Gravity is the engine behind the universe’s processes, and much of its action is dark. Opening a gravitational window on the universe will let us go further than any alternative. Gravity has its own messenger: Gravitational Waves, ripples in the fabric of spacetime, which travel essentially undisturbed and let us peer deep into the formation of the first seed black holes, exploring redshifts as large as ~ 20, prior to the epoch of cosmic re-ionisation.
Exquisite and unprecedented measurements of black hole masses and spins will make it possible to trace the history of black holes across all stages of galaxy evolution, and at the same time constrain any deviation from the Kerr metric of General relativity. The survey mission LISA will be the first ever mission studying the entire universe with Gravitational Waves. LISA is an all-sky monitor and will offer a wide view on a dynamic cosmos using gravitational waves as new and unique messengers to unveil the Gravitational Universe: It provides the closest ever view of the early processes at TeV energies and can probe the entire universe from its smallest scales around singularities and black holes all the way to cosmological dimensions.