with olfaction, taking quantum mechanics into consideration, suggest that ultimately both theories might work in harmony - first the scent molecules need to fit, as in the docking theory of olfaction model, but then the molecular vibrations of the chemical/atom bonds take over. So in essence your sense of smell could be much more like your sense of hearing, where your nose could be 'listening' to the acoustic/vibrational bonds of aroma molecules. Some studies support vibration theory while others challenge its findings. Major proponents and history The theory was first proposed by Malcolm Dyson in 1928 and expanded by Robert H. Wright in 1954, after which it was largely abandoned in favor of the competing shape theory. A 1996 paper by Luca Turin revived the theory by proposing a mechanism, speculating that the G-protein-coupled receptors discovered by Linda Buck and Richard Axel were actually measuring molecular vibrations using inelastic electron tunneling as Turin claimed, rather than responding to molecular keys fitting molecular locks, working by shape alone. In 2007 a Physical Review Letters paper by Marshall Stoneham and colleagues at University College London and Imperial College London showed that Turin's proposed mechanism was consistent with known physics and coined the expression "swipe card model" to describe it. A PNAS paper in 2011 by Turin, Efthimios Skoulakis, and colleagues at MIT and the Alexander Fleming Biomedical Sciences Research Center reported fly behavioral experiments consistent with a vibrational theory of smell. The theory remains controversial. Support Isotope effects A major prediction of Turin's theory is the isotope effect: that the normal and deuterated versions of a compound should smell different, although they have the same shape. A 2001 study by Haffenden et al. showed humans able to distinguish benzaldehyde from its deuterated version. However, this study has been criticized for lacking double-blind controls to eliminate bias and because it used an anomalous version of the duo-trio test. In another study, tests with animals have shown fish and insects able to distinguish isotopes by smell. Deuteration changes the heats of adsorption and the boiling and freezing points of molecules (boiling points: 100.0 °C for H2O vs. 101.42 °C for D2O; melting points: 0.0 °C for H2O, 3.82 °C for D2O), pKa (i.e., dissociation constant: 9.71×10−15 for H2O vs. 1.95×10−15 for D2O, cf. Heavy water) and the strength of hydrogen bonding. Such isotope effects are exceedingly common, and so it is well known that