InflationA solution to the problems of the Big Bang

Ian HustonAstronomy Unit, Queen Mary, University of London

Big Bang Problems

• Flatness Problem

• Horizon Problem

• Relics Problem

Flatness ProblemUniverse is poised on knife-edge between collapse andover-expansion

Horizon ProblemWhy were opposite sides of the universe the sametemperature?

Relics ProblemWhere are the monopoles and other relics?

What is the solution?

• Problems solved if the universe expandedrapidly at early times.

• Universe then driven towards flatness.

• Much smaller universe initially would havetime for temperatures to become equal.

• Expansion pushes relics outside observableregion.

Spectacular RealizationAlan Guth’s notebook with his first description of inflation

InflationAccelerated expansion at very early times

R > 0

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

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

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

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

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

Physics of Inflation FieldWhen bottom of potential is reached inflation ends andnormal Big Bang expansion begins.

Potential needs to be flatIn order for inflation to last sufficiently long the potential isin reality much flatter.

“Slow Roll” conditions impose this flatness on potential.

End Result of Inflation

Universe increases insize by a factor of

1030 = 10000000000

0000000000

0000000000

in approximately

10−33 s = 0.0000000000

0000000000

0000000000

001 seconds.

Solution to problemsHow 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 beforeinflation⇒ all regions could be in contact.

• Relics Problem:Inflation massively dilutes any relics⇒ we should notobserve them today.

Origin of StructureBig Bang model has no method of beginning creation ofstars, galaxies and clusters.

Origin of StructureInflation provides a physical reason for the creation of thestructure we see around us.

FluctuationsQuantum Fluctuations make scalar field values bigger orsmaller in different regions.Different areas experience different amounts of inflation.

Simple Harmonic MotionThe quantum oscillations obey the Klein-Gordon equationof motion.

This is simply a form of damped harmonic oscillator.

A = −DA︸ ︷︷ ︸damping

−ω2A

Simple Harmonic MotionThe quantum oscillations obey the Klein-Gordon equationof motion.

This is simply a form of damped harmonic oscillator.

A = −DA︸ ︷︷ ︸damping

−ω2A

Cosmic Microwave BackgroundCan now identify hot and cold regions in CMB withfluctuations in energy during inflation.

Overall Picture of Universe

Future & ObservationsMany questions remain about the inflationary scenario:

• Which model of inflation is correct?Many models including hilltop, hybrid, natural, largefield, small field, DBI, racetrack, …

• Why did inflation happen?Is there an explanation in terms of higher energytheories, e.g. string theory?

• What about other parts of the inflating universe? Weonly see a very small part of the initial universepre-inflation. What is the rest like?

Is the CMB Random?Is the distribution of temperatures on the CMB randomlyselected?

Simulations: Michele Liguori

Is the CMB Random?Is the distribution of temperatures on the CMB randomlyselected?

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 inearly 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 Planckand other missions

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 Planckand other missions

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 Planckand other missions

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 Planckand other missions

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 Planckand other missions