Gravitational Theory and Cosmology

Gravitational Theory and Cosmology

The Lise Meitner Research Group’s primary focus involves applications of mathematical and numerical relativity to study theories of the origin, evolution, and future of the Universe and the relationship to black hole physics and other aspects of gravitational theory.

Physical cosmology offers some of today's most exciting science opportunities. There is plenty of observational data, and the data points to novel puzzles: What is the dynamical mechanism responsible for the seemingly special initial conditions that seeded all structure, including all planets, stars, and galaxies? What is the origin of the fundamental constituents of matter? What drives the current accelerated expansion phase? And what is the future of our universe?

Our goal is to develop complete theories of the origin, evolution, and future of the universe addressing these issues. We are particularly interested in scenarios that are based on replacing the big bang with a classical (non-singular) bounce from a previous phase of contraction to the current phase of expansion. Apart from providing a powerful explanation for the origin of all structure, bouncing models yield a potential solution to the cosmic singularity problem and hint at the exciting possibility that we could be living in a cyclic universe with bounces occurring every 100 billion years or so.

In addition to model building, we create new tools for solving fully non-linear equations of Einstein general relativity and beyond, for the purpose of testing the viability of the cosmological models and identifying their predictions for forthcoming observations, especially the Simons Observatory and gravitational wave interferometry.

Furthermore, we are interested in investigating the connections to fundamental physics and the implications for gravitational theory in other situations involving space-time singularities, such as black holes.


Ijjas, A.; Pretorius, F.; Steinhardt, P. J.; Garfinkle, D.: Dynamical attractors in contracting spacetimes dominated by kinetically coupled scalar fields. (2021)
Ijjas, A.; Steinhardt, P. J.: Entropy, Black holes, and the New Cyclic Universe. (2021)

Recent publications

Ijjas, A.; Kolevatov, R.: Sourcing curvature modes with entropy perturbations in non-singular bouncing cosmologies. Journal of Cosmology and Astroparticle Physics 2021 (06), 012 (2021)
Ijjas, A.; Kolevatov, R.: Nearly scale-invariant curvature modes from entropy perturbations during graceful exit. Physical Review D 103 (10), L101302 (2021)
Ijjas, A.; Pretorius, F.; Steinhardt, P. J.; Sullivan, A. P.: The Effects of Multiple Modes and Reduced Symmetry on the Rapidity and Robustness of Slow Contraction. Physics Letters B 820, 136490 (2021)
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