Petrichor

As I was walking out of work on Monday, I was greeted by one of my favourite things – this:

The Royal School of Mines in the rain

The Royal School of Mines in the rain

On first glance you may think, “wow, what a miserable sky.” What you also need to know is that this grey blanked overhead full of heavy rain clouds followed three days of hot, sunny, dry weather. The heavens had just opened, breaking the short but very warm dry spell with a torrential downpour of huge raindrops. What greeted me and blew me away as I left work was not the grey sky as such, but what it had produced – the heady aroma of petrichor in the air.

The Royal Albert Hall in the rain

The Royal Albert Hall in the rain

Petrichor is one of my favourite words, and one of my favourite things. It is the word that sums up the smell of wet rain on dry ground after a long period of dry weather. It is the scent of summer storms – the kind of weather where you can run through the heavy rain in a t shirt – sadly the kind of weather we rarely have a chance to enjoy here in England. Sometimes I think I can detect a delicate note of petrichor in the peaty, smokey flavours of my favourite whisky, Laphroaig. I imagine that petrichor is that same earthy perfume that filled the air when George Peppard rather romantically kissed Audrey Hepburn after she rescued Cat, or when Hugh Grant  kissed Andi McDowell in Four Weddings. Was it still raining? She hadn’t noticed. It must have been warm leading up to that summery shower, as we had Hugh Grant getting soaked to the point of see-through in a white shirt, and no one would do that in winter. OK, it may instead have been because Richard Curtis knows how women respond to men in soggy white shirts, but I like to presume the former, as I feel a little less manipulated that way!

Paul Varjak and Holly Golightly kiss in the rain while protecting a freshly rescued Cat in one of my all time favourite films (via Breakfast at Tiffany's)

Paul Varjak and Holly Golightly kiss in the rain while protecting a freshly rescued Cat in one of my all time favourite films (via Breakfast at Tiffany’s)

'That kiss' (via Four Weddings and a Funeral)

‘That kiss’ (via Four Weddings and a Funeral)

I first came across the word ‘petrichor’ in Neil Gaiman’s book American Gods, and always remembered it because it is a scent that everyone is familiar with, and everyone has their own description of, yet very few people know what word to use to sum it up. Gaiman later used the word again in one of the excellent episodes of Doctor Who that he wrote entitled ‘The Doctor’s Wife’, where a conjured memory of the scent of rain on dry earth was used as a telepathic passkey to enter a TARDIS control room. It was also the name of Amy Pond’s perfume in a later episode, ‘for the girl who’s tired of waiting’.

An advert for Amy's perfume, Petrichor, from Doctor Who (via BBC)

An advert for Amy’s perfume, Petrichor, from Doctor Who (via BBC)

A few weeks ago I attended a choral performance of a composition documenting Alan Turing’s life. While they referred to the very same scent in the lyrics, they didn’t use the word ‘petrichor’, presumably because the composer didn’t feel like it fit in the lyrics or the melody. I can’t imagine he would have let such a beautiful word go easily. While the meaning was still the same, it didn’t invoke the same response in me as petrichor would have. When I hear the word, my mind immediately visualises a single rain drop falling in slow motion until it reaches the dry earth, where a small cloud of dust is propelled into the air above the rain drop on impact.

Despite only having heard the word via Neil Gaiman in the last few years, it has been around for a long time, and was originally coined by two academics working on the composition of this scent from a scientific point of view. The word is constructed from Greek ‘petros’ meaning ‘stone’ or ‘soil’ and ‘ichor’ which is the fluid that flows like blood in the veins of Greek gods.

Researchers have identified what this scent is, and how it comes about thanks to the combination of a warm, dry spell followed by torrential rain. During the dry spell, plants start to release oils into the soil around them that slow down seed germination and the growth rate of plants, as they rather cleverly realise that there may not be enough water for them to grow properly if it is very warm. When the rain starts to fall, the soil is agitated, and these oils mix with other chemical products from certain bacteria that live in the soil. This combination of chemicals released in the soil and mobilised by the rain evaporate off the ground and into the air around, creating the smell of rain on dry ground. Petrichor.

