redefinition of SI units

Opposition at Antipode, Hammersmith

Antipode coffee Hammersmith
Outside Antipode, Hammersmith.

At the end of Fulham Palace Road, just next to the Hammersmith gyratory is Antipode, an Australian influenced (the clues to this are not so subtle) cafe. In truth, I have been to Antipode a few times now but not to take time to properly take it in. Once was after a tricky teaching session where it was difficult to sit back and reflect on anything but what had happened in the previous few hours, another time I was talking to someone rather than taking time to think about the location. There seems an urgent need for us now to take some time out and think about where we are and what we think. Indeed, part of the point of Bean Thinking is to explore how this space to ponder can be found in any cafe, if we but pause to look. Would this visit to Antipode be different?

Outside the cafe, a few tables were arranged so that you can enjoy your coffee in the open, next to the glass front window. Strangely the chairs/stools for these tables were stacked inside, possibly because it had become chilly again after a brief warm spell earlier in the year. A picture of a takeaway cup was drawn on the window as if to emphasise what you may expect to find inside, reminiscent of the old signs advertising coffee houses of the past. Going in, the counter is on the right and, while there was a selection of cakes etc. I opted to stick with the long black that afternoon. A seating area is at the back of the cafe where there are about 4 separated tables with a bench seat running along behind them with a fifth table along the rear wall.

Coffee at Antipode, pink salt, brown sugar, reflections and shadows. And a hint as to Bean Thinking
Coffee, salt and sugar. What do you see?
The coffee was drinkably fruity. More apples and redcurrants to my palette. On the table behind my coffee was a jar of pink salt and another of brown sugar. Which got me thinking about crystal structures and how it is often impurity, rather than purity that gives precious stones their colour. Is there a metaphor there?
 
But a second effect jolted to my attention. Someone sat down on the bench seat just along from me and as she sat down so I went up: a little see-saw. Across the room from me was a picture which, somewhat strangely, had two picture hooks either side of it, almost balancing each other on an imaginary line across the frame. Behind the table adjacent to me was a picture with a caption, to the effect of there being a very thin line between love and hate. Was this another instance of balance and equivalence?

Balance is something that we use in physics a lot, from the balance of forces to the use of balances in experiments. The imminent redefinition of the unit of the kilogram is based on a balance of forces. In the new definition, a balance is used so that the gravitational force pulling a mass down will be perfectly balanced by an electrically induced magnetic field pushing the mass up. The redefinition means that to calibrate 1Kg, scientists will no longer have to compare their 1Kg mass to the mass of a lump of platinum-iridium kept in Paris. The redefined kilogram will instead be calibrated based on its relation to Planck’s constant. This means that any lab around the world can calibrate the kg, they do not have to rely on copies of the mass kept in Paris.

Victoria Regina: What changes have happened since this post box was installed here in Hammersmith? What changes will do so before it is finally retired?
Victoria Regina: What changes have happened since this post box was installed here in Hammersmith? What changes will do so before it is finally retired?

The redefinition of the kg is going to happen on 20 May, 2019 (world metrology day). On a day to day basis, it probably will not affect many of us that much. Our 20g of coffee measured out to brew our morning coffee is going to be, to all intents and purposes, the same 20g as we would have measured on the 19 May 2019. Nonetheless, the changes are important not just for the metrology community but also for the way that we do science. In the past, all of our units were related to fixed, physical objects. The metre was defined by the length of a metal rod, the second was originally defined as being 1/86400 of the mean solar day and the kilogram by the aforementioned lump of PtIr in Paris. The kg was the last of the units to still be defined by a unique physical object. As of 20 May 2019, each of these units will be related to physical constants meaning that at no point will we have to go to a lab elsewhere and check that my kg is the same as your kg.

As I left Antipode, I noticed the post box just outside with “VR” on it. The post box has been there since the time of Queen Victoria. How things have changed since scientists wrote to each other with news of their latest experiments, scientific papers were posted to journals and measured lengths were compared to a physical ‘metre’ long metal rod! How things change as we move ever faster emailing results around and tweeting our latest news. We are, in 2019, moving from calibrations based on weighing physical objects to measuring the balance relative to physical constants that were just being discovered at the point that post box first came into service. And yet we humans don’t change much. We still need time to ponder balance from false balance, equivalence from false equivalence. It is not a contradiction to say that it is urgent that we find a way of pausing and reflecting on some very weighty issues.

Antipode is at 28 Fulham Palace Road, W6 9PH

Metrology and the Press Room, Twickenham

Press Room coffee Twickenham

The arrival of the pour over at the Press Room, Twickenham.

