Fifth-Century Greek philosopher Democritus, the putative founder of modern science and atomic theory, who laughed constantly and lived more than one hundred years, once had occasion to ponder our sense of smell. It was, he theorized, the result of our nose reading the shape of airborne particles. Democritus called these particles “atoms,” and he thought sweet atoms were “round and of a good size,” while sour ones were “bulky, jagged, and many angled.”
This “shapist” theory of smell, or olfaction, continues to this day. It boils down to the essential concept of tiny pieces of things being “read” by receptors in our nose. Democritus called these pieces “atoms,” but he had no sense of atomic theory in the modern sense, which asserts that these pieces are, in fact, molecules. But that’s just a theory, and the truth is that no one really knows how our sense of smell works. The shapist theory has many inconsistencies and demonstrated limitations. Molecules with the same shape produce different smells; inversely, two molecules with completely different shapes can produce the same smell (sandalwood).
On August 6, 1945, at 8:15am, miles away from the site of the Hiroshima bombing, people reported an impossibly bright light and the smell of burning rubber. This posed a problem for the shape theory of smell: If smell was the result of particulate matter – molecules – landing on receptors in the nose, how then to explain the instantaneous travel of molecules from the blast site to noses miles away?