Not only is petrichor a beautiful word, it is also a wonderfully emotive scent, and the result of a clever mechanism that enables plants to respond to their sometimes unpredictable environmental conditions and survive in spite of these challenges.

Alan’s apple?

“Hyperboloids of wondrous light,

Rolling for aye in space in time.”

“In space and time!”, the Hertfordshire Chorus exclaimed, filling my heart with love for the wonders of science, and making my neck tingle with contentment and delight at the fact that I can indulge that passion for science as my day job. On the evening of Saturday 26th April 2014, I attended the world premiere of James McCarthy’s new production Codebreaker at The Barbican Theatre with the London Orchestra da Camera and the Hertfordshire Chorus, conducted by David Temple. Codebreaker is based on the fascinating and tragic life story of one of my favourite scientists, Alan Turing. In case you missed Alan Turing Year in 2012, Turing was a British mathematician, chemist (really!) and wartime cryptanalyst, who is regarded as the father of computer science, and the brains behind the cracking of the German Enigma code. Not just an incredibly intelligent man, Turing was also a marathon runner, regularly running from London to Bletchley Park, the home of codebreaking near Milton Keynes. I discovered in the short talk with mathematician James Grime before the performance that Turing had completed a marathon in 2 hours 46 minutes which, had he competed in the Olympics at the time, would have gained him a 15th place spot. I completed the London Marathon in 2012 and it took me over twice that time to complete it then, so my respect for him increased even further upon learning this.

Alan Turing, the marathon mathematician (via Andrew Hodges, whose biography of Turing, 'Alan Turing - an Enigma', is a must-read)

Alan Turing, the marathon mathematician (via Andrew Hodges, whose biography of Turing, ‘Alan Turing – The Enigma’, is a must-read)

Codebreaker incorporates letters and quotes from himself and his family with poems that perfectly reflect the mood of some very happy and very sad moments in his life. The above quote is from the fourth in a series of postcards that Turing send to Robin Gandy, another British mathematician, that were collectively entitled ‘Messages from the Unseen World’. The performance was very emotional, and made me cry on several occasions, which would have been fine had I not been sat on the front row illuminated by the stage lighting in a shimmery jumper! Through the beautifully composed music, the audience were able to experience some of the many facets of his previously unknown personality, and some of the life-changing moments in his short existence, bringing Turing’s story to life, and driving my synaesthesia wild with emotion-filled colours. In a round-about way there was an element of Turing’s legacy there, as the actor playing him in the up and coming film of his life, The Imitation Game, was also present for the performance. Codebreaker was another fine example of how scientific concepts and stories can be conveyed so effectively and emotively through the arts, and I cannot wait to see the film when it is released. Having already played another of my favourite scientists, Stephen Hawking, so brilliantly about a decade ago, I am now secretly hoping he secures a role as Galileo for a science hattrick.

Turing's postcard to Gandy (via www.turing.org.uk)

Turing’s postcard to Gandy (via http://www.turing.org.uk)

In the interval, I told my friend Ben and the first few rows of the Barbican Theatre the story of how and why I always think of Turing at least once a day. After years of persecution for being in love with a man, which at the time was illegal, Turing tragically took his own life at the age of 41. Inspired by his favourite story, Snow White, he laced an apple with cyanide, bit into it and died.

Snow White and her poisoned apple (via Disney)

Snow White and her poisoned apple (via Disney)

Rumour has it that Steve Jobs and Steve Wozniak decided that the logo for their new company, Apple, would be a subtle nod to Turing’s advances in computer science and his tragic death. Thus the Apple logo came about, with the famous ‘byte’ taken out of it (pun intended – I can only apologise). When I was younger, we had Apple Macs in school that proudly displayed the older rainbow Apple logo. Was this a nod to the rainbow flag adopted by the LGBT movement? The story may not even be true, as an interview with graphic designer Rob Janoff, the artist behind the Apple logo, denies any link to Turing or to any reference to the other myth that the apple symbolises the knowledge of the forbidden fruit in the Garden of Eden. Despite his denial, every time I look at my phone or tablet, I think of Alan Turing, and I am grateful to live in a world that he helped shape, but also a world where almost everyone is now free to love anyone they like.

