Speaker: Alex Brown
The theory of gravity is one of the most important theories in modern physics. It governs everything from the oceans’ tides to the large scale structure of our universe. Since 1915, when Einstein revolutionised our understanding of gravity, we have used his theory of general relativity to underpin mountains of research. But what if Einstein wasn’t right? What if general relativity is wrong? How would we know, and what would we do? This talk is a brief introduction to gravity theories beyond general relativity. I will discuss the extremely successful theory of general relativity as well as its alternatives: what they are, why we have them, and how we can test them.
Speaker: Jacob Osman Hjortlund
Type Ia supernovae (SNe Ia) have played a significant role in measuring the acceleration of the Universe’s expansion and the existence of dark energy. This is all made possible by the relatively uniform brightness of SNe Ia explosions, making it possible to use them as measures of cosmological distances. Although these events are instrumental in constraining cosmological parameters, we surprisingly enough have very little knowledge about the progenitor systems that lead to these explosions. Examples of such systems are star–white dwarf binaries and white dwarf–white dwarf binaries, the rates of which change over cosmological time. Can we be sure that such progenitor systems lead to exactly the same SNe Ia explosions? This known unknown may lead to systematic biases, impacting both current and future large-scale surveys aiming for percent-level precision constraints. In this talk, I will introduce you to the field of SNe Ia cosmology, including the current state-of-the-art results, issues and our proposed solution. I will present a novel two-population model of SNe Ia, that links cosmological measurements together with current work on SNe Ia progenitor systems. Using both simulations and the latest observations, we will explore what impact such unknown progenitor systems may have on cosmological constraints.