"Aún no sabemos si los universos paralelos existen": Christophe Galfard, el discípulo de Stephen Hawking, les responde a nuestros lectores You might have previously done the quiz just before. That's why you could not begin it once again. Quiz is loading... You will need to sign up or register to https://www.youtube.com/watch?v=5LF34uf-LC4