Dark Matter

I introduce here the problem of dark energy, a substance that appears to be pushing the Universe to expand ever faster and discuss the large effort currently in place to understand its origin. I describe the surprising recent discovery of a widening crack in the cathedral of modern cosmology arising from the measurement of the expansion rate of the Universe. And I argue that gravitational waves observations can help us to either repair that crack, or to bring down that magnificent building, in case it turns out to be fatally flawed. Before all women and all men. Before animals, plants, archaeans, bacteria. Before the Earth was formed and the stars were lit. Before everything we know, the Universe was immersed in an amorphous and oblivious darkness.