Tom Hartman's Physics Homepage


I work on quantum gravity, string theory, and black holes.

Black hole video

This is a video (not a simulation!) of stars orbiting the supermassive black hole at the center of the Milky Way, over a 14-year period.

Source: R. Narayan.



Research Overview

String theory aims to unify the four forces and to provide a consistent framework for quantum gravity. Despite many theoretical successes, it has yet to make contact with experiment, or to answer some of the key questions that a theory of quantum gravity must address: What is dark energy? How do we describe the very early universe, where ordinary notions of space and time break down? What degrees of freedom make up black holes, and how do they evolve? Are there consistent alternatives to string theory?

To answer these questions, or to make robust, testable experimental predictions, it is likely that fundamentally new ideas are required. A promising candidate for such an idea is holography, an approach to quantum gravity based on the observation that the laws of gravitation can be recast as the laws of thermodynamics. This suggests that gravity is an emergent, statistical phenomenon. The most detailed incarnation of holography is the AdS/CFT correspondence, which equates a theory of quantum gravity in d + 1 dimensions to a field theory on the d-dimensional boundary. Though many details of the correspondence are understood, how the underlying degrees of freedom reorganize themselves into an emergent spacetime remains a mystery.

One goal of my research is to use holography to understand quantum gravity, and ultimately, to use holography to make experimental predictions for physics below the Planck scale. Another goal is to use gravity to gain insight into quantum field theory. Some specific topics include: