This is a post that I wrote a while ago but never got around to publishing. It’s no longer a current news story, but still interesting!
There’s a story recently reported by the BBC and others about a theory of the sense of smell – what’s interesting about this theory is that it’s not based purely in biology, as you might think, but instead applies quantum physics to biological systems.
This is particularly interesting for me as it’s related to my own work (I study the theory of vibrations in quantum nanostructures). Anyway, the essence of the story is this: conventionally, biologists have always thought that our noses process smell by using the shape of molecules. Each molecule has a specific shape that fits another “detector” molecule in the nose, like a key fitting in a lock. This then sends a signal to the brain which it then interprets as “mmm, coffee” (or more likely, “oh dear, time for a nappy change”, in my house).
But this new theory depends not on the shape of the molecules, but on the way they vibrate. You can imagine a molecule as little balls (the atoms) held together by springs. If you could give one of the balls a little flick, you give it some energy that travels through the springs and makes the whole molecule vibrate. Each molecule has its own special way of vibrating, with several “notes” at different frequencies, much as the way different musical notes make up a chord. Physicists call these different vibrational frequencies (notes) “phonon” modes – a phonon is quantum of vibrational sound energy, and each phonon has an associated frequency, or mode.
The new study that’s been published used fruit flies (Latin name drosophila) to see if they could tell the difference between normal molecules and ones where the hydrogen atoms in the molecules were replaced with deuterium (just the same as hydrogen, but it’s heavier as it has a proton in addition to hydrogen’s neutron and electron). Changing the hydrogen to deuterium is a good test because the extra mass changes the vibrational frequencies of the molecules, but not their shape. In my musical analogy, this is as if a molecule that would normally “play” a chord of C major now plays a C minor chord instead. So if the flies can tell the difference between the ordinary molecules and the heavy molecules, this would be good evidence that smell is based on the vibration of the molecule, not the shape.
And guess what? The flies can tell the difference! Apparently they didn’t like the molecules with deuterium rather than hydrogen and flew away from them (I am no fly-behaviourist, so not sure how they did this bit of the research).
I think there’s a lot more work to be done in this area before we can know for certain what role vibration plays in the sense of smell, but this is a very interesting piece of research that couples together phenomena normally only found in quantum physics with biology.
More information:
- The original research was published in the Proceedings of the National Academy of Science journal.
- Take a look at this great TED talk by Luca Turin, one of the authors of the vibrational theory of smell.
The Alliance of Science 