Physics Colloquium 29th January 2016 delivered by Professor Per Helender The Princeton astrophysicist Lyman Spitzer famously figured out how a magnetic field can be used to confine a fully ionised plasma in steady state. His solution, the so-called stellarator, involves a counter-intuitive twisting of the field without employing an electric current, and is mathematically related to the Berry phase in quantum mechanics. Six decades later, Spitzer’s idea is put to a billion-euro test in the Wendelstein 7-X experiment of the Max Planck Society. This talk will describe some basic physics and mathematics underpinning stellarators, including the use of “hidden symmetries” to improve plasma confinement. An overview will also be given of Wendelstein 7-X, which after a decade of construction has just started operation. If successful, it should produce steady-state plasmas under conditions suitable for extrapolation to a fusion reactor. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/

Physics Colloquium 12th February 2016 delivered by Professor Mark Newman Many systems of interest in science and engineering can be represented as networks: the internet, the power grid, transport networks, metabolic networks, ecological networks and social networks are just a few of the many well studied examples. The structure of these networks has deep implications for the behaviour of the systems they represent (for traffic flow on the internet, for instance, or the spread of a disease over a human social network). Their structure is complex and we need new tools to help make sense of it. Physics, perhaps surprisingly, has proved a rich source of such tools. This talk will introduce some of the fundamental ideas in this growing field. It will also demonstrate how techniques borrowed from quantum and statistical physics are helping us to understand a wide range of networked systems. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/

The Scientific Legacy of Dick Dalitz On February 11 2016, the weekly seminar of the Particle Theory Group in the Rudolf Peierls Centre for Theoretical Physics was devoted to a celebration of the work of Richard H Dalitz FRS (1925-2006) who founded the group in 1963. His distinguished ex-students Frank Close (DPhil 1969) and Sir Christopher Llewellyn-Smith FRS (DPhil 1971) gave accounts of the seminal contributions Dick made to our understanding of the fundamental structure of matter. The talks were enlivened with personal reminiscences and are being made available on-line especially for the many alumni who could not come to the event. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/

Physics Colloquium 5th February 2016 delivered by Professor Alán Aspuru-Guzik Quantum computers promise the numerically exact simulation of molecules and materials. Furthermore, they are amongst the algorithms that have the lowest resource requirements for surpassing the power of classical computers. In this talk, I will briefly introduce the basic concepts of quantum computing and quantum simulation. Then, I will review the recent rapid progress in developing more efficient algorithms that have been achieved by many researchers in the field including our research group. I will describe the families of available algorithms (phase estimation, adiabatic and variational quantum eigensolver approaches) as well as the status of several experimental implementations of them either carried out or underway. These implementations span most of the currently available quantum architectures including quantum optics, ion traps, NV centers and superconducting quantum bits. I will provide a prelude of the relevance of these applications to society and will conclude with the prospects of the field.

Members of the Rudolf Peierls Centre for Theoretical Physics hosted the 3rd morning of Theoretical Physics covering the subject of Inner Space Meets Outer Space: Covering the Connections Between Cosmology and Particle Physics

The 2015 Hintze Biannual Lecture delivered by Professor Meg Urry Using multi-wavelength surveys, we measure the growth of supermassive black holes at the centres of galaxies over the last 12 billion years. Most actively growing black holes are heavily obscured and not seen in large optical surveys; at the same time, the deep multi-wavelength surveys too little of the sky to find rare objects like luminous quasars. So completing the census of black hole growth requires a large-volume X-ray survey, to explore hidden, high luminosity and distant black holes. Theorists have suggested that mergers of gas-rich galaxies trigger Active Galactic Nuclei (AGN), whose radiation and outflows may quench star formation and strongly affect galaxy evolution. Our morphological analyses show that mergers probably do trigger luminous quasars but not the far more numerous moderate-luminosity AGN, which grow slowly through secular processes.

Physics Colloquium 20th November 2015 delivered by Professor Tom Ray This year marks the centenary of Einstein’s General Theory of Relativity. As is well known, physicists became convinced that Einstein was right after Eddington’s and Dyson’s famous expedition to measure the gravitational deflection of starlight. Recently the speaker has found the equipment that proved critical in testing Einstein’s theory after it being lost for almost 70 years. Remarkably its discovery has led to the finding that earlier eclipse data may have been conveniently ignored. The finger of suspicion points at Sir Frank Dyson, the Astronomer Royal, who was trying to protect Eddington from being conscripted into the British Army during World War I.

Physics Colloquium 30th October 2015 delivered by Professer Paul Ginsparg Over twenty-five years into the internet era, over twenty years into the WorldWideWeb era, fifteen years into the Google era, and a few years past the Facebook/Twitter era, we’ve yet to converge on a new long-term methodology for scholarly research communication. I will provide a sociological overview of our current metastable state, and then a technical discussion of the practical implications of literature and usage data considered as computable objects, using arXiv as exemplar. From the physics standpoint, there is a surprising amount of statistical mechanics in text-mining and machine learning.

Physics Colloquium 23rd October 2015 delivered by Professor Myles Allen Physics is the foundation of current concerns about climate change, but climate policy sometimes appears like a baroque superstructure built with little reference to the foundations. For example, global temperatures depend on the accumulated stock of carbon dioxide emissions released into the atmosphere over all time, not the flow of emissions in any given year, but climate policy remains overwhelmingly pre-occupied with emission flows, not carbon stocks. Michal Kalecki once called economics “the science of confusing stocks with flows”, and while this is probably unfair on economics, it isn’t a bad characterisation of UN climate negotiations. As physicists, we are professionally concerned with the complexities of the climate system, so it may come as something of a shock to learn that many of the numbers that really matter for major policy decisions, like deciding on the right combination of prices and regulations to reduce greenhouse gas emissions or the “social cost of carbon” to use in evaluating investments, depend on models that are astonishingly simple compared to models of the general circulation of the atmosphere and oceans. I will introduce some of the ideas behind these ‘Integrated Assessment Models’ and show how, even though the units may be PetaDollars rather than ExaJoules, our basic physical intuition can be used to understand how they behave, and how they can give some rather surprising results. This talk should be accessible to anyone interested in the climate problem, and won’t assume any prior knowledge of either climate physics or economics. There will be some maths, but I’ll explain what I’m up to as I go along. Both physicists and economists welcome, to heckle the speaker or each other as they see fit.

The 2015 Halley Lecture delivered by Professor Peter J. Webster Each year the monsoons bring rainfall to nearly half the population of the planet. Small variations in monsoon rainfall can lead to flood or drought, feast or famine. Therefore, explaining the physics driving the monsoon and turning this knowledge into predictions is one of the great problems in science. In 1686 Sir Edmund Halley, with trade and navigation on his mind, suggested that the monsoon was driven by the buoyancy induced by the differential heating between the Indian Ocean and the landmass of South Asia. With a few embellishments, such as noting the importance of the rotation of Earth, his theory has stood the test of time. However, during the last 20 years, advances in our understanding of global fluid dynamics, suggest that a land-sea heating contrast is not sufficient. In fact, at the same latitudes of maximum monsoon summer rainfall, in other parts of the world there are deserts. Here we will develop an alternative, albeit simple, general theory of the monsoons and discuss how this may be translated into useful predictions and a greater understanding of how the monsoons will fair in a changing climate.