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?
The
Physics of Smell