Tehdy-a-dnes (82 years since the discovery of cosmological expansion)

1. Tehdy-a-dnes.ppt(82 years since the discovery of cosmological expansion) J. Jersák, RWTH Aachen 12.2009

2. Kosmologie tehdy a dnes J. Jersák, RWTH Aachen (= Cáchy) Teoretická Fyzika V.V. oslava, Praha, prosinec 2009

3. One of numerous contemporaryillustrations The most important aspect: expansion of space

4. History of the expansion paradigm (I) • Expansion predictedtheoretically in early 1920´s,before Hubble • Originaltheory of expansion based on General Relativity (GR) Friedmann (Russia), Lemaître(Belgium, L'Hypothèse de l'Atome Primitif), (FL-equations)

5. A. Friedmann

6. Georges Lemaître

9. Einstein to Lemaître , 1927 (Solvay): Vos calculs sont corrects, mais vôtre physique est abominable

10. History of the expansion paradigm (II) 1929 Hubble (USA) establishes: Redshift ofclose Galaxies increases linearly with their distance (no mention of the expansion of space!) 1930: Lemaître´s work discovered and idea of expansion of space accepted (Eddington, de Sitter, Einstein, Robertson, Walker, …) [but the terms „Hubble law“, „Hubble discovery“, etc, persist … ]

11. Millikan, Lemaître, Einstein

12. History of the expansion paradigm (III) 1931: Lemaître suggests the idea of Big Bang („l´atome primitif“) and devises a model of expanding space with both matter and cosmological constant („Lemaître model“), which is today called the ΛCDM model of our Universe or Standard model of cosmology

13. Friedmann-Lemaître cosmology is a wonderful application of GR! • Conceptually clear • Mathematically simple • Correct – as we know today • But information was nearly inaccessible • Did V.V. know/like that in ´60-es? • I do not remember anything about relativistic cosmology from my studies during that time • Quantum mechanics + particle physics + QFT were of higher interest

14. ´30 - ´60´s:Period of confusionfor FL-cosmology • It was without a convincing observational evidence until 1964 (CMB) • Many wrong ideas seriously coexisted (e.g. steady state model, Newtonian cosmology, …) • Age crisis (Ho = ?) • Some famous cosmologists spotted about expansion of space („Big Bang“) • CMB radiation discovered by engineers(!!!)

15. Cosmic microwave background (CMB)averaged over all sky directionsT0 = 2,730+/-0,001° (COBE)T-fluctuations onlyvery fine0,000 02 °K (COBE and WMAP satellites)

16. Cosmic microwave background (CMB) as seen from an absolute rest frame atlower T-resolution:

17. CMB ´64(CBR, CMBR, relict radiation) • Convincing evidence for BB and FL cosmology … • CMB defines in a global way structure of space-time: - local absolute rest frames comoving with expansion of space - universal cosmic timet => an absolute spacetime reference frame enters the theory of relativity on observational basis (fixed points in space, absolute foliation)

18. Sun´s motion with respect to CMBi.e. with respect to thelocal absolute rest frame370 km/s

19. Cosmic (absolute) time t Defined in all local absolute rest frames applicable in the whole observable Universe Since the Universe is equal everywhere, it has also the same age everywhere • Cosmic aget Defined by the expansion as by a sandglass Now (today): t = t0 ( = 14 Gy)

20. Cosmic („proper“) distance D(t) All directions are equal: It suffices to consider thedistanceD(t) between pairs of distant galaxies in arbitrary directions Space is flat, though spacetime is curved: A Euclidean model of elastic space is suitable • 1-dimGR-space:a straight rubber band

21. The space expands, but remains locally always the same.Galaxies recede from each other,but they are at restin space and do not expand. t

22. Cosmic scale factor a(t) • Distances normalized with respect to the present ones • All length scales in cosmology are proportional to the cosmic scale a(t)determines the expansion at all distances simultaneously

23. Comoving coordinate • Dimensionles coordinates of fixed points (galaxies) in . space • Defined by the present distances of these points • -independent • … distance of a point with

24. Comoving coordinates of fixed points (galaxies) t

25. THEORY of space expansion • Simplified eqs. of the Einstein´s general relativity (Friedmann-Lemaître eqs. without radiation and the pressure term) t > 0.000 1 Gy

