1) The talk discusses the origin of structure in the universe, from the small density fluctuations after the Big Bang to the galaxies, stars and planets we see today. 2) It explains how quantum fluctuations during an early period of exponential expansion called inflation were stretched to cosmological scales by inflation, seeding these initial density fluctuations. 3) The talk outlines how measurements of the cosmic microwave background have revealed correlations in the fluctuations that can only be explained by a period of inflation in the early universe that was faster than the speed of light.

1. Daniel Baumann
University of Amsterdam
On the Origin of Structure
in the Universe
Inaugural Lecture

4. Hubble Ultra-Deep Field

5. Sloan Digital Sky Survey

6. Where did it all
come from?

7. The answer involves a fascinating connection between the physics
of the very small and the very large:

8. Plan of the Talk
Quantum Origin
Structure Formation
Future Prospects Thank You’s

9. Disclaimer: This talk was written for my parents …

10. Structure Formation

11. The First Light
380,000 years after the Big Bang, the first atoms formed and light was
released from the cosmic fireball:
The variations in the intensity of the light correspond to variations in the
density of the primordial matter.

12. 380,000 years 13.8 billion years
The Rich Are Getting Richer
These small density fluctuations grew over time and became the structures
we see around us: galaxies, stars, planets, …

13. Where Did It All Come From?
We have reasons to believe that the initial fluctuations were created just
fractions of a second after the Big Bang.
?
380,000 years 13.8 billion years
10-32 sec

14. ?
A Detective Story
To learn about this time in the history of the universe, we must decode the
pattern of fluctuations in the afterglow of the Big Bang.

15. Correlated, Not Random
We have discovered that these fluctuations aren’t just random noise, but
are correlated over large distances.
two-point
correlation
angular separation
90 1 0.1

16. A Clue
In fact, the fluctuations are found to be correlated over distances that are
larger than the distance light travelled since the Big Bang:
distance light travelled
since the Big Bang
This seems to be in conflict with causality.
observable
universe

17. Inflation
10-32 sec = 0.00000000000000000000000000000001 seconds
This can be explained if the early universe expanded faster than light,
doubling in size at least 80 times within a fraction of a second:

18. Inflation
10-32 sec = 0.00000000000000000000000000000001 seconds
This can be explained if the early universe expanded faster than light,
doubling in size at least 80 times within a fraction of a second:

19. The entire observable universe originates from a microscopic, causally
connected region of space:
Subatomic scales get stretched to cosmological scales.
From Micro To Macro

20. Quantum Origin

21. Empty Space Isn’t Empty

22. Empty Space Isn’t Empty

23. These vacuum fluctuations are real, but usually have very small effects:
Empty Space Isn’t Empty
Lamb shift

24. The correlations observed in the afterglow of the Big Bang are inherited
from the correlations of the quantum fluctuations.
From Micro To Macro
During inflation, these quantum fluctuations get amplified and stretched:

25. It Works!
The predicted correlations are in remarkable agreement with the data:
There is growing evidence that something like inflation must have occurred,
but the physics of inflation remains a mystery.

26. The inflationary expansion requires a substance with nearly constant
energy density:
Vacuum Energy

27. Like for a radioactive substance, the inflationary energy in each region
of space has a small probability to decay:
Vacuum Decay

28. One of these bubbles
is our universe
Vacuum Decay

29. Due to quantum uncertainty, the decay inside each bubble will not be
exactly simultaneous, creating the density fluctuations after inflation:
Quantum Fluctuations

30. Models of Inflation
Inflationary models are distinguished by
• the source of vacuum energy
• the rate of vacuum decay
• the types of correlations

31. A Landscape of Models
A lot of work has gone into mapping out the space of inflationary models:
landscape
slow-roll
inflation
large-field
inflation
DBI inflation
brane
inflation
multi-field
inflation
axion
inflation

32. Landscape vs Swampland
Some models seem incompatible with basic principles of quantum gravity.
These models are said to live in the swampland.
landscape
swampland
global
symmetries
superluminal
propagation
gravity is not the
weakest force

33. Landscape vs Swampland
Some models seem incompatible with basic principles of quantum gravity.
These models are said to live in the swampland.
landscape
swampland
Which theories are consistent with observations?
global
symmetries
superluminal
propagation
gravity is not the
weakest force

34. Future Prospects

35. How can inflation become part of the
standard history of the universe with the
same level of confidence as BBN ?

36. Primordial Gravitational Waves
The strength of the signal depends on the energy scale of inflation, which
may be as high as 1016 GeV.
Inflation predicts ripples in spacetime = gravitational waves (GWs):

37. Primordial Gravitational Waves
Inflationary models with observable GWs live at the boundary of the
swampland. On which side is a subject of very active debate.
swampland
landscape GWs
A detection would be a spectacular discovery.

38. LIGO detected GWs with wavelengths
of order thousands of kilometers
The GWs produced by inflation have
wavelengths of order billions of light-years.
How do we detect them?

39. B-modes
The presence of gravitational waves during the formation of the first
atoms leads to a swirl pattern in the polarization of the first light:

40. The Hunt for B-modes
Detecting gravitational waves from inflation is the holy grail of modern
observational cosmology:
Atacama Desert
South Pole

41. Primordial Interactions
The strength of these higher-point correlations depends on the type of
substance that created inflation and its interactions.
Inflation also predicts correlations between more than just two points:

42. Quantum fluctuations during inflation can produce very massive particles
whose decays lead to higher-order correlations:
Primordial Interactions

43. Some interactions cannot arise from a consistent quantum theory of
gravity and therefore live in the swampland:
Primordial Interactions
swampland
landscape
< 0
A detection would teach us a lot about the origin
of the inflationary expansion.

44. LSS
21cm
CMB
Future observations will map out density fluctuations over the entire
observable universe:
This allow us to search for the subtle imprints of primordial interactions.
The Hunt for Non-Gaussianity

45. Where Did It All Come From?
380,000 years 13.8 billion years
10-32 sec

46. Cosmology in Amsterdam
String theory
GRAPPA
Cosmology
http://cosmology.amsterdam

47. A Few Thank You’s

48. Mentors
Paul Steinhardt Liam McAllister Matias Zaldarriaga

49. Collaborators
Daniel Green
Amin, Arkani-Hamed, Assassi, Beutler, Bird, Chia,
Cooray, Dymarsky, Ferraro, Flauger, Friedman, Goon,
Hartman, Huterer, Ichiki, Kachru, Kamionkowski,
Klebanov, Lee, Maldacena, McAllister, Meyers,
Murugan, Nicolis, Pajer, Peiris, Pimentel, Porto,
Sarkar, Schmidt, Senatore, Serra, Sigurdson, Slosar,
Smith, Steinhardt, Stout, Takahashi, Turok, Vargas-
Magana, Wallisch, Welling, van der Woude, Yeche,
Zaldarriaga

50. Students
Valentin Assassi Hayden Lee Benjamin Wallisch
Carlos Duaso Pueyo
Horng Sheng Chia
Lotte ter Haar

51. Research Group

52. Colleagues

53. Colleagues

54. Family

55. Family
Fritz Anna

56. Family
Julian
Fritz Anna

57. Family

58. Bedankt voor uw aandacht