IMAGINE yourself at a magic show. The magician brings out a tiger and coaxes it into a large, colorful box on the stage. He closes the lid, says a few mysterious words and then — poof — opens the side panel, revealing the inside of the box to be empty. The tiger is gone. Cue applause.

We know, of course, that tigers are not apt to vanish into thin air; we know that such magic tricks are more trick than magic. But how is it possible that our eyes can be deceived so easily?

The answer has much to do with the way our sense of sight works. As we look around a room, our eyes detect the light that bounces off nearby people or objects, and our brains interpret the images formed from the patterns of light received. We can even figure out what material something is made of based on the way it reflects and transmits light: metal is opaque and typically very reflective; plastic, which is more dull and often translucent, absorbs some of the light and reflects the rest in all directions. Our brains, then, turn these signals from reflections into breathtakingly complex pictures of the world around us. And it all happens faster than the blink of an eye. Indeed, after every blink of an eye.

Such lightning-fast cognitions are possible partly because the brain makes certain automatic assumptions: it figures that light has traveled in a straight line from the object to our eyes. Remarkably, in that built-in assumption is the recipe for a bit of magic that humans (and mythical humans) have sought, from the time of Plato to the age of Harry Potter: invisibility.