A quantum sense of smell

03/24/15 • 11 min

On the face of it, Johnjoe McFadden and Jim Al-Khalili make unlikely collaborators. McFadden is a molecular geneticist who specializes in the study of tuberculosis. He thinks in pictures and concepts, and his laboratory at the University of Surrey in the UK is full of machines oscillating flasks and people monitoring colonies of bacteria. Al-Khalili, meanwhile, is a theoretical nuclear physicist. He thinks in mathematics and equations, and for the most part his work requires only a whiteboard and a computer.

What unites this apples-and-oranges pair of scientists is their interest in quantum biology – a new and growing field where practitioners seek to understand how quantum-mechanical processes affect biological systems. Biological systems such as the human nose.

In this podcast, you will hear McFadden and Al-Khalili discuss a possible quantum solution to a long-standing biological puzzle: how does the nose “know” the difference between scent molecules? One of the most intriguing theories, developed by the biophysicist Luca Turin, is that it might come down to a process called inelastic quantum tunnelling. As Al-Khalili explains in the podcast, inelastic quantum tunnelling occurs when an electron dumps a bit of excess energy in order to tunnel to an empty energy level in a nearby atom. Turin’s theory is that this type of tunnelling event is what triggers the firing of olfactory neurons in the nose, thus sending a signal to our brains that gives us the “experience” of smelling something. However, such tunnelling can only take place when a scent molecule is present and able to absorb the electron’s excess energy – and that will only happen if one of the chemical bonds in the scent molecule has the right vibrational frequency. So when we slice into an orange and take a sniff, our noses may actually be sensing the vibrations of chemical bonds in a molecule called limonene, which is responsible for most of the orange’s citrusy scent.

The nose isn’t the only biological system with a possible quantum connection, though. If this podcast whets your appetite for some more examples, you might want to check out McFadden and Al-Khalili’s new book Life on the Edge. The book is written for a popular-science audience, and at the end of the podcast, you’ll hear the pair discussing some of the challenges they faced in writing it.

Previous Episode

An adjustable vision for the world

The standard approach in the developed world is for people with a vision impairment to visit an optician for an eye test. They are given a prescription, the lenses are produced and they can choose the frames they would like from a shop. In this scenario one relies on the presence of trained opticians and the infrastructure to produce and distribute the required materials. But these are not present in many parts of the world. “Roughly speaking, in parts of sub-Saharan Africa there’s going to be about one optician per million of the people,” says Silver.

To get round this limitation, Silver – who is an atomic physicist at Oxford University – developed a concept in the 1980s for glasses that can be self-tuned to meet an individual’s prescription. The basic idea is that each lens consists of two flexible membranes filled with a liquid. So, by adding or removing fluid, the shape and thus the power of the lens can be adjusted by the individual wearer.

In this podcast, Silver talks about how the first incarnations of his so-called Adspecs have already made a huge difference to individual lives in some parts of the world. But he has also been busy developing the technology to improve the quality and make it more accessible. Silver’s team at the Centre for Vision in the Developing World is now producing an updated version of the glasses called “New Adspecs”, which make it easier for individuals to set their own prescriptions. Some 500 pairs of these were distributed to Syrian refugees in Jordon in 2014. He is also looking to develop new styles of glasses, which could also help to improve the uptake of the technology.

Silver was interviewed by Physics World reporter James Dacey at the UNESCO headquarters in Paris during the opening ceremony of the International Year of Light (IYL 2015). Find out more about that event and some of the other light-based technologies in the spotlight this year in this short film.

Also, don’t forget to check out our free-to-read digital collection of 10 of the best Physics World features related to the science and technology of light, including an in depth article about Silver’s Adspecs initiative.

Next Episode

The masters of antimatter

Physics World reporter Tushna Commissariat recently visited the ALPHA antimatter experiment at CERN and caught up with its spokesperson Jeffrey Hangst. In this podcast, they talk about the perfect recipe for making antihydrogen, they discuss dealing with the fact and fiction that surrounds the field, and reveal the everyday realties of being an antimatter architect.

Housed within CERN’s Antimatter Factory, which includes the Antiproton Decelerator (AD) (the source that provides low-energy antiprotons), ALPHA and the other antimatter experiments – ACE, AEGIS, ATRAP and ASACUSA – all study the many puzzling facets of antimatter. From its interaction with regular matter to the biological effects of antiprotons to how it falls under gravity, the various experimental teams hope that all will be revealed about antimatter’s true nature in the coming years.

In particular, the ALPHA experiment – which won the Physics World Breakthrough of the Year in 2010 for trapping 38 antihydrogen atoms for about one-fifth of a second – is gearing up to scrutinize the stuff, as it will begin an experimental run this summer with the newly updated ALPHA2 device, which uses lasers to spectroscopically study the internal structure of the antihydrogen atom.

In addition to finding out how exactly one makes and holds a few thousand atoms of the most volatile stuff in the universe, listen to this podcast to find out why Hangst thinks he has the coolest job in the world and what it is like to visit the one place in the universe where, as far as we know, antimatter is actively being produced.