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Evidence for accelerated expansion Interpretation – “phenomenology” Explanation – “theory”

Ram Brustein. Irit maor (BGU  Cambridge) P. Steinhardt (Princeton) PRL 86 (2001), PRD 65 (2002), PRD 67 (2003). אוניברסיטת בן-גוריון. The Accelerating Universe: A Challenge to Fundamental Physics. Evidence for accelerated expansion Interpretation – “phenomenology”

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Evidence for accelerated expansion Interpretation – “phenomenology” Explanation – “theory”

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  1. Ram Brustein Irit maor (BGU Cambridge) P. Steinhardt (Princeton) PRL 86 (2001), PRD 65 (2002), PRD 67 (2003) אוניברסיטת בן-גוריון The Accelerating Universe: A Challenge to Fundamental Physics • Evidence for accelerated expansion • Interpretation – “phenomenology” • Explanation – “theory”

  2. 01/02/2003 La Recherche Et pourtant il accélère !L'expansion de l'Univers, loin de ralentir comme on le pensait depuis soixante-dix ans, est en train de s'accélérer sous la pression d'une mystérieuse énergie noire. Les astrophysiciens tentent de comprendre la nature de ce constituant majeur de l'Univers. La concordance de toutes ces expériences a fait sursauter plus d'un cosmologiste. À l'aube du XXIe siècle, il devient clair que 95 % de l'Univers nous est totalement étranger ! Les astrophysiciens s'aperçoivent que toutes leurs théories ne se fondent que sur l'observation des cinq petits pour cent visibles de l'énergie totale [fig. 4]. De quoi rendre sceptique le commun des mortels, mais pas les scientifiques, qui continuent à bâtir leur édifice théorique contre vents et marées. Leur plus grand défi est aujourd'hui de dévoiler la nature de cette énergie noire,

  3. Geometry GR: a(t), 1+ z =a(now)/a(t), Matter r(z), p(z), w(z) = p/r. מפץ גדול חם : המודל הסטנדרטי rC- critical density (Euclidean space) WX - rX / rC

  4. Accelerated expansion ?! Radiation r = 3p, w = 1/3 Matter (normal and dark) p=0, w = 0 Attractive gravity + “normal” matter  decelerated expansion

  5. Mapping the Universe Luminosity – energy/time emitted by source Flux – energy /time/area absorbed by detector Due to expansion: Energy/timeq(1+z)2 (1+z) – red shift of energy (1+z) – increased time Need “standard candles”

  6. Luminosity distance dL vs. redshift z: Hubble Diagram For light Example: SNIa

  7. Angular distance dA vs. redshift z Proper diameter - d Observed angular diameter – q q= d/(a r)  Example: Peaks in CMB spectrum Need “standard feature”

  8. Evidence for Accelerated ExpansionDirect and Indirect • Cosmic Microwave Background : inhomogeneities in radiation • Large Scale Structure : inhomogeneities in matter object counts: galaxies, clusters, weak lensing, strong lensing, … • SuperNovae Ia– most direct

  9. SNIa התפוצצות גרעינית של ננסים לבנים מתאם בין בהירות שיא, צורה וספקטרום של עקומת האור  ~% 10 פיזור בבהירות שיא

  10. D m L d i m m e r AC/DC purematter z more distant Current SNIa Data Lpreferred fiducial models: Wm= 0.3 wQ= const. Key issue:systematic errors Previous version: Sci. Am. 1/2001

  11. Current Data -.5 wQ • Wm vs. wQ (assume flat U.) -1.5 -2.5 -3.5 Wm 0.7 0.3 0.5

  12. Cosmic variance! CMBdata: WMAP February 2003

  13. One more point on theHubble diagram (z ~ 1,000) ~ Flat U. Cosmic variance!

  14. astro-ph/0302209 Combined results • Interim report I • flat universe • acceleration • consistent • reasonable?! n small

  15. The end of the universe is cancelledBy Robert Matthews, Science Correspondent(Filed: 09/02/2003) Professor Hawking, we have a problem. Nasa, the American space agency, is expected to announce this week that it has proved the existence of "dark energy", a cosmic force that counteracts gravity and will keep the universe expanding forever. The announcement will effectively demolish the theory that life will be wiped out in a "Big Crunch" when the universe collapses, and should end decades of academic dispute over the forces at work on the universe

  16. Interpretation: theoretical expectations • Dark energy is not just L • Dynamical field (s): • Kinetic & potential energies • Interactions with other particles • Cosmic friction • Very small mass  time-dependence

  17. Dark Energy EOS • Parametrization in terms of (time-dependent) Energy density rQ(z) Pressure pQ(z) EOSwQ(z)=pQ(z)/rQ(z) • previously : wQ = -1 L wQ = 0 cold matter oscillations, “sudden start”, “decay to a constant”

  18. Luminosity distancedLvs. redshiftz Maor et al. g= Wm /(1- Wm) Current SnIA data: some acceleration in the last 8 billion years (0 < z < 1)

  19. snap.lbl.gov l'avenir: SNAP (F) SNAP proposal: 1000’s de SNIa, surtout 0 < z < 1.2, quelques-uns1.2 < z < 1.7 Also: ESSENCE CFHLS (F) GOODS, SNFactory (F)

  20. wQ = -1 wQ = -1/3 wQ = 0 fiducial models: Wm= 0.3 wQ= const. See: Sci. Am. 1/2001

  21. Degeneracy! Maor et al. • DL • D DL/DL • wQ (z) • For 9 differentEOS

  22. CMB cannot help much … Maor & Brustein • Dark energy expected to “disappear” for z > 2 • CMB photons propagate most of the way through matter dominated U.  No gain compared to “low z” probes • Best accuracy for dL from CMB ~ 1%  CMB comparable to other probes

  23. Interim report II • recent acceleration (0 < z < 1, today < t < 8 billion years) • evidence from many sources, consistent. • qualitative information only (on fundamental physics) from most accurate planned experiments

  24. Dark sector &the standard model of particle physics

  25. Dark sector &gravity and quantum mechanics Does not make sense as a normal source

  26. : "We live where we can live," NYT: 2 Sept. 2003 (R.B.) : Cloud No. IV: Black Hole Entropy

  27. Gravity Something has to give • Quantum mechanics • More space dimensions • Cherished principles: causality, … • Matter – additional fields, light, extremely weakly coupled – “quintessence” and the ugliest(?) of them all: theAnthropic principle

  28. The “boring” option: Quintessence Maor & Brustein Degeneracies • “Tracker” fields • Many other possibilities m ~ H = 10 –33 eV V ~ rcrit ~ (10-3eV)4 Steinhardt + … Rhatra+Peebles Wetterich …

  29. The Anthropic Principle R. Dicke (1961): “ carbon-based life can only arise when the Dirac large numbers hypothesis is true because this is when burning stars exist” B. Carter (Early 1970’s): “what we can expect to observe must be restricted by the conditions necessary for our presence as observers” (Leslie ed. 1990). The word "anthropic" was intended as applying to intelligent beings. A possible argument for preferring the God hypothesis: think in terms of many possible fundamental theories, God selecting a theory which permitted life's requirements to be fulfilled without contradictions.

  30. Conclusions • Excellent measurements are not good enough as clues for fundamental physics ! • A large source of error: theory • Need: • either a new “local” test -what is it? • or radically new theoretical input -what is it ? • Theory situation in a nut-shell “we don’t have a clue” • Personal hope: revolutionary resolution

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