1. L. Perivolaropoulos http://leandros.physics.uoi.gr Department of Physics University of Ioannina

3. Dist. Ind. Obs

4. 2 12 Know L Measure l(z) Distance Modulus: 1

6. Accelerating Universe: (rate of expansion) was smaller in the past. Thus H -1 (t) was larger in the past.

7. Expand. Phot. Meth./SnII Best Choice for Cosmology Planetary Nebulae Surf. Brightness Fluct. Tully Fisher Brightest Cluster Gal. Glob. Cluster Lum. Fun. Sunyaev-Zeldovich Gravitational Lensing

9. Degeneracy pressure always fails at same mass.

10. HST

12. closeby SnIa

14. Gold Dataset (157 SNeIa): Riess et. al. 2004 Decelerating Accelerating ?

15. Gold Dataset (157 SNeIa): Riess et. al. 2004

17. dust produced from vacuum with time Gold Dataset (157 SNeIa): Riess et. al. 2004

18. ESSENCE CFHT Legacy Survey Higher-z SN Search (GOODS) SN Factory Carnegie SN Project SNAP

19. Expected: Decelerated Expansion due to Gravity Observed: Accelerated Expansion Q: What causes the Acceleration?

20. Equation of State: Necessary condition for acceleration:

21. (from large scale structure observations)

23. Einstein (1915) G.R.: Einstein (1917) G.R. + Static Universe + Matter only: G  =  T  G  -  g  =  T  The biggest blunder of my life

24. Since I introduced this term, I had always a bad conscience.... I am unable to believe that such an ugly thing is actually realized in nature A. Einstein 1947 letter to Lemaitre

26. 1. Measurements of the Cosmological Parameters Omega and Lambda from the First 7 Supernovae at z >= 0.35 S. Perlmutter et al., Astrophys.J. 483 (1997) 565 2. Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant S. Perlmutter et al., Nature 391 (1998) 51 3. Discovery of Supernova Explosion at Half the Age of the Universe A.G. Riess et al., Astron.J. 116 (1998) 1009-1038

27. 4. Cosmological results from high-z supernovae Tonry et al. The Astrophysical Journal, 594:1-24, 2003 September 1 5. New Constraints on Ω M, Ω Λ, and w from an Independent Set of 11 High-Redshift Supernovae Observed with the Hubble Space Telescope R.A. Knop et al., The Astrophysical Journal, Volume 598, Issue 1, pp. 102-137 Decelerating Expansion starts at z=0.46 11 new SnIa observed from HST 6. Type Ia Supernova Discoveries at z > 1 From the Hubble Space Telescope: Evidence for Past Deceleration and Constraints on Dark Energy Evolution A. Riess et al. The Astrophysical 607:665-687,2004 16 new SnIa observed from HST 7 of them with z>1.25

38. What theory produces the features of best parametrizations? What is the Fate of the Universe? (extrapolating w(z) to z<0 (w(z)<-1))

39. Quintessence: tracking scalar fields (Ratra & Peebles, Wetterich 1988, Coble et al. 1997, Ferreira & Joyce 1998, Liddle & Scherrer 1999, Steinhardt et al. 1999, Perrotta & Baccigalupi 1999, Brax & Martin 2000, Masiero et al. 2001, Doran et al. 2001, Corasaniti & Copeland 2003,Perivolaropoulos 2005,Tsujikawa 2005) Extended Quintessence: non-minimal coupling to Gravity (Chiba, Uzan 1999, Perrotta et al. 2000, Baccigalupi et al. 2000, Faraoni 2000, Bartolo & Pietroni 2000, Esposito-Farese & Polarski 2001, Perrotta & Baccigalupi 2002, Perivolaropoulos 2005,Tsujikawa 2005) Coupled Quintessence: coupling with dark matter (Carroll 1998, Amendola 2000, Matarrese et al. 2003) k-essence: modified kinetic scalar field energy (Aramendariz-Picon et al. 2001, Caldwell 2002, Malquarti et al. 2003) Quantum Fluctuations of Scalar Field: (Onemli and Woodard 2004)Quantum Fluctuations of Scalar Field: (Onemli and Woodard 2004) Spacetime microstructure: self-adjusting spacetime capable to absorb vacuum energy (Padmanabhan, 2002)Spacetime microstructure: self-adjusting spacetime capable to absorb vacuum energy (Padmanabhan, 2002) Matter-Energy Transition: dark matter undergoes a phase transition to dark energy at low redshifts (Basset et al. 2003)Matter-Energy Transition: dark matter undergoes a phase transition to dark energy at low redshifts (Basset et al. 2003) Brane worlds: brane tension (Shani & Sthanov 2002, Sami & Dadhich 2004, Brown, Maartens Papantonopoulos, & Zamarias 2005); cyclic-ekpyrotic cosmic vacuum (Steinhardt &Tutok 2001)Brane worlds: brane tension (Shani & Sthanov 2002, Sami & Dadhich 2004, Brown, Maartens Papantonopoulos, & Zamarias 2005); cyclic-ekpyrotic cosmic vacuum (Steinhardt &Tutok 2001) Exotic particle physics: photons oscillating in something else at cosmological distances (Csaki et al. 2002)Exotic particle physics: photons oscillating in something else at cosmological distances (Csaki et al. 2002) Chaplygin gas: dark matter and energy described by a single gas having variable equation of state (Den et al. 2003, Carturan & Finelli 2003)Chaplygin gas: dark matter and energy described by a single gas having variable equation of state (Den et al. 2003, Carturan & Finelli 2003) Scale-dependent Gravity: Gravity weaker on large scales (Dvali et al. 2003)Scale-dependent Gravity: Gravity weaker on large scales (Dvali et al. 2003)

40. +: Quintessence -: Phantom To cross the w=-1 line the kinetic energy term must change sign (impossible for single phantom or quintessence field)

41. L.P., astro-ph/0504582

42. Radial Geodesics: S. Nesseris, L. P., Phys.Rev.D70:123529,2004

44. S. Nesseris, L. Perivolaropoulos, Phys.Rev.D70:123529,2004

45. 2m Telescope ~1 billion pixels, 144 CCDs 350-1700 nm wavelength coverage Finds and follows 2500 SnIa each year, out to z = 1.7 Place good limits on both w and its time evolution

46. Dark Energy with Negative Pressure can explain SnIa cosmological data indicating accelerating expansion of the Universe. The existence of a cosmological constant is consistent with SnIa data but other evolving forms of dark energy crossing the w=-1 line provide better fits to the data. New observational projects are underway and are expected to lead to significant progress in the understanding of the properties of dark energy.

47. We measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial. The search will continue. E. Hubble in The Realm of the Nebulae,