Imagine you're sitting on a beach. You start digging a hole just at the water line for fun and let the ocean fill it up. You build a little dam out of sand at the edge of this reservoir, and put a hole in the dam between the little reservoir you dug out and the ocean. It's a calm day so there are no waves. You splash in the reservoir. The waves move through the hole and continue out into the ocean just like you'd expect. That makes sense, right? But you make a second hole in the reservoir and start splashing again. The waves move out through both the holes, but when they meet again on the other side, the pair of waves cancel each other out, creating a pattern of waves and still water on the other side. The pattern looks like a line of stripes if you look at a slice of it from above. Anything that moves in waves does this when it passes through two slits, including water, sound, light, radio waves, etc. Imagine you had a paintball gun and fire it a thousand times at a pair of slits cut in a wall with a bedsheet on the other side. What would happen? Obviously some would miss the slits and hit the wall, but some would pass through and hit the bedsheet. You'd end up with a pair of stripes on the bedsheet. When you shoot subatomic particles or atoms at a pair of slits you get a pair of stripes, right? No. You get a line of stripes. Particles move like waves, not like paintballs. Unless you measure the particles just as they pass through the slits before they hit the sheet. Then they turn into a pair of stripes. A particle or atom passes through both slits at the same time unless you watch it, then it only passes through one. Basically, quanta need to become entangled with a measuring device to behave like particles, otherwise they act like waves. So basically all matter is waves propagating through space, and the waves only collapse into particles once they become entangled in some outside context. Matter is fuzzy until you look at it.
