What is the Universe Made of?

1
What is the Universe Made of?

• The Case for Dark Energy
• and Dark Matter
• Cliff Burgess

2
1905 A Big Year for Ann. Phys.

• Photo-electric Effect
• On a Heuristic Point of View concerning the
  Production and Transformation of Light. rcd Mar
  18, pub Jun 9
• Brownian Motion
• On the Movement of Small Particles Suspended in
  Stationary Liquids Required by the
  Molecular-Kinetic Theory of Heat. rcd May 11,
  pub Jul 18
• Special Relativity
• On the Electrodynamics of Moving Bodies. rcd
  Jun 30, pub 26 Sep
• Size of Molecules
• A New Determination of Molecular Dimensions.
  rcd Aug 19, pub Feb 8
• Mass-Energy Equivalence
• Does the Inertia of a Body Depend upon Its
  Energy Content? rcd Sep 27, pub Nov 21

Albert Einstein
PhD Thesis and most cited
3
1905 A Big Year for Ann. Phys.

• Photo-electric Effect
• On a Heuristic Point of View concerning the
  Production and Transformation of Light. rcd Mar
  18, pub Jun 9
• Brownian Motion
• On the Movement of Small Particles Suspended in
  Stationary Liquids Required by the
  Molecular-Kinetic Theory of Heat. rcd May 11,
  pub Jul 18
• Special Relativity
• On the Electrodynamics of Moving Bodies. rcd
  Jun 30, pub 26 Sep
• Size of Molecules
• A New Determination of Molecular Dimensions.
  rcd Aug 19, pub Feb 8
• Mass-Energy Equivalence
• Does the Inertia of a Body Depend upon Its
  Energy Content? rcd Sep 27, pub Nov 21

Albert Einstein
PhD Thesis and most cited
4
Outline

• The Hot Big Bang
• Evidence for a Hot Expanding Universe
• Dark Matter and Dark Energy
• Contact With Fundamental Physics
• Dark Matter
• Why Dark Energy is Harder
• Outlook

5
Visible Matter in the Universe

• Only two things are infinite, the universe and
  human stupidity, and Im not sure about the
  former.

Albert Einstein
6
Visible Matter in the Universe
2MASS Galaxy Survey

• Visible matter is distributed as stars and gas
  within galaxies and clusters of galaxies.
• These appear to be distributed roughly
  isotropically and homogeneously about us.

Courtesy Jason Ware
7
A 3D View
Courtesy Sloan Digital Sky Survey WMAP
8
Evidence for an Expanding Universe
In all directions galaxies are seen to be
receding from us with a speed which is
proportional to their distance from us
As expected if all started at the
same point at the same instant.

• The sky is dark
• The Hubble Law
• The homogeneity and isotropy of the universe
• The slower decay of more distant supernovae

9
Evidence for an Expanding Universe

• The sky is dark
• The Hubble Law
• The homogeneity and isotropy of the universe
• The slower decay of more distant supernovae

Courtesy Ned Wrights Cosmology Page
10
Evidence for an Expanding Universe

• The sky is dark
• The Hubble Law
• The homogeneity and isotropy of the universe
• The slower decay of more distant supernovae

Courtesy Ned Wrights Cosmology Page
11
Evidence for an Expanding Universe

• The sky is dark
• The Hubble Law
• The homogeneity and isotropy of the universe
• The slower decay of more distant supernovae

Courtesy Ned Wrights Cosmology Page
12
The Hot Big Bang

• Matter in an expanding container cools.
• Extrapolating back in time suggests the Universe
  was once very small and very hot.
• The Hot Big Bang theory assumes the Universe was
  initially a small, hot soup of elementary
  particles.
• This theory is just now being redundantly tested.
• Surprise! Most of the matter in the Universe is
  in two completely unknown forms!

13
Evidence for a Hot Big Bang
When the universe cools to the point
where nuclei can form (around 1010 K) then
the relative abundances of the light
elements can be calculated. The
predictions for the isotopes of H, He, Li and
Be agree with the measured abundances.
Agreement is very sensitive to the total
number of atoms present.

