The physicist John Wheeler once proposed a challenge: How can you best explain quantum mechanics in five words or fewer? In the modern world, it’s easy to get suggestions for any short-answer question: Simply ask Twitter, the microblogging service that limits posts to 140 characters. When I posed the question about quantum mechanics, the best answer was given by Aatish Bhatia (@ aatishb): “Don’t look: waves. Look: particles.” That’s quantum mechanics in a nutshell.
Sean Carroll, The particle at the end of the universe