A theorist’s view of dark energy

Andreas Albrecht (UC Davis)UCSC Colloquium

Jan 19 2012

CONCLUSIONS

•Cosmic acceleration has made life really exciting for the theorist•Hardly a closed case

CONCLUSIONS

•Cosmic acceleration has made life really exciting for the theorist•Hardly a closed case

OUTLINE

•The Basics: Data, Directions and Issues

•Anthropics, Landscape & Critique

•Alternative Viewpoints

•Conclusions

OUTLINE

•The Basics: Data, Directions and Issues

•Anthropics, Landscape & Critique

•Alternative Viewpoints

•Conclusions

Supernova

Preferred by data c. 2003

“Ordinary” non accelerating matter

Cosmic acceleration

Accelerating matter is required to fit current data

(Includes Dark Matter)

Amount of “ordinary” gravitating matter A

mount

of

w=

-1 m

att

er

(“D

ark

energ

y”)

Friedmann Eqn.

2

2 8

3 k r m

aH G

a

7

Friedmann Eqn.

2

2 8

3 k r m

aH G

a

CurvatureRelativistic Matter

Non-relativistic Matter

Dark Energy

8

Scale factor

Friedmann Eqn.

2

2 8

3 k r m

aH G

a

CurvatureRelativistic Matter

Non-relativistic Matter

Dark Energy

A. Albrecht @ UCD 10/3/11 9

223

8

i ii

c cH

G

Scale factor

Friedmann Eqn.

22 8

3 k r m

aH G

a

10

2

43

3 3P

ap

a m

Friedmann Eqn.

22 8

3 k r m

aH G

a

11

2

43

3 3P

ap

a m

Supernova

Preferred by data c. 2003

“Ordinary” non accelerating matter

Cosmic acceleration

Accelerating matter is required to fit current data

(Includes Dark Matter)

Amount of “ordinary” gravitating matter A

mount

of

w=

-1 m

att

er

(“D

ark

energ

y”)

MSupernova

Preferred by data c. 2003

“Ordinary” non accelerating matter

Cosmic acceleration

Accelerating matter is required to fit current data

(Includes Dark Matter)

Amount of “ordinary” gravitating matter A

mount

of

w=

-1 m

att

er

(“D

ark

energ

y”)

Cosmic acceleration

Accelerating matter is required to fit current data

“Ordinary” non accelerating matter

Preferred by data c. 2008

BAO

Kowalski, et al., Ap.J.. (2008)

M (Includes Dark Matter)

Amount of “ordinary” gravitating matter A

mount

of

w=

-1 m

att

er

(“D

ark

energ

y”)

Cosmic acceleration

Accelerating matter is required to fit current data

“Ordinary” non accelerating matter

BAO

Suzuki, et al., Ap.J.. (2011)

Preferred by data c. 2011

M (Includes Dark Matter)

Amount of “ordinary” gravitating matter A

mount

of

w=

-1 m

att

er

(“D

ark

energ

y”)

Positive acceleration requires

• (unlike any known constituent of the Universe) or

• a non-zero cosmological constant or

• an alteration to General Relativity.

/ 1/ 3w p

43

3 3

a Gp

a

Positive acceleration requires

• (unlike any known constituent of the Universe) or

• a non-zero cosmological constant or

• an alteration to General Relativity.

/ 1/ 3w p

43

3 3

a Gp

a

Positive acceleration requires

• (unlike any known constituent of the Universe) or

• a non-zero cosmological constant or

• an alteration to General Relativity.

/ 1/ 3w p

43

3 3

a Gp

a

Positive acceleration requires

• (unlike any known constituent of the Universe) or

• a non-zero cosmological constant or

• an alteration to General Relativity.

/ 1/ 3w p

43

3 3

a Gp

a

Positive acceleration requires

• (unlike any known constituent of the Universe) or

• a non-zero cosmological constant or

• an alteration to General Relativity.

