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Andreas Albrecht UC Davis APS Meeting Philadelphia, April 2003

Title. Cosmic acceleration and fundamental physics . Andreas Albrecht UC Davis APS Meeting Philadelphia, April 2003. II) Exciting Directions II.1 The quantum physics of II.2 Dark energy/quintessence, Stage I (adventures) II.3 Dark energy/quintessence, Stage II (getting serious).

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Andreas Albrecht UC Davis APS Meeting Philadelphia, April 2003

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  1. Title • Cosmic acceleration and fundamental physics Andreas Albrecht UC Davis APS Meeting Philadelphia, April 2003

  2. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  3. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  4. As far as we can tell so far, the cosmic acceleration might be the result of • I.1 The cosmological constant problem / fundamental gravity

  5. Greatest unsolved problem in physics: Why is  = 10120 Vacuum Fluctuations   0 ? • I.1 The cosmological constant problem / fundamental gravity

  6. Challenges: •   0 dream may not work • A more mature fundamental theory of gravity could overturn ideas about the origins of acceleration • Huge potential for observations to impact fundamental theories • I.1 The cosmological constant problem / fundamental gravity

  7. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  8. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  9. Why this?  Where does this strange parameter come from? (not really a separate “why now problem”, with  ) • I.2 The “why this/why now” problems

  10. Why now?  If the source of acceleration is some dynamical matter (“quintessence”), then it has to acquire the value today (t=14.5 Gyr). (not some other time) Time  Today • I.2T he “why this/why now” problems

  11. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  12. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  13. If the acceleration is produce by a scalar field (quintessence): • i) The quintessence field must have a mass • How can this value stay safe from quantum corrections? • I.3 Quantum corrections/long range forces

  14. If the acceleration is produce by a scalar field (quintessence): • ii) If such a small mass is preserved, there is a new long range force mediated by the quintessence field. • How can 5th force bounds be evaded? • (Carroll) • I.3 Quantum corrections/long range forces

  15. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  16. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  17. ia) The entropy bound: • If there really is a , the late-time asymptotic state of the universe will have a horizon with area: • This implies a Hawking-Beckenstein type upper bound on the entropy: • Are we then compelled to only consider only models of physics with a finite dimensional Hilbert space? (Excludes field theory, M-theory, SHO, etc.) T. Banks & W. Fischler • II.1 The quantum physics of

  18. ib) Holography & the Causal Patch • Two basic facts about de Sitter space: 1)Objects never appear to leave the horizon Const. t 2)A free field appears at Temp: Observer’s Worldline  Const. r (Gibbons & Hawking) [Black Hole Analogy] • II.1 The quantum physics of

  19. NB: Tollman taught us  Increasing (divergent) T(r) ib) Holography & the Causal Patch • Two basic facts about de Sitter space: 1)Objects never appear to leave the horizon Const. t 2)A free field appears at Temp: Observer’s Worldline  Const. r See Kaloper (Davis Inflation Meeting ’03) (t’ Hooft: BH case) • II.1 The quantum physics of

  20. ib) Holography & the Causal Patch Banks Bousso Fischler t’Hooft Susskind • Causal Patch “unification” hypothesis: 1)Objects never appear to leave the horizon 2)A free field appears at Temp. (divergent at horizon) No physics out here • Holographic (quantum gravity) “magic” gives • Cutoff for “divergent” entropy at rH  area entropy law • “All Physics” inside causal patch*. Objects thermalize as they approach the horizon (no “outside” = no “inside” of Black Hole) • Consistency of the above across different observers. • *The end of inflation? (Dyson et al ’02) O This observer sees divergent entropy here, cut off by quantum gravity. • II.1 The quantum physics of

  21. ii) Other constraints on fundamental theories with : • Do scattering states exist? (Banks, Fischler) • Does string theory exist in de Sitter space? (see Kachru et al ’03) • Does quantum de Sitter space exist? (Goheer et al ’03) • II.1 The quantum physics of

  22. iii) Causal set theory of gravity: a prediction of causal set theory?! (Ahmed et al. Sep 2002) • II.1 The quantum physics of

  23. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  24. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  25.  Inflation has taught us how to accelerate the universe with a scalar field… why not try again? PNGB: Frieman, Hill, Stebbins, & Waga 1995 With f  1018GeV, M  10-3eV Zlatev, Wang & Steinhardt 1998 Scalar field domination/ acceleration M=1 meV - 1GeV • II.2 Dark energy/quintessence, Stage I (adventures)

  26.  Inflation has taught us how to accelerate the universe with a scalar field… why not try again? N.B Resurrect the   0 dream PNGB: Frieman, Hill, Stebbins, & Waga 1995 With f  1018GeV, M  10-3eV Zlatev, Wang & Steinhardt 1998 Scalar field domination/ acceleration M=1 meV - 1GeV • II.2 Dark energy/quintessence, Stage I (adventures)

  27. Time   Some more scalar field models of dark energy: Shadowing Oscillating Albrecht & Skordis 1999 There are many other examples Dodelson Kaplinghat & Stewart 2000 • II.2 Dark energy/quintessence, Stage I (adventures)

  28.  A note about the “why this/now” problem: • Essentially all existing quintessence models “solve” it by relating to parameters in the quintessence equations • Attractor behavior gets rid of initial conditions dependence • How compelling this “solution” is depends on how convinced you are that nature has chosen those parameters. • II.2 Dark energy/quintessence, Stage I (adventures)

  29.  A note about Quantum corrections/long range forces: • Almost all models of dynamical dark energy/quintessence completely ignore these issues.  “adventures” • II.2 Dark energy/quintessence, Stage I (adventures)

  30. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  31. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  32. Stage II: Take quantum corrections/long range forces seriously * Supergravity Kalosh et al. 2002 *PNGB: Frieman, Hill, Stebbins, & Waga 1995 * Extra dimensions A.A, Burgess, Ravndal 2001 • Challenging particle physics issues • II.3 Dark energy/quintessence, Stage II (getting serious)

  33. Stage II: Take quantum corrections/long range forces seriously * Supergravity Kalosh et al. 2002 *PNGB: Frieman, Hill, Stebbins, & Waga 1995 * Extra dimensions A.A, Burgess, Ravndal 2001 • Challenging particle physics issues • Also: Risky because more radical developments could invalidate these efforts • II.3 Dark energy/quintessence, Stage II (getting serious)

  34. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  35. II) Exciting Directions • II.1 The quantum physics of • II.2 Dark energy/quintessence, Stage I (adventures) • II.3 Dark energy/quintessence, Stage II (getting serious) • I) Challenges for models of cosmic acceleration • I.1 The cosmological constant problem / links to fundamental gravity. • I.2The “why this/why now” problems • I.3 Quantum corrections/long range forces III) Conclusions • Cosmic acceleration and fundamental physics, APS April 2003

  36. III) Conclusions Modeling cosmic acceleration leads to:  Exciting challenges and new directions, many of which are connected with very fundamental questions.  Real opportunity for dramatic observational advances Weller & AA

  37. % deviation z NB: Don’t be afraid of degeneracies!! Data can still distinguish among many interesting models Degeneracy Maor et al. Parameters and Cosmic Confusion IV-37

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