Lam Hui- Dark Energy and the Homogeneous Universe

8/3/2019 Lam Hui- Dark Energy and the Homogeneous Universe

1/33

Dark Energy and the

Homogeneous UniverseLam Hui

Columbia University


2/33

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


3/33

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.


4/33

There is by now much evidence for

homogeneity and isotropy.There is also firm evidence for anexpandinguniverse.


5/33

Blandton & Hogg

scale 1023

cm


6/33

Hubble deep field

scale 1024

cm


7/33CfA survey

scale 1025

cm


8/33

Sloan Digital Sky Survey scale 1026 cm


9/33

Ned Wright


10/33




11/33



But how should we think about it?


12/33


13/33

Frequently Asked Questions:1. What is the universe expanding into?

2. Where is the center of expansion?

3. Is our galaxy itself expanding?


14/33

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.


15/33

A B

C

A B

C

Therefore:

dAC = 2 dAB dAC = 2 dAB

dAC

t= 2

dAB

t

Hubble law: Velocity Distance


16/33

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


17/33


18/33

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


19/33

Slope = Distance/Velocity = 10 billion years

Age of Universe


20/33

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:


21/33

Apply to the expanding universe:

R

1

2v2 =

GM

R, but remember :M =

4

3R3


22/33

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


23/33

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


24/33

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


25/33

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


26/33

What is dark energy?

1. Vacuum energy(Einsteins cosmological constant)

2. Scalar field (Bose Einstein condensate)

3. Modified gravity (Einstein was wrong!)


27/33

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.


28/33


29/33

LH & Greene 06


30/33

(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


31/33

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.


32/33


33/33

Let there be light.Genesis 1:3

Documents

Lam Hui- Dark Energy and the Homogeneous Universe