Physicist Carlo Rovelli is asked about his disagreements with friend and frequent collaborator Lee Smolin. He quotes Smolin as saying, “If both of us had the same ideas, one of us would be superfluous,” then comments, “It’s useless, someone who agrees with you.”

(A brief note about the substance of their disagreement: As Rovelli describes things, he and Smolin agree that happenings (physical events) are more basic than things. But Smolin believes that the past and future are fundamentally different while Rovelli does not.)