Quantum Physics: An Example

Family Guy this week was awesome. For once, it was more than just a clever story with jokes, it actually had a theme. AND the cast of Star Trek: The Next Generation. I mean, come on, obvious Emmy.

As I watched the Christians throwing books on the fire, I laughed when one was Stephen Hawking's "A Brief History of Time". Because that was arguably the first book I read that opened my eyes to existence. I devoured it and anything else I could find after that. I would (and still do) check the "Science" section at Borders every time I went in the store, for anything new. Why? Because Quantum Physics reads like an entire volume of "The Truth-Is-Stranger-Than-Fiction Files". Let me give you some examples, and if I butcher the content I apologize.

It is my task to convince you not to turn away because you don't understand [quantum physics]. You see my physics students don't understand it. ... That is because I don't understand it. Nobody does.
(Feynman, Richard P. Nobel Lecture, 1966, 1918-1988, QED, The Strange Theory of Light and Matter)

Quantum Electrodynamics (QED):

Straight from the horse's mouth at Wikipedia:

In classical optics, light travels over all allowed paths and their interference results in Fermat's principle. Similarly, in QED, light (or any other particle like an electron or a proton) passes over every possible path allowed by apertures or lenses. The observer (at a particular location) simply detects the mathematical result of all wave functions added up, as a sum of all line integrals.

Allow me to explain. :D When you turn over a CD/DVD to look at the recordable surface, you will see rainbow, or prismatic, lighting. Now, what you are actually looking at is a set of very tightly packed concentric circles. Like an old LP, but with grooves so small that it uses a laser to read/write data. When you see the prism effects, you'll notice that they aren't related to what is recorded on the disc. That is because they are caused by the physical shape of the disc, with its millions of concentric circles. They are actually effects explained by QED.

Light can be thought of as behaving as both a particle and a wave, as known from the most famous QM experiment, the double-slit experiment. In this case, think of it as a wave. Now, think about a beam of light, as it travels from a light source to your eye. It's oscillating along, like a slalom skiier, when it bounces off of the surface of the optical disc and is reflected towards your eye.

Since the data on the DVD is written in the visible-light spectrum, the following aspect of Quantum Physics becomes visibly apparent:

When light travels from point A to point B, it does not take the shortest path, or in fact any ONE path. It simultaneously takes all of the possible paths.

The evidence? The prisms you see when reflecting the light. The colors come from the fact that light takes on multiple paths. Some are directly reflected to your eye, some take a more roundabout way to get there, and interfere with nearby lightwaves which are also bouncing off the surface. What you end up seeing is a wave-addition of ALL the beams traveling ALL of the possible paths to get from the source to your eye.

It may seem like something simple is happening here, but trust me, it's far weirder than it first appears. It's not just that a bunch of light beams get blended to form constructive/destructive interference. If you take it down to one light particle or "photon", and fire one singular photon at an optical disc, it alone will travel ALL possible paths to get to your eye.

Now this is including the paths that take it to Mars and back, although those paths are of the "less likely" sort. Why does that matter? Because the light that reaches your eye isn't a sum of all of the paths of light treated equally, but rather, each path is weighted according to how likely it is. The most likely path in this case IS the shortest path. Paths very close to the shortest are the next most likely candidates. Very quickly as you get further from the shortest path, they become astronomically unlikely, and contribute virtually nothing to the end result.

But the close ones, the REALLY close ones, do count in the final result. And some of those really close ones bump into the adjacent walls of the grooves of the optical disc, causing them to take slightly altered paths, creating the prismatic intereference that we see.

*****

Quantum Physics is like that up-and-down. When Newtonian physics describes an object (apple) falling towards another object (the earth), it talks about some strange force that draws all bodies together. Einstein saw that instead, the universe, space itself is bent by gravity, so that "the apple falling" is actually just, if you'll excuse the hyperbole, "the universe settling into a more comfortable position." It's not that the apple and the ground are separate objects attracted to each other, but rather one giant mesh that shifts around. And did I mention that space and time are also the same thing? Think about it, you've heard of "space-time" before, but have you considered the ramifications? Space = time = space? Interchangable like currencies? The ramifications are huge, but I'll discuss those another day.

If you're looking for good reading choices to get started on your own, "A Brief History of Time" is a wonderfully accessible introduction to quantum physics and cosmology, by the guy who predicted the existence of black holes. Another great author, and the "discoverer" of QED, is quoted above, Richard Feynmann. He has a famous series of lectures among other materials, and is both brilliant and delightfully entertaining, especially for all of the non-physicists in the world.