Skip to main content

Lens grinding and Avogadro's number

A bunch of scientists are working on defining the kilogram using fundamental constants of physics, rather than the weight of a particular chunk of metal, as it is now.  But before they can do that, they've got to determine Avogadro's number—the number of atoms in a particular mass of an element, 6.022 x 10^23 if I'm not mistaken—to unprecedented precision.  One strategy is to make a sphere weighing exactly one kilogram, and then count the number of atoms, thereby reverse-engineering the kilogram.  The trouble is, the sphere has to be as close to perfect as humanly possible.  How is the world's most perfect sphere created?  By hand.  No, really:
To improve on the precision of his result from the 1970s and ’80s, Becker needed to reduce the irregularity of his silicon surfaces. He commissioned one of the world’s most renowned lensmakers — a German immigrant in Australia named Achim Leistner — to craft the most perfect sphere ever created, a flawless orb honed precisely to the mass of Le Grand K.
Leistner describes his job as “massaging atoms.” He works by hand because he believes — and the most advanced computer imaging has confirmed — that no machine can match his touch. Taking a 1.01-kilogram silicon ball crudely cut on a 3-D lathe to within 10 micrometers of sphericity, Leistner spends several months polishing the surface by spinning the object inside a pair of funnels — like a scoop of ice cream held between two cones — until he can feel the molecular structure of the cubic silicon crystal itself with his fingertips, 12 edges and eight corners barely protruding from the rounded surface. Then the hard work begins. Without letting the mass of the sphere drop below the 1-kilogram mass of the international prototype, Leistner must polish each of the nearly imperceptible edges and corners, removing mere nanometers of material per week. Since a several-atom layer of silicon dioxide (more familiarly known as quartz) forms on the surface whenever he stops spinning the sphere, and since quartz is much harder than pure silicon, he can spend as many as six hours a day carefully buffing off the oxide layer before reaching the silicon atoms to be shaved.
 Unbelievable.

Comments

Post a Comment

Popular posts from this blog

Why Did Reality Winner Leak to the Intercept?

So Reality Winner, former NSA contractor, is in federal prison for leaking classified information — for five years and three months, the longest sentence of any whistleblower in history. She gave documents on how Russia had attempted to hack vendors of election machinery and software to The Intercept , which completely bungled basic security procedures (according to a recent New York Times piece from Ben Smith, the main fault lay with Matthew Cole and Richard Esposito ), leading to her capture within hours. Winner recently contracted COVID-19 in prison, and is reportedly suffering some lingering aftereffects. Glenn Greenwald has been furiously denying that he had anything at all to do with the Winner clusterfuck, and I recently got in an argument with him about it on Twitter. I read a New York story about Winner, which clearly implies that she was listening to the Intercepted podcast of March 22, 2017 , where Greenwald and Jeremy Scahill expressed skepticism about Russia actually b

On Refusing to Vote for Bloomberg

Billionaire Mike Bloomberg is attempting to buy the Democratic nomination. With something like $400 million in personal spending so far, that much is clear — and it appears to be working at least somewhat well, as he is nearing second place in national polls. I would guess that he will quickly into diminishing returns, but on the other hand spending on this level is totally unprecedented. At this burn rate he could easily spend more than the entire 2016 presidential election cost both parties before the primary is over. I published a piece today outlining why I would not vote for Bloomberg against Trump (I would vote for Sanders, Warren, Buttigieg, Klobuchar, or Biden), even though I live in a swing state. This got a lot of "vote blue no matter who" people riled up . They scolded me and demanded that I pre-commit to voting for Bloomberg should he win the nomination. The argument as I understand it is to try to make it as likely as possible that whatever Democrat wins t

Varanus albigularis albigularis

That is the Latin name for the white-throated monitor lizard , a large reptile native to southern Africa that can grow up to two meters long (see pictures of one at the Oakland Zoo here ). In Setswana, it's called a "gopane." I saw one of these in my village yesterday on the way back from my run. Some kids from school found it in the riverbed and tortured it to death, stabbing out its eyes, cutting off its tail, and gutting it which finally killed it. It seemed to be a female as there were a bunch of round white things I can only imagine were eggs amongst the guts. I only arrived after it was already dead, but they described what had happened with much hilarity and re-enactment. When I asked why they killed it, they said it was because it would eat their chickens and eggs, which is probably true, and because it sucks blood from people, which is completely ridiculous. It might bite a person, but not unless threatened. It seems roughly the same as killing wolves tha