Freese’s work is in theoretical cosmology, at the interface of astrophysics and particle physics. This field has seen remarkable successes in the past decade, yet many questions remain, including: What is the universe made of? What is the dark matter? What is the dark energy? What makes the universe accelerate, both now and during an early period of inflation? Freese’s research seeks to address these questions.
Dark Matter
The ordinary atoms that make up the known universe, from our bodies and the air we breathe to the planets and stars, constitute only 5% of all matter and energy in the cosmos. The remaining 95% is made up of a recipe of 25% dark matter and 70% dark energy, both nonluminous components whose nature remains a mystery. Identifying the nature of dark matter, which constitutes most of the mass in the Universe, is one of the longest and most important outstanding problems in modern physics. One focus of my research is the search to solve this mystery.
Dark Stars
The first stars to form in the history of the Universe may be Dark Stars, powered by dark matter heating rather than by nuclear fusion — an idea I proposed with Spolyar and Gondolo in 2007. Dark matter is the predominant mass in the universe and may play an important role in the first stars, which formed 200 million years after the Big Bang. Dark Matter particles which are their own antimatter can collect inside the first stars and annihilate to produce a heat source that powers the stars. A new stellar phase results, a Dark Star, which lasts as long as there is dark matter fuel, with lifetimes from millions to billions of years.
Cosmic Inflation
Inflation is an early accelerating phase of the Universe that explains its large-scale smoothness and sows the seeds for the future growth of galaxies and other large-scale structures. Natural Inflation, a model I proposed in 1990 (together with Frieman and Olinto), postulates a new symmetry of nature that ensures the desired properties of inflation, without any unnatural fine-tunings: shift symmetries can naturally provide the required flat potentials.
Cosmic Microwave Background
One of the premier probes of the Universe is the Cosmic Microwave Background, the leftover light from the Big Bang. I have joined two CMB experiments: the Simons Observatory in the Atacama Desert in Chile (17,000 feet above sea level) and the SPIDER balloon experiment at the South Pole.
Dark Energy and the Accelerating Universe
Cosmological data indicate that the expansion of the universe is accelerating. To explain this acceleration, a new paradigm has emerged in which 70% of the mass density of the universe is some kind of “dark energy.” One possibility for this dark energy is the cosmological constant that Einstein called his biggest blunder.
The Future of The Universe
Freese has investigated the fate of future life in an accelerating universe. Whereas life cannot persist if the dark energy is constant in time, as long as it decreases in time, life should be able to go on (but certainly not as we know it!). Journalist Philip Ball in New Scientist said: “Katherine Freese and William Kinney may not look much like superheroes, but they may have just saved the fate of life in the universe.”