Cosmology
Cosmologists try to answer questions about our universe on the largest scales in both space and time:
We have entered an era of precision cosmology, in which observations of the universe are able to place constraints on cosmological models at the 1% level. The Big-Bang model that has emerged gives a clear picture of the history of our universe over the past 13.8 billion years.
My research uses observations of the cosmic microwave background (CMB) to further understand our universe. The CMB is remnant light from just 380,000 years after the Big Bang, providing a snapshot of the universe at that early stage. It also acts as a backlight to the universe as it evolves, giving additional information about the formation of structure (galaxies and clusters of galaxies) at later times.
I currently focus on making observations of the polarization of the CMB, which offer the exciting prospect of probing the earliest times in the history of our universe and testing the theory of cosmic inflation. Cosmic inflation may explain why our universe is nearly perfectly flat and homogeneous, and it also offers a possible origin of all the matter and energy we see around us. Inflation would be a period of rapid exponential expansion in the early universe that blew microscopic quantum fluctuations up to the scale of our whole universe.
Inflation would have created a gravitational-wave background that would leave a unique, curl pattern of polarization in the CMB, called B-modes. Without such a gravitational-wave background, only a divergence-like, curl-free pattern called E-modes would have been produced. An observation of B-modes in the CMB polarization would thus be a clear sign of gravitational waves from inflation and important confirmation of inflationary theories. I currently work on two projects that aim to measure this B-mode signal from inflation - the Cosmology Large Angular Scale Surveyor (CLASS) and the Atacama B-mode Search (ABS).
- What is the age of the universe?
- What is it made of?
- How large is our observable universe?
- Where did the matter and energy comprising our universe come from in the first place?
We have entered an era of precision cosmology, in which observations of the universe are able to place constraints on cosmological models at the 1% level. The Big-Bang model that has emerged gives a clear picture of the history of our universe over the past 13.8 billion years.
My research uses observations of the cosmic microwave background (CMB) to further understand our universe. The CMB is remnant light from just 380,000 years after the Big Bang, providing a snapshot of the universe at that early stage. It also acts as a backlight to the universe as it evolves, giving additional information about the formation of structure (galaxies and clusters of galaxies) at later times.
I currently focus on making observations of the polarization of the CMB, which offer the exciting prospect of probing the earliest times in the history of our universe and testing the theory of cosmic inflation. Cosmic inflation may explain why our universe is nearly perfectly flat and homogeneous, and it also offers a possible origin of all the matter and energy we see around us. Inflation would be a period of rapid exponential expansion in the early universe that blew microscopic quantum fluctuations up to the scale of our whole universe.
Inflation would have created a gravitational-wave background that would leave a unique, curl pattern of polarization in the CMB, called B-modes. Without such a gravitational-wave background, only a divergence-like, curl-free pattern called E-modes would have been produced. An observation of B-modes in the CMB polarization would thus be a clear sign of gravitational waves from inflation and important confirmation of inflationary theories. I currently work on two projects that aim to measure this B-mode signal from inflation - the Cosmology Large Angular Scale Surveyor (CLASS) and the Atacama B-mode Search (ABS).
the CLASS Experiment
I am a lead member of the CLASS experiment. The Cosmology Large Angular Scale Surveyor (CLASS) is a next-generation CMB polarization experiment that will comprise an array of four telescopes observing in four frequency bands centered at 38, 93, 148, and 217 GHz. This broad frequency coverage will allow CLASS to distinguish galactic emission foregrounds from the CMB. A rendering of the site is shown at the right. There will be two telescopes each on each of two telescope mounts.
CLASS will observe from a site in the Atacama Desert of Chile on Cerro Toco at an altitude of 5200 meters. The CLASS site is very close to the ABS, ACT, and POLARBEAR telescopes. CLASS will map 70% of the sky, allowing recovering of CMB polarization up to the largest angular scales, which has to date been limited to observations from satellites. A key enabling technology for these large-scale observations is the variable-delay polarization modulator (VPM). The VPM will allow CLASS to modulate and "lock-in" to the polarized signal of interest and discard the much larger unpolarized emission from the atmosphere. CLASS is currently beginning its deployment, so more exciting news will follow! |
The ABS experiment
The Atacama B-Mode Search (ABS) experiment, shown ready to observe at its site in the Atacama Desert of Chile on the left, is a 145-GHz polarimeter that observed from February 2012 until September 2014. We are currently analyzing the three seasons of data from ABS to place tighter constraints on inflationary gravitational waves. I am a leader of the ABS project and have been involved in all aspects of the experiment from initial survey and instrument design through to deployment and data analysis. In particular, I took the lead on the focal plane design and most elements of the optics, including a rapid-rotating, ambient-temperature, half-wave plate (HWP) polarization modulator. With its HWP, ABS has demonstrated the ability of fast polarization modulation to produce very stable observations of polarization.
ABS shared its observation site with the ACT project (see below). Results from three years of observations are coming soon! ABS will be able to place tight constraints on inflationary gravitational waves. |
previous research with act
I began my CMB career working on the Atacama Cosmology Telescope (ACT). ACT is a 6-meter telescope also in the Atacama Desert of Chile. With ACT, we have made high-angular-resolution measurements of the CMB temperature that have facilitated a wide range of science, including:
The ACT telescope now has a polarization-sensitive receiver installed on it, and is continuing to make observations of the CMB at small angular scales. |