Outreach lecture delivered to secondary school teachers participating in Goldsmith\'s Company Astrophysics training course.

1. Inflation
A solution to the problems of the Big Bang
Ian Huston
Astronomy Unit, Queen Mary, University of London

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

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

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

5. Relics Problem
Where are the monopoles and other relics?

6. 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.

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

8. Inflation
Accelerated expansion at very early times
¨
R>0

9. 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.

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

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

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

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

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

15. 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.

16. 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.

17. 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.

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

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

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

21. 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

22. 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

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

24. Overall Picture of Universe

25. 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?

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

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

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

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

30. 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

31. 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

32. 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

33. 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

34. 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