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

14
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

Burles, Nolette Turner, 1999
Courtesy Ned Wrights Cosmology Page
15
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

Total Mass Density of Atoms
Burles, Nolette Turner, 1999
Courtesy Ned Wrights Cosmology Page
16
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

Total Mass Density of Atoms
Burles, Nolette Turner, 1999
Courtesy Ned Wrights Cosmology Page
17
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

Total Mass Density of Atoms
Burles, Nolette Turner, 1999
Courtesy Ned Wrights Cosmology Page
18
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

Total Mass Density of Atoms
Burles, Nolette Turner, 1999
Courtesy Ned Wrights Cosmology Page
19
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

Total Mass Density of Atoms
Burles, Nolette Turner, 1999
Courtesy Ned Wrights Cosmology Page
20
Evidence for a Hot Big Bang
When the universe cools enough for atoms
to form (around 103 K) it becomes transparent
to light. The light present at this time is
still running around the universe. This
light is now seen as microwaves due to the
intervening expansion of the universe.

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

21
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

22
Evidence for a Hot Big Bang

• Primordial element abundances
• The cosmic microwave background
• TCMB vs distance

COBE collaboration
23
Outline

• The Hot Big Bang
• Evidence for a Hot Expanding Universe
• Dark Matter and Dark Energy
• Contact With Fundamental Physics
• Dark Matter
• Why Dark Energy is Harder
• Outlook

24
Evidence for Dark Matter

• Mass in galaxies
• Mass in clusters of galaxies
• Temperature fluctuations in the CMB
• Start of galaxy formation.

25
Evidence for Dark Matter

• Mass in galaxies
• Mass in clusters of galaxies
• Temperature fluctuations in the CMB
• Start of galaxy formation.

26
Evidence for Dark Matter

• Mass in galaxies
• Mass in clusters of galaxies
• Temperature fluctuations in the CMB
• Start of galaxy formation.

Courtesy Ned Wrights Cosmology Page
27
Evidence for Dark Energy
Very distant objects should not precisely
follow Hubbles Law because gravitational
attraction should decelerate the universal
expansion. This can be tested by looking
for deviations from Hubbles Law for very
distant supernovae.

• Brightness of very distant supernovae
• Flatness of the universe as a whole

28
Evidence for Dark Energy

• Brightness of very distant supernovae
• Flatness of the universe as a whole

29
Evidence for Dark Energy
Expect this

• Brightness of very distant supernovae
• Flatness of the universe as a whole

The universal expansion should be decelerating
due to gravitational attraction
Courtesy Ned Wrights Cosmology Page
30
Evidence for Dark Energy
Tonrey et.al., 2003

• Brightness of very distant supernovae
• Flatness of the universe as a whole

Courtesy Ned Wrights Cosmology Page
31
Evidence for Dark Energy
Tonrey et.al., 2003

• Brightness of very distant supernovae
• Flatness of the universe as a whole

Amount of Dark Energy
Amount of Dark Matter
Courtesy Ned Wrights Cosmology Page
32
Evidence for Dark Energy

• Brightness of very distant supernovae
• Flatness of the universe as a whole

WMAP collaboration
Small temperature variations, at the level
of one part in 100,000, are visible in the CMB
33
Evidence for Dark Energy

• Brightness of very distant supernovae
• Flatness of the universe as a whole

WMAP collaboration
These are due to sound waves in the
primordial gas which emitted this light.
34
Evidence for Dark Energy

• Brightness of very distant supernovae
• Flatness of the universe as a whole

Size of the CMB fluctuations depends on the
geometry of space the light traverses.
Courtesy Ned Wrights Cosmology Page
35
Evidence for Dark Energy

• Brightness of very distant supernovae
• Flatness of the universe as a whole

but the geometry of space depends on the amount
and kind of matter it contains
Courtesy Ned Wrights Cosmology Page
36
Evidence for Dark Energy
WMAP collaboration

