A theorist’s view of dark energy Andreas Albrecht (UC Davis) UCSC Colloquium Jan

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 “Ordinary” non accelerating matter Cosmic acceleration Accelerating matter is required to fit current data (Includes Dark Matter)  Amount of “ordinary” gravitating matter   Amount of w=-1 matter (“Dark energy”) 

Friedmann Eqn. 7

Curvature Relativistic Matter Non-relativistic Matter Dark Energy 8 Scale factor

Friedmann Eqn. Curvature Relativistic Matter Non-relativistic Matter Dark Energy A. UCD 10/3/119 Scale factor

Friedmann Eqn. 10

Friedmann Eqn. 11

Supernova Preferred by data c “Ordinary” non accelerating matter Cosmic acceleration Accelerating matter is required to fit current data (Includes Dark Matter)  Amount of “ordinary” gravitating matter   Amount of w=-1 matter (“Dark energy”) 

Supernova Preferred by data c “Ordinary” non accelerating matter Cosmic acceleration Accelerating matter is required to fit current data (Includes Dark Matter)  Amount of “ordinary” gravitating matter   Amount of w=-1 matter (“Dark energy”) 

Cosmic acceleration Accelerating matter is required to fit current data “Ordinary” non accelerating matter Preferred by data c BAO Kowalski, et al., Ap.J.. (2008) (Includes Dark Matter)  Amount of “ordinary” gravitating matter   Amount of w=-1 matter (“Dark energy”) 

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 (Includes Dark Matter)  Amount of “ordinary” gravitating matter   Amount of w=-1 matter (“Dark energy”) 

Positive acceleration requires (unlike any known constituent of the Universe) or a non-zero cosmological constant or an alteration to General Relativity.

Positive acceleration requires (unlike any known constituent of the Universe) or a non-zero cosmological constant or an alteration to General Relativity. 

Positive acceleration requires (unlike any known constituent of the Universe) or a non-zero cosmological constant or an alteration to General Relativity. 

Positive acceleration requires (unlike any known constituent of the Universe) or a non-zero cosmological constant or an alteration to General Relativity. 

Positive acceleration requires (unlike any known constituent of the Universe) or a non-zero cosmological constant or an alteration to General Relativity. Two “familiar” ways to achieve acceleration: 1) Einstein’s cosmological constant and relatives 2) Whatever drove inflation: Dynamical, Scalar field?

Positive acceleration requires (unlike any known constituent of the Universe) or a non-zero cosmological constant or an alteration to General Relativity. Two “familiar” ways to achieve acceleration: 1) Einstein’s cosmological constant and relatives 2) Whatever drove inflation: Dynamical, Scalar field?

Today, Field models typically require a particle mass of Some general issues: Numbers: from

Today, Field models typically require a particle mass of Some general issues: Numbers: 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: 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  =   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)  =   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 Time  Density  Structure forming zone Basic idea: When Λ or radiation dominates the universe structure (i.e. galaxies) cannot form

Anthropics and the value of Λ Time  Density  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 Time  Density  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 Λ 2)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 Λ 2)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 Λ 2)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)

LAB Comment on how we use knowledge (“A” word!) Total knowledge about the universe  InputTheoryOutput

LAB Comment on the “A” word: Total knowledge about the universe  InputTheoryOutput

LAB Comment on the “A” word: Total knowledge about the universe  InputTheoryOutput

LAB Comment on the “A” word: Total knowledge about the universe  InputTheoryOutput

LAB Comment on the “A” word: Total knowledge about the universe  InputTheoryOutput LAB PREDICTIONS

LAB InputTheoryOutput LAB PRED 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 2 nd 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 2 nd 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 Λ 2)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 2 nd 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 Λ 2)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

Further comments on anthropics: Replace “life” with more humble “correlations” and one has a commonplace part of physics (non-controversial) In my view 2 nd 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 Λ 2)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 2 nd 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 Λ 2)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 2 nd 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 Λ 2)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 2 nd 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 Λ 2)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 2 nd 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 Λ 2)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

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 2 nd 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 Λ 2)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

“De Sitter Space: The ultimate equilibrium for the universe? Horizon 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 63

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 64 dSE cosmology

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:

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

degrees of freedom temporarily break off to form baby universe: A. UCD 10/3/1173 time Eqm. Seed Fluctuation Tunneling Evolution Inflation Radiation Matter de Sitter Recombination

74 Image by Surhud 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 Work in progress on expected values of (Andrew Ulvestad & AA)

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

DETF Stage 4 ground [Opt]