Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
This paper has two aims. The first is to improve upon the diverse and often muddled philosophical characterizations of emergence by articulating reasonably precise necessary and sufficient conditions for a phenomenon to count as emergent in physics. Central to this account of emergence is the idea that emergent phenomena cannot be explained reductively. The second aim of the paper is to apply this account to the use of effective field theories in gravitational physics.
Prominent philosophers of physics, including Craig Callender and John Earman, have issued stern warnings against drawing any foundations of physics conclusions from theories obtained by taking the thermodynamic limit. Without dismissing these worries entirely, I argue that we shouldn't take them too seriously.
At the level of effective field theory it is possible to establish analogies between non-gravitational and gravitational systems. For example, first order perturbation equations in an analogue gravity model can be written as a wave equation in a curved spacetime. Perhaps the most intriguing application of analogue gravity systems is the possibility to experimentally investigate open questions in semi-classical quantum gravity, such as the black hole evaporation process. I will briefly discuss our recent black hole experiment, which demonstrates the universality of the Hawking process.
The concepts of emergence and analogy are very closely related -- A is like B vs A is B. I will discuss this in the context of the emergence of/analogy with Hwking radiation in the arena of fluid systems, and the possibility of doing experiments in the lab. Does this mean gravity is emergent from some aether like theory? I think attempts to do that are fraught with difficulties, and will briefly discuss why I think so.
It is widely held that string theory shows that spacetime geometry and topology are emergent rather than fundamental. Often it is said that this follows from the various interesting dualities that exist within string theory. I will discuss the argument from duality, contrasting it with older arguments for the non-objectivity of spatiotemporal topology. I hope that this will clarify some questions about the role of spacetime in string theory---and about the differences between the ways that philosophers and physicists approach these questions.
Our ability to understand the physical world has to a large extent depended on the existence of emergent properties, and the separation of scales that permits effective field theory descriptions to be useful. Exploiting this fact, we can construct minimal models that enable efficient calculation of desired quantities, as long as they are insensitive to microscopic details. This works in many instances in physics, and I give some examples drawn from the kinetics of phase transitions mediated by topological defects.
We provide a microscopic understanding of the nucleation of topological quantum liquids that arise due to interactions between non-Abelian anyons. With the pairwise anyon interactions typically showing RKKY-type oscillations in sign, but decaying exponentially with distance, we show that the character of the nucleated phase is fully determined by anyon interactions beyond nearest neighbor exchange. We investigate this issue in the context of Kitaev's honeycomb lattice model.
It is usually assumed that the quantum wave-particle duality can have no counterpart in classical physics. We were driven into revisiting this question when we found that a droplet bouncing on a vibrated bath could couple to the surface wave it excites. It thus becomes a self-propelled "walker", a symbiotic object formed by the droplet and its associated wave.
This talk considers the extent to which the intertheoretic relation between an EFT and its (possibly hypothetical) high-energy theory supports a notion of emergence. When a high-energy theory exists, this relation is based on a process that involves the elimination of high-energy degrees of freedom. This elimination results in an EFT that formally bears little resemblance to the high-energy theory. I investigate the extent to which this lack of formal resemblance underwrites notions of novelty and autonomy that may be appropriately associated with emergence.
In the philosophical literature, effective field theories have been regarded as emergent in the sense of furnishing novel explanations. In particular, Batterman has argued that effective field theories in statistical mechanics are emergent in this sense. I will argue that effective field theories in quantum field theory do not furnish analogous novel explanations. There are relevant disanalogies between statistical mechanics and quantum field theory with regard to the roles played by idealizations and the explanatory goals of the application of renormalization group methods.