A controversial theory that the way we smell involves a quantum physics effect has received a boost, following experiments with human subjects. It challenges the notion that our sense of smell depends only on the shapes of molecules we sniff in the air.
Instead, it suggests that the molecules’ vibrations are responsible. A way to test it is with two molecules of the same shape, but with different vibrations. A report in PLOS ONE shows that humans can distinguish the two.
Tantalisingly, the idea hints at quantum effects occurring in biological systems – an idea that is itself driving a new field of science, as the BBC feature article Are birds hijacking quantum physics? points out.
But the theory – first put forward by Luca Turin, now of the Fleming Biomedical Research Sciences Centre in Greece – remains contested and divisive. The idea that molecules’ shapes are the only link to their smell is well entrenched, but Dr Turin said there were holes in the idea.
He gave the example of molecules that include sulphur and hydrogen atoms bonded together – they may take a wide range of shapes, but all of them smell of rotten eggs. “If you look from the [traditional] standpoint… it’s really hard to explain,” Dr Turin told BBC News.
“If you look from the standpoint of an alternative theory – that what determines the smell of a molecule is the vibrations – the sulphur-hydrogen mystery becomes absolutely clear.”
Molecules can be viewed as a collection of atoms on springs, so the atoms can move relative to one another. Energy of just the right frequency – a quantum – can cause the “springs” to vibrate, and in a 1996 paper in Chemical Senses Dr Turin said it was these vibrations that explained smell.
The mechanism, he added, was “inelastic electron tunnelling”: in the presence of a specific “smelly” molecule, an electron within a smell receptor in your nose can “jump” – or tunnel – across it and dump a quantum of energy into one of the molecule’s bonds – setting the “spring” vibrating.
But the established smell science community has from the start argued that there is little proof of this.