Abstract Details
| Name: Abhisek Swain Affiliation: Indian Institute of Science Education and Research Bhopal Conference ID: ASI2025_584 Title : The end of the End of Greatness: Exploring the scale of homogeneity of our Universe Authors and Co-Authors : Abhisek Swain1, Rajib Saha2 Abstract Type : Poster Abstract Category : Galaxies and Cosmology Abstract : The Cosmological Principle serves as a foundational concept in modern cosmology, shaping our understanding of the universe's structure and evolution. This principle asserts that, on large scales, the universe is isotropic and homogeneous. Homogeneity entails that the universe appears uniform when observed on sufficiently large scales, whereas isotropy implies that it looks the same in all directions from any given point. We placed constraints on the size of the largest possible scale of homogeneity in our universe. Specifically, we found a lower bound for the largest homogeneous patch in which our observable universe resides. A large-amplitude inhomogeneity on that scale would manifest itself as temperature fluctuations on the CMB sky map and would thus have a contribution in the temperature anisotropy power spectrum via the Grishchuk-Zel'dovich effect. The GZ effect is the contribution of an extremely large scale adiabatic density disturbance to the anisotropy of the microwave background. By setting a condition that the contribution to the quadrupole from the GZ effect cannot be greater than the WMAP upper limit on the quadrupole value, we can place constraints on the size of this inhomogeneity. We employed two models to describe large amplitude peaks in the primordial power spectrum, yielding two distinct lower bounds. For a delta peak function, we obtained L_(GZ)>2727L_0, where L_(GZ) and L_0 represent the size of the homogeneous patch and the current particle horizon, respectively, considering the Integrated Sachs-Wolfe effect. For the second model, which physically translates to a universe that is inhomogeneous and anisotropic when observed within a spherical shell of scale length between L_2 and L_1, we found L_2=L_(GZ), extending to 2196 times the observable universe, assuming L_1 approaches infinity. |