It is not often that I have an errand to run in Twickenham, but when one popped up just two weeks after reading Brian’s Coffee Spot review of The Press Room, it was obvious where we were going to have a coffee. The Press Room serves pour over coffees (along with a good selection of other drinks). It is always great to find somewhere that serves pour overs well and so I had no hesitation in ordering a Nicaraguan “Los Altos” prepared by V60. Hot chocolate was available as white, milk or dark chocolate and there were a number of alternative non-dairy milks on offer as well as a large variety of tea. A lovely feature of The Press Room is that they offer suspended coffees, the idea being that you buy a coffee now for someone later who may not otherwise be able to afford one. The total number of coffees (given/claimed) is recorded on a blackboard behind the counter. It was nice to see that at the time of our visit 800+ coffees had been paid forward (and just less than 800 claimed), suggesting that the Press Room is having a positive effect on its local community.

clock wall Twickenham coffee

The large clock on the wall at The Press Room in Twickenham.

A great thing about ordering a pour over is watching as the barista expertly prepares your coffee, taking the time to do this properly. To be fair, this is part of the reason that finding a café serving pour-overs is becoming more difficult. After a while, the coffee was brought over to our table together with a bowl ready for me to place the filter cone on it when I was ready to enjoy the coffee. After taking the obligatory photograph, and pondering when would be the best time to remove the filter from the top of the mug and place it onto the empty bowl, the clock next to us took our attention. It is a large time piece that dominates this corner of the room. It is revealing to consider how the accuracy and availability of clocks have changed the way we live as a society.

Considering measurement (of time and other things), I used to be in this area more frequently a few years ago when I worked on a project in collaboration with the National Physical Laboratory (which is down the road, on the same bus route that Brian’s Coffee Spot notes takes you to a few good cafés). Partly, NPL’s work is to ensure that we know how to measure things properly. Take the pour over I enjoyed at The Press Room. A known amount (perhaps 12 g) of coffee was weighed out before 200 g of water was poured slowly over the coffee. But how do you know that the 12 g measured at Press Coffee is the same 12 g as you measure at home? And while perhaps it may not be critical for the coffee culture (even the most extreme home-brewer does not need to know the amount of coffee they are using to the nearest 0.000 002%), knowing accurately how heavy something is can be extremely important. Hence the need for a standard kilogram (and a standard metre, second, Candela etc) so that we have a way of knowing that what you call a kg is the same as what I call a kg.

coffee bowl pour over

The coffee that escaped! But was it a measure of my patience or hesitation?

Oddly, the kilogram is the last fundamental unit still defined with reference to a physical object (the other fundamental units are seconds, metres, Kelvin, Amperes, Moles, Candelas). The kilogram reference block is a PtIr alloy kept at the International Bureau of Weights and Measures near Paris. However all this may change next year depending on a decision due in November 2018. If all goes to plan, from May 2019 all units will be defined with respect to natural constants such as the speed of light etc. For the kilogram, this has meant measuring mass relative to a magnetic force generated by a coil of wire in a device known as a Kibble balance. In this way, the kg can be defined with respect to Planck’s constant and an era in which we measured substances relative to known objects will end.

On a day to day level though, how much do these things matter to us? Sometimes the way we measure things affects how we view them (and therefore what questions we ask next). Take for example temperature. We are used to measuring degrees of ‘hot’, so on the centigrade scale 0ºC is the freezing point of water and 100ºC is the boiling point. But it wasn’t always this way. Celsius devised his original scale to measure degrees of cold so 0º was the boiling point of water and 100º was the freezing point (you can read more about that story here). It is arguable that changing to measuring degrees of ‘hot’ enabled us to more easily conceptualise the idea of heat as energy and the field of thermodynamics. Certainly for a while, considering the idea of ‘degrees of cold’ meant that some looked for a substance of ‘cold’ called “frigorific“¹. There’s a similarity here with the coffee at The Press Room, was the amount of coffee in the bowl used to hold the filter after I removed it from the mug a measure of my impatience before trying the coffee or my hesitation at testing the coffee? How we ask that question affects how we view the coffee and the café (for reference, I would take the positive interpretation: the amount of coffee in the bowl measures my impatience; I was eager to try the coffee).

droplets on the side of a mug

Condensation on the side of the mug. These droplets can reveal many aspects of physics, which do you think about?

Partly this suggests some of the ways in which language, and philosophy, underpin all science. It certainly suggests one further connection with this bright and comfortable café. Erich Fromm in “To have or to be”² considered an interesting linguistic usage that reveals our way of being. Do we “have an idea”, or do we “think”? Are we consumers or people with experiences? Do we wish to have, to acquire, to consume or do we wish to exist, to be. Our language affects how we perceive the world which in turn changes the language we use about it. Linguistically, depending on how we interpret the cafe’s name “The Press Room”, we either have a café that offers a space to read the latest news or one that is reflective of the coffee brewing process (specifically espresso); a space to get up to date or one in which to contemplate? The symbol of the café visible in the frontage of the shop and on the mugs suggests the latter, but maybe it is something we need to experience to truly know?

¹Inventing Temperature, Hasok Chang, Oxford University Press, 2008

²To have or to be, Erich Fromm, Jonathan Cape, 1978

The Press Room is at 29 London Road, TW1 3SW