Talk like a physicist!

Today is Talk like a Physicist Day! It coincides with Pi Day.

Many people seem to be interpreting this in different ways. From my perspective, I always talk like a physicist, by definition, at least insofar as I'm a physicist. I coauthored a paper once, so I think that qualifies me! So what is the point of setting aside a special day to talk like I always do?

Well, it must be so I can get all of you to talk like physicists too!

Here's some physicist-speak that deserves to be normal-speak:

Negligible - This word describes something so small that we can easily neglect it without affecting our calculations. In fact, we should neglect it, in order to simplify the calculations. Example: "Walking to the trash can takes a negligible amount of time, so stop littering!"

First-order approximation - This is the best rough estimate we can get of something by only considering the biggest numbers in our calculations. If we look more closely at the details, it becomes a second-order approximation. Example: "To a first-order approximation, I like all music."

Non-trivial - This describes a problem that is so complicated that the first-order approximation is wildly inaccurate, and the details are not negligible at all. Example: "Figuring out what he wants for his birthday is a non-trivial problem."

There's probably more that I'm not thinking of, but those are the most important ones. Did you expect me to say things like "muon", "Fourier transforms", or "wavefunction collapse"? Don't be ridiculous! That's not at all how a physicist normally speaks! Except perhaps when they speak to each other. ;)

Update: See Uncertain Principles and the comment discussion for a more complete list! How could I have forgotten "orthogonal"?