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Confirmation of the Copernican principle at Gpc radial scale and above

Confirmation of the Copernican principle at Gpc radial scale and above. 张鹏杰 Zhang, Pengjie 中科院上海天文台 Shanghai Astronomical Observatory. ZPJ and Stebbins, 2010. The standard cosmology. Initial condition: inflation Laws: General relativity+SM Ingredients:

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Confirmation of the Copernican principle at Gpc radial scale and above

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  1. Confirmation of the Copernican principleat Gpc radial scale and above 张鹏杰 Zhang, Pengjie 中科院上海天文台 Shanghai Astronomical Observatory ZPJ and Stebbins, 2010 9th Sino-German workshop, Hangzhou, 2011

  2. The standard cosmology • Initial condition: inflation • Laws: General relativity+SM • Ingredients: • Baryons, photons, etc.(SM particles) • Cold non-baryonic dark matter • Non-zero cosmological constant 9th Sino-German workshop, Hangzhou, 2011

  3. Foundation of modern cosmology • Cosmological Principle • Is our universe (statistically) homogeneous and isotropic? • CMB: The universe is (statistically) isotropic with respect to us. • Copernican principle: No special regions in the universe • The universe must be statistically homogeneous. • General relativity • Is GR valid at cosmological scales? • Gravity with infrared modification? • Is the standard simplification in treating GR cosmology valid? • Backreaction, metric-observable relations, etc. ? 9th Sino-German workshop, Hangzhou, 2011

  4. Non-Copernican universe consistent with CMB/galaxy distribution: the LTB universe • Lemaitre-Tolman-Bondi model • The universe is onion-like • Mass distribution is isotropic with respect to the center • But varies along the radial direction • We live near the center • Isotropic with respect to us (and only to us) 9th Sino-German workshop, Hangzhou, 2011

  5. Dark energy: mirage of gigantic void? In this inhomogeneous universe, type Ia supernovae can appear dimmer than in a FRW universe. No cosmic acceleration, No dark energy No modified gravity compensating shell Low density region （~Gpc void) background universe (higher density) Gravitational potential distance 9th Sino-German workshop, Hangzhou, 2011

  6. Testing the Copernican principle M(r), E(r),t_b(r) r • Type Ia supernovae, BAO, etc. • Suffers from a severe degeneracy problem • Galaxy distribution test • Uncertainties in galaxy evolution • New tests free of the above degeneracy • CMB non-blackbody test (Goodman 1995, Caldwell & Stebbins, 2008) • Cluster kinetic Sunyaev Zel'dovich (kSZ) effect test (Goodman 1995, Garcia-Bellido & Haugbolle 2008) • Diffuse kSZ background test (ZPJ 2010; ZPJ & Stebbins, 2010) 9th Sino-German workshop, Hangzhou, 2011

  7. The key to test the Copernican principle:Space travel to billion light years away to do observation 8 Gyr 4 Gyr the light cone effect 2 Gyr 1 Gyr 9th Sino-German workshop, Hangzhou, 2011

  8. Free electrons as mirrorsGoodman 1995; Caldwell & Stebbins, 2008 Compton scatterings allow us to sit at distant universe and judge whether CP holds consequence 1: CMB spectrum will be non-blackbody T1 e T2 T3 9th Sino-German workshop, Hangzhou, 2011

  9. 2008， PRL, arxiv:0711.3459 rules out many void models capable of replacing dark energy, but not all of them. Furthermore, ICS induces non-blackbody too. void density Void size 9th Sino-German workshop, Hangzhou, 2011

  10. Galaxy clusters (a bunch of electrons) as moving mirrors CMB frame Dust (matter) frame Violation of the Copernican principle prediction • Violation of CP causes relative motion between CMB and the matter comoving frame • Causes a large cluster kSZ effect In a homogeneous universe, no motion between the two rules out many void models capable of replacing dark energy, but not all of them observations Goodman 1995 9th Sino-German workshop, Hangzhou, 2011

  11. A more sensitive test: the anisotropic kinetic Sunyaev Zel'dovich effect ` CMB Anisotropic due to inhomogeneous electron distribution All free electrons contribute Up to the z~10 reionization ZPJ 2010 matter frame e X 9th Sino-German workshop, Hangzhou, 2011

  12. Void model predicts much larger kSZ than allowed by observations 13 uK^2(SPT)->8 uK^2 (ACT)->6.5 uK^2 (SPT) Allowed by kSZ observations Consistent with SN data l=3000 a few arcminute ZPJ & Stebbins 2010 9th Sino-German workshop, Hangzhou, 2011

  13. Testing the Copernican Principle • CMB and galaxy distribution are isotropic→ the metric is LTB • SN Ia→ Giant (~Gpc) void must exist in the center, if we do not resort to dark energy, modified gravity or GR backreaction. • The kSZ test rules out these void models. • Violations of the Copernican principle cause motions between CMB and matter frame • Typical velocity: 10,000 km/s • Such motion is modulated by electron density inhomogeneity and hence induces a first order anisotropic kSZ effect • The induce KSZ power spectrum is much larger than the existing ACT/SPT upper limit • Adiabatic void models are ruled out. • The Copernican principle at Gpc scales and above is confirmed. • Copernican principle+SN Ia: cosmic acceleration indeed exists! 9th Sino-German workshop, Hangzhou, 2011

  14. When shall we resort to Occam's razor? 9th Sino-German workshop, Hangzhou, 2011

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