A friend recommended that we try a café in her neighbourhood near Outram, in Singapore. So, with some time to spare we walked up the hill and into the welcoming air conditioning of The Populus Cafe in Neil Road. The coffee is roasted by 2º North and there is an extensive menu of both coffee based drinks and a seasonal filter selection. There was also a range of iced drinks on the menu which in the Singapore heat were tempting, but I opted for the 6oz Long Black. Given more time, or a second visit, I would certainly try the filter, but this time an appointment across the island was calling. There seemed too to be a very good lunch selection on the menu, but again, the lunch appointment elsewhere meant that it was just the 6oz long black that day.
It should be possible to take some time back from a busy schedule full of appointments and concerns and sit back and ponder the connections in any café. Having run from one set of concerns and soon to have to go off to another, would this be possible in 30ºC+ heat? The comfortable space of Populus provided a perfect place to test this question. Sitting back while sipping my coffee, the first thing that struck me was the wood, arranged in different geometrical patterns on the walls. The floors too were decorated with hexagonal stone tiles while the door was glass. There was a different pattern on the door, but what was it? Staring at it for a while, I thought about the schematics you sometimes see for a connected world, each of us a point connected to the others (how true is it that we are all 6 hand shakes away from everyone else?). Maybe this fitted with the name of the café? My companion in these reviews instead thought of crystals and the way that crystal structures are represented with lines between the atoms. While loading the photograph of the door onto the website, I saw a pattern of flowers. It seems that the pattern on the door formed and reformed with each new view.
Then there was the cup. A black coffee in a black cup, with umbral and penumbral shadows (as pointed out by @Bob_MatPhys on Twitter). A few years ago there was great excitement about a new material that had been made to be blacker than any known material. The substance used a coating of carbon nanowires (of just 20nm diameter which is about 1/1000 the size of a grain of espresso grind) to absorb light across the visible, ultra-violet and infrared spectrum. And just as nano-structuring a material helps it to appear the ‘blackest’ object ever, so changing the structure of a material can make it invisible to other parts of the electromagnetic spectrum such as microwaves. Quite why various defence companies and governments would invest so much into this research I will leave for your imagination (it is not to avoid heating soup). A more peaceful and beautiful side of the effect of nanostructure on optical properties is the way that the feathers of a peacock have a striking green-blue hue. It is another example of light interacting with a structure and so producing different optical effects; all is not as it appears.
And the fact that all is not as it appears gives another connection to the Populus cup. For although it seemed quite black to my eyes, it was clearly shining in the infra-red. The hot coffee inside was radiating through the cup and onto my hands. Which could prompt us to consider what ‘black’ really means? And for that matter, what about transparent? Just as ‘black’ only absorbs light over a certain set of frequencies, so transparent only lets light through over certain frequencies. The door that we can see through with our eyes may be opaque to a different frequency range that we cannot see. Just over two hundred years ago Carl Wilhelm Scheele deduced the presence of the infrared by contemplating how his stove heated him in the winter. Although he could not see them, the ‘heat rays’ seemed to come straight towards him and yet did not cause a candle flame to flicker, clearly the heat was ‘radiating’ like light rather than travelling like a breeze on the air.
The knowledge that structure, as well as pigment, provides the colour to our world, or that what is transparent at some frequencies may be opaque to others, these things give us plenty to think about, scientifically and perhaps more philosophically, while enjoying our black coffee. Which shows that even ten minutes spent sitting with your coffee can result in a series of thought connections that you may not have enjoyed had you rushed from appointment to appointment while checking your smartphone. That we could all enjoy a good ten minutes (or more) in the Populus Cafe!
The Populus Cafe is at 146 Neil Road, Singapore 088875