Wave and Wave Speeds (aka, the Boring Backround to Interesting Stuff)

So we left off with the most basic mathematical description of a wave. It’s a function of the form f(x – vt), or in words a disturbance that moves from one place to another at a constant speed without changing shape. This is a nice start, but it’s both too general and not general enough…

What’s a wave?

So, what’s a wave? In his deservedly ubiquitous undergrad electrodynamics textbook, David Griffiths emphasizes the fact that the whole idea is pretty nebulous. Any rigid definition is likely to exclude things that are usually thought of as waves or to include things that aren’t. He suggests that one possible vague definition is “a disturbance of…

Dropping Rocks: Los Angeles

So there’s this alien invasion flick called Battle: Los Angeles. It’s getting mixed reviews. Ebert hates it – “an insult to the words “science” and “fiction,” and the hyphen in between them.” With the caveats that his judgment is usually questionable, I haven’t seen the movie, and I don’t plan to see the movie, I’m…

On Free Parameters

In the last post I talked about a measurement we did in our lab to characterize some properties of two parallel laser beams. The theory, if you want to dignify that equation with such a title, gave the power of the two beams as a function of mow much of the beams we cut off…

Random Thoughts on a Trivial Lab Measurement

A while back in the lab we were conducting an experiment that involved passing a laser beam through a narrow iris, using a beamsplitter to take half the intensity of the beam and send it one way, with the remaining half passing through undisturbed. Then we arranged our mirrors in such a way as to…

The Hydrogen Partition Function, or, How Matt Didn’t Pay Attention

I always tell my students that they should never just write down an equation blindly and start plugging things in. If you don’t understand what you’re doing, you’re much more likely to make a mistake. Sometimes I don’t take my own advice. On a science forum I read occasionally, a person who was just taking…

Quantum Bouncing Ball, Concluded

Well, last time we were looking about the classical probability density for a bouncing ball, and the quantum mechanical probability distribution for the same. They looked not even a little bit alike. This is kind of a problem, since we know from experience that classical physics works pretty well, and from more modern work we…

Amateur Lunar Ranging? Hmm.

All right, I’m gonna delay the next installment of the quantum bouncing ball for a brief diversion. I have a friend who’s also a physics grad student, and he suggested that we along with a few other fellow students form a yet-to-be-named unofficial club whose raison d’etre is to get together every few weeks and…

Classical Wavefunctions

Right now I’m on the 4th floor of the physics building. If I walk down the hall to the balcony overlooking the atrium, I could drop a bouncy ball and watch its trajectory. It’ll fall to the ground, bounce up to some fraction of its initial height, and repeat the process with a loss of…

Data or Dust Speck?

Shortly after the invention of the laser, a torrent of discoveries began pouring in thanks to the previously unreachable intensities that became available. Many of these discoveries fall under the general category of “nonlinear optics”, which you could more or less say is the study of the behavior of light in a medium whose optical…