Apple rainbow logo

The Apple logo in full rainbow colours (via Apple Inc.)

‘Tis the season to eat chocolate!

Today is Easter Day. Traditionally a celebration of fertility and birth and more recently combined with the story of the resurrection of Jesus Christ, Easter is often symbolised by eggs, newly hatched fluffy chicks, happy hopping bunny rabbits, and of course, CHOCOLATE. I for one am a fan of both adorable animals and chocolate, but what is it about chocolate that drives us so wild, and how much science was involved in creating your chocolate bunnies? My science hero, top bloke, and one of the best materials scientists around, Prof. Mark Miodownik, has dedicated a whole chapter of his book Stuff Matters to the marvellous material that is chocolate. If you are yet to read the book, I urge you to buy it, as it is beautifully written and explores chocolate as a material. As I was a chemist before I was a Materials Scientist, I am also curious about the chemistry of this wondrous substance, and the scientific reason behind why it drives so many of us to unhealthy obsession!

Easter is all about chocolate bunnies. And some other symbolic stuff. (via www.sodahead.com)

Easter is all about chocolate bunnies. And some other symbolic stuff. (via http://www.sodahead.com)

Chocolate is made from cocoa solids (although there is none of this ingredient in white chocolate), cocoa butter, sugar and milk in varying proportions. The cocoa components come from the seed of the Theobroma cacao tree. The journey of chocolate from revolting-tasting seed through bitter drinks, fermented heaps in forests and hot beverages to the solid chocolate that we know and love today is a long story. I hope to cover it in a future post when I will share my experience of visiting the Thorntons Chocolate Factory in Derby, where I was lucky enough to check out 3D printing in chocolate and the science behind creating confectionery masterpieces.

Cocoa butter is one of the main components of chocolate. Unlike dairy butterfat, cocoa butter does not go rancid very quickly, thus preserving chocolate for prolonged periods of time. On a molecular level it also displays polymorphism, which means that the overall composition of the cocoa butter stays the same, but the molecules can be positioned differently in relation to one another, giving rise to different types of cocoa butter with varying physical properties. A common example of polymorphism can be seen in diamond and graphite, both of which are made of carbon, but vary greatly in terms of their hardness and physical appearance due to the arrangement of carbon atoms in each. Depending on the arrangement of molecules in cocoa butter, the various types display differences in their appearance, melting point and hardness among other things. The melting points of each of the six types can be seen in the table below.

Melting points of cocoa butter (Wille and Lutton, Journal of the American Oil Chemists Society, August 1966, Volume 43, Issue 8, page 491-496)

Melting points of cocoa butter (Wille and Lutton, Journal of the American Oil Chemists Society, August 1966, Volume 43, Issue 8, page 491-496)

For chocolate to look and feel appealing to us while also being stable enough to be portable, it must have the correct melting temperature; high enough to ensure it does not melt too easily when being transported or stored, but low enough to melt quickly and smoothly on the tongue, releasing all the delicate aromas and flavours in the chocolate. The perfect cocoa butter type to achieve this is Type V. This type has an optimal hardness that gives that familiar snap or bite to good quality chocolate. It is also the glossiest type, which results in an aesthetically more appealing shiny chocolate than the duller chocolate that would result from the presence of other cocoa butter types. The cocoa butter polymorphs have varying degrees of thermodynamic stability. Each type of cocoa butter will want to change to the most stable form where the molecules are in their most comfortable, lowest energy position in relation to all others. This can once again be compared to the thermodynamic instability of many carbon polymorphs; less thermodynamically stable diamond will, eventually, turn into more thermodynamically stable graphite, although for those of us that like shiny things, this is thankfully an incredibly slow process. Again, analogous to carbon polymorphs, it is a less thermodynamically stable form of cocoa butter that we favour for its more desirable material properties; Type V instead of Type VI. Each one of the six types of cocoa butter can be encouraged to form over other types by changing the formation conditions; the rate of heating and cooling of chocolate, and the temperatures at which chocolate is heated and cooled are incredibly important and very precise. Meandering outside this very narrow range of temperatures will allow less desirable types of cocoa butter to form. Anyone that has ever tried tempering chocolate in the kitchen will be aware of how tricky this process can be.

