The lesson I draw from these theories is that to extend quantum mechanics to a theory of the whole universe, we have to choose between space and time. Only one can be fundamental. If we insist on being realists about space—as Barbour and Gomes do—then time and causation are illusions, emergent only at the level of a coarse approximation to the true timeless description. Or we can choose to be realists about time and causation. Then, like Rovelli, we have to believe that space is an illusion.
