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Artwork for Theoretical Physics - From Outer Space to Plasma
Education

Theoretical Physics - From Outer Space to Plasma

Oxford University

Learn about quantum mechanics, black holes, dark matter, plasma, particle accelerators, the Large Hadron Collider and other key Theoretical Physics topics. The Rudolf Peierls Centre for Theoretical Physics holds morning sessions consisting of three talks, pitched to explain an area of our research to an audience familiar with physics at about second-year undergraduate level.

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  • 97 episodes
  • Updated May 7, 2025

Episodes97

Newest first
  • May 16, 2019 · 36 min

    From protons to collisions…

    We learn about the Higgs Boson and its interactions at the LHC by examining the debris produced by colliding protons head-on at unprecedented high energies. However, we know from our theory of strong interactions - quantum chromodynamics (QCD) - that protons themselves are highly complex bound states of more fundamental 'quarks', held together by the force carriers of QCD, the 'gluons'. The question is then: how do we go from the collision of these complicated protons to a theoretical prediction that we can use to test the properties of the Higgs boson itself? In this talk, I will discuss what we know about the proton, and how we apply this to LHC collisions and our understanding of the Higgs sector.

  • May 16, 2019 · 44 min

    What the Large Hadron Collider is telling us about the Higgs sector and its new interactions

    Over the past two years, CERN’s Large Hadron Collider (LHC) has started to directly probe a qualitatively new class of interactions, associated with the Higgs boson. These interactions, called Yukawa interactions, are unlike any other interaction that we have probed at the quantum level before. In particular, unlike the electromagnetic, weak and strong forces, they have an interaction strength that does not come in multiples of some underlying unit charge. Yukawa interactions are believed to be of fundamental importance to the world as we know it, hypothesised, for example, to be responsible for the stability of the proton, and so the universe and life as we know it.

  • Feb 15, 2019 · 38 min

    Why the world is simple - Prof Ard Louis

    The coding theorem from algorithmic information theory (AIT) - which should be much more widely taught in Physics! - suggests that many processes in nature may be highly biased towards simple outputs. Here simple means highly compressible, or more formally, outputs with relatively lower Kolmogorov complexity. I will explore applications to biological evolution, where the coding theorem implies an exponential bias towards outcomes with higher symmetry, and to deep learning neural networks, where the coding theorem predicts an Occam's razor like bias that may explain why these highly overparamterised systems work so well.

  • Feb 15, 2019 · 38 min

    Topology in Biology - Prof Julia Yeomans FRS

    Active systems, from cells and bacteria to flocks of birds, harvest chemical energy which they use to move and to control the complex processes needed for life. A goal of biophysicists is to construct new physical theories to understand these living systems, which operate far from equilibrium. Topological defects are key to the behaviour of certain dense active systems and, surprisingly, there is increasing evidence that they may play a role in the biological functioning of bacterial and epithelial cells.

  • Dec 3, 2018 · 42 min

    Entropy from Entanglement

    Siddharth Parameswaran, Associate Professor, Physics Department. The usual picture of entropy in statistical mechanics is that it quantifies our degree of ignorance about a system. Recent advances in cooling and trapping atoms allow the preparation of quantum systems with many interacting particles isolated from any external environment. Textbook discussions of entropy — that invoke the presence of a “large” environment that brings the system to thermal equilibrium at a fixed temperature --- cannot apply to such systems. Sid Parameswaran will explain how “entropy” of subsystems of such isolated quantum systems arises from quantum entanglement between different parts of the system, and how their approach to thermal equilibrium is best described as the `scrambling’ of quantum information as it is transferred to non-local degrees of freedom.

  • Dec 3, 2018 · 39 min

    Entropy: two short stories

    John Chalker, Head of Theoretical Physics, gives a talk on entropy. Thermodynamics and statistical mechanics give us two alternative ways of thinking about entropy: in terms of heat flow, or in terms of the number of micro-states available to a system. John Chalker will describe a physical setting to illustrate each of these. By applying thermodynamics in a realm far beyond its origins, we can use the notion of an ideal heat engine to find the temperature of a black hole. And by applying combinatorial mathematics to hydrogen bonding, we can find the entropy of ice.

  • Dec 3, 2018 · 52 min

    Entropy: Gaining Knowledge by Admitting Ignorance

    Alexander Schekochihin, Professor of Theoretical Physics, gives a talk on entropy. When dealing with physical systems that contain many degrees of freedom, a researcher's most consequential realisation is of the enormous amount of detailed information about them that she does not have, and has no hope of obtaining. It turns out that this vast ignorance is not a curse but a blessing: by admitting ignorance and constructing a systematic way of making fair predictions about the system that rely only on the information that one has and on nothing else, one can get surprisingly far in describing the natural world. In an approach anticipated by Boltzmann and Gibbs and given mathematical foundation by Shannon, entropy emerges as a mathematical measure of our uncertainty about large systems and, paradoxically, a way to describe their likely behaviour—and even, some argue, the ultimate fate of the Universe. Alex Schekochihin will admit ignorance and attempt to impart some knowledge.

