Astronomy and Astrophysics
Featuring three original articles on general relativity and current topics of interest in cosmology.
An Undergraduate Review of General Relativity and Cosmology
Author: Andrew Valentini
Abstract: General relativity is a subject that has too far-reaching of conclusions about the nature of reality and our universe to be only understood by specialists. If a non-specialist wishes to understand the theory without having to spend months or years studying it, they are often forced to resort to popular science articles that do not provide the theory's full depth and often simplify its details to the point of misrepresentation. In this report, I provide an introduction to general relativity at the undergraduate level that provides more insight into the theory than popular science treatments but does not utilize the level of rigor that is typically encountered in graduate-level treatments. I first give a justification for the hallmark of general relativity, the Einstein field equations, then show how they can be applied to describe a class of universes, and end by briefly reviewing the experimental results that confirm theoretical predictions made by these cosmological models. The intention of this report is not to properly educate a reader on general relativity and cosmology but to expose them to the basic theoretical structure of the matter and should serve as a starting point for the curious reader.
An introductory review of gravitational physics
Author: Kaitlyn Prokup
Abstract: Gravitational physics is a field that centers around analyzing the physical implications and theoretical consequences of Einstein’s theory of general relativity. For decades, gravitational physics was a niche field restricted to mostly theoretical conjecture and mathematical investigations. However, in the past few years, the detection of significant gravitational phenomena has caused gravitational physics to grow into a high-interest field with a multitude of subfields and applications in both theoretical and experimental realms. With the ability to now utilize data to test long-standing theories and motivate the development of new ones, as well as merge the study of gravitational physics with other areas of cosmology, it is clear we are entering a new age of gravity. As such, it is worthwhile to provide an accessible introduction to the field of gravitational physics to give insight into its rising relevance. This paper serves as a preliminary review of gravitational physics, beginning with the basic concept and ideas of general relativity and discussing some of the more prominent subfields of gravitational physics, such as alternate gravity theory, gravitational wave astronomy, and quantum gravity. We address the motivations behind alternative and modified theories of gravity and explain some of the most prevalent gravity theories, f(R) gravity and Moffat’s Scalar-Tensor-Vector gravity. We also discuss the existence of gravitational waves and some of the exciting prospects posed by gravitational waves astronomy. In addition, we examine the recent detection of a gravitational wave background by the North American Nanohertz Observatory for Gravitational Waves and the computation of the Hubble constant through gravitational wave data. We conclude by briefly assessing string theory and loop quantum gravity, the two most prominent theories in quantum gravity.
A crisis in cosmology? An overview of disagreements in the Hubble constant
Author: Riley H. Johnson
Abstract: Over recent years, a disagreement has emerged between the ways of measuring the Hubble constant. This constant describes the expansion rate of the universe and is critical in estimating its age. To determine the Hubble constant we use the relation between a measured distance, along with a velocity from a measured redshift of the light. This literature review seeks to provide a brief history of the constant, an overview of processes for measuring cosmological distances to calculate the Hubble constant, and present proposed solutions to the emerging "Hubble tension."