“What we are proposing,' Alicia said, 'is that the laws of physics are such that causality violation is subject to a form of version control, one that prevents a forking of history. That instead of causality violation creating an alternate universe, one version of history is outright overwritten by another. One past is replaced with another future. Which means that the memories of the past of the people in that future are replaced with memories of a different past.'Carson interrupted. 'Including the memories of any—''Purely hypothetical—''—time travelers.''So take our time traveler from the traditional story,' Carson continued. 'He leaves his utopian future for the past. He kills the butterfly. The Magna Carta is never written. He returns to the dystopian future that his misstep created. But he doesn't see it as a dystopia: he sees it as home, the world he grew up in, the world he left to go back in time. Because he doesn't remember that first future, and has no other world to which he can compare this one. Maybe he even sees it as a utopia. Maybe everyone does. Maybe everyone in this dark place believes that they live in the best of all possible worlds.”

“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?”