Can Quantum Mechanics Explain How We Smell?

The idea is controversial, but gaining ground.

(PhysOrg.com) -- Since 1996, when biophysicist Luca Turin first suggested that quantum mechanics may help explain how we smell various odors, the idea has met with controversy. In the past 15 years, some studies have found evidence supporting the theory, while other studies have found problems with it. Now Turin - who is currently at MIT and the Fleming Biomedical Sciences Research Centre in Vari, Greece - along with his colleagues, has published a study that provides further evidence for the vibration theory of smell, and may make the theory a bit less controversial.

In the traditional “lock and key” model of smell, odorant molecules of different shapes and sizes fit into different receptors, similar to the current understanding of how drugs affect the body. When a molecule enters a receptor, the receptor sends a signal to the brain, and we smell that molecule.

However, there is one problem with this model, which is that some molecules with nearly identical shapes smell very different. This evidence suggests that some other criteria in addition to size and shape must cause receptors to react differently and to send different signals to the brain.

According to Turin’s theory, the additional criteria are the vibrational frequencies of odorant molecules. A molecule’s vibrational frequency can cause electrons in the nasal receptors to tunnel between two energy states if the vibrational frequency matches the energy difference of the two states. Tunneling is a quantum mechanical phenomenon, since the electrons do not have enough energy to move between the two states by classical means.

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