Associate Professor, UC San Diego

Research

research

Cosmology is perhaps the most far reaching science, spanning from the microscopic scales that describe the Universe’s initial moments to the geometry of the universe on scales as large as we can see. Most remarkably, the history of the Universe ties these disparate scales together. ¬†Ultimately, the creation of the largest structures in the Universe today (likely) originated from quantum physics at scales smaller than we can probe on earth with even the most powerful colliders.

My research is aimed at understanding this rich history both on purely theoretical grounds and from observed maps of the universe (like comic microwave background or the distribution of galaxies). While traditionally theorists have been most effective calculating predictions for individual models, one of my primary interests is how to invert this process to infer properties of the universe directly from data. Making inferences about the universe without a specific model often requires connecting specific patterns in the data to fundamental principles like locality (the influence of one place on another requiring something to travel from one point to the other) and causality (the future does not affect the past).

Some recent examples from my group include:

  • Evidence for the cosmic neutrino background from (a) the cosmic microwave background and (b) the distribution of galaxies. The central idea of this work is that cosmic neutrinos travel close to the speed of light. This is much faster than the speed at which sound travels in the hot plasma that described the early universe. The supersonic nature of these neutrinos leaves a distinct pattern in observations that cannot be mimicked by other processes. We recently identified and measured this effect in the locations of galaxies. Popular articles discussing our work can be found at Forbes, Science News, and UC San Diego
  • A signal of the quantum origin of structure: it is widely believed that quantum mechanical zero point fluctuations are the reason for structure in the universe, from stars and planets to galaxies and beyond. Unfortunately, this compelling idea has not be confirmed by observations. In fact, a large body of work suggested that tests of this idea (cosmic Bell tests) are effectively impossible. However, a careful exploration of the kinds of statistical patterns that can be generated during inflation reveals that quantum vacuum fluctuations can be uniquely identified by the properties of a so-call equilateral signature. Remarkably, this connection is closely related to the prediction that every particle as an anti-particle. ¬†Popular articles discussing our work can be found at APS Physics, Scientific American, and UC San Diego

More generally, my group uses techniques from the modern understanding of quantum field theory to shed light on how fundamental physics impacts the evolution of the universe as a whole.