Black Hole Universe: An Alternate Model for Expansion of the Universe

Pradhan, Swaraj (2024) Black Hole Universe: An Alternate Model for Expansion of the Universe. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Swaraj Pradhan (19MS063)) 19MS063.pdf - Submitted Version Restricted to Repository staff only Download (3MB)

Abstract

Despite the success of the standard ΛCDM model in fitting observational data with only six parameters, it has problems accounting for a number of open questions in cosmology. Its main weakness is the requirement for the ad hoc introduction of inflation, dark matter, and dark energy, which are yet to be understood. The cosmological constant added by Einstein to his GR field equations to achieve a static universe by counterbalancing the gravitational force was re-interpreted as vacuum energy. The cosmic acceleration is assumed to be due to dark energy, which is attributed to this so-called Λ term in the standard model. However, there is no direct evidence for dark energy, dark matter and inflation. Here, we present an alternate model which overcomes some of the shortcomings related to the aforementioned concepts. Our model proposes that cosmic acceleration results from a “Big Bounce” of Matter inside a black hole that creates our universe, and the dynamics inside the black hole induce a Λ term to Einstein’s field equations. To investigate this alternative scenario, we study the cold collapse of a very large, low-density, uniform cloud of matter under its own gravity. In the first step, we perform numerical simulations to study the collapse for values of w (where w comes from the equation of state p = wρ) lower than 1/3 approaching 0. These simulations are performed using the SPriBHoS (Spectral Primordial Black Hole Simulator) code. For the trivial case of dust, the collapse into a black hole is inevitable since there is no pressure to balance the gravitational pull. We show that this particular case (p = 0) has an exact Newtonian solution. With this simplification, we simulate BH formation with a Newtonian code (CASTRO). CASTRO is a hydrodynamic code designed to model astrophysical flows using a second-order finitevolume scheme. Using CASTRO with a polytropic equation of state to roughly mimic the unknown behaviour of cold matter at supranuclear densities, we investigate the possibility of the bounce back of accumulated matter. We study the mechanism of this bounce back and the conditions it requires. This “Big Bounce” has the potential to leverage some of the problems of cosmic expansion without needing inflation, dark energy and the complex concept of the Big Bang singularity.

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