Lam Hui- Dark Energy and the Homogeneous Universe
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Transcript of Lam Hui- Dark Energy and the Homogeneous Universe
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Dark Energy and the
Homogeneous UniverseLam Hui
Columbia University
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This is a series of 3 talks.
Today: Dark energy and the homogeneous
universe July 11: Dark matter and the large scale
structure of the universeJuly 18: Inflation and the early universe
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OutlineBasic concepts: a homogeneous,
isotropic and expanding universe.
Measurements: how do we measurethe universes expansion history?Dynamics: what determines the
expansion rate?Dark energy: a surprising recent finding.
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There is by now much evidence for
homogeneity and isotropy.There is also firm evidence for anexpandinguniverse.
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Blandton & Hogg
scale 1023
cm
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Hubble deep field
scale 1024
cm
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scale 1025
cm
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Sloan Digital Sky Survey scale 1026 cm
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Ned Wright
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There is by now much evidence for
homogeneity and isotropy.There is also firm evidence for anexpandinguniverse.
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There is by now much evidence for
homogeneity and isotropy.There is also firm evidence for anexpandinguniverse.
But how should we think about it?
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Frequently Asked Questions:1. What is the universe expanding into?
2. Where is the center of expansion?
3. Is our galaxy itself expanding?
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Frequently Asked Questions:1. What is the universe expanding into? Nothing.2. Where is the center of expansion? Everywhere and nowhere.
3. Is our galaxy itself expanding? No.
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A B
C
A B
C
Therefore:
dAC = 2 dAB dAC = 2 dAB
dAC
t= 2
dAB
t
Hubble law: Velocity Distance
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SupernovaDiscovery
(as seen from
Hubble SpaceTelescope)
Difference
(as seen from
telescopeson Earth)
3 WeeksBefore
Supernova 1998baSupernova Cosmology Project
(Perlmutter,et al., 1998)
Supernovaas standard candle
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Calan/Tololo
(Hamuy et al,A.J. 1996)
SupernovaCosmologyProject
effective
mB
(0.5,0.5) (0, 0)
( 1, 0 ) (1, 0)(1.5,0.5) (2, 0)
(,) =
( 0, 1 )
Flat
=
0
redshift z
14
16
18
20
22
24
26
0.02 0.05 0.1 0.2 0.5 1.00.02 0.05 0.1 0.2 0.5 1.0
Perlmutter, et al. (1998)
MORE REDSHIFT(More total expansion of universesince the supernova explosion)
See also Riess et al. 98
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Slope = Distance/Velocity = 10 billion years
Age of Universe
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Dynamics: what determines the expansion
rate and how it changes with time?R
12mv2
GMm
R= E
For simplicity setE= 0 :1
2v2 =
GM
R
Secondary school physics:
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Apply to the expanding universe:
R
1
2v2 =
GM
R, but remember :M =
4
3R3
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1
2v2=GM
Rwhere M =
4
3R
3Important equation:
Example 1 - ordinary matter
3
4R3(M = constant) = v2
1
R
Therefore : v R
Example 2 - cosmological constant = constant = v2 R2
Therefore : v R Acceleration! drops slower than
1
R2Dark Energy:
i.e. R3(1+w) with w < 1/3
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Calan/Tololo
(Hamuy et al,A.J. 1996)
SupernovaCosmologyProject
effective
mB
(0.5,0.5) (0, 0)
( 1, 0 ) (1, 0)(1.5,0.5) (2, 0)
(,) =
( 0, 1 )
Flat
=
0
redshift z
14
16
18
20
22
24
26
0.02 0.05 0.1 0.2 0.5 1.00.02 0.05 0.1 0.2 0.5 1.0
Perlmutter, et al. (1998)
MORE REDSHIFT(More total expansion of universesince the supernova explosion)
See also Riess et al. 98
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0.0 0.5 1.0 1.5 2.0M
0.0
0.5
1.0
1.5
2.0
ESSENCE+SNLS+gold(M,) = (0.27,0.73)
Total=1
Wood-Vasey et al. 07
70% dark energy, 30% matter
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0.0 0.2 0.4 0.6 0.8 1.0M
2.0
1.5
1.0
0.5
0.0
w
ESSENCE+SNLS+goldBAOSNeIa+BAO
(M,w) = (0.27,1)
ESSENCE+SNLS+goldBAOSNeIa+BAO
(M,w) = (0.27,1)
Wood-Vasey et al. 07
Dark energy R0.6
to R1.2
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What is dark energy?
1. Vacuum energy(Einsteins cosmological constant)
2. Scalar field (Bose Einstein condensate)
3. Modified gravity (Einstein was wrong!)
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What is dark energy?
1. Vacuum energy(Einsteins cosmological constant)
2. Scalar field (Bose Einstein condensate)
3. Modified gravity (Einstein was wrong!)
Observed value too small.Required mass too small.
No compelling theory.
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LH & Greene 06
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(grow)
g
eom
0.66 0.70 0.74 0.78 0.820.66
0.70
0.74
0.78
0.82
w
(grow)
w
geom
2.5 2 1.5 1
2.5
2
1.5
1
Wang, LH, May & Haiman 07
See also Li & Chu, Li, Chan & Chu 06
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Summary
- Basic concepts of a homogeneous,isotropic and expanding universe.
- Surprisingly, our current expansionappears to be accelerating. Explainingit, and measuring it precisely, is a major
goal of cosmology today.
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Let there be light.Genesis 1:3