Talk about a no-brainer: it weighs a kilogram, duh! Ah, but it’s not as simple as that. For time, it’s easy to figure out.  The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom (official BIPM definition). See? Easy-peasy!

Once we’ve defined time, we’ve got the wonderfully constant speed of light to help us sort out distances. The metre is “the length of the path travelled by light in vacuum during a time interval of 1⁄299,792,458 of a second”. Simple-pimple.

A computer-generated image of the International Prototype Kilogram (“IPK”).

So, how much does a kilogram weigh? Up until recently, scientists were satisfied that this cylinder made of a platinum-iridium allow was THE kilogram. This as been the big-boy of weights since 1889. Unfortunately, there’s a hitch: it’s weight is changing. Bad idea, to have the object that forms the world’s basis for determining all weights change. Weight Watchers and Jenny Craig would be destroyed, for crying out loud!

Well, those wacky scientists, they just loves them some numbers. Even more, they love constants that represent numbers. Constants, by their very nature, don’t change. Hence their consistency. If they can figure out a way to define a kilogram in relation to one of those consistently constant numbers, we won’t have to worry if the mass of a little shiny chunk of metal loses (or gains) mass.

Since weighing the kilogram against another mass contains all the same pitfalls that have led to the current dilemma, the brilliant boys and girls over at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD, have set physicist Richard Steiner the task of calibrating the kilo against a concrete constant, namely Planck’s constant. NPR had a neat article on this morning chronicling the herculean effort being made out in a racoon-infested shed in Maryland to nail down the kilogram.

I won’t spoil the surprise and tell you how it turns out. Go read the article to find out how this nail-biter turns out.  Perhaps if they are successful, the United States will finally switch to the metric system. Sh’yeah, and monkeys might fly out of my butt!

(via NPR)

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