Featured scientist: Prof Amanda Weltman

NITheCS Associate Prof Amanda Weltman (University of Cape Town) is a leading theoretical physicist and cosmologist. In this interview with NITheCS, she reflects on her academic journey, explains her pioneering work on chameleon gravity and fast radio bursts, and shares her perspective on the strengths and future development of theoretical physics and cosmology in South Africa.

Could you take us through your academic journey and explain what first drew you to theoretical physics and cosmology?

I have always loved solving problems. Any kind of problem – I love figuring things out and understanding all kinds of systems. As a child, this meant puzzles, riddles and maths problems. As an adult, it has evolved into understanding how the Universe works, how group dynamics work, what helps people thrive and how we learn.

Theoretical physics was always the most fundamental area for me. I have always been someone who works from first principles, trying to understand a problem from its very roots – and there is nothing more fundamental than physics. I was always drawn to it, as well as to mathematics, which is very much the language we work in as physicists.

Cosmology came much later, when I was trying to solve some very difficult and long-standing problems in string theory. I realised that the solution we had found could also solve a long-standing problem in cosmology. In that sense, cosmology is almost an application of theoretical physics.

Your research explores some of the biggest questions about the Universe. What are the main scientific questions or challenges driving your current work?

My current work is centred on understanding the anomalies we observe in our large-scale standard picture of cosmology. To do this, I am using Fast Radio Bursts as tools for discovery. These are short-lived, bright bursts observed across the sky in the radio part of the spectrum.

They were discovered relatively recently, yet they have been out there all along. It is therefore a very exciting time for this field, with a huge amount of new data becoming available and corresponding developments in our theories. These advances allow us not only to use the bursts as measures of our Universe, but also to understand the physics that drives them and their behaviour.

You are well known for your work on chameleon gravity. Could you explain what this idea is and why it is important for our understanding of gravity and dark energy?

Of course. Chameleon gravity is a theory I developed as a PhD student as an alternative to – or perhaps an extension of – Einstein’s general theory of relativity.

The idea is that there may be a fifth force in nature that we do not easily observe on Earth because of our dense local environment. On large and even cosmological scales, however, the effects would be profound. A number of observations on astrophysical and cosmological scales are discordant and cannot currently be explained. Chameleon gravity is a possible explanation, including for the observed accelerated expansion of the Universe – the so-called dark energy you asked about.

What does your day-to-day work as a theoretical physicist involve, and what excites you most about the research you are currently doing?

No two days are the same, which I quite love. We discuss and debate a lot at the board, calculating and writing, and then returning to rehash it all.

I also do a lot of strategic planning, as I am responsible for a large and growing research group. I need to ensure that the group’s research needs are met and that its members are supported in developing their own careers and ideas.

I love working with our young people. My group members are all wonderful people with creative ideas and brilliant insights of their own. It is a real privilege to work in an environment that is both supportive and intellectually challenging.

Looking at the development of theoretical physics and cosmology in South Africa, where do you think the country has strengths, and where is there still room to grow?

What a great question. We have many strengths, especially in the areas that underlie the development of radio astronomy. However, investment in basic research falls well below international averages, even when compared with other developing economies.

South Africa has unique competitive advantages and could excel – and uplift our entire nation within just one generation – if we had substantial investment in basic science research.

As researchers, we understand the interconnectedness of ideas. We know that cosmology informs, and is informed by, mathematics, AI, gravity research, astrophysics, computer science and even materials research. We know that investment lifts all these areas and will transform our country into a knowledge economy. Yet securing that investment in science remains a core challenge.