The professor of physics with an aptitude for popular education


His calm and methodical way of explaining the most advanced cosmological concepts has made him much in demand for everything from lectures and debates to radio and TV programmes. After five books, many awards and academic assignments, the question is which new goals are attracting the professor. “I am very glad just to be where I am,” says Ulf Danielsson, Professor of Theoretical Physics.

Ulf Danielsson explaining equations in front of a black board
“Knowledge of the universe is important to me, it has to do with a world view where I’m trying to make everything fit together,” says Ulf Danielsson, Professor of Theoretical Physics.
Photograph: Mikael Wallerstedt

On the same day as the interview was made, the news arrived that an international team of scientists had succeeded in taken the first image of a super-massive black hole in the centre of the Milky Way. The media were quick to contact Ulf Danielsson for his comments – a well-established practice in fact. Few researchers have the same ability to make concepts such as black holes and string theory seem comprehensible. Fortunately, the professor from Uppsala never seems to tire of trying to explain the state of things, or at least of the universe.

“At the end of the day, it’s all about my own curiosity. What drives me on is the will to understand these questions, that is the objective. And then it’s fun to be able to contribute just a little bit to the whole thing,” says Ulf Danielsson.

It is just over thirty years since he began to research how string theory in particular could offer answers to how the universe was created. One of the really great mysteries in modern physics is about cosmology and especially the fact that the universe is expanding more and more quickly. The reason is believed to be what is known as dark energy.

“Basically, dark energy is a constant energy density that exists in the universe. Since it has been demonstrated to be able to cause accelerating expansion, it could be behind the fact that the galaxies are moving apart more and more quickly. We are now in the process of measuring this very precisely with large telescopes.”

According to string theory, the smallest constituent parts of matter, such as protons and electrons, take the form of vibrating oblong “strings”. Ulf Danielsson designs mathematical models so as to be able to develop this theory.

“In practice it isn’t on such a grand scale. You find some little corner, some little mathematical problem or something you are trying to solve, so that you build on what others have done where you know you can make a contribution. Then someone else can use it to build up a realistic model. And yet another person looks at how this model can be adapted to observations before yet another makes the observations.”

He maintains that the mathematics is not a goal in itself but only a tool: everything is about solving real problems and understanding how the universe is arranged. The path to such an overall understanding is via the concept of curved space-time, part of Einstein’s gravitation theory of how every gravitating mass changes the geometry of space and curves time. The thing that puts a spanner in the works for the scientists is the existence of black holes, whose gravitation is so strong that not even light can escape them.

“Black holes are mysterious. Partly because we still have not succeeded in fusing together Einstein’s general theory of relativity and quantum mechanics into one general theory,” explains Ulf Danielsson.

Some progress has been made, however. When black holes collide, gravitational radiation is emitted that we can now capture in the powerful radio telescopes of the Event Horizon Telescope network. Ulf Danielsson believes that such observations can give us new ideas about the structure of black holes. But he also points out that it is not generally possible to plan for new discoveries.

Ulf Danielsson
Few theoretical physicists have had as much public
impact as Ulf Danielsson. Photo: Mikael Wallerstedt

“With large and expensive facilities, we must prioritise and attempt to make our efforts as well as we can. But in general, when it comes to processing all this data that comes in, as well as other types of research, I think that we must be more permissive when it comes to thinking more freely. We must encourage it in a different way than we do now.”

He has found an outlet for his own creativity and curiosity in many different areas and contexts. As well as being a regular contributor to Radio P1, contributing to TV programmes such as SVT’s Muren and being heard in pods, Ulf Danielsson has also performed at the National Theatre. In 2018 he took part in Performance Lecture: About the Universe, in which he gave a cosmic overview of the history of the universe.

“What made that so enjoyable was to be able to live the dramaturgical aspects and convey a narrative, and weave it together with a greater history.”

His popular science books on physics and natural science can also be seen as part of a larger narrative. Questions that have been important to him at various times in his life have been brought into a broader reasoning about modern physics and the mathematical-scientific world view. He has given a perspective to everything from climate and natural history, philosophy and an outlook on life to technology and artificial intelligence.

But in the autumn a different kind of book will be published: Handbook for Citizens of the Universe, of which Ulf Danielsson calls himself the editor.

“Those who are behind the book are a collection of extraterrestrial civilisations that have written to mankind to try to explain where we stand. The extraterrestrials are very secretive and do not reveal anything we don’t already know about basic physics. Because it would be dangerous for us to acquire knowledge that we are not mature enough to handle. On the other hand, they are extremely generous about revealing some things about how other civilisations have got on in other parts of the universe,” he smiles.

He thinks that writing books is just getting more and more fun. As he says himself, he can straighten things out and try to explain and describe the world in a new way for anyone who happens to listen. But when asked about his teaching, he gets an extra glint in the eye.

“If I am teaching a course on electromagnetism, it is just so terribly fun to get the students to try to understand the physics, the experiments, the equations, everything! When you look at these mathematical equations and how you can lead from one to another and how you can explain experiments that they could actually have done themselves – that is something amazing! That is when it is possible to have a really emotional experience, when things suddenly start to mean something and to move you. Then you can’t just stay as you are. Quite simply, you must find out more.”

Anneli Björkman


Age: 58

Family: Partner Viktoria, son Emanuel aged 10, Viktoria’s son Olof aged 15, and children Klara aged 26 and Oskar aged 31.

Title: Professor of Theoretical Physics at Uppsala University.

Education: Doctorate in Theoretical Physics at Princeton University, USA 1992. Professor of Theoretical Physics at Uppsala University since 2000.

Selection of qualifications: Vice-rector of the Disciplinary Domain of Science and Technology, Uppsala University, 2011 – 2014; member of the Royal Swedish Academy of Sciences, the Royal Society of Arts and Sciences and the Royal Society of Sciences in Uppsala.

Selection of prizes and distinctions: Disa Prize 2005, Göran Gustafsson Prize for physics 2008, Thuréus Prize 2009, H.M. The King’s Seraphim Medal 2022 “for outstanding popular education performance as a theoretical physician”.

Most proud of: “I don’t really like going on about prizes, but if there is one thing I am a little proud of it was receiving the Harry Martinson Prize in 2016. I thought that was really enjoyable. Harry Martinson’s starting point was the literary, but given his interest in science he moved from one position to another. I started somewhere quite different and have tried to move myself in that direction. Not to get there, you understand, because I can’t write in that way. But I came far enough that I can catch the eye of those who appreciate him.”

Hidden talent: “My partner says that I am very good at deciding whether an avocado is ripe or not, which is a mystery to both her and me since I have poor colour vision. On the other hand, I am very bad at identifying the ripeness of bananas.”

If I was not a scientist: “Then I would probably have been a forest keeper like my father. Being out in nature in that way and still having the quite intellectual job of planning the forest management to get everything to come together, that combines reflection with the natural experience. In that way, the similarity with theoretical physics is quite striking.”


Theoretical Physics at the Department of Physics and Astronomy, Uppsala University

Personal website of Ulf Danielsson

Research publications by Ulf Danielsson

Researcher’s pod: The physics behind everything