Why is gravity the most mysterious force of nature? Lavinia Heisenberg studies how the universe was formed, and how it is changing. She has now been awarded the ETH Zurich Latsis Prize for her outstanding achievements in the field of theoretical physics.
Anyone who observes the sky at night may have an idea of what Lavinia Heisenberg does for a living. She is a cosmologist. Her field of research is space and what is to be found there, whether visible or dark matter, light or energy, particles or waves, bodies or forces. Her interest lies not in individual planets, a solar system or a galaxy, such as our Milky Way. Her research drive is oriented much more towards entire galactic clusters and the forces of nature that tell us something about the origin of the universe.
There are times when Heisenberg finds herself overwhelmed when looking at the billions of galaxies in the sky. "Curiosity was always the driving force for me," she says on the Hönggerberg campus, as her long curly hair is caught by a gust of wind. "There is so much unknown out there. And we should just keep exploring."
Exciting times, mysterious forces
For a physicist such as Heisenberg, who investigates the interaction between particle physics and cosmology, these are most certainly exciting times, with two major discoveries having significantly expanded the possibilities for research. A new particle, the Higgs boson, was discovered at CERN in July 2012, and the first direct observation of gravitational waves was made in September 2015. Heisenberg is convinced that gravitational waves will open up further potential for discovery: "All the information so far that we have about the universe has only come through photons, through light. And now we also have this new channel of gravitational wave observations. You can compare it with a situation where we were completely blind, and now suddenly we can actually see all these beautiful colours."
Gravity is a key element in her research. "When you think of cosmological scales, of large scales, the gravitational force is the dominant one. So if you want to describe the nature or the physics behind the universe, you need to know what the fundamental law of gravity is," she explains. "If you now combine precision measurements coming from gravitational waves with all the observations that we already had through light, at the end of the day we will come closer to what really is the true nature of gravity." To date, a conclusive explanation has not been found. Approaches that describe the world on a large scale - i.e. in space - explain gravity differently than those approaches that describe the world on a small scale, i.e. in the innermost part of the atomic nucleus.
These explanatory differences are based on the two great theoretical achievements of physics in the 20th century - the theory of relativity and quantum mechanics. The fact that it can still not be explained in a uniform way with a single theory makes gravitation the most mysterious of the four fundamental forces of physics. These basic forces determine the behaviour of bodies, fields, particles and systems; the other three are the weak interaction, the strong interaction and electromagnetism.
Many perspectives, stable solutions
Heisenberg’s approach is characterised by the way in which she studies gravity from a range of perspectives: like a telescope, each theory opens up another outlook on reality. She uses these perspectives to obtain new insights into the essential and fundamental properties of gravity. "We combine the various interpretations of gravity in order to find stable solutions to the problems of general relativity," she adds. Heisenberg has now won the ETH Zurich Latsis Prize for her detailed analysis of gravity in the light of classical and quantum physics and the corresponding conclusions drawn from astrophysical, cosmological and particle physics experiments. The prize will be awarded at ETH Day 2020.
Heisenberg’s multidisciplinary approach combines gravitational physics, cosmology, particle physics and computational astrophysics. As a theoretical physicist, she does not perform experiments in the lab or particle accelerators - she works with a pen and notebook, and carries out computer calculations. Mathematics is her most important tool. The quality of her theories is measured by the extent to which the mathematical equations can explain the data from particle physics experiments or from cosmological and astrophysical observations.
Beethoven, bouldering and a bow and arrow
Her multidisciplinary approach is reflected in the composition of her team and in her teaching. Heisenberg is a team player, and it is important to her to see open questions discussed: "I really enjoy interacting with my team and my students." For her, enjoyment is the best compensation for disappointment and stress.
Heisenberg also finds balance in running, climbing, fitness training and archery, and in activities that require a high level of concentration: "In archery I have to focus very closely on my position if I want to hit the target. In moments like these, I’m completely present in the here and now - not thinking about the past or worrying about the future." She also experiences such inspiring moments of complete immersion in her research, moments when she is fully absorbed in what she is doing. In difficult times she finds stability in music, in the symphonies of Beethoven.
Heisenberg’s career path is as diverse as her research: she has lived in various countries since childhood, "and in every country, I have learned the language." Today she can speak six languages, including German. She originally arrived at ETH as a fellow of the Institute for Theoretical Studies. In 2018, she received an ERC Starting Grant, which is awarded only to the best researchers, and was appointed assistant professor in the Department of Physics. Her future is literally written in the stars - ever since she was a child, Heisenberg has dreamed of becoming an astronaut. And this goal continues to drive her: "To see Earth from such a perspective - it must be an amazing feeling to see how fragile our Earth is."
Heisenberg L: A systematic approach to generalisations of General Relativity and their cosmological implications. Physics Reports 796 (2019) 1-113. doi: doi.org/10.1016/j.physrep.2018.11.006
Jiménez JB, Heisenberg L, Koivisto TS: The Geometrical Trinity of Gravity. Universe 2019, 5(7), 173. doi: doi.org/10.3390/universe5070173
Heisenberg L: Generalization of the Proca Action. Journal of Cosmology and Astroparticle Physics, JCAP05 (2014) 015. doi: doi.org/10.1088/1475-7516/2014/05/015