imagine taking a walk through your favorite park you can smell the morning
dew the unique smells of plants soil and distant flowers a feeling of calm and
relaxation saturates you all these sensations are due to the very special
nature of your sense of smell what you may not realize is that inside your nose
rests a very sensitive quantum device that uses complex physics to give you
the ability to distinguish according to the latest estimates one trillion
different smells how does your sense of smell actually work and what does
quantum mechanics have to do with it that's coming up right now in order for
you to smell anything molecules from that thing have to make it to your nose
everything you smell is volatile in some way meaning it is giving off molecules
that float into the air and land inside your nose so whether it's the morning
flowers or your coffee or bacon or the foul stench of dog feces the molecules
from that source are floating in the air and entering their nose but how did
these molecules trigger the sensation of smell at the top of your nasal passages
behind your nose there's a patch of special neurons about the size of a
postage stamp called the olfactory epithelium they have here like
projections called cilia that increase their surface area any molecule from
anything with a smell binds to special smell receptors on these cilia and
triggers the neuron causing a signal to your brain
this signal ends up in a primitive part of the brain called the limbic system
which is associated with emotions and memory so that's why smells can trigger
strong memories and emotional reactions these neurons are unique in that they
come directly from your brain and are out of the open where they can come into
contact with the air so this is the only place on your body where your central
nervous system is directly exposed to the environment now the question is how
did the neurons get triggered the standard explanation going back to
the 1950s had been that the receptors and the ends of these olfactory neurons
and there are about 400 such smell receptors can only accept particular
shapes of molecules and the exact type of smell is determined by how the
molecules from the smelly compounds fit in the set of receptors of the receiving
factory neurons by triggering a particular combination of the 400 smell
receptors the brain interprets a particular kind of smell it's like a
lock and key the key is the shape of the molecules of the smelly compounds and
the lock is the olfactory receptors one combination can trigger the smell of a
rose another combination can trigger the smell of rotten eggs and so on so the
thought is that what you are really smelling are shapes of molecules this
was the standard explanation for the mechanism of the smell
until researchers discovered that you can have molecules of different shapes
that have the same smell so for example cyanide smells the same as benzaldehyde
a bitter almond smell but they're vastly different shapes so scientists concluded
that there must be something more than just the shapes that determine smell
well it turns out that although the shapes are different cyanide and
benzaldehyde had the same vibration a new research suggests that it is indeed
not just the shapes of the molecules but also the vibrations of these molecules
that determines how we perceive smell all molecules vibrate with a certain
frequency and temple based on their structure bonds and weight it's
analogous to sounds coming from various instruments due to their various shapes
Luca Turin a bio physicists at the Alexander Fleming Research Centre in
Greece conducted experiments using the smell of sulfur compounds he identified
molecules that have the same vibrational frequency as sulfur but with completely
different molecular shapes than sulfur what he found was that these compounds
with the same vibrational frequency of sulfur do indeed smell
like sulfur even though their molecules are shaped completely differently
Turin's research is not accepted by all olfactory researchers but if he's right
how is our nose able to smell the vibration of molecules in quantum
mechanics so-called particles like electrons are really waves of
probabilities until the moment they're measured the probability wave is such
that when the particle encounters a barrier the probability wave does not
stop at the barrier but continues through for a short distance so there's
a nonzero probability that the electron will go straight through the barrier and
show up on the other side of the barrier or the tunnel through that's why this is
called quantum tunneling in classical physics this would be forbidden but it
is observed in nature due to the laws of quantum mechanics it is theorized that
the vibrations of certain molecules might allow electrons from certain smell
receptors to tunnel through to other small receptors and trigger signals in
the neurons and then subsequently to the brain different molecules with different
vibrations can cause different rates of tunneling when the molecule of the order
has a certain frequency that matches the energy of the receptor quantum tunneling
works in such a way that it opens a gateway for an electron to tunnel more
preferentially than went the molecule and it's vibration is not present in a
way you might say our noses not only small shapes but here shapes too using
the complex physics of quantum mechanics to do it how could our noses have
evolved its sophisticated sensory mechanism turing has an interesting
answer he says four billion years of R&D with unlimited funding it's a long time
indeed evolution is a process we've probably greatly underestimated far
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