Women in STEM: Dr Francesca Chadha-Day

Dr Fran Day is a theoretical physicist, a research fellow at Peterhouse, and a science comedian. Here, she tells us about her lifelong love of physics, her work on dark matter and particles called axions, and the high that comes with making a roomful of people laugh. 

Feb. 6, 2020 | Original article
Cambridge University News | cambridge
7 mins

I can’t remember a time when I didn’t want to be a physicist. That’s always been my ambition, because it’s the most fundamental thing in the universe, so that’s what I wanted to study. I went through school knowing that I wanted to be a physicist, so I had a lot of drive. I read about quantum physics and bought books by Richard Feynman, which I found really beautiful and inspiring.

I’ve never had a problem seeing a woman as a scientist. I think I’m quite lucky in that my Mum is a biologist, so, while that’s a fairly different subject area, I’ve always seen that you can have a family and a career. My Mum was the main breadwinner when I was growing up and my Dad did most of the childcare, so I think that always made it very clear that you didn’t have to go by traditional gender roles.

My interest in particle physics was cemented when I attended the CERN Summer Student Programme in Geneva. The whole experience was inspirational, and I was lucky enough to be there when the Higgs boson was discovered. That was a really amazing moment. We’d had a theory for decades that predicted this particle existed, and then they managed to build a machine that actually showed, unambiguously, that the theory was correct.

I can only hope that there will be more huge discoveries in my lifetime. I applied to read Natural Sciences for my undergraduate degree, and when I started I wasn’t quite sure what kind of physics I wanted to do. Going to Geneva helped me to decide the path I wanted to follow with my research. Before then I’d been told by a number of people that ‘theoretical particle physics is very hard’ and ‘it might not have a future’, and ‘maybe you should do something easier’. But then going to CERN really showed me that it does have a future, and it was something that I really wanted to do. I completed my PhD in Theoretical Particle Physics at Oxford University, and was then awarded a junior research fellowship at Peterhouse.

I work on the boundary between theoretical physics and x-ray astronomy. Cambridge is one of the leading universities in the world for physics and has really good research groups for both of these disciplines. And the college system is really great because it means you bump into people from all kinds of different subjects in college and have really interesting discussions that I wouldn’t have if I just hung around the department.

I work on particles called axions, mostly. We don’t currently know whether axions exist but they are motivated to exist by a number of different problems. One of these is string theory, which is the main candidate for a theory that explains both quantum physics and gravity. A problem with string theory is that it doesn’t have a lot of other predictions so it’s ‘mathematically nice’ but it’s hard to know if it’s true or not. One of the predictions is that you would get a lot of axions, so searching for those helps. If we found them it would provide some evidence for string theory but wouldn't prove it.

The other main motivation for axions is dark matter. So dark matter is matter that we know exists, because we can see its gravitational pull on other matter, by looking at, for example, the velocities of stars in the Milky Way. They are going faster than we expect, which means there must be more mass in the middle than we can see. But we don’t know what it is, and axions can also act as dark matter. So they’re motivated from a number of different angles. People are trying lots of different ways of searching for them, and I’m using an interdisciplinary approach that’s on the boundary between particle physics and astrophysics. I’m looking at analysing astrophysical spectra to try and work out whether it matches what we think it should just from the particles that we definitely know exist. Or whether there are other effects that might be signatures from new particles.

My advice to others who are thinking about studying a STEM subject is; absolutely, go for it. It’s likely that people will tell you that you can’t do it. That happened to me at every stage, from applying to Cambridge, applying for my PhD, applying for fellowships, people have always advised against it, and they’ve always been wrong. But you definitely won’t get anything if you don’t try, so it’s always worth just going for it. More specifically, for those who want a career in physics, study further maths. Do as much maths as possible, and also experiment with the conditions that your brain works best. So I have different places where I work in different ways and soundtracks for working on different problems, and so it’s quite important to curate how you’re working, that’s probably more important than putting in 12 hours a day. 

My daily work involves a lot of reading papers, keeping up to date with the literature, programming is a big part of my job, to do simulations of, for example, what effects we might expect axions to have, so I’m asking the question, if axions existed, what would we expect this spectrum to have. And normally the way to answer that is to write some code. Talking to colleagues about different ideas for projects, different things we could study or look at, writing papers, there’s a lot of working out the different conversions between different units and minus signs and so on.

Away from work, I perform as a science comedian. I used to be quite bad at public speaking, and I wanted to get better because it’s really important for any career in science. Even if you don’t do public engagement, you give a lot of seminars and talks, so I challenged myself to take up every speaking opportunity that came my way for a while, and then I’d get better by practising. We got an email around the department from an organisation that facilitate academics to do stand-up comedy about their research. So according to my self-imposed rule, I had to sign up for it. So I thought, what have I got to lose, and it went from there. I find it really enjoyable, when you can make a room full of people laugh hysterically it’s such a high. Most of my material is about physics, so it’s a public engagement talk, but it’s funny, it’s interesting and people learn something as well.