Post by Jens Eisert

What a blast! During the #EinsteinLecture at Freie Universität Berlin, Markus Aspelmeyer of the University of Vienna took a large audience on a journey from the foundations of quantum physics—whose key structural element is superposition—to those of gravity, a tiny force operating on fundamentally different principles. Both theories are extraordinarily well established by experimental observation, and we have no evidence that either of them is wrong. The trouble is that their basic assumptions contradict each other. Markus captivated the audience with his ultra–high-precision experiments that come closer and closer to unveiling the physics of systems in which both superpositions and gravitational effects come together. The levitated objects, undergoing very little decoherence and kept in ultra-high vacuum, approach the regime that may finally show how these theories play together. I see two major take-home messages. The first is that quantum gravity is not only decided in theory: there is an empirical, experimental approach. The second is that physics in general, and quantum physics in particular, remains one of the most fascinating fields to which one can dedicate a scientific life. His words at the end of his inspiring talk can be seen as a flamboyant invitation to the next generation. Markus is known for giving excellent talks. He was generously and eloquently introduced by our president, Günter M. Ziegler, and the science historian Jürgen Renn, and then took it away. As an old friend and companion, I was truly happy to see Markus in the form of his life—extremely precise and clear in his wording, yet at the same time great fun and wonderfully entertaining. Chapeau.