Is the observable Universe inside a black hole? We begin by developing this hypothesis (previously proposed by R.K. Pathria in 1972 and subsequently explored by Stuckey in 1994 and by Poplawski in 2010) by recalling the Schwarzschild metric and stating postulates regarding physical space. We then present the River model of Black Holes by astrophysicist Andrew J. S. Hamilton. We then propose a mathematical expression based on an analogy between the FLWR and Kerr metrics, linking the scale factor a(t) of our universe to the black hole rotation parameter aK(t). We then show that the observable universe could be inside a black hole by interpreting the spectrum of angular anisotropies of the CMB based on this hypothesis. Finally, we show that the observable Universe could be all or part of a black hole by analyzing the relationships between the universal constants c, G, h, and Λ—which may be the “ingredients” of gravity—that make up the gravitational coupling constant, which is itself the mass of the cosmic black hole divided by the mass of the hypothetical graviton.
Thomas CLAPIES (Sun,) studied this question.