21.04.2020

For many years, researchers have been searching for an all-encompassing theory of the universe that unites the four fundamental forces of nature known so far. While three of the four forces can be described uniformly using quantum theory, the fourth force, gravity, has persistently eluded these attempts so far. String theory is a promising approach to also represent gravity by means of a quantum model, i.e. to develop a "quantum gravity". In the PRISMA^{+} program, string theory is an important cornerstone of theoretical research - and is now represented by Timo Weigand, an internationally renowned expert in the field.

Timo Weigand was appointed to JGU in January 2019, but last year he worked as a Long-Term Staff Member at CERN in Geneva. He moved to Mainz at the beginning of 2020.

String theory describes the basic building blocks of matter not as point-like particles, but as extended objects. At the beginning, these were often illustrated as threads - "strings" - and gave the theory its name. Furthermore, string theory envisages the existence of a ten-dimensional space-time and describes physics originally at very high energies.

In order to derive statements about physics in a (lower) energy range from string theory or to make them experimentally verifiable in this way, physicists have to formulate further assumptions and develop models. "How else would it be possible to explain that string theory in its mathematical description assumes a ten-dimensional space, but our observable environment has only four dimensions - three spatial and one temporal," is how Timo Weigand describes the challenge. The solution: Six of the ten dimensions are combined into a compact unit that exists in addition to the known dimensions - in string theory this is called compactification. Among other things, Timo Weigand's research focuses on describing this phenomenon physically and mathematically.

"All in all, string theory provides us with a controlled and calculable framework to study quantum gravity," says Timo Weigand, "both from a theoretical perspective and with regards to the possibly far-reaching implications for the description of physics at lower energies. At the same time, it opens surprising and deep connections with mathematics. These can also be used to test general ideas about the structure of quantum gravity via string theory". His conclusion: The fundamental question for a unified theory of all forces of nature in the context of string theory has already led to fascinating relations between quantum gravity in general, black hole physics and the geometry of string compactification spaces. "And there are many more to discover!"

**About Timo Weigand**

Timo Weigand studied physics in Munich and Cambridge. After completing his doctorate, he did postdoctoral research at the University of Pennsylvania and at the Stanford Linear Accelerator Center (SLAC) before joining the Institute of Theoretical Physics at the University of Heidelberg in 2009. From 2017 to the end of 2019 he worked in the Theory Department at CERN and was appointed a professorship at the Johannes Gutenberg University Mainz in 2019. Since the beginning of 2020, Timo Weigand has been part of the team at the Mainz Institute for Theoretical Physics (MITP), one of the main initiatives of the PRISMA^{+} cluster of excellence.