Quantum theory + gravitation = ?
If physicists want to describe the interior of black holes or the beginning of the universe, they need a theory of quantum gravity encompassing both Einstein's theory of general relativity and quantum theory. However, the search for such a theory has proved to be exceedingly difficult. Even now, more than 60 years after they began, physicists do not have a complete answer. However, there are promising candidate theories: We briefly present the most important ones in the sequences A world based on oscillations: string theory and Building blocks of space and time: Loop quantum gravity