Search Talks

Motivated by the consistency of black hole complementarity, Sekino and Susskind have conjectured that no physical system can "scramble" its internal degrees of freedom in time faster than (1/T) log S, where T is temperature and S the system's entropy. By considering a number of toy examples and general Lieb-Robinson-type causality bounds, I'll explore the range of validity of the conjecture. Some of these examples suggest that nonlocal Hamiltonians can delocalize information at rates exceeding the fast scrambling bound, but the physical relevance of these examples is unclear. Joint work with Nima Lashkari and Douglas Stanford.

We investigate a simple FRW spacetime realized by a brane construction. This also comes from a Coleman-de Luccia decay from a metastable de Sitter. We motivate a dual description in terms of a low energy effective field theory (EFT) on FRW in one lower dimensions. This EFT is coupled to gravity with a time-dependent Planck mass that grows to infinity at late times. We investigate the entropy bound, correlation functions, and various particle/brane probes as first steps to understand the degrees of freedom building up the EFT. This is work in collaboration with B. Horn, S. Matsuura, E. Silverstein, and G. Torroba.

I will discuss recent work engineering "semi-holographic" constructions of de Sitter space in string theory, using elliptic fibrations and orientifolds to uplift known Freund-Rubin compactifications. The dual brane construction is compact and provides a microscopic realization of the dS/dS correspondence of Alishahiha et al., realizing de Sitter space in d dimensions as a warped compactification down to d-1 dimensional de Sitter space coupled to a pair of large N matter sectors. This provides a parametric microscopic accounting of the Gibbons-Hawking entropy. I will discuss an explicit example in three dimensions as well as ongoing work in four dimensions.

Starting from AdS/CFT, one can introduce ingredients which produce cosmological solutions, including metastable de Sitter and its decay to FRW. In the de Sitter case, this produces a compact brane construction which mirrors the dS/dS correspondence realizing de Sitter as a pair of warped throats coupled to gravity. In the FRW case, I will present simple solutions sourced by magnetic flavor branes and explore their holographic description. The basic strategy is to exhibit a time-dependent warped metric on the solution and test the interpretation of the resulting region of gravitational redshift as a low energy effective field theory (EFT) by analyzing particle dynamics and correlation functions. At finite times, the EFT has a finite cutoff since system has a propagating lower dimensional graviton and a finite covariant entropy bound, but the graviton decouples at late times as the Planck mass goes off to infinity along with the entropy. This is work in collaboration with X. Dong, B. Horn, S. Matsuura, and G. Torroba. Along the way I will make some comments on the role of microscopic (UV complete) physics in cosmological holography and mention several different approaches to deriving landscape duals.

Gauge/gravity duality is our most complete construction of quantum gravity, but it gives in a simple way only the observations of an observer at the AdS boundary. I discuss various issues regarding the representation of the bulk physics.

I'll discuss some recent insights regarding the complexity of simulating highly entangled quantum systems using classical and quantum computers, and what these advances might imply about the quantum state of the early universe.

Classical transition is one of the simplest consequences of cosmic bubble collisions. In quite a few simple toy model landscapes, collisions always result in classical transitions. Can it be generalized to the "real" string theory landscape? If so, does it imply some sort of hidden structure of the landscape?

In this talk, I explain how twistors can be used to provide a covariant UV cut-off for 4-D gauge theory. I'll then motivate the conjecture that the cut-off gauge theory automatically contains 4-D Einstein gravity. As evidence, I describe how the theory reproduces the gravitational MHV amplitudes.

Present treatments of eternal inflation regulate infinities by imposing a geometric cutoff. We point out that some matter systems reach the cutoff in finite time. This implies a nonzero probability for a novel type of catastrophe. According to the most successful measure proposals, our galaxy is likely to encounter the cutoff within the next 5 billion years.

By combining insights from black holes and string theory we argue for the existence of a hidden phase space associated with an underlying fast dynamical system, which is largely invisible from a macroscopic point of view. The dynamical system is influenced by slow macroscopic observables, such as positions of objects. This leads to a collection of reaction forces, whose leading order Born Oppenheimer force is determined by the general principle that the phase space volume of the underlying system is preserved. We propose that this adiabatic force is responsible for inertia and gravity. This fact allows us to calculate the hidden phase space volume from the known laws of inertia and gravity. We find that in a cosmological setting the appearance of dark energy is naturally explained by the finite temperature of the underlying system. The adiabatic approximation that leads to the usual laws of inertia and gravity breaks down in the neighborhood of horizons. In this regime the reaction force degenerates into an entropic force, and the laws of inertia and gravity receive corrections due to thermal effects. A simple estimate of these effects leads to the conclusion that they coincide with observed phenomena attributed to dark matter.