Eyes on the dark ages of the Universe


Australia is an exciting place for astrophysicists to be right now. Katie Mack explains why to Elizabeth Finkel.


Katie Mack may look like a university student, but she spends her working day travelling back in time. – JAIME MURCIA

Katie Mack is an astrophysicist with an insatiable curiosity about the early Universe and its telltale signs of exotic physics. Tall and athletic, in jeans and a t-shirt she looks like just a university student. But huddled over her laptop in her plain white office, she is travelling back in time, some 13.7 billion years, to the universe’s “dark ages”, around 100 million years after the Big Bang. It is a perfect place to look for traces of cosmic strings, primordial black holes, and dark matter.

When she was 16 in Los Angeles, Mack’s mother took her to hear Stephen Hawking speak. “I wanted to do what he does,” she says. She went on to a bachelor’s degree at Caltech, a PhD at Princeton, and a postdoctoral fellowship in Cambridge.

Australia is an exciting place for astrophysics right now. Cosmologists are flocking to the action at the Square Kilometre Array in Western Australia. The array will allow them to see nearly back to the dark ages – to where Mack has her sights set.

She joined the University of Melbourne’s Astro Group 18 months ago, and is working on theoretical calculations that will guide cosmologists in the search for dark matter. No visible light emanates from these dark ages. Instead, radio waves suggest a simpler universe of hydrogen and helium molecules, pristine enough to detect weird things like dark matter. Katie’s calculations show that dark matter should leave traces in this sea of hydrogen.

What does it feel like to be probing the secrets of the Universe? “I’m constantly in a state of awe and wonder. The fact that space-time does bend, that dark matter does exist, is mind-blowing. On one hand it makes you feel very small; on the other it’s awe-inspiring that we have the capacity to understand these things.”

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Elizabeth Finkel is editor-in-chief of Cosmos.
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