In this science café we dive into the big mysteries of the Universe: dark energy and dark matter. We know that the Universe is expanding at an increasing rate due to dark energy, while dark matter tries to slow it down. But what are dark energy and dark matter, how can these be observed, and how do they fit in the current theories of the evolving Universe? Our two cosmic speakers from Leiden will explore these matters with us in Wageningen. Professor Alessandra Silvestri will focus on the theoretical challenges surrounding these mysterious ingredients and the laws of gravity, while Professor Henk Hoekstra will show how we can study the dark Universe observationally.

Prof. Alessandra Silvestri is professor of Theoretical Physics at the Institute Lorentz, Leiden University. She is specialized in the field of cosmology, using cosmological data and theoretical physics to study the Universe, with particular focus on dark energy and the laws of gravity. Prof. Silvestri obtained her Master in Trieste (Italy), and PhD at Syracuse University (US). After postdocs at MIT (US) and at SISSA Trieste she joined Leiden University in 2014, where she became full professor in 2025. In 2019 she was awarded a VIDI grant for understanding the expanding Universe and in 2024 an ERC Consolidator grant to put gravity to the test on cosmological scales. Since 2024 she is cosmology coordinator for the ESA Euclid mission. 

Prof. Henk Hoekstra is professor of Observational Cosmology at Leiden Observatory, Leiden University. His main area of research is observational cosmology, with a particular focus on the study of dark matter and dark energy using weak gravitational lensing. After completing his PhD cum laude in Groningen in 2000, he moved to Toronto for a postdoc. After that he moved to the University of Victoria for a faculty position and returned to the Netherlands in 2008 to work at Leiden University where he became a full professor in 2017. He obtained numerous awards, including a Marie-Curie, VIDI, VICI, ERC starting grant, and in 2022 an ERC advanced grant for dark matter research. Since 2011 he is cosmology coordinator for the ESA Euclid mission and from January 2027 he will be the Scientific Director of Leiden Observatory.