“You could consider the idea of the multiverse, and think of it as something like a tree—that is, the universe we live in is one of an uncountable number of branches of possible universes, created by random chance and the decisions of sentient beings. So, for instance, when I rang you up in the morning, there was a possible future universe in which you answered the phone, and another in which you did not, and by answering the phone you put us in one universe and not the other. In that instance the time traveler doesn't just move from the future to the past and back to the future: he moves down one branch of the universe, toward the root that's back at the beginning of time, and back up another branch.”

“She closed her eyes, and as had been her habit over these past couple of days, she began to imagine possible past histories and what she might have done to change them into the new one in which she lived, either inadvertently, or out of a misguided attempt to play God and make the world a better place, or, worse, with malice aforethought. Any time she spent in the past would have been clipped out of history, as neatly as if it had never happened, because it hadn't happened.”

“Later—how much later? Hard to tell. In times of tragedy clocks will trick you—Philip stood in the kitchen doorway.”

“And so Rebecca consigned herself to, not ignorance, but a judicious incuriosity: she decided, for the time being, to live with the constant, cryptic reminders that the scope of another person's soul could never be fully surveyed.”

“I can’t comprehend why any black man with even a lick of sense would have the slightest bit of interest in time travel. Going backward in time? A black man? You have got to be out of your mind.”

“As he drifted off, his father came to visit him, clothed in all his possible shapes.”

“But who, in these modern times, slept well?”

“She drank the glass with breakfast and poured herself another. By the time she'd gotten Sean off to school (second grade) the edges had been taken off her thoughts and the world seemed as it should be: not too real, but real enough.”

“He felt that race was not a characteristic that was a part of his identity, but one that was projected upon him by the gaze of others who looked on him; as such it was ephemeral, there and gone as soon as the gaze was broken.”

“And yet Rebecca felt that it was hard to tell whether the secret algorithms of Big Data did not so much reveal you to yourself as they tried to dictate to you what you were to be. To accept that the machines knew you better than you knew yourself involved a kind of silent assent: you liked the things Big Data told you you were likely to like, and you loved the people it said you were likely to love. To believe entirely in the data entailed a slight diminishment of the self, small but crucial and, perhaps, irreversible.”

“The scientific method entails two assumptions that are so basic that, even if you spell them out, they are still difficult to keep in mind. First: that the observer stays the same while the world changes. Second: that cause precedes effect.But the very nature of the experiment we are conducting means that the second of these assumptions is thrown into doubt. We are deliberately attempting to engineer an event in which effect chronologically precedes cause.If one of these assumptions is under threat, why not the other?”