# ERC Advanced Grant for Hermann Nicolai

Professor Hermann Nicolai, Director at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute), has received one of the prestigious Advanced Grants of the European Research Council (ERC). The ERC is funding Prof. Nicolai´s research on a unified theory of quantum gravity with approximately € 1.9 million. In Nicolai’s approach symmetries play a decisive role.

One of the greatest challenges in theoretical physics is the unification of quantum field theory and Einstein´s general relativity into a theory of quantum gravity. The two fundamental theories are not compatible with each other within the known physical laws. But if we want to understand what happens inside a black hole or at the Big Bang, we need a theory that combines both. At the Max Planck Institute for Gravitational Physics, the Department of Quantum Gravity and Unified Theories, led by Prof. Nicolai, is searching for such a comprehensive theory. Nicolai's innovative research is now being funded for five years with an Advanced Grant of the ERC.

"Of course, I am very happy and greatly honored by this recognition!" says Nicolai, "especially since the success rate for applications in the field of mathematical physics is, as in previous years, very small. Only two of the funded projects are in the area of theoretical gravitational physics and cosmology."

With the ERC Advanced Grant, Nicolai will establish a working group specifically dedicated to this project. The funding sum of €1.9 million will mainly be used for the employment of scientific staff. "It is very important to me to share the excitement for these fundamental issues with a younger generation of scientists", says Nicolai.

## With symmetry towards a "Theory for Everything"

Both Einstein's general relativity theory and the standard model of quantum field theory are based on principles of symmetry. Based on symmetry considerations, new elementary particles (such as W and Z vector bosons) were predicted from the standard model, which could later be detected in accelerator experiments. Nicolai's hypothesis is that the unification of gravity with the interactions of elementary particles can only be achieved by finding a symmetry which, on the one hand, goes beyond what we have already known, but on the other hand contains all known symmetries of physics as partial symmetries. Nicolai's approach to unifying gravitation and elementary particle effects is based on symmetry E10, a unique infinite-dimensional mathematical structure that is still extremely mysterious, even 50 years after its discovery.

In this context, "infinite-dimensional" means that the symmetry operates in infinitely many dimensions (whereas, for example, ordinary rotations operate only in three-dimensional space). This is not only hard to imagine, but also mathematically extremely difficult to analyze. The physical interpretation of this mathematics is a perhaps even greater challenge: the theory postulates, inter alia, that space and time are "emergent", meaning that physics should unfold from a theory "without space and time". Just like, for example, the physics of macroscopic objects "emerges" from the very different quantum world of atoms and molecules. First steps have already been taken: a principle of classification for the infinitely many axes of rotation, with which E10 can be characterized, has been developed in Prof. Nicolai’s department.

"Our basic hypothesis is that this uniquely distinguished mathematical structure plays an essential role in the understanding of nature’s laws," says Nicolai. "Although we are still far from fully understanding the E10 symmetry, we do know that this symmetry contains many of the insights that we have gained with string theory and supergravity since about 1980. At the same time, it opens a completely new approach to the understanding of the big bang and black holes."

The main focus of further research is to find out how symmetry E10 can lead to a theory of quantum gravity, which are the peculiarities of the quantized theory, and which physical predictions can be deduced from it.

**Hermann Nicolai**, born 1952, studied and received his doctorate 1978 at University of Karlsruhe and his habilitation 1983 in Heidelberg. Until 1986 he has been fellow and staff member of CERN in Geneva. He has become Professor in Theoretical Physics at University of Karlsruhe in 1986 and University of Hamburg in 1988. Since 1997 he is Director at the Max Planck Institute for Gravitational Physics leading the division Quantum Gravity and Unified Theories. He is also an honorary professor at the Humboldt University Berlin and at the Leibniz University in Hannover. He has been awarded numerously for his scientific contributions, i.e. the Otto Klung Prize in physics 1991, the Einstein Medal by the Albert Einstein Society in Bern, Switzerland 2010 and the Guy-Lussac-Humboldt-Prize in 2013. In 2016 Nicolai was awarded the honorary doctorate of the Swedish Chalmers University of Technology in Gothenburg.

## ERC Advanced Grants

With the Advanced Grant, the European Research Council honors leading scientists who combine excellent science with innovative approaches. The highly endowed grants are awarded to support research projects that have a potentially ground-breaking impact on their research field.

In the current selection, the ERC selected 231 projects of 2.404 research applications from all fields of science, which corresponds to a success rate of 9.6%.