'Quantum smell' idea gains ground

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 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.

Columbia University's Richard Axel, whose work on mapping the genes and receptors of our sense of smell garnered the 2004 Nobel prize for physiology, said the kinds of experiments revealed this week would not resolve the debate - only a microscopic look at the receptors in the nose would finally show what is at work.

"Until somebody really sits down and seriously addresses the mechanism and not inferences from the mechanism... it doesn't seem a useful endeavour to use behavioural responses as an argument," he told BBC News.

"Don't get me wrong, I'm not writing off this theory, but I need data and it hasn't been presented."