You don’t have to read this article. But if you do, could you have chosen otherwise? You probably feel that you were free to skip over it, but were you? Belief in some measure of free will is common to all cultures and a large part of what makes us human. It is also fundamental to our ethical and legal systems. Yet today’s scientists and philosophers are busily chipping away at this social pillar—apparently without thinking about what might replace it. What they question is a folk psychology that goes something like this: Inside each of us is a self, a conscious agent who both observes the world and makes decisions. In some cases (though perhaps not all), this agent has a measure of choice and control over his or her actions. From this simple model of human agency flow the familiar notions of responsibility, guilt, blame, and credit. The law, for example, makes a clear distinction between a criminal act carried out by a person under hypnosis or while sleepwalking, and a crime committed in a state of normal awareness with full knowledge of the consequences. All this may seem like common sense, but philosophers and writers have questioned it for centuries—and the attack is gathering speed. “All theory is against the freedom of the will,” wrote British critic Samuel Johnson. In the 1940s, Oxford University philosophy Professor Gilbert Ryle coined the derisory expression “the ghost in the machine” for the widespread assumption that brains are occupied by immaterial selves that somehow control the activities of our neurons. The contemporary American philosopher Daniel Dennett now refers to the “fragile myth” of “spectral puppeteers” inside our heads. For skeptics of free will, human decisions are either determined by a person’s preexisting nature or, alternatively, are entirely arbitrary and whimsical. Either way, genuine freedom of choice seems elusive. Physicists...