Fiona McCarthy

I am broadly interested in data-oriented cosmology, in particular the cosmic microwave background (CMB), the oldest light in the Universe that was released ~300,000 years after the Big Bang (almost 14 billion years ago!). By extrapolating this light to even earlier times we can learn very fundamental things about the physics that governs the Universe and what there was at the very beginning. 

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Major focuses of my research are the CMB secondaries, the name we give to effects that have changed the CMB since its release, through its interactions with late-Universe structure. The most famous of these are the CMB lensing and and Sunyaev-Zel'dovich signatures, the former of which is due to the gravitational interaction of the CMB with matter, and the latter of which is due to the electromagnetic interaction of the CMB with late-Universe electrons (Compton scattering of the photons).

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Until September 2026 I was an Assistant Research Professor at the Department of Applied Mathematics and Theoretical Physics, also in Cambridge, where I was part of Blake Sherwin's group. Until September 2025 I retained my joint appointment at the Center for Computational Astrophysics (CCA), at the Flatiron Institute in New York City, part of the Simons Foundation, where I spent the first (almost) two years of my postdoc as a Flatiron Research Fellow. I did my PhD and my masters at the Perimeter Institute / University of Waterloo in Waterloo, Ontario, Canada, where I spent 5 years. Before that I completed my undergraduate in theoretical physics in Trinity College Dublin.