Hawking Building the Future of Cosmological Weak Lensing

This research seeks answers to some of the biggest questions in the Universe. How did it all begin? How long ago? And what will happen to our Universe in the future?

In order to solve these mysteries, we have to first answer another question: what is the Universe made of, on distance scales of billions of lightyears? The answer to this determines how we understand the past, present, and future evolution of our Universe. Indeed, if the Universe contains copious amounts of matter, which feels and generates the attractive force of gravity, then the expansion of the Universe will slow, potentially even grinding to a halt before collapsing. Alternatively, if the Universe contains a surplus of cosmic fuel powering its expansion - an energy source we call 'dark energy' - then the Universe could expand forever, getting faster all the time. The balance of these two cosmic components determines the Universe's fate, as well as its history.

Fortunately, it is possible to measure this balance using a technique called gravitational lensing. This is the phenomenon in which the light from distant galaxies, whilst travelling through the cosmos to our telescopes here on Earth, is deflected by the gravity of intervening matter. The deflection - or 'lensing' - causes the images of said galaxies to appear distorted, much like the image of a candle is distorted when viewed through a wineglass. The strength of the distortion, measured across millions of galaxies, allows us to estimate how much matter exists between those galaxies and us (more distortion = more matter). This technique is especially powerful as it allows to indirectly measure the abundance of dark matter, a mysterious matter source which bends the light's path in the same way as ordinary matter, but is rendered invisible by virtue of the fact it does not emit, scatter or reflect electromagnetic radiation.

This project will improve how precisely we can measure the abundance of matter in the Universe with gravitational lensing. This will be achieved by using computer simulations of gravitational lensing to make maps of the matter distribution across the sky. Artificial intelligence (AI) will be trained on the simulated maps, and then used to estimate the abundance of matter in the real Universe from observational data.

Another key question this research hopes to solve is whether we have an accurate understanding of how gravity works on distances of billions of lightyears. As our observations of the Universe have improved over time, our understanding of gravity has evolved, from the theories of Isaac Newton, to Albert Einstein's General Relativity. It could be possible that over cosmic distance scales, gravity behaves according to an as-of-yet unknown theory.

To shed light on this, my research develops a framework in which alternative models of gravity can easily be investigated using only computer simulations of Einstein's gravity. This make it much simpler to check how our observations of the Universe would vary if the laws of gravity were different. We can then look for these observational signatures in the real Universe to diagnose whether Einstein's theory, or some other model, reigns supreme when it comes to the Universe as a whole.

The final objective of my research is to ensure that a brand new survey beginning in 2023, produces sufficiently clear images of galaxies in order to measure their gravitational lensing. Many things can distort astronomical images, from defects in the camera, the structure of the telescope, and to turbulence in Earth's atmosphere. I will confirm that this is a small effect, so that we can trust the upcoming gravitational lensing science results.