Light behaves as a wave…. it can also behave as a particle, so guess what? Particles can behave like waves too! You spend the first semester of physics learning classical (Newtonian) mechanics and then learned it doesn’t quite work if you’re going near the speed of light so we learn about relativity. Now we find out that when we start looking at very small things, like individual atoms or electrons that once again, classical mechanics doesn’t quite work because at that point the particles are also behaving like waves. This is a very strange thing to think about but the textbook we’re using, Light and Matter, had a fun example where we calculate the de Broglie wavelength of a trotting elephant…. its very very small, too small to even think about it, which is why classical mechanics works just fine on an elephant. But when you calculate the wavelength of an electron you find its wavelength is about the size of an atom, so fairly significant since an electron is much smaller than that.
We also talked about how its very hard to measure something as small as an electron without disturbing it when we make our measurement. The wavelength of visible light that we use to ‘see’ things is much bigger than a typical atom so if we ‘shine’ some light on an atom to observe it, its like hitting a ping pong ball with hot air from a hair dryer. So we learned that just by making a measurement we can affect its outcome.
The Heisenberg Uncertainty Principle also states that we can not know both the momentum and the position of a particle simultaneously with great precision. Again, we showed in class that for things like moving cars, the uncertainity principle really doesn’t effect our measurements, but when were looking at tiny particles we can know its position pretty well or its momentum, but we can’t know both exactly.
Here are some videos on the topics we covered in class.
There’s not much in the way of labs I can set up in my kitchen for quantum mechanics, but a double slit slide that was backordered arrived Monday so we repeated the double slit interference lab that we did earlier this year but with the slits at different distances apart. This isn’t quite the same as the variable slit show in the veritasium video, unfortunately I don’t have one of those…. yet. Once again with the diffraction experiment we found our results to depend very strongly on our measurements of the fringe distances and if I do this lab again I’l make sure we use a much bigger L (distance between the slits on the board we project the interference fringes on), so it will make the fringe separation easier to measure.