/ 1/ 3w p

43

3 3

a Gp

a

Two “familiar” ways to achieve acceleration:

1) Einstein’s cosmological constant and relatives

2) Whatever drove inflation: Dynamical, Scalar field?

1w

Positive acceleration requires

• (unlike any known constituent of the Universe) or

• a non-zero cosmological constant or

• an alteration to General Relativity.

/ 1/ 3w p

43

3 3

a Gp

a

Two “familiar” ways to achieve acceleration:

1) Einstein’s cosmological constant and relatives

2) Whatever drove inflation: Dynamical, Scalar field?

1w

• Today,

• Field models typically require a particle mass of

Some general issues:

Numbers:

4120 4 310 10DE PM eV

31010Qm eV H 2 2

Q P DEm M from

• Today,

• Field models typically require a particle mass of

Some general issues:

Numbers:

4120 4 310 10DE PM eV

31010Qm eV H 2 2

Q P DEm M from

Where do these come from and how are they protected from quantum corrections?

• Today,

• Field models typically require a particle mass of

Some general issues:

Numbers:

4120 4 310 10DE PM eV

31010Qm eV H 2 2

Q P DEm M from

Where do these come from and how are they protected from quantum corrections?

Some general issues

A cosmological constant

• Nice “textbook” solutions BUT

• Deep problems/impacts re fundamental physics

Vacuum energy problem

= 10120

0 ?

Vacuum Fluctuations

Some general issues

A cosmological constant

• Nice “textbook” solutions BUT

• Deep problems/impacts re fundamental physics

Vacuum energy problem (not resolved by scalar field models)

= 10120

0 ?

Vacuum Fluctuations

OUTLINE

•The Basics: Data, Directions and Issues

•Anthropics, Landscape & Critique

•Alternative Viewpoints

•Conclusions

OUTLINE

•The Basics: Data, Directions and Issues

•Anthropics, Landscape & Critique

•Alternative Viewpoints

•Conclusions

Anthropics and the value of Λ Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form

Anthropics and the value of Λ

-5 -4 -3 -2 -1 0 1 2

-10

-5

0

5

10

15

log(a/a0)

log( / c0 )

r

m

Time

Den

sity

Structure forming zone

Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form

Anthropics and the value of Λ

-5 -4 -3 -2 -1 0 1 2

-10

-5

0

5

10

15

log(a/a0)

log( / c0 )

r

m

Time

Den

sity

Structure forming zone

Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form

Anthropics and the value of Λ Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form

-5 -4 -3 -2 -1 0 1 2

-10

-5

0

5

10

15

log(a/a0)

log( / c0 )

r

m

Time

Den

sity

Structure forming zone

Anthropics and the value of Λ Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form •Can we input that data that we have cosmic structure and predict the (very small) value of Λ? (Life?!)•To do this one requires:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” sufficiently

Anthropics and the value of Λ Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form •Can we input that data that we have cosmic structure and predict the (very small) value of Λ? (Life?!)•To do this one requires:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” sufficiently

•Weinberg used some simple choices for 1) and 2) and “predicted” a value of Λ in 1987 similar to the value discovered ~10 years later. •Since then string theorists have argued that the string theory landscape delivers a suitable ensemble of Λ’s (Bousso & Polchinski)

Anthropics and the value of Λ Basic idea:•When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form •Can we input that data that we have cosmic structure and predict the (very small) value of Λ? (Life?!)•To do this one requires:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” sufficiently

•Weinberg used some simple choices for 1) and 2) and “predicted” a value of Λ in 1987 similar to the value discovered ~10 years later. •Since then string theorists have argued that the string theory landscape delivers a suitable ensemble of Λ’s (Bousso & Polchinski)

LABLA

BLABLA

BLABLA

B

Comment on how we use knowledge (“A” word!)

