Jim Carrey as Truman Burbank, a man living in someone else's dream. The 1998 movie The Truman Show asks us to look at experience and reality with fresh eyes. Melinda Sue Gordon/The Kobal Collection/Paramount hide caption

A computer designed by hobbyists to look like a brain on display at a Berlin fair in 2012. What happens when we go from crude models to complete working simulations of this all-important organ? Britta Pedersen/DPA/AFP/Getty Images hide caption

Swarms of locusts in Madagascar, or clouds of elementary particles, without sound, odor, flavor or color? Reality is harder to pin down than you first might think. Bilal Tarabey/AFP/Getty Images hide caption

It's looking at you. But is it conscious? How do we know? iStockphoto.com hide caption

Reality? Of a kind. iStockphoto.com hide caption

A car cannot be reduced to an engine, just as a person cannot be reduced to a brain. Cameron Spencer/Getty Images hide caption