Musing about units
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s materials researchers, all of us (whether we’re materials scientists, physicists, chemists, biologists, geologists, engineers, or other) very quickly learn the importance of units. Many introductory textbooks have special sections or chapters discussing units and how to use them. The world standard now is SI units 1 (otherwise known as mks units), but for most of us our choice of units (including cgs units) is probably based upon whether or not the units seem natural for the problem that we’re working. For me, it seems more natural to use mks units for some problems, cgs units for other problems, and use other units as needed. So I reacted rather badly when I received a request from a colleague the other day who wanted a group of us who are working on various aspects of a complex problem to provide all of our results in cgs units. I responded by
sending out the following intemperate email message: “Cgs units?!! Cgs units??! You guys are killing me! What is this cgs nonsense? Hasn’t the entire world settled on SI units, i.e., mks for old-timers like me? Do any reputable people use cgs units? Isn’t this anathema—blasphemy of the highest order? Won’t we be reviled in the bastions of science? Won’t there be newspaper, radio, and tv reporters camped at our doorstep? Won’t our role as the guardian of public virtue be debated in the halls of Congress? Won’t we find protestors howling in the streets about our lack of conformity to the norms of civilized society? I call for a vote! Nay, I demand my day in court! If we allow you to force us to use cgs units today, tomorrow you’ll take our lunch money, and then you’ll force us to wear white dress MRS BULLETIN
shirts and even (Gasp!) neckties. You’ll have to pry my mks units from my cold dead hands! I’d sooner eat turnips!” [Note: I do apologize to those of you who like white dress shirts and turnips, but I loathe neckties and am unrepentant in my distaste for them.] This started me thinking about our confusing approach to units and the inconsistencies surrounding our use of them. Notwithstanding the fact that most of us probably use the units most appropriate for the problem at hand, I know that there are communities that prefer a select set of units for a given field. Some of this may be because those involved feel that they understand science or engineering analysis better when framed in one set of units than another. Some of this may be due to their teachers, who chose particular sets of units. An example of this involves the classic (pun fully intended) text on •
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electrodynamics by John D. Jackson,2 which uses electrostatic units. Over the years, I’ve been around numerous debates involving defenders of Jackson’s excellent text as well as those who don’t like it because of the use of electrostatic units. I remember other debates about which units are best for nonlinear optics as well as other more esoteric subjects, although I must admit that those debates were so long ago that I’ve forg
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