What’s In a Name?

On Monday, I lectured about the strong nuclear force. It’s called that because it’s, well, a force, that acts within the nucleus of the atom, and is, um, strong.

On Wednesday, I’m lecturing about quarks, which are called that because, um, well, because Murray Gell-Mann is a pretentious git, and wanted to show off the fact that he’d read Joyce.

These pretty much span the full range of names in physics, which are either incredibly dull, or painfully dorky. Physicists have many talents, but coming up with good names for things isn’t one of them.

The worst offenders, in terms of sheer numbers, are probably the particle physicists, but that’s because they have so damn many things to name that they might as well be botanists. After the fifteenth different mystery particle, I imagine you start to get a little punchy. The whole spectrum is really there to see in the Standard Model, with the first generation of quarks having boring names (“up” and “down”), while the second get dorky names (“strange” and “charm”). I’m a little disappointed that they chickened out on using “truth” and “beauty” for the third generation– once you have “strange” and “charm” on the books, why not go to eleven. Instead, we got stuck with the incredibly boring “top” and “bottom,” more’s the pity.

Astrophysics is also a target-rich environment for silly names. Here, though, many of them seem to have been given in scorn, but adopted in pride– “Big Bang” is an excellent example. The name was originally a derisive term coined by Fred Hoyle, but it stuck, and now people use it with a perfectly straight face. Worse yet, I’ve seen otherwise serious talks use “gnaB giB” to refer to the possible collapse of the universe back to a singularity. That ought to be a hanging offense, but in a world where dark matter candidates are divided into “WIMP’s” and “MACHO’s” (for “Weakly Interacting Massive Particles” and “MAssive Compact Halo Objects”– excessively cutesy acronyms are another blight on the field), it barely rates a mention.

Of course, my own field of quantum optics/ atomic physics has perpetrated what might be the worst offense of nomenclature in all of science. It takes a bit of explaining, though: in quantum theory, you often talk about “expectation values,” which are roughly like average values of observable quantities. You represent the expectation value using angle brackets, like so:

< O > = ∫ Ψ* O Ψ

where Ψ is the wavefunction for the system of interest, Ψ* is the complex conjugate of the wavefunction, and O represents the operator of interest. You integrate the right-hand side of that equation over all space to get a numerical value for the expectation value.

There’s another form of notation used in quantum optics circles, though, in which you represent the wavefunction and its conjugate as state vectors. The normal wavefunction is:

| Ψ >

while the complex conjugate is:

< Ψ |

In this scheme, the former is called a “ket,” and the latter a “bra,” and when you put them together to make an expectation value:

< O > = < Ψ | O | Ψ >

you get a bracket.

Just shoot me now.