Total knowledge about the universe

Input Theory Output

LABLA

BLABLA

BLAB

LAB

Comment on the “A” word:

Total knowledge about the universe

Input Theory Output

LABLA

BLABLA

BLAB

LAB

Comment on the “A” word:

Total knowledge about the universe

Input Theory Output

LABLA

BLABLA

BLAB

LAB

Comment on the “A” word:

Total knowledge about the universe

Input Theory Output

LABLA

BLABLA

BLAB

LAB

Comment on the “A” word:

Total knowledge about the universe

Input Theory Output

LABPREDICTIONS

LABLA

BLABLA

BLAB

LAB

Input Theory Output

LABPR

ED

The best science will use up less here and produce more here

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently

Can get very different answers depending on how these ingredients are realized Banks, Dine & Motl

Can get very different answers depending on how these ingredients are realized

Phillips & Albrecht 2011

• Use "entropy production weighting” (Causal Entropic Principle, Bousso et al)

• Include variability of world lines due to cosmic structure• Two different behaviors for late time entropy producing in

halos

Un-normalized probability density

log

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently

Can get very different answers depending on how these ingredients are realized Banks, Dine & Motl

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently

Can get very different answers depending on how these ingredients are realized Banks, Dine & Motl

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently•In my view the string theory landscape is unlikely to survive as a compelling example of 1)

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently•In my view the string theory landscape is unlikely to survive as a compelling example of 1)

Eternal inflation

Eternal inflation

• Eternally exponentially expanding regions of the universe (driven by the ensemble of Λ’s), producing baby universes at some rate per volume per time

Eternal inflation

• Eternally exponentially expanding regions of the universe (driven by the ensemble of Λ’s), producing baby universes at some rate per volume per time

• ∞’s measure problems (which type of baby universe is more probable if there are ∞ of each?)

Eternal inflation

• Eternally exponentially expanding regions of the universe (driven by the ensemble of Λ’s), producing baby universes at some rate per volume per time

• ∞’s measure problems (which type of baby universe is more probable if there are ∞ of each?)

• Born Rule Crisis (Page, AA): If there is more than one copy of “you” in the wavefunction the Born rule cannot provide probabilities for the questions you want to ask.

Eternal inflation

• Eternally exponentially expanding regions of the universe (driven by the ensemble of Λ’s), producing baby universes at some rate per volume per time

• ∞’s measure problems (which type of baby universe is more probable if there are ∞ of each?)

• Born Rule Crisis (Page, AA): If there is more than one copy of “you” in the wavefunction the Born rule cannot provide probabilities for the questions you want to ask.

• I argue that the BRC cannot be circumvented by extra (“classical” or “xerographic”) distributions.

Eternal inflation

• Eternally exponentially expanding regions of the universe (driven by the ensemble of Λ’s), producing baby universes at some rate per volume per time

• ∞’s measure problems (which type of baby universe is more probable if there are ∞ of each?)

• Born Rule Crisis (Page, AA): If there is more than one copy of “you” in the wavefunction the Born rule cannot provide probabilities for the questions you want to ask.

• I argue that the BRC cannot be circumvented by extra (“classical” or “xerographic”) distributions.

• vs Page, Hartle and Srednicki, see also Aguirre and Tegmark, Bousso & Susskind)

Eternal inflation

• Eternally exponentially expanding regions of the universe (driven by the ensemble of Λ’s), producing baby universes at some rate per volume per time

• ∞’s measure problems (which type of baby universe is more probable if there are ∞ of each?)

• Born Rule Crisis (Page, AA): If there is more than one copy of “you” in the wavefunction the Born rule cannot provide probabilities for the questions you want to ask.

• I argue that the BRC cannot be circumvented by extra (“classical” or “xerographic”) distributions.

