Studying gravitational waves has enormous potential for discovering those parts of the Universe that are not yet observed such as the gravitational repercussions from the Big Bang, the ripples of spacetime emerging from perturbations of the primaeval plasma, and other, as yet unknown, objects. Working in conjunction with other astronomical methods and gravitational-wave observatories on Earth, LISA scientists will contribute to the next big discoveries to answer questions such as “What are the fundamental laws of the Universe?” and “How did the Universe originate and what is it made of?