Cambridge Festival: Speaker Spotlight

Hiranya Peiris holds the Professorship of Astronomy (1909) at Cambridge, the first woman to do so in the 115-year history of this prestigious chair. As a cosmologist, she delves into cosmic mysteries at the edge of our understanding, reaching back to the very first moments of the Universe after the Big Bang, often treading the path of high risk and high reward.

She is noted for interdisciplinary research bridging fundamental physics with astronomical data. Peiris recently contributed to the anthology “The Sky Is For Everyone” and works to reach beyond traditional audiences for public engagement, including through science/art collaborations and live science/music events. Her work has been recognised by awards such as the Max Born Prize of the German Physical Society and the Institute of Physics (2021), the Eddington Medal of the Royal Astronomical Society (2021) and the Breakthrough Prize in Fundamental Physics (2018).

Hiranya will be speaking at the Cambridge Festival in Decoding the Cosmos.

Tell us about your research

I am a cosmologist, which means that I work to understand the origin and evolution of the Universe as a whole. Because we can’t do experiments with the whole Universe, the way we make progress in this field is by comparing ever-more-refined models with observational data from a variety of epochs in the history of the Universe. My work sits at the intersection of theory and data from the distant Universe, and is increasingly branching out into interdisciplinary collaborations where we approach big questions about the cosmos in new innovative ways.

What is dark matter and why are we searching for it?

It may surprise you to know that dark matter outweighs ordinary matter (like what you and I and everything we can see in the world is made of) by a factor of 5-to-1. It appears to be a kind of matter that we have never seen or tested in the laboratory. There have been hints since the 1930s that there is all this missing matter in the Universe, and firm evidence for it started building up since the 1970s. Now we are at the stage where we can map the distribution of dark matter across the sky in intricate detail and understand its co-evolution with the galaxies and gas that we do see. While this phenomenological evidence is overwhelming, unless we can detect dark matter in the laboratory and identify the elementary particle responsible, we don’t know how dark matter fits into our understanding of fundamental physics. The hunt for the dark matter particle is a very intensive international endeavour, and experimentalists have conceived ingenious technologies to try to capture these elusive particles.

You were awarded the IOP Fred Hoyle Medal and Prize in 2018 for your work on understanding of the origin and evolution of the cosmos. Can you tell us how the cosmos had evolved?

The cosmos started out looking very simple and now it looks very complicated. The early universe was hot and dense, and has been expanding and cooling ever since. The early universe was also very smooth, with tiny variations in its density from place to place. Over time, regions where there was more matter than average collapsed under gravity to form all the intricate structure we see today in the cosmic web. We now know that not only is our Universe expanding, but that it is expanding at an ever-increasing rate. Fuelled by a mysterious driver called Dark Energy, galaxies, such as our Milky Way are rushing away from each other at such enormous acceleration that not even the powerful force of gravity can hold the universe together.

Tell one thing about the universe that will blow our minds

According to our current best understanding, everything we see in the Universe grew from tiny quantum ripples generated just after the Big Bang.

What do you like to do away from work?

I like travelling to exotic, interesting places, and walking in the mountains. I enjoy a wide range of music, read voraciously, and love yoga.

What’s the one takeaway you would like people to take from your talk?

Because of the finite speed of light, observing the distant universe is a sort of time travel. As we look out into the depths of space, we see the Universe as it was in the past. And by piecing together data from different epochs in the history of the Universe, we have worked out the story of our origins from an instant after the Big Bang till today, 13.8 billion years later.

While answering age-old questions, we have also uncovered mysteries which point to big holes in our understanding of fundamental physics. We are lucky to be alive at a time when we can bring together technology, data, and theory to unravel these deep mysteries.