What is your name, affiliation, academic position, and job title?
Geraint F. Lewis, Professor of Astrophysics, The University of Sydney, Australia.

What is your journey?
I was born in the UK, in South Wales. I come from coal-mining country, and my father was a coal miner. None of my family had been through higher education, and I did not have any plan of being a university professor, but I did well enough in high school to do a degree in Physics & Astronomy at the University of London, followed by a PhD at the University of Cambridge. This was followed by postdocs in the US and Canada before I joined the Anglo-Australian Telescope in 2000. I moved to the University of Sydney in 2002 and have been there ever since.

What is your field of research and/or what project are you involved in?
I decided early in my career that I want to work on what interests me, so I have projects in theoretical, computational and observational astrophysics. The central theme of my research is understanding the dark side of the universe, the dark matter and evolution that shape its evolution, with a focus on cosmology, gravitational lensing and galactic archaeology.

What are your research plans?
My current focus involves several key pieces. Observationally, I am a leader in a major survey, the Southern Stellar Stream Spectroscopic Survey (S5), which is mapping out all of the tidal streams in the Southern Hemisphere, with the goal of using their properties to reveal the Milky Way’s unseen dark matter. My other focus is on the Cosmic Dipole tension, one of the challenges facing modern cosmology. My group are bringing new statistical approaches to this difficult problem, with the goal of understanding just how challenging this challenge is.

How does CosmoVerse fit within those plans?
One of the most important aspects of science is the ability to get together, see what everyone else is doing, and understand your work in context. In bringing people together, CosmoVerse provides excellent opportunities for this, sparking new ideas and collaborations to drive science forward. For me, it is especially important to see the impact of the next generation in tackling cosmological questions.

What new skills would you like to learn in the next year?
I like to try and learn something new every day, and I feel that expanding my skills is a life-long aspect of a scientific career. I am currently growing my understanding of how AI and ML (machine learning) can further boost my research in supporting various tasks that can be particularly time-consuming. So far, I am quite impressed with AI and can only see it growing in impact.

What are the most exciting open questions in your research area?
I have so many (the older I get, the less I feel truly understand), but as well as the nature of dark matter and dark energy, I want to know if we really live in a universe described by the simplest picture of spacetime. The question of where our universe actually came from keeps me awake at night!

What advances or new results are you excited about or looking forward to?
I believe we are on the cusp of a revolution in astronomy, with data pouring in from new telescopes across the spectrum and across the sky. With AI to help, this wealth of data is bound to reveal new secrets about the cosmos, from the formation of the planets to the birth of the universe. I really can’t single out a discovery I am looking forward to, as I am looking forward to being surprised.

What is your view on cosmic tensions? How does your work connect with this open question in the community?
The tensions are intriguing. I am not convinced that all of the tensions people talk about are true challenges, but I feel it is clear that there is something not quite right with our understanding. Maybe we are being fooled by our interpretation of the data and maybe we really do live in a simple universe, but the alternative, that the universe is a complicated and messy place, is becoming a realistic possibility. This would really shake the foundations of cosmology as we understand it.

What role do you think a community network like CosmoVerse can play in developing theoretical astroparticle physics and cosmology?
It is absolutely crucial for scientific communities to communicate and collaborate, as we need to understand the multiple viewpoints of various phenomena. This will undoubtedly spark new collaborations focused on new ideas, which is the path to new breakthroughs. Networks that provide opportunities for this are essential!

What’s your favourite food? Why?
I’m not sure I have a favourite food, but I do love to cook (although I will not claim to be particularly good at it), and when I travel, I love to try local food and drink. My attendance at the recent CosmoVerse meeting in Krakow was an excellent opportunity to sample authentic Polish food for the first time (which I thoroughly enjoyed).

Your favourite scientist and/or science fiction film?
I don’t have many scientific heroes, but if I had to name one, it would be Fred Hoyle. When he was wrong, he was very wrong, but when he was right, it changed astronomy. At least he was willing to stick his neck out with his ideas. As for movies, there are far too many, but I can always watch Aliens and The Thing, and I am a soppy fan of It’s A Wonderful Life (which, at a stretch, is science fiction!).

If you were not a scientist, what do you think you would be doing?
I would like to have worked in computer-generated imaging for movies. I still would like to!

What non-physics interests do you have and want to share?
I read a lot of history, popular science and economics. I also love listening to podcasts when walking or running. I also do a lot of writing and I’ve published four popular science books and have a fifth in preparation, as well as writing numerous scripts for YouTube channels. I’m also a fan of old movies, especially classic science fiction and horror.

In your view, what’s the most important challenge that humanity faces currently?
I’ve come to the conclusion that intelligent life is extremely rare in the cosmos, and I would not be surprised if we were the only intelligent species in the Milky Way. We need to understand how special this makes us and try to put Earthly squabbling behind us. I know it is a dream, but I would like to see an end to conflict and for humans to face the immediate challenges of climate change and the suffering of their fellow humans.