Brown Marmorated Stink BugThe Physics of Smell
                                    Copyright of Bigstock                action, reaction, and olfaction synthesized...               

Ian MacDougall, Physics 104, Spring 2012

    Introduction         Shape Theory       
   Electron Tunneling             Vibration Theory           Bibliography

    Smell is one of our five basic senses, but key steps in the mechanism of smell (olfaction) remain unknown. We know that particles move from the source of smell through the air to our nasal membranes by the process of diffusion, and we're very familiar with the neurological pathways that happen after the odor has been detected, but the happenings in between are still in debate. Previous science suggested that molecules and receptors functioned as simple 'lock and keys' - that a molecule has a categorical shape that fits into a corresponding receptor in our noses. This is known as the Shape Theory - smell influenced by the shape of odorant and receptor. However, folks began to notice that similarly-shaped molecules sometimes have different smells, and very different-shaped molecules sometimes have similar smells. This led to the proposal of a new theory - Vibration Theory. In order to explain the mechanisms of vibration theory, we have to turn to the darker side of physics: quantum mechanics - specifically electron tunneling. If correct, this is truly exciting science: every sip of wine, bite of cake, fist of fries; every smell-triggered memory of spring and love; every repulsive or irresistible smell has an explanation directly grounded in quantum physics. Pretty cool, huh?