Why is Quantum Gravity so hard?

The spaghettification of stars by supermassive black holes: understanding one of nature’s most extreme events - Andrew Mummery On a rare occasion an unfortunate star will be perturbed onto a near-radial orbit about the supermassive black hole in its galactic centre. Upon venturing too close to the black hole the star is destroyed, in its entirety, by the black hole’s gravitational tidal force, a process known as “spaghettification”. Some of the stellar debris subsequently accretes onto the black hole, powering bright flares which are observable at cosmological distances. In this talk I will discuss recent theoretical developments which allow us to describe the observed emission from these extreme events in detail, allowing them to be used as probes of the black holes at their centre. I am a Leverhulme-Peierls Fellow in the Department of Physics and Merton College. I completed both my undergraduate degree and DPhil at Oxford, working for my DPhil in the astrophysics department under the supervision of Steven Balbus. I work on astrophysical fluid dynamics, with a particular focus on the behaviour of fluids when they are very close to black holes.

Extreme value statistics and the theory of rare events - Francesco Mori Rare extreme events tend to play a major role in a wide range of contexts, from finance to climate. Hence, understanding their statistical properties is a relevant task, which opens the way to many applications. In this talk, I will first introduce extreme value statistics and how this theory allows to identify universal features of rare events. I will then present recent results on the extreme values of stochastic processes, including Brownian motion and active particles. I moved to Oxford in October 2022 to take the position of Leverhulme-Peierls Fellow at the Department of Physics and New College. Previously, I was a PhD student at Paris-Saclay University, working with Satya Majumdar. During my PhD, I worked on extreme value statistics of stochastic processes. I am interested in out-of-equilibrium physics, extreme value theory, and large-deviation theory. In particular, I am currently applying ideas from statistical physics to study living systems.

Inflation and the Very Early Universe - Georges Obied The universe we observe seems to have come from surprisingly fine-tuned initial conditions. This observation is at the heart of two of the most important puzzles in cosmology, called the horizon and flatness problems. To explain these puzzles, cosmologists invoke a period of accelerated expansion in the early universe (called inflation). As a bonus inflation, when considered with quantum mechanics, produces fluctuations in the energy density that become the galaxies, planets and other structures we see around us. In this talk, I will explain the motivation and physics of the inflationary paradigm. I am Leverhulme-Peierls Fellow at New College. Before coming to Oxford, I completed my PhD at Harvard University under the supervision of Prof. Cumrun Vafa. My research interests lie at the interface of particle physics, string theory and cosmology. At this junction, I work on various aspects of dark energy, dark matter and early universe cosmology from a fundamental physics point of view.

Will strings be the theory of everything?, presented by Prof Luis Fernando Alday.

Prof March-Russell explains our latest understanding of black holes, some of the most mysterious objects in the Universe.

A pressing question in our quest to understand the Universe is how to unify quantum mechanics and gravity, the very small and the very large.

The power of available computers has now grown exponentially for many decades. The ability to discover numerically the implications of equations and models has opened our eyes to previously hidden aspects of physics. Many exciting phenomena observed in condensed matter systems, such as superconductivity and the quantum Hall effect, emerge due to the quantum mechanical interplay of many electrons. The laws of quantum physics are governed by the Schrödinger equation, whose complexity grows exponentially with the number of particles it describes. Hence, even an approximate numerical solution of the Schrödinger equation is impossible for only just a few particles, not to mention for the millions of particles that are present in real materials. This talk focuses on a new approximation scheme in terms of so-called Tensor Network States, which allow for an arbitrarily accurate description of realistic quantum solid state systems at merely a polynomial overhead in the particle number, thus enabling efficient simulations of such systems on today's computers.

The power of available computers has now grown exponentially for many decades. The ability to discover numerically the implications of equations and models has opened our eyes to previously hidden aspects of physics. In physics, "complex systems" are systems of many similar interacting parts, such as the interacting atoms that make up a solid or liquid, but also interacting organisms in an ecosystem, or interacting traders in the stock market. This lecture will discuss how recent advances in modeling and computer simulation have allowed us to apply physics-style approaches to these previously challenging real-world systems to learn about such things as the spread of diseases, the flow of traffic or the structure of entire human societies.

The power of available computers has now grown exponentially for many decades. The ability to discover numerically the implications of equations and models has opened our eyes to previously hidden aspects of physics. In this lecture, Myles Allen addressed how computers have transformed our understanding of the role of chaos and exponential error growth in weather forecasting; and our understanding of how climate change is impacting regional weather. He showed how research in Oxford Physics, made possible by high-end computing, is demonstrating the crucial role of eddies in controlling ocean climate; and how the probability of extreme weather events may respond to rising greenhouse gas concentrations. He concluded by throwing out a more controversial suggestion that super-computers haven’t really contributed very much to the problem of predicting century-timescale changes in global average temperature, however much they may have contributed to understanding the regional implications of large-scale warming.

Members of the Rudolf Peierls Centre for Theoretical Physics hosted the eighth Saturday Morning of Theoretical Physics on 19 September 2015. Talk 3 by Professor James Binney.