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Space-Time Defects and the Accelerated Expansion of the Universe: An Alternative to Dark Energy?

This talk explores the possibility of an alternative explanation for the accelerated expansion of the universe, proposing the existence of space-time defects as opposed to dark energy. The speaker discusses the Cosmic Defect theory and its fit with observational data, highlighting open problems and potential modifications to general relativity.

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Space-Time Defects and the Accelerated Expansion of the Universe: An Alternative to Dark Energy?

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  1. Space-time defects and the accelerated expansion of the universe: an alternative to dark energy? Angelo Tartaglia DIFIS – Politecnico and INFN Torino, Italy Beijing -24 September 2008

  2. Plan of the talk • Starting point and motivation • Outline of the Cosmic Defect theory • Fit of the observational data • Open problems Beijing -24 September 2008

  3. Give up GR and look for another theory Puzzlesof standard cosmology • Inflation • Gravity in clusters and galaxies • Accelerated expansion There is something missing Introduce new fields in standard GR Modify GR 3 Beijing -24 September 2008

  4. Add “matter” components Accept a four- (N-) dimentional spacetime manifold Perfect fluid Isotropy and homogeneity 4 Beijing -24 September 2008

  5. Λ Cold Dark Matter • Simplest and most effective model for the universe; however: • “matter” must be 7 times more than what we “see” (~30% of the cosmic source); • Λ corresponds to 70% of the cosmic souce but … what is Λ? 5 Beijing -24 September 2008

  6. The Cosmic Defect theory: strain in a continuumN-dimensional “sheet” Strain induced by boundary conditions Elasticity 6 Beijing -24 September 2008

  7. A defect Internal “spontaneous” strain state 7 Beijing -24 September 2008

  8. Natural manifold Geometry, elasticity and defects Reference manifold 8 Beijing -24 September 2008

  9. In a strained medium each point is in one to one correspondence with points in the unstrained state Displacement Intrinsic coordinates Extrinsic coord. In the purely elastic case the new situation is diffeomorphic to the old one may be expressed as a function of x as well as of ξ 9 Beijing -24 September 2008

  10. Strain tensor (represented in the reference manifold) Induced metric 10 Beijing -24 September 2008

  11. “Radial” displacementfield(spaceisotropy and homogeneity) Strained 11 Beijing -24 September 2008

  12. A Robertson-Walker universe 12 Beijing -24 September 2008

  13. How can we choose a Lagrangian expressing the presence of the defect? Start from the phase space of a Robertson-Walker universe and look around for similar phase spaces 13 Beijing -24 September 2008

  14. Inertial expansion Accelerated expansion Decelerated expansion Free motion Driving force Braking force Phase space analogy FRW universe Point particle 14 Beijing -24 September 2008

  15. A simple classical problem Motion of a point massive particle in a viscous medium 15 Beijing -24 September 2008

  16. Spacetime“Dissipative” action integral • Same structure as in the classical simple case • The “viscous” properties of space-time arecontainedin the vector field 16 Beijing -24 September 2008

  17. Impose the 4-isotropy around the origin and use cosmic time as the “radial” coordinate 17 Beijing -24 September 2008

  18. Symmetry and application of the minimal action principle do not commute Defect means Symmetry first 18 Beijing -24 September 2008

  19. Divergence free vector 19 Beijing -24 September 2008

  20. Accelerated expansion Asymptoticstop Expansion rate 20 Beijing -24 September 2008

  21. Acceleration Inflation Expansion versus cosmic time 21 Beijing -24 September 2008

  22. Fitting the data from SnIa One has to account for the presence of matter 22 Beijing -24 September 2008

  23. Distance modulus vs z (192 SnIa) 23 Beijing -24 September 2008

  24. Reduced 2 of the fits 2 = 1.029 ΛCDM 2 = 1.092 CD 24 Beijing -24 September 2008

  25. The Hubble parameter H0 = (62.8 ± 1.7) km/sMpc Most models ~64 km/sMpc Observation ~75 km/sMpc 25 Beijing -24 September 2008

  26. Weaknesses and open problems • Fitting the SnIa luminosity data with a logarithmic function and two parameters is “too easy” • The heuristic definition of the Lagrangian (though working) needs more stringent arguments: why is it working? 26 Beijing -24 September 2008

  27. The null divergence condition should be a consequence of the singularity in correspondence of the defect, rather than a formal constraint imposed on the vector. 27 Beijing -24 September 2008

  28. Correspondences • Defect theory in solids • Bimetric theories: “pre-shaped container” • Vector-tensor theories • Curvature fluid 28 Beijing -24 September 2008

  29. Final remarks The CD theory provides a consistent physical interpretation of space-time giving a heuristic tool to move across the Lagrangian “forest” set up by Lagrangian “engineering” mostly driven by the formal search for the desired result. This conceptual framework looks promising 29 Beijing -24 September 2008

  30. A. Tartaglia, M. Capone, Int. Jour. Mod. Phys. D, 17, 275-299 (2008) A. Tartaglia, N. Radicella, Phys. Rev. D, 76, 083501 (2007) A. Tartaglia, M. Capone, V. Cardone, N. Radicella, arXiv:0801.1921, to appear on Int. Jour. Mod. Phys. D 30 Beijing -24 September 2008

  31. VII Friedmann Seminar 31 Beijing -24 September 2008 João Pessoa 1 July 2008

  32. Ether again …. according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. ….. But this ether may not be thought of as endowed with the quality characteristic of ponderablemedia, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it. Albert Einstein, Leiden, 1920 32 Beijing -24 September 2008

  33. Some history “Ether is a very wonderful thing. It may exist only in the imagination of the wise, being invented and endowed with properties to suit their hypotheses; but we cannot do without it. How is energy to be transmitted through space without a medium?” Oliver Heaviside, Electrical Papers, 1892 33 Beijing -24 September 2008

  34. Ether is superfluous The introduction of a “luminiferous ether” will prove to be superfluous inasmuch as the view here to be developed will not require an “absolutely stationary space”….. Albert Einstein, 1905 34 Beijing -24 September 2008

  35. The cosmological constant “Much later, when I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder of his life.  ----” George Gamow, My World Line, 1970 35 Beijing -24 September 2008

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