Once the chocolate has melted on the tongue, it continues to display more fascinating physical properties. Among these, my favourite is the fact that molten chocolate is a ‘non-Newtonian’ fluid; it disobeys the normal laws of physics and mechanics. A normal Newtonian fluid that follows the classical laws of physics would move out of the way when a force is applied to it, maintaining a regular viscosity or thickness.

Non-Newtonian fluids can be grouped into two categories; those that become more viscous (thicker) when a force is applied to it, such as a classic suspension of cornflour in water which behaves as a solid when hit but otherwise behaves as a liquid (and also D3O that I mentioned in my previous post about ballet pointe shoes), and those that become less viscous (more runny) when a force is applied to it, such as ketchup that will only shift from the bottle after a lot of bottle bashing. Molten chocolate behaves like ketchup. As we press the molten chocolate against the roof of our mouth, we are making it more liquid, allowing all of the wonderful flavours to flood across our taste buds.

Once the flavours have stimulated our taste buds, the chemicals in chocolate get to work and stimulating our minds. Chocolate is packed with mood-enhancing chemicals such as theobromine, phenylethylamine, tryptophan and caffeine, as well as sugar. Theobromine is a chemical cousin of caffeine, and the two occur naturally in chocolate in higher and much lower concentrations respectively. While caffeine promotes alertness, theobromine works in a slightly different way, by inhibiting the feeling of relaxation by competing with the chemical adenosine. Adenosine promotes sleepiness, so by preventing adenosine from working, theobromine contributes to the increase in alertness of a post-chocolate pick-me-up. Adenosine also lowers feelings of arousal and excitement, so by inhibiting the effect of this, theobromine also allows the consumer to feel excited, which could be one of the reasons that chocolate could possibly be addictive. In medicine, theobromine is used to treat high blood pressure. It is a vasodilator and lowers blood pressure by widening blood vessels. Like caffeine, theobromine is also a diuretic, a chemical that makes you want to pee, and has been used to treat oedema, or water retention. Some animals cannot break down theobromine, so chocolate is poisonous to animals like dogs and cats. Accidental consumption of chocolate occurs more in dogs, who are attracted by the sweetness of the sugar in chocolate, compared to cats, who are unable to detect sweet flavours in chocolate and are not very keen on eating it.

The lowering of blood pressure is a great side effect, but eating lots of chocolate will lead to other problems owing to the high sugar content. While theobromine is getting us excitable and sugar is fuelling us, the two other chemicals further contribute to these feelings of chocolate-related elation and obsession, albeit at a lower level. Tryptophan is a precursor for serotonin, which promotes happy feelings, again contributing to that contented high achieved when you eat chocolate. Phenylethylamine is a chemical that can be produced by the body when you are in love, which from what I remember is a very lovely feeling indeed, and this is why we keep coming back for more. Chocolate is packed with mood-enhancing chemicals, and engineered to makes us want to eat it just by looking at it and hearing it break. The United Kingdom is often rated one of the top five chocolate consuming countries in the world based on mass consumed per person, with the chocolate industry here worth around £3.5 billion. When we compare this to the UK fashion industry, known to be big business and estimated to be worth £21 billion, it is easy to see why such scientific precision is used in creating the most tempting chocolate. It is an excellent investment.

On that note, I’m off to see whether the Easter Bunny has visited, and to scientifically test out the snap, smoothness of melt, and non-Newtonian properties of my chocolate treasure. For science, you understand… I suggest you do the same, as ‘n=1’ will never create a scientific study that will stand up to peer review. Happy Easter!

