Colloquia Archive 2019

Long-range translational order is forbidden in low dimensional systems with short-range interactions: solid phases only have quasi long-range translational order. A mechanism for the transition from solid to liquid led by the dissociation of dislocation pairs was proposed by Kosterlitz & Thouless in their 1972 & 1973 Nobel prize papers ...

The last decade has witnessed unprecedented advances in the observational characterisation of protoplanetary discs and their nascent planetary systems, thanks in large part to the transformative capabilities of ALMA (the Atacama Large Millimetre Array). In the first part of my talk I will describe how the relatively simple physics governing ...

Abstract: Modern inflationary cosmology avoids the shortcomings of the old hot big bang model by making crucial use of quantum phenomena occurring during inflation as well as at its end. This simple fact entails a drastic revision of the traditional view identifying the big bang and the beginning of time ...

Galaxies are the fundamental building blocks of the Universe. Gas-rich spiral disk galaxies are the cosmic islands where stars and planets form and where the chemical buildings blocks of life are generated. However, despite their importance, we are still far from a detailed understanding of their structure and the processes ...

I will discuss how the first image of a black hole was recently obtained by the Event Horizon Telescope collaboration. In particular, I will describe how modelling the dynamics of the plasma accreting onto the black hole with super-computers using millions of compute hours was essential to generate synthetic black-hole ...

Abstract: Many animal aggregations display collective patterns on the large scale, ultimately due to the interactions between the individuals in the group. Recent findings on flocks of birds and swarms of insects show that these groups exhibit strong mutual correlations and quick mechanisms of information propagation, signatures of the efficient ...

Abstract: A new class of time-energy uncertainty relations is directly derived from the Schroedinger equations for time-dependent Hamiltonian H(t). Only the initial states and the Hamiltonians are required for our time-energy relations, with no requirement of a full solution for a time-dependent Hamiltonian. The general relations we find could ...

Abstract: Feynman's path integral provides an elegant formulation of quantum physics, particularly suited to theories with continuous symmetries, like gauge theories and general relativity. However, it has proven difficult to rigorously define path integrals without first performing a Wick rotation to Euclidean time. Unfortunately, this significantly compromises the study ...

Abstract: The most important question of our time is whether, and how, we will be able to run our planet sustainably. Answering this question requires a deep understanding of the earth system, a vast non-equilibrium system which abounds with different active-matter susbsystems. Two of them are within the focus of ...

ABSTRACT: Gravity is intrinsically different from other physical forces. Gravity is geometry. This raises the fundamental question: how does geometry emerge from a quantum theory? Black holes have inspired revolutionary ideas to attack this question, with one impressive outcome being the holographic principle. In this talk I will review how ...

Abstract: Shared histories lead to strong correlations. Thus, particles which find themselves in the same evolving environment have a tendency to cluster and approach an interesting state. This talk is about such states, their scaling properties, and how they develop in time. A key signature is that the scaled correlation ...

Abstract: Quantum field theory is the modern manifestation of "force equals mass times acceleration": it is the underlying, mathematical framework in which understand and describe physical laws today—from the most fundamental to the merely effective or approximate. Quantum field theory is the modern manifestation of "force equals mass times ...

Small quantum computers are now a reality. They provide the instrument to test new ways to process information using quantum logic. We analyze novel ideas to build hybrid quantum algorithms that combine machine learning with quantum circuits. In particular, variational methods open the possibility of dealing with non-trivial optimization problems ...

One of our greatest challenges in cosmology is understanding the origin of the structure of the universe, and in particular the formation of the galaxies. I will describe how the fossil radiation from the beginning of the universe, the cosmic microwave background, has provided a window for probing the initial ...

Ever since the dawn of time people have (literally) asked the question -- what is the most effective way to grill food? Timing is everything, since only one surface is exposed to heat at a given time. Should we flip only once, or many times? I will show a simple model ...

Abstract: General Relativity (GR) is immensely successful. With the late discovery of gravitational waves from black hole and neutron star mergers, it has passed all the tests with flying colors. But so far, observations have mainly tested the vacuum equations of GR. The most important non-vacuum case, cosmology, is in ...

The recent direct detection of gravitational waves marks the beginning of a new era for physics and astronomy with an opportunity the probe gravity at its most fundamental level. I will discuss how the behaviour of gravity on large scales may differ from General Relativity and its implications for early ...

Abstract: Certain Quantum Many-body states can be efficiently described in terms of tensor networks. Those include Matrix Product States (MPS), Projected Entangled-Pair Etates (PEPS), or the Multi-scale Entanglement Renormalization Ansatz (MERA). They play an important role in quantum computing, error correction, or the description of topological order in condensed matter ...

Quantum gravity is the name of a problem, not a theory. The problem is that we do not have a unified framework for fundamental physics in which both gravity and quantum theory are incorporated. Causal Set Theory is an approach to the problem based on the hypothesis that spacetime is ...