• Brightness of very distant supernovae
• Flatness of the universe as a whole

Amount of Dark Energy
Courtesy Ned Wrights Cosmology Page
Amount of Dark Matter
Measured H0 with CMB fluctuations prefers a flat
universe.
37
Evidence for Dark Energy
WMAP collaboration

• Brightness of very distant supernovae
• Flatness of the universe as a whole

Amount of Dark Energy
Courtesy Ned Wrights Cosmology Page
Amount of Dark Matter
Dark Energy required to explain CMB is
consistent with what universal acceleration
requires.
38
Concordance Cosmology

• From best fits to the Concordance Cosmology

Courtesy Ned Wrights Cosmology Page
39
Outline

• The Hot Big Bang
• Evidence for a Hot Expanding Universe
• Dark Matter and Dark Energy
• Contact With Fundamental Physics
• Dark Matter
• Why Dark Energy is Harder
• Outlook

40
Contact With Fundamental Physics

• If you are out to describe the truth, leave
  elegance to the tailor.

Albert Einstein
41
What is the Dark Matter?

• Ordinary atoms?
• Modifications to the Law of Gravity?
• New kind of particles?

42
What is the Dark Matter?

• Ordinary atoms?
• Modifications to the Law of Gravity?
• New kind of particles?

Courtesy Ned Wrights Cosmology Page
43
What is the Dark Matter?
The devil is in the details No
proposals yet succeed for galaxies and
clusters and the CMB. Very
difficult to modify gravity at long
distances without having problems
with fundamental principles.

• Ordinary atoms?
• Modifications to the Law of Gravity?
• New kind of particles?

44
What is the Dark Matter?
Weakly Interacting Massive Particles arise
in most theories of microscopic physics.
Their residual cosmic abundance is
naturally the right size to agree with
the observed amount of Dark
Matter.

• Ordinary atoms?
• Modifications to the Law of Gravity?
• New kind of particles?

45
Outline

• The Hot Big Bang
• Evidence for a Hot Expanding Universe
• Dark Matter and Dark Energy
• Contact With Fundamental Physics
• Dark Matter
• Why Dark Energy is Harder
• Outlook

46
What Cosmology Requires

• Small, positive energy density

47
What Cosmology Requires

• Small, positive energy density
• Negative pressure p lt - r /3

This expresses how the universal acceleration
depends on the Dark Energys energy and pressure
according to Einstein.
48
Vacuum Energy as Dark Energy
log r

• The energy, l, of the vacuum has the negative
  pressure required to be the Dark Energy.
• The vacuum energy is only observable through
  gravity because non gravitational measurements
  only see energy differences.

log a
49
Vacuum Energy as Dark Energy
log r

• If the vacuum can change slowly with time, so can
  the Dark Energy density.
• The condition p lt - r /3 requires
  the kinetic energy of the vacuums motion to be
  small at present.

log a
Albrecht et.al., 2001
50
The Cosmological Constant Problem

• The vacuum energy is calculable within any theory
  of elementary particles, such as the Standard
  Model of particle physics.
• All elementary particles contribute quantum
  zero-point energy to the vacuum energy, l.
• Each particle of mass m contributes l m4
• Since, for example, even the electron has m 5
  105 eV 10-3 eV, how can the vacuum have such
  a small energy density l m4 ?

51
Outlook

• If I had only known, Id have become a
  locksmith.

Albert Einstein
52
Outlook

• Cosmological observations are now redundantly
  testing the Hot Big Bang model.
• Observations support the Concordance Cosmology.
• The concordance involves several lines of
  independent evidence for both Dark Matter and
  Dark Energy.
• Neither can be dark forms of ordinary atoms.
• Dark Energy is difficult to embed into a
  fundamental theory, but a candidate now may exist
  which does so.
• If so, well know from a variety of observational
  tests.

53
1905 2005 A Centennial of Ideas

• The most incomprehensible thing about the world
  is that it is at all comprehensible.

Albert Einstein