extremely small before inflation ⇒ all regions could be in contact. • Relics Problem: Inflation massively dilutes any relics ⇒ we should not observe them today.

Origin of Structure Big Bang model has no method of beginning creation of stars, galaxies and clusters.

Origin of Structure Inﬂation provides a physical reason for the creation of the structure we see around us.

Fluctuations Quantum Fluctuations make scalar ﬁeld values bigger or smaller in different regions. Different areas experience different amounts of inﬂation.

Simple Harmonic Motion The quantum oscillations obey the Klein-Gordon equation of motion. This is simply a form of damped harmonic oscillator.¨ ˙A = −DA −ω 2A damping

Cosmic Microwave Background Can now identify hot and cold regions in CMB with ﬂuctuations in energy during inﬂation.

Overall Picture of Universe

Future & Observations Many questions remain about the inflationary scenario: • Which model of inflation is correct? Many models including hilltop, hybrid, natural, large field, small field, DBI, racetrack, … • Why did inflation happen? Is there an explanation in terms of higher energy theories, e.g. string theory? • What about other parts of the inflating universe? We only see a very small part of the initial universe pre-inflation. What is the rest like?

Is the CMB Random? Is the distribution of temperatures on the CMB randomly selected? Simulations: Michele Liguori

Planck Satellite • Launched 2009 • European Space Agency Mission • UK teams from Cardiff, Imperial, and others • Lots of outreach material on their website Image: ESA

Planck Media Coverage Expect more when CMB data is released in early 2013!

Quick Recap • Inflation is accelerated expansion of universe • Need exotic matter to drive it ⇒ Scalar field • Quantum fluctuations are origin of structure • Still many unanswered questions • Some of these should be resolved by Planck and other missions

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Inflation as a solution to the problems of the Big Bang

by Ian Huston

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