a theorist’s view of dark energy andreas albrecht (uc davis) ucsc colloquium jan 19 2012
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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
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
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
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
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
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