Physicists have long sought to find a general theory to explain everything, preferably neatly and symmetrically. Wallenberg Academy Fellow Agnese Bissi is using string theory in her search for pieces of the big puzzle.
Associate Professor in Theoretical Physics
Wallenberg Academy Fellow 2016
Quantum field theories and classification of them based on their symmetries
Even as a teenager Bissi was fascinated by Stephen Hawking’s books about time and the universe. Her passion for fundamental physics took her from her home in Italy to live as a doctoral student in Copenhagen, followed by a postdoctoral position at Oxford, then at Harvard, and now to the Ångström Laboratory at Uppsala University, where she heads a research team in the field of theoretical physics.
“Sweden is a fantastic country to develop in as a researcher. The research environment is good – we have the Nordic Institute for Theoretical Physics close by in Stockholm, and here in Uppsala we receive many visitors and guest researchers from around the world.”
In principle, Bissi could work from anywhere using her laptop, but in practice it would be doomed to failure. She explains:
“We are all people, and we live in a community. Technology and computers aren’t enough – we exchange ideas in discourse and by meeting. Some ideas really do come to you when you’re in the lunch room having a coffee with your colleagues. The working environment is extremely important – if you’re happy and enjoying yourself, it will have a positive impact on your research.”
“Feedback is a very scarce commodity for a theoretical physicist. Being chosen as a Wallenberg Academy Fellow is therefore a huge mark of recognition. It also gives me the chance to establish my own research team, and start working more independently as a researcher.”
Different descriptions of reality
Reality as we know it is described by a theory that is often referred to as the Standard Model. When the Higgs boson was detected at the CERN particle physics facility in 2012, it gave important experimental confirmation of the Standard Model. The model covers all forces existing in nature except one: gravity, which is instead described by Einstein’s Theory of Relativity.
For several decades physicists have been striving to reconcile the different forces so they fit into a general theory.
“Even when I was doing my PhD I thought this must be the ultimate goal, to achieve an understanding of all of nature, including gravity. It sounds ambitious, and we need to take it one step at a time, of course,” says Bissi, laughing.
To get closer to solving the riddle, researchers are using various theories, including string theory. This provides a framework within which to study a multitude of models, and analyze constituent problems to ultimately gain a deeper understanding.
Focusing on theories with symmetrical characteristics
At present Bissi is focusing on a field closely related to string theory: conformal field theories. The word “conformal” refers to the invariance of angles. If, for example, two lines cross each other, this means that the angles will remain the same even if the lines are bent. An everyday example is that of the maps used to help car drivers to navigate.
But conformal field theories are also used to describe phase transitions in materials, e.g. the process when water boils and turns to steam or when superconductors conduct electrons without resistance at a certain temperature.
“Another example is if you take a lump of iron, and magnetize it, this creates a phase transition that can be described by conformal field theories. The occurrence of this phenomenon everywhere is usually referred to as ‘universality’, i.e. that several systems behave in the same way.”
Conformal field theories have highly specific symmetrical characteristics. The idea is to study a broad range of theories that have specific symmetries, and classify them.
“The more symmetry there is, the more predictability the models display. This means that good progress can be made, and fruitful results achieved even with a very limited amount of information. The method is usually known as bootstrap, implying that only a little effort is needed to get one’s boots on.”
String theory – a basis for the future
Most physicists seem to agree that string theory is the right way to go in describing the very smallest building blocks of matter, to resolve the problem of reconciling all fundamental forces in a single model at some point in the future. String theory is a theoretically correct and mathematically sound approach, according to Bissi:
“String theory lacks contradictions and is consistent – not something you can say about all theories – but we also need experiments to persuade ourselves as researchers, and also the public, that it describes all of nature.”
The advanced technology to perform all the necessary experiments does not yet exist, and no one knows whether it will be available in the future. But theoretical physics is nonetheless a hot field of research, and Bissi says there is exciting news every day. Her morning routine includes a visit to the website arXiv.org, where she skims through numerous new research articles over a cup of coffee.
“All wise ideas and thoughts are needed, even though I do believe that nature made its mind up long ago, and actually uses the theories I’m exploring.”
Text Nils Johan Tjärnlund
Translation Maxwell Arding
Photo Magnus Bergström