Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

classical physics is deterministic: provide the mathematics of classical physics—Newton’s equations—with the precise locations and speeds of all particles at any one moment and the equations will tell you their locations and speeds at any future moment. With such rigidity, with the future fully determined by the past, how can there be any room for free will? The state of your particles right now, reading these words and contemplating these ideas, was determined by their configuration long before you were even born and so, surely, could not have been selected by your will. But in quantum physics, as we have seen, the equations predict only the likelihood of how things will be at any future moment. By inserting an element of probability—chance—quantum mechanics seems to provide a modern and experimentally motivated version of the Epicurean swerve, slackening the deterministic reins. However, loose language can be deceptive. The mathematics of quantum mechanics, Schrödinger’s equation, is just as deterministic as the mathematics of classical Newtonian physics. The difference is that whereas Newton takes as input the state of the world now and produces a unique state for the world tomorrow, quantum mechanics takes as input the state of the world now and produces a unique table of probabilities for the state of the world tomorrow. The quantum equations lay out many possible futures, but they deterministically chisel the likelihood of each in mathematical stone. Much like Newton...