Search Talks

How sure are you that spacetime is continuous? One approach to quantum gravity, causal set theory, models spacetime as a discrete structure: a causal set. This talk begins with a brief introduction to causal sets, then describes a new approach to modelling a quantum scalar field on a causal set. We obtain the Feynman propagator for the field by a novel procedure starting with the Pauli-Jordan commutation function. The candidate Feynman propagator is shown to agree with the continuum result. This model opens the door to physical predictions for scalar matter on a causal set.

We review some recent results on tachyon nonperturbative solutions of the nonlocal, lowest-level, effective action of string field theory. It is shown how nonlocality is encoded in a spacetime diffusion equation and how the latter emerges from the symmteries of the full, background-independent theory.

In 1981 Bill Unruh showed that the equation of motion for sound waves in a convergent fluid flows is given by a wave equation in an acoustic metric geometry. More importantly it is possible to set up sonic horizons in transsonic flows, and thus in principle to mimic experimentally the black-hole evaporation process. Almost 30 years later we have set up an experiment at the University of British Columbia to find out if indeed it is possible to detect (traces of) black hole radiation. We will discuss the necessary theoretical milestones, such as the effective field theory description for water to explore the robustness of Hawking radiation, and the avoidance of shock waves using surface waves rather then sound waves. In theory we should be able to detect the classical component of the thermal emission of black holes in our system and answer the ultimate question: How much do we trust our effective quantum field theory in curved spacetimes?