Interferencia con electrones Sabemos lo que ocurre cuando iluminamos dos rendijas estrechas muy cercanas y estrechas. Se produce un patrón de interferencia en una pantalla situada detrás de las rendijas. ¿Pero qué piensa Ud. que ocurriría cuando objetos sólidos se muevan a través de las rendijas ? objects go through the slits? No entiendo. ¿Qué quiere decir Ud. con objetos sólidos? ¿Se trata a de rocas? Las cosas sólidas no viajan como las ondas, o sí? Olvide Ud. las ondas por un segundo. Imagine un arma disparando balas contra una plancha de hierro con dos rendijas. Si existiera una pared de concreto detrás de la plancha de hierro, ¿qué tipo de patrón Ud. piensa se obtendría por el choque de las balas contra la pared?  Bueno yo pienso que las balas se apilarían justamente detrás de las dos rendijas. Me imagino que  I guess they would bounce off the edges of the holes a little bit, so it wouldn't be real neat, but mostly they would just be in two areas. Right! The bullets don't interfere with each other like waves do... Wait a second! But they might! Two bullets, one from each hole, might bounce into each other and knock each other all over the place. That's a kind of interference, right? Let's think about that. For two bullets to bump into each other would mean they left the gun at the same time. Do machine guns work like that? I hadn't thought about it, but I guess not. No matter how fast the machine gun seems to shoot, it's still just one bullet at a time. So there's no way the bullets could interfere. OK. Now we're going to try an experiment. Using our two slits from before, we're going to use an "electron gun" which shoots a steady stream of electrons, the same particles that orbit atoms, at a sensitive screen... Like a machine gun that shoots really small bullets. Yes. Each time an electron hits the screen it will make a green dot. Try switching it on... Wait a second; it's slowly building up an interference pattern, just like with light. But that doesn't make sense. Are you sure the electrons aren't interfering with each other as they go through the slits? Maybe the electron gun doesn't work like a machine gun, and it shoots a bunch of electrons at once. OK, maybe so. How could we test that? Maybe we could turn down the electron gun until the electrons were coming out slowly enough for us to be sure it was one at a time. Lucky for us it does just that. Use the minus and plus keys on your keyboard to control the speed of the gun, and slow it down a lot. Then press your backspace key to clear the screen. Hey! The interference lines are building up anyway! How can it do that if the electrons are really like little bullets? What are the electrons interfering with? This is so strange... This is quantum physics. What does it mean? How do you explain it? We call it "particle/wave duality"... TO BE CONTINUED