Yes, I've been writing, just not blogging away, until today.
A new thought on A Serious Man: the first words in English in the movie are “when the truth is found to be lies…” This is what eventually happened to us, the innocent viewers, with the Coen Bros’ movie Fargo. They billed it as a true story, but it wasn’t. I was rather happy to hear that, however, and all the joy in me did not die. Given all the suffering that goes on in the world, it was and is good to know that the particular suffering shown in that movie had not actually happened. The trick of telling viewers it was a true story had the desired effect, at least in me. It intensified the emotional experience of watching the movie. So I’m not pissed at the Bros for lying. I can imagine the subterfuge of Fargo was on their minds while they were writing A Serious Man, which is itself a subterfuge on a more humorous level.
Now, how is the three-polarizer experiment a demonstration of quantum superposition? I wanted to talk about Gary Zukav’s description of the experiment, but I haven’t found The Dancing Wu Li Masters amongst my approximately 1,000 books. I was reading from it earlier this year, so it’s around somewhere, but I’ll have to do without it for now.
First of all, what the heck does “superposition” mean? Sounds vaguely sexual to me, but then so does about everything else. Classically, as opposed to quantumly, superposition means just what it sounds like, at least in the case of waves being superimposed. As Frank Blatt, a physicist with a physical sounding last name, puts it in his first-year physics textbook, “when a transverse wave on a string is reflected at a fixed end, the incident and reflected waves superpose so as to create a standing wave.”
You can create this condition by tying one end a rope or cord to a doorknob (works best with the door closed) and shaking the other end up and down. If you shake at the right rate, you can see a standing wave pattern: one hump, two humps, three humps, etc. Under these conditions, waves traveling in opposite directions are combining with each other (linearly) to produce a standing wave. It’s also called resonance.
If you yourself have taken a first-year physics course, you might have seen the demonstration of this standing wave phenomenon in the lab, where a mechanical vibrator is used (yeh, the sexual innuendos again). I myself have done that experiment many times as a lab assistant or lab instructor. With the rope on the doorknob, ya cain’t hardly get a good standing wave, but with a long piece of string in the lab, it looks very neat—big good vibrations, showing a larger and lower frequency version of what happens with stringed instruments as they are being played
In addition to standing waves on strings, there are acoustic standing waves (wind instruments and singing—in the shower especially), and electromagnetic standing waves, and water or other liquid standing waves. You know about the “rubbing the rim of the wine glass” sound, right? You get standing waves in the wine and the glass then. Also, waves combine with each other to produce the phenomena of interference and diffraction.
Like waves on a string, electromagnetic waves are transverse. For transverse waves (try the polarization hand waving thing again) the oscillatory motion is perpendicular to the direction the wave is traveling. In contrast, sound in air is composed of longitudinal waves. The oscillatory motion of the medium is along the same direction as the direction of travel of the wave. If you and a friend stretch a Slinky along a flat surface, and then one of you pushes on the Slinky and pulls back, the compression travels to the other end as a longitudinal wave. The same thing happens with air when it carries a sound wave: a back and forth motion along the direction the wave is traveling.
Going back to the cord tied to the door knob: you choose the direction of polarization of the wave by choosing whether to move your hand up and down or sideways, or in between. So now do you think you’ve got the idea of the polarization thing? Sure you do! Congratulations! So you can see that a longitudinal wave isn't subject to being polarized! (Gettin’ out of the necessary range of the eventual quantum superposition discussion now. But anyway, happy 4th of July weekend.)
