Physics of the Universe

How did the Universe begin, and how did it evolve to its current state? What is driving the accelerated expansion of the Universe? What are the dark matter and dark energy that compose most of the Universe, and what do they tell us about fundamental physics? 

At KIPAC, we are working to understand the physics that shapes the origins, evolution and fate of the Universe. We develop theoretical models that describe the first moments of the Universe, devise experiments to detect dark matter particles, analyze data from cosmic surveys to uncover the properties of dark matter and dark energy, and search for signatures of new physics using ancient light. 

Dark Matter

The matter we can see, which makes up every planet, star and galaxy, accounts for less than five percent of the contents of our Universe. Over a quarter of the Universe is composed of dark matter, which reveals its presence through gravitational effects on systems ranging from individual galaxies to the entire cosmic web. At KIPAC, we aim to understand the nature of dark matter by studying its behavior in diverse cosmological settings. Using state-of-the-art cosmic surveys, we search for imprints of dark matter’s interactions with regular matter and its particle properties in the sky. KIPAC scientists also devise novel experiments, including underground detectors, to directly detect different kinds of dark matter particles.

Dark Energy

Our Universe is expanding at an accelerating rate. This acceleration is driven by dark energy, which makes up 70 percent of the contents of our Universe and whose nature remains mysterious. Dark energy affects both the expansion history of the Universe and the growth of cosmic structure. At KIPAC, cosmologists play a leading role in large-scale surveys aimed at uncovering the nature of dark energy, including DES, DESI, the Vera Rubin Observatory LSST and surveys of the cosmic microwave background. By measuring the growth of cosmic structure and the Universe’s expansion history, these surveys test whether dark energy changed its behavior throughout the history of the Universe.

The Early Universe

The most widely accepted explanation for the origin of the Universe is that it underwent a phase of extremely rapid expansion known as cosmic inflation. Inflation occurred when the Universe was a tiny fraction of a second old, at extremely high energy densities, far beyond those reached by terrestrial particle accelerators. Inflation is sensitive to physics at these high energy scales, so any observational clues about that era are uniquely valuable. KIPAC scientists study how ancient light emitted from the early Universe reveals the workings of this primordial phase..

We collaborate with LITP@S scientists to connect theories of the early Universe to data from cosmic surveys. For example, we develop techniques to measure the spectrum of primordial gravitational waves, which may hold key insights into the inner workings of inflation.

The Cosmic Microwave Background (CMB)

One of the most powerful tools to study physics of the Universe is the cosmic microwave background (CMB), the Universe’s oldest light. It was produced around 400,000 years after inflation and provides a picture of the Universe in its infancy. We can use the CMB to probe inflation, the nature of dark matter and dark energy, and the physics of particles produced at extremely high energies. As CMB photons travel to us, they are deflected by intervening structures in the cosmic web, and some scatter off hot gas in galaxy groups and clusters. These phenomena, respectively known as gravitational lensing and the Sunyaev-Zel'dovich effect, allow CMB observations to not only reveal the early Universe, but also the growth of structure as the Universe evolved. KIPAC scientists play key roles in several current- and next-generation CMB experiments that are advancing the precision of our measurements of the millimeter-wave sky.

Large Scale Structure

Galaxies are everywhere we look in the sky. Their seemingly random placements are in fact part of a massive interconnected structure called the cosmic web. Hidden in their spatial distribution is a treasure trove of information about the past, present, and future fate of the Universe. KIPAC's cosmologists use both computer simulations and pen-and-paper calculations to try to figure out how the observed distribution of galaxies came about. They also study how this distribution depends on the properties of dark matter, dark energy, and other properties of the Universe, and develop new statistical tools to extract all of the information available in this distribution.

Observational cosmologists at KIPAC are studying the formation of this cosmic web, observing millions of galaxies as well as the largest bound structures in the Universe, galaxy clusters, with optical surveys including DES, DESI and the Vera Rubin Observatory LSST. KIPAC scientists combine these observations with measurements of the cosmic microwave background (CMB), which reveal the initial seeds of structure, formed in the early Universe, that led to the creation of the galaxies we see today.