• vs Page, Hartle and Srednicki, see also Aguirre and Tegmark, Bousso & Susskind)

The downfall of eternal

inflation

Further comments on anthropics:

•Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial)•In my view 2nd law is most robust candidate for anthropic analysis• These ingredients still not well developed in case of Λ anthropics:

1) A theory with an ensemble of values of Λ2) A way to quantify “having structure” (or alternative condition)

sufficiently•In my view the string theory landscape is unlikely to survive as a compelling example of 1)

Eternal inflation

OUTLINE

•The Basics: Data, Directions and Issues

•Anthropics, Landscape & Critique

•Alternative Viewpoints

•Conclusions

OUTLINE

•The Basics: Data, Directions and Issues

•Anthropics, Landscape & Critique

•Alternative Viewpoints

•Conclusions

Bounded alternatives to the landscape and eternality

• de Sitter equilibrium cosmology

• Does holography imply non “self reproduction” ( no eternal inflation)?

• Causal patch cosmology

• Banks-Fischler Holographic cosmology

2 1S A H

“De Sitter Space: The ultimate equilibrium for the universe?

Horizon

8

3GH

GT H

62

Banks & Fischler & Dyson et al.

Implications of the de Sitter horizon

• Maximum entropy

• Gibbons-Hawking Temperature

• Only a finite volume ever observed

• If is truly constant: Cosmology as fluctuating Eqm.

• Maximum entropy finite Hilbert space of dimension

12

3S A H

8

3GH

GT H

63

SN e

Banks & Fischler & Dyson et al.

Implications of the de Sitter horizon

• Maximum entropy

• Gibbons-Hawking Temperature

• Only a finite volume ever observed

• If is truly constant: Cosmology as fluctuating Eqm.?

• Maximum entropy finite Hilbert space of dimension

12

3S A H

8

3GH

GT H

64

?SN e

dSE

cosm

olog

y

65

Equilibrium Cosmology

Rare Fluctuation

66

Rare Fluctuation

67

Concept:

Realization:

“de Sitter Space”

68

Rare Fluctuation

69

70

Fluctuating from dSE to inflation:

• The process of an inflaton fluctuating from late time de Sittter to an inflating state is dominated by the “Guth-Farhi process”

• A “seed” is formed from the Gibbons-Hawking radiation that can then tunnel via the Guth-Farhi instanton.

• Rate is well approximated by the rate of seed formation:

• Seed mass:

s s

GH

m m

T He e

1/2416

3110

0.0013s I II

GeVm cH kg

71

Fluctuating from dSE to inflation:

• The process of an inflaton fluctuating from late time de Sittter to an inflating state is dominated by the “Guth-Farhi process”

• A “seed” is formed from the Gibbons-Hawking radiation that can then tunnel via the Guth-Farhi instanton.

• Rate is well approximated by the rate of seed formation:

• Seed mass:

s s

GH

m m

T He e

1/2416

3110

0.0013s I II

GeVm cH kg

Small seed can produce an entire universe Evade “Boltzmann Brain” problem

72

Fluctuating from dSE to inflation:

• The process of an inflaton fluctuating from late time de Sittter to an inflating state is dominated by the “Guth-Farhi process”

• A “seed” is formed from the Gibbons-Hawking radiation that can then tunnel via the Guth-Farhi instanton.

• Rate is well approximated by the rate of seed formation:

• Seed mass:

s s

GH

m m

T He e

1/2416

3110

0.0013s I II

GeVm cH kg

See important new work on G-F process by Andrew Ulvestad & AA

degrees of freedom temporarily break off to form baby universe:

A. Albrecht @ UCD 10/3/11 73

time

Eqm.

Seed Fluctuation

Tunneling

Evolution

Evolution

Evolution

Inflation

Radiation

Matter

de Sitter

IS SN e e

Recombination

74

Image bySurhud More

Predicted from dSE cosmology is:•Independent of almost all details of the cosmology•Just consistent with current observations•Will easily be detected by future observations

k

k

0 /m

Work in progress on expected values of (Andrew Ulvestad & AA)

Bk

0.5Bk

0.25Bk

0.1Bk

CONCLUSIONS

• Cosmic acceleration has made life really exciting for the theorist

• Hardly a closed case

DETF Stage 4 ground [Opt]

1 1/c

2 2/c

i ii

w c f

DETF Stage 4 ground [Opt]

3 3/c

4 4/c

i ii

w c f