  • Jul 6, 2018 · 54 min

    The ultimate limits of privacy and randomness...for the paranoid ones

    This talk explains how qubits are used to represent numbers in a way that permits 'quantum-mechanical parallel' computing. We show how this can used to achieve fast factorisation of large numbers, and hence the breaking of current codes. We end by explaining how entangled pairs of particles can be used to provide an alternative and entirely secure cryptographic system.

  • Jul 6, 2018 · 47 min

    “Open” Quantum Systems

    This talk reviews how to deal with quantum systems that are coupled to the outside world, as in reality all systems are. We first introduce density operators and explain how quantum states give rise to them. We then turn to measures of entanglement that can be computed from a density operator, and show that entanglement grows with time. Finally, we show how the interaction with the environment gives rise to the phenomenon of decoherence.

  • Jul 6, 2018 · 40 min

    Quantum Systems from Group up

    This talk reviews the modern formulation of the basic ideas of quantum mechanics. We start by explaining what quantum amplitudes are, how they lead to the idea of a quantum state and how these states evolve in time. We then discuss what happens when a measurement is made before describing correlated ('entangled') systems. Applying these ideas to two-state systems ('qubits') we point out that the complexity of computing the evolution of an N qubit system grows like exp(N)

  • Jan 25, 2018 · 39 min

    Galaxy Dynamics: The chemical evolution side

    Dr Ralph Schoenrich will talk about the chemical evolution side Spiral density waves patterns re-distribute stars throughout the entire system, making it impossible to know a star's origin from just its kinematics. However, stars are more than just points in phase space: every star is labelled with the elemental abundances of the gas cloud from which it was formed. Over the last few years a number of observational campaigns have started to measure these labels for millions of stars in our own Galaxy's disc. Ralph Schoenrich will describe how chemodynamical models are being used to piece together the evolution of our Galactic environment from presolar times to the present.

  • Jan 25, 2018 · 44 min

    Galaxy Dynamics: The dynamics of galaxy discs

    Dr John Magorrian will talk about the dynamics of galaxy discs In galaxy discs it is energetically favourable for angular momentum to move outwards and mass to move inwards. This transportation is effected by spiral arms, but what causes them? Simple linear response calculations demonstrate that even the smallest perturbation is amplified manyfold, while the differential rotation of the disc means that the response is stretched out into a spiral-like pattern. John Magorrian will introduce the notion of the disc as a resonant cavity, within which spiral density perturbations rattle back and forth.

  • Jan 25, 2018 · 51 min

    Galaxy Dynamics: Stellar systems: a new state of matter

    Prof James Binney FRS will talk about stellar systems: a new state of matter The long range of gravity means that many concepts from undergraduate statistical mechanics do not apply: energy is not extensive; there is no microcanonical or canonical ensemble. Stars and dark matter particles have long mean free paths, which means that to a very good approximation their motion is determined by the mean-field gravitational potential. James Binney will identify a hierarchy of timescales, explaining how the Boltzmann equation for the full 6N-dimensional many-particle phase space distribution function can be reduced to an evolutionary equation of a function of a mere 3 variables that is governed by the resonances among the particles' orbital frequencies.

  • Nov 3, 2017 · 43 min

    Superfluids in Flatland: Topology, Defects, and the 2016 Nobel Prize

    In this talk, Siddharth Parameswaran discusses how a topological approach to 2D systems reveal that they can indeed become superfluid, and lead to surprising and beautiful universal results whose implications continue to resonate today. Superfluids spontaneously break a continuous symmetry linked to the conservation of particle number in a many-body system. Standard lore holds that such symmetries must remain unbroken at any temperature above absolute zero in a two-dimensional material, such as a thin sheet or film, apparently precluding superfluidity in such systems.

  • Nov 3, 2017 · 35 min

    Quantum mechanics on the human scale

    Stephen Blundell reviews a theory of superconductivity that was developed in Oxford in the 1930’s by Fritz London. The idea is that under certain conditions quantum coherent effects can become manifest on a large scale. In an effect such as superconductivity, this idea can be put to use in such applications as magnetic resonance imaging, in which a living human patient is inserted inside a quantum coherent wave function. He will explain how coherent effects can be measured in real superconductors.

  • Nov 3, 2017 · 46 min

    From Identical Particles to Frictionless Flow

    John Chalker discusses how the laws of quantum mechanics lead us from the microscopic world to macroscopic phenomena. The notion that atoms of a given isotope are indistinguishable has profound consequences in the quantum world. For liquids made of identical bosons, indistinguishability forces the particles into a quantum condensate at low temperature, where they all dance in perfect synchrony. Treated gently, such a condensate has no viscosity: once it is set in motion --say around a circular pipe -- flow will persist indefinitely (so long as the fluid is kept sufficiently cold!).