Monday, March 1, 2010

B Fwd: Metamodern Chemists deserve more credit: Atoms, Einstein, and the Matthew Effect

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Date: Wed, Feb 17, 2010 at 7:33 PM
Subject: Metamodern (1 new item)

Metamodern (1 new item)

Item 1 (02/17/10 23:41:52 UTC): Chemists deserve more credit: Atoms, Einstein, and the Matthew Effect

Cork cells, from Hooke's Micrographia
Johann Josef Loschmidt
Chemist, atomic scientist

Chemists understood the atomic structure of molecules in the 1800s, yet many say that Einstein established the existence of atoms in a paper on Brownian motion, "Die von der Molekularkinetischen Theorie der Wärme Gefordete Bewegung von in ruhenden Flüssigkeiten Suspendierten Teilchen", published in 1905.

This is perverse, and has seemed strange to me ever since I began reading the history of organic chemistry. Chemists often don't get the credit they deserve, and this provides an outstanding example.

For years, I've read statements like this:

[Einstein] offered an experimental test for the theory of heat and proof of the existence of atoms….
["The Hundredth Anniversary of Einstein's Annus Mirabilis"]

Perhaps this was so for physicists in thrall (or opposition) to the philosophical ideas of another physicist, Ernst Mach; he had odd convictions about the relationship between primate eyes and physical reality, and denied the reality of invisible atoms.

Confusion among physicists, however, gives reason for more (not less!) respect for the chemists who had gotten the facts right long before, and in more detail: that matter consists of atoms of distinct chemical elements, that the atoms of different elements have specific ratios of mass, and that molecules consist not only of groups of atoms, but of atoms linked by bonds ("Verwandtschaftseinheiten") to form specific structures.

When say "more detail", I mean a lot more detail than merely inferring that atoms exist. For example, organic chemists had deduced that carbon atoms form four bonds, typically (but not always) directed tetrahedrally, and that the resulting molecules can as a consequence have left- and right-handed forms.

The chemists' understanding of bonding had many non-trivial consequences. For example, it made the atomic structure of benzene a problem, and made a six-membered ring of atoms with alternating single and double bonds a solution to that problem. Data regarding chemical derivatives of benzene indicated a further problem, leading to the inference that the six bonds are equivalent. Decades later, quantum mechanics provided the explanation.

The evidence for these detailed and interwoven facts about atoms included a range of properties of gases, the compositions of compounds, the symmetric and asymmetric shapes of crystals, the rotation of polarized light, and the specific numbers of chemically distinct forms of molecules with related structures and identical numbers of atoms.

And chemists not only understood many facts about atoms, they understood how to make new molecular structures, pioneering the subtle methods of organic synthesis that are today an integral part of the leading edge of atomically precise nanotechnology.

All this atom-based knowledge and capability was in place, as I said, before 1900, courtesy of chemical research by scientists including Dalton, van 't Hoff, Kekulé, and Pasteur.

But was it really knowledge?

By "knowledge", I don't mean to imply that universal consensus had been achieved at the time, or that knowledge can ever be philosphically and absolutely certain, but I think the term fits:

A substantial community of scientists had a body of theory that explained a wide range of phenomena, including the many facets of the kinetic theory of gases and a host of chemical transformations, and more. That community of scientists grew, and progressively elaborated this body of atom-based theory and technology to up to the present day, and it was confirmed, explained, and extended by physics along the way.

Should we deny that this constituted knowledge, brush it all aside, and credit 20th century physics with establishing that atoms even exist? As I said: perverse.

But what about quantitative knowledge?

There is a more modest claim for Einstein's 1905 paper:

…the bridge between the microscopic and macroscopic world was built
by A. Einstein: his fundamental result expresses a macroscopic quantity — the coefficient of diffusion — in terms of microscopic data (elementary jumps of atoms or molecules).
["One and a Half Centuries of Diffusion: Fick, Einstein, Before and Beyond"]

This claim for the primacy of physics also seem dubious. A German chemist, Johann Josef Loschmidt, had already used macroscopic data to deduce the size of molecules in a gas. He built this quantitative bridge in a paper, "Zur Grösse der Luftmoleküle", published in 1865.

I had overlooked Loschmidt's accomplishment before today. I knew of Einstein's though, and of a phenomenon that the sociologists of science call the Matthew Effect.
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