If you knew the wavelength of a beam of light, you could tell me what most people would see when they looked at it: 480 nanometers looks blue, and 650 nanometers looks red. If you knew the frequency of a musical note, you could name that note: 261 Hertz is middle C.
But if you saw the chemical structure of a molecule, you wouldn’t know what it smelled like—or even if it smelled of anything at all. Unless you actually stick your nose over some benzaldehyde, you wouldn’t be able to predict that it smelled like almonds. If you saw dimethyl sulfide drawn on a page, you couldn’t foresee that it carried the scent of the sea.
— Andreas Keller, Leslie Vosshall and Pablo Meyer are working on the "first step towards reverse-engineering smells". Read more at Scientists Stink at Reverse-Engineering Smells at The Atlantic.