Dr. Fotini Markopoulou

Perimeter Institute
Quantum Gravity from a Quantum Information Theoretic Perspective

Quantum gravity is the problem of joining quantum theory to general relativity to make a theory of space and time. I study models of quantum space-time, which I treat as analogous to problems in condensed matter physics in that the challenge is to understand how macroscopic behavior is emergent from a many body system. In my work I have shown these can be addressed by using methods initially developed to model quantum computers. I propose to use these new methods to investigate the theoretical and observational consequences of specific models of quantum space-time.

We suggest a new direction in quantum gravity in which general relativity is to be viewed as the effective theory of an underlying one that is background independent in the most direct sense, i.e. it contains no geometric/gravitational degrees of freedom. This is distinct from current background independent approaches to quantum gravity, which are based on quantum gravitational/geometric degrees of freedom in the formulation of the fundamental theory and seek to derive general relativity as the low energy classical limit.

The basic premise is that an effective theory is characterized by effective coherent excitations and their interactions and that this must be also the case if the effective theory is general relativity and the underlying theory is a pre-geometric background independent quantum theory. We implement this, first, by formulating the pre-geometric theory as a quantum information processor and, second, using the method of noiseless subsystems in quantum error correction to extract such coherent excitations.

It follows that the locality and causal structure of a space-time are effective notions that apply only to these effective excitations. A dynamical underlying theory will have its own notion of locality and causality. In the present approach, the consequence of no fundamental gravitational degrees of freedom is that the effective locality and time directions are not simply Planck scale corrections on the classical ones as is the case in other theories. This suggests a new direction in quantum gravity phenomenology that we propose to investigate in the context of specific models, such as a background independent formulation of Wen's string networks.

If it turns out to be true that there is a radical difference between fundamental and effective locality as suggested here, it is possible to provide a solution to long-standing problems such as the problem of time and explain the thermodynamical nature of the Einstein equations.

Hide Technical Abstract
Back to List of Awardees