Part 1 of Essay
Toss a pebble in a pond -see the ripples? Now drop two pebbles close together. Look at what happens when the two sets of waves combine -you get a new wave! When a crest and a trough meet, they cancel out and the water goes flat. When two crests meet, they produce one, bigger crest. When two troughs collide, ....

Part 2 of Essay
.... objects. Your brain processes this information so that you see the apple, and the rest of the world, in 3-D. You can look around objects, too -if the apple is blocking the view of an orange behind it, you can just move your head to one side. The apple seems to "move" out of the way so you can see the orange or even the back of the apple. If that seems a bit obvious, just try looking behind something in a regular photograph! You can't, because the photograph can't reproduce t ....