Zenith Grant Awardee

Raphael Bousso

University of California, Berkeley

Project Title

Dynamics of Observer-Dependent Holographic Screens

Project Summary

When we smash particles in accelerators, we stand aside and wait for the debris to come out. Experiments can be repeated arbitrarily often, allowing us to measure any quantity arbitrarily well. A successful theory will simply predict the outcome of all possible experiments, without ever referring to the observer. But when we study the universe, we are inside, looking out. Especially if our description is to include quantum mechanics, this makes us inseparable from our subject. Does this mean that observers are an important part of the fundamental description of Nature? There are intriguing hints that the choice of observer plays a role in the emergence of spacetime and matter from a deeper theory. We know that the world behaves like a hologram: its information can be stored on holographic screens. This suggests that the fundamental theory (quantum gravity) “lives” on these surfaces, in one less dimension. But different observers will construct different holographic screens. They are all large enough to encode the universe, but they will have different shape and location. This project will investigate how the shape of the screen, and with it the fundamental description of Nature, depends on the choice of observer.

Technical Abstract

Holographic screens manifest the counterintuitive idea that the true number of degrees of freedom in Nature is set by the area of certain preferred surfaces. This connection involves both gravity and quantum mechanics. Thus, screens are likely to play a role in the emergence of spacetime from an underlying quantum gravity theory. But screens are highly nonunique. A holographic screen can be associated to any observer, and its location will depend on the observer’s path. In this project, we will formulate the detailed dynamical laws of holographic screens. How does their evolution depend on local data? What data is associated with a choice of observer, and what is “objective”? Some universal laws apply to every screen: recently, an area law was proven and a Generalized Second Law formulated. We will investigate whether screens obey other laws of thermodynamics. Can appropriate thermodynamic variables be defined, and how do they depend on the observer? Since the evolution and thermodynamics of screens must reflect the behavior of coarse-grained quantities of quantum gravity, this study will reveal aspects of the role of the observer in any fundamental description of Nature.