The science of CHoCoLaTe BUnNiEs?

The science of CHoCoLaTe BUnNiEs?

Science and art go together like a horse and cart

Last month, I was one of many people enjoying the BAFTA awards ceremony. From the comfort of my sofa, I should add – I was not one of those lucky enough to be at the Royal Opera House. Had I been there, I have no doubt that a scientist like me would have been confined to the cheap seats far away from the stage, so it was just as well that I watching the show on BBC One, as I may not have noticed the intricate design on the reverse of the iconic BAFTA mask award. As the talented and charming Dame Helen Mirren spoke of her career on screen, I became fixated with a familiar symbol on the back of her award.

Dame Helen Mirren accepts her BAFTA award (via BBC)

Dame Helen Mirren accepts her BAFTA award (via BBC)

Behind the right eye of the mask is a classic simplified diagram representing an atom. A quick Google search and a couple of disproportionately excitable tweets led me to the BAFTA website and the history behind the design of this unmistakable award.

Close up of the reverse side of the BAFTA award (via BAFTA)

Close up of the reverse side of the BAFTA award (via BAFTA)

The mask award was designed by American sculptor Mitzi Cunliffe in 1955, and the BAFTA website states that “the hollow reverse of the mask bears an electronic symbol around one eye and a screen symbol around the other, linking dramatic production and television technology”. Over 50 years ago, C. P. Snow gave a lecture in which he vocalised his concern over the fact that science and art were becoming two distinct cultures moving further away from one another. Surely 50 years on, in this very small and well-connected world in which we live, this cannot still be the case. So why was I surprised to see that symbol there?

As a scientist, I have often noticed that science and art are rarely linked, with one discipline often dismissing the other. This has always broken my heart. Thanks to my parents’ hard work and daily after-school ferrying around, I have been lucky enough to have been brought up with a diverse range of hobbies including music, dance and drama. As a scientist, I like to think that I can appreciate the aesthetic beauty of the work I do, and that of my colleagues. Why is it that so many people still believe that you must choose between science or arts? The movie industry itself has its roots firmly anchored within historic scientific discoveries, from the invention of celluloid and its application as photographic film to the current computer graphic imaging technology that allows films such as Gravity to be made.

Small steps are being taken to reunite the ‘two cultures’, with my alma mater UCL now awarding BASc degrees, and events such as my current employer Imperial College’s monthly Fringe events. There is now a greater awareness of careers that allow for, and indeed increasingly require, a combination of these two strands, although continued extensive outreach work is required to reach school age students and open their eyes to this new world where they are not forced to choose between science and art.

Tonight, all eyes are on Hollywood, Los Angeles, where the 86th Academy Awards, or the Oscars, are to be held. While I am torn between the utterly brilliant, harrowing and moving 12 Years a Slave and the beautifully shot, science-flavoured Gravity for Best Picture, I can relax knowing that some equally important awards have already been handed out. The Oscars’ website revealed a whole section dedicated to Science and Technology, and the news that a separate star-studded ceremony is held two weeks prior to the awards ceremony that we hear about, honouring those that have advanced film making through the use of science and technology. There are three levels of award available; Technical Achievement Awards, Scientific and Engineering Awards (my personal favourite, as a materials scientist and engineer!), and Academy Awards of Merit. It is great to see scientists and engineers being honoured in such a way, and I think that film and TV are a great example of how there is no such thing as two cultures. The two are inextricably linked, and that should be celebrated.

Purely by chance, I stumbled across this great project by film maker Lucia Helenka. With Minky Productions, she is making a film called STEM (which in my world stands for Science, Technology, Engineering and Maths, but is also presumably a pun on the subject matter) which is about love, life, science and plants engineered to include green fluorescent protein that makes them glow in the dark. If you are in a position to support this project or are even just curious, head over to their Indiegogo site, watch the excellent trailer, and if you like what you see throw a few pounds their way. Let’s keep science and art going together. See you at the screening!