Feature Story
Searching the cosmos for the origins of the universe
Published on 24 Mar 2021

Most people look at the night sky to admire the stars and galaxies. But for Dr Kimmy Wu, far more intriguing are the spaces in between. In those dark patches, a faint glow – like background noise – may hold the key to understanding how the universe was formed.

Dr Kimmy Wu (Croucher Fellowship 2015) is a fellow at the Kavli Institute for Cosmological Physics at the University of Chicago where she researches gravitational waves and radiation in the universe. In 2015, she received a doctoral degree in physics at Stanford University, where she worked on the design, testing, and integration of the BICEP3 telescope before moving to Chicago.

Wu, who was born and raised in Hong Kong, travelled to Antarctica in 2014 as part of an expedition investigating the cosmic microwave background (CMB) radiation.

The scientific community generally agrees that the CMB is the relic of electromagnetic radiation left over from the Big Bang. It was discovered by chance in 1964 by Arno Allan Penzias and Robert Woodrow Wilson, who went on to win the Nobel Prize for the accomplishment.

“The CMB was emitted at an early time when there were no stars or galaxies in the universe,” Wu said. “As this light propagates in all directions, structures like galaxies start forming.” These galaxies and stars are more likely found in gravitational potential wells, she explained.

A portion of the CMB is polarised, meaning its electric field vibrates in non-random directions. Variation in levels of polarisation lets researchers see what happened to the light in the moments after the Big Bang.

To measure the polarisation of the CMB, Wu’s team installed the BICEP3 telescope at the Amundsen-Scott South Pole Station, a US research station at the geographic South Pole.

Earth’s southernmost continent, Antarctica, is a polar desert. Despite the inhospitable weather, regularly reaching minus 60° Celsius, low atmospheric water vapour makes for ideal conditions when probing deep into space. “Water is extremely relevant to millimetre wave observations because water absorbs mm-wave photons and contaminates our observations,” Wu explained.

“Telescopes on satellites don’t have this problem, because there’s no atmosphere. But if you’re observing from the ground, you want to find a place where the amount of water vapour is as low as possible.”

The continent is prized by scientists for other reasons as well. The sun only rises and sets once a year, making it “unlike any other site on earth,” Wu said. Because the sun’s position moves so slowly, the atmosphere remains a near-constant temperature. This is a boon to researchers who do not need to account for the daily heating and cooling of the environment.

Using data collected at the South Pole, scientists like Wu can now map subtle changes in the CMB (see illustration). “Red and blue spots represent the temperature of that spot, fluctuations of temperature lay on the scale of hundreds of micro Kelvin/ μK(a unit of temperature),” she said.

Fluctuations in the cosmic microwave background. Image courtesy of the ESA

In turn, fluctuations in the polarisation of the CMB can be generated by ripples in space-time which is a tell-tale marker for primordial gravitational waves.

“Now, the search is to look for primordial gravitational waves and either measure them or set upper limits on their fluctuations,” Wu explained. This is her current focus, working as a member of the Deep Skies collaboration, which is bringing together researchers from institutions across the world to probe the farthest corners of the universe using big data and artificial intelligence.

“If we can [measure the waves], we can learn about the earliest 10^{-33} seconds of the state of the universe,” she said.

The scientist has not been to the South Pole since 2015, though she hopes to one day return to the place that informs her current research but that she described as a summer camp for passionate scientists. “You don’t have to worry about making food or anything, instead you can just focus on work.”

For someone who loves her job as much as Wu, that’s as good as it gets.

Dr Kimmy Wu is a fellow at the Kavli Institute for Cosmological Physics at the University of Chicago. She moved from Hong Kong to Ann Arbor, Michigan, for her undergraduate studies in mathematics and physics at the University of Michigan. In 2015 she received a doctoral degree in physics from Stanford University, before moving to Chicago. Dr Wu received her Croucher Fellowship in 2015.

Extended Reading:

  1. Dr Wu’s personal page (The Croucher Foundation): https://scholars.croucher.org.hk/scholars/w-l-kimmy-wu
  2. Dr Wu’s personal page (Stanford University): https://web.stanford.edu/~wlwu/