26. ´80´s: Particle theorists enter cosmology…

28. Elementary particle aspects of BB • … • Radiation epoch (pressure: number of relativistic degrees of freedom like photons and neutrinos) • QCD deconfinement transition (quark-gluon plasma) • EW transition (Higgs?) • GUT transition (???) • Inflation à la SSB mechanism (?????) • „Estimate“ of Λ(catastrophic!!!) • Dark matter speculations (-inos ????) + physics of condensed matter

29. APOD IRRELEVANT for dynamics of expansion

30. Dark matterin halo around some galaxydark matter≈ 10x visible matterRELEVANTArtist‘s viewD.B.Cline, SciAm March 03 Can particle physicists explain it?…

31. Buffling mistake of cosmologists and relativists,(up to some exceptions:de Sitter, Lemaître, …?) • Cosmological constant .Λbanishedfor 60 years

33. Willem de Sitter

34. Cosmological constant Λ • Positivecontribution to the acceleration, accelerates the expansion • Remains constant with t • Tension of space(„negative pressure“) • Λ≠0is generic in GR(see QFT) ( term in E. eqs.,but ist value ?) • It is not something exotic and it is Einstein´s merit to introduce it into GR

35. The cause of the acceleration? „DARK ENERGY“: • Most natural: New constant of Nature = cosmological constant Λà la Einstein It is not an energy, and it is not dark Some alternatives: • Energy of the vacuum (quantum effect)? To be expected, but theoreticians cannot calculate ist value • Quintessence?A new scalar field≈Λ(t)? Suggested first by Ch. Wetterich (Heidelberg)

36. Further components in the early Universe • t < 0,000 1 Gy:radiation must be included (photons, neutrinos, other particles with v ≈ c). • Seeds of inhomogeneities must be included [as sub-models in the ΛCDMmodel, CPT]. • t < 0,0…01 sec: big speculationsabout big bang (inflation, quantum gravity in D=4, strings, big bounce, pre-big bang universe, ekpyriotic universe, branes, multiverse, baby universes, … enter your own one)

37. Quantum cosmology (in D=4) • t < 0,00…001 sec • Many competing approaches • No data • Sociological + ideological aspects + blogs … • Nevertheless: some insight crystalizes: absolute space-time foliation, as indicated by observations of CMB, may be essential („there is no Lorentz trafo of BB“ or „local and global come together“)

38. Loop quantum gravity Ashtekar, Rovelli, Smolin, Thiemann, … Discrete space-time structure important in high-energy regimes, but not necessarily just at the Planck scale. Use universe as microscope. Propagation at high energies: Dispersion relations from effective equations including quantum space-time structure. Possible implications for observations of Gamma Ray Bursts

40. M. Bojowald

41. Lifshitz-like anisotropic scalingat high energies (at BB) Hořava-Lifshitz gravity in D=4 from physics of condensed matter Because of this, we do not have 4-d diffeomorphism invariance. foliation preserving diffeomorphism At highenergies, the graviton propagator is dominated by the anisotropic term Z = 3

42. P. Hořava … we adopt the perspective that Lorentz symmetry should appear as an emergent symmetry at long distances, but can be fundamentally absent at high energies. R. Brandenberger, … if Hořava-Lifshitz cosmology leads to a cosmological bounce, then it is not necessary to invoke a period of inflationary expansion to produce the observed spectrum of cosmological perturbations.

43. My opinion: Learn to properly renormalize the initial singularity in GR instead of inventing new universes

45. The Universe from ScratchJ. Ambjørn, J. Jurkiewicz and R. Loll Causal dynamical triangulation (CDT) = dynamical lattice approach

46. Instead of a conclusion: Weirdness of BB should not hide the fact that fort > 0,000 1 Gy simplified ΛCDM model is reliable on cosmological scales (above the scales of inhomogeneities). It should be teached in general physics courses and made familiar to a broad public, like revolution of planets around the Sun. „Elementary cosmological dynamics“

47. ΛCDM model of our Universe Assumptions on cosmological scales: • Observable Universe is („cosmological principle“) homogeneous and isotropic (2) CMB((1) → isotropic, observable everywhere) (3) Expanding space is flat (4) Simplified GR eq. of motion for a(t) (5) Evolution of a(t) is determined (t> 0.000 1Gy) by - cold dark matter (CDM) (dominates earlier epoch) - cosmological constant Λ(dominates later epoch)

48. (1)-(5) → Eq. of motion for a(t) • Conveniently reparameterized form:

49. Exact solution Applicable during 99.999% of the age of our Universe Small t: Larget:

50. (1) → Hubble law • Recessionvelocity of distant points Thus linear dependence on the distance at fixedt