Thursday, August 20, 2009

What's a henweigh? About a KILOGRAM??

Ok, this story on NPR this morning about the weight of the kilogram had me thinking that analytical people just need to take some lessons from general chemistry and significant figures.

I mean, seriously, everyone's freaking out because "THE" kilogram no longer weighs exactly the same as its copies, and flapping their hands about dramatically that they don't know whether the kilogram "ITSELF" has changed in weight, or if the copies have changed.

When I was taking Gen Chem, then Organic, and then teaching these things to others in subsequent years, I came to accept that all numerical amounts in calculations (even in P-Chem) are only relevant to within certain significant figures because our means of interacting with those amounts are fundamentally limited. Limited by both technical possibility and effect on observed outcome. There may be theoretical applications in which we need to define certain constants, certain amounts, to more precise figures and sometimes those theories get tested, but even then the results are always measured in replicate and determined within a given error.

Similarly, how about if we just accept that there's a certain range of weights out to the Nth decimal place that correspond to "a kilogram" and that there is a margin of standard error, represented by its deviation among "THE" kilogram and all its certified copies? Is it really that big of a deal to know the cosmically most precise, TRUE nature of the kilogram for use in practice? Given the following:

  • a) it's something we made up

  • b) no balance in the world is capable of measuring anything to its exactitude*

  • c) no application in which someone would need to weight out some amount of something for use or characterization would likely ever need to be THAT close
  • d) even if the application wanted to be that precise, the readout/outcome would likely NOT be precisely enough reproducible, for the very same reasons that make "THE" kilogram so hard to measure in the first place

Can't we just accept that we mortal, biological beings cannot manifest the abstract so pedantically and with such theoretical precision? Can't we just let the kilogram be like Plato's ideal, and be comfortable with our ability to represent it as closely as we are reasonably capable? Do we seriously need to go to such lengths as working for about 12 years to get it measured on a Watt balance*, or relate a material construct of it to a physical, mathematical constant? I love NIST, but this is one enterprise that boggles my mind.

*The Watt balance at NIST is barely even stable enough to do this, and also THEY HAVE A RACCOON PROBLEM! Unless I totally misheard the radio story, raccoons get into their rafters and chew up stuff that falls into some of the rooms in the place that houses the Watt balance. I'm sure they work hard not to let their raccoon problem affect their balance, but it just highlights my point that the world, reality and our interactions with them are heterogenous things, so why can't we accept that maybe so is our ability to actually manifest a theoretical amount?


Comrade Physioprof said...

I have no idea what they are, but my understanding is that there are quite practical reasons for NIST to go to these lengths to measure and standardize shit as accurately as humanly possible. I could be wrong, but as far as I'm aware it's not just a bunch of neurotic anal dweebs.

Arlenna said...

I'm sure there are very good reasons for it, but the way it was described just made me laugh. Like "OH MY GOD, WHAT IS THE REAL KILOGRAM???!!11!!!" And the raccoon problems completely cracked me up.

PhizzleDizzle said...

i was listening to this story this morning too!!! it was kind of funny they way they described the raccoons :).

ScientistMother said...

So I didn't listen to the program, but I read the synopsis and thought "wow thats so cool."

I know I am a dweeb, as CPP would say. though CPP, haven't heard any one say dweeb in decades!

Anonymous said...

What molecular models would you suggest for demonstrations in an organic calss?

Arlenna said...

I'm not sure where you can get the ones we use--one of the student groups sells them as a fundraiser, and they are a great set. They are the "Organic Chemistry Set for Student," from Maruzen. The website is, and they have an online store.

Arlenna said...

lol p.s.: I answered my own "not sure" question by the end of my last comment.