Tag: Aeropress

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Vacuum fillers

inverted Aeropress and coffee stain
The Aeropress on top of a mug, with a coffee spill. Clearly a badly performed inversion method brew.

The Aeropress is a lovely way to make a fairly quick cup of great coffee. Part filter, part immersion, it is a coffee brewer designed by an engineer. There are many ways to make coffee with an Aeropress but common to all is the ‘press’ towards the end where the plunger is pressed down onto the coffee pushing the liquid through the filter paper and into the mug. As you remove the Aeropress at the end, it can drip leading to coffee stains on the work surface. However there is a trick to prevent this. While watching James Hoffmann videos to improve my Aeropress technique, he mentioned that after pressing, he pulls the plunger back up a bit and this helps to prevent dripping. Genius. You can see his recommended Aeropress technique here.

The trick presumably works because the plunger has a rubber (or silicone) seal into the Aeropress base. This ensures that when you pull back the piston, there will be a slight vacuum created just behind the filter paper. As the air flows back into the space behind the filter it will primarily do so via the filter-end of the Aeropress (not the seal) and so any drips that were forming will be pushed back into the brewer. Rubber seals are not fantastically air-tight and will let air in eventually but for the few seconds that you need to take the Aeropress off of the mug and replace it upside down on the work surface this level of vacuum is sufficient.

So how air tight is a rubber seal? The seal in the Aeropress will not be very air tight at all. The seal created is purely through the rubber piston being pushed into the Aeropress body. However purpose-built rubber o-rings can support fairly respectable vacuums. Normal air pressure is 1 Bar or 1000 mBar. Using rubber o-rings that are clamped into place between separate parts of a vacuum chamber, it is perfectly possible to achieve vacuum levels of around 0.01 mBar**. For higher vacuum levels (or equivalently lower pressures), you would need to use a metal seal such as copper. As copper is slightly malleable, if you use it as a join between two parts of a vacuum chamber and clamp it together, you can create a very good (air-tight) seal. In this way you could pump the vacuum chamber to pressures of 10^-8 mBar or even lower. You would need this level of vacuum to make some of the components that are contained in your mobile phone or laptop, possibly even some of the components in the measuring scales you use to weigh the coffee. You would not need that sort of vacuum to make coffee itself.

How to brew a perfect cup? Would a bit of physics help with the clean-up?

The Aeropress is a fairly recent invention and yet similar problems, and solutions to Hoffmann’s trick would have been noticed in the past. And yet there is a common saying that “nature abhors a vacuum”, originally attributed to Aristotle. If we think that the explanation for the effect above seems sensible, how do we reconcile these two ideas? Descartes noted a similar problem in a wine keg. It is like the lid of a take-away coffee cup: for wine (or coffee) to flow out of a hole in a container, another hole is needed. Did the extra hole allow the wine to avoid the vacuum? Instead, Descartes explained it differently:

“When the wine in a cask does not flow from the bottom opening because the top is completely closed, it is improper to say, as they ordinarily do, that this takes place through ‘fear of a vacuum’. We are well aware that the wine has no mind to fear anything; and even if it did, I do not know for what reason it could be apprehensive of this vacuum…”*

The idea was that everything including space was absolutely filled with matter. So the extra hole in the wine keg allowed this extra matter to flow into the keg and the wine to flow out; if the Aeropress plunger is pulled back, matter would immediately flow back into the space created. The drops would be pushed back into the Aeropress and it would not drip. A very similar mechanism to the reason suggested for the behaviour above. It perhaps could cause us to question, what evidence do we have from our own daily lives about the existence of vacuums? How could we personally prove that they exist even as we rely on their existence for our consumer electronics?

Joseph Wright ‘of Derby’ An Experiment on a Bird in the Air Pump 1768 Oil on canvas, 183 × 244 cm Presented by Edward Tyrrell, 1863 NG725 https://www.nationalgallery.org.uk/paintings/NG725

There is a famous painting from the eighteenth century that demonstrates the creation of a vacuum in a home-setting. In “An experiment on a bird in the air pump” (pictured), Joseph Wright depicts the moment that air is taken out of a vacuum chamber containing a bird. The bird collapses in the vacuum as the audience looks on. We know the vacuum exists because the bird no longer has air to breathe. At the moment that we encounter the picture the scientist demonstrating could either let air back into the chamber and allow the bird to live or continue reducing the air pressure at which point the bird will die. What will he choose? The audience display a variety of reactions from the indifference of the couple on the left to the impotent horror of the girls on the right. Only two of the audience seem to be paying attention, even the experimentalist appears to be performing, and not participating in, the experiment. It could be argued that the painting speaks to us of the scientific method and the idea of being detached, outside of and observing the natural world. Imagining ourselves “independent observers” of a situation we are participating in. We are all detached and looking on, both controlling the life of the bird as well as claiming indifference to its fate.

As this was written, COP26 was continuing in Glasgow. We are at a specific point in time, just as with the “experiment on a bird”. Are we going to continue as we are or will we intervene and allow life to recover? Do we tell ourselves that we are indifferent observers or are we co-inhabitants of a common home? These are perhaps not considerations for a website about the physics of coffee. They may be considerations to have while enjoying, or certainly contemplating, a coffee. Whether or not you use a trick from vacuum science to help you clear up.

*Descartes, “The World”, ~1632

**Basic Vacuum Technology, 2nd Ed. Chambers, Fitch and Halliday, Institute of Physics publishing, 1998

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Details

Aeropress bubbles on one side, coffee experiments
Do the bubbles always (often) form on the opposite side of the Aeropress to the hand you used to pour the water from the kettle?

Last week, I revealed the results of an experiment into an odd observation while brewing coffee in my Aeropress: why was it that the bubbles formed on the opposite side to the hand I used to pour the water from the kettle? On the face of it, it was an easy experiment, with a simple explanation and a fairly clear set of results. But behind this story is a series of decisions and psychology that can illustrate, on a small level, some of how experimental science is done. It’s not for nothing that there’s the saying, the devil is in the details.

Theory, experiment and the impartial observer

There can be an erroneous idea about the progress of science, repeated even among people who should realise the fallacy. A theory, with testable predictions is proposed, which is subjected to experiment by a series of dispassionate observers in order to provide evidence that either supports the theory or disproves it. We dehumanise the theoreticians and experimentalists to observers who can emotionally disconnect and observe the results from an objective distance.

There are countless examples against this within the history of science (both for theories that have now been rejected but also for theories that we still consider good models) but I want to keep to the example that we can all have in front of us in our kitchen: that of the bubbles in an Aeropress.

With the Aeropress it was an odd experimental result that prompted a theory that then fitted the odd observation. The theory came with some extra ‘predictions’, but theory and experiment evolved together. Again, there are examples of this in the history of science but the experiment prompted the theory that prompted further experimental tests.

The problem then is that the experimenter (in this case me) was well aware of the theoretical predictions. Could I dispassionately, and completely subconsciously, pour a kettle as I had always poured the kettle, or would part of me, however much my conscious was opposed, change how I poured the kettle subsequent to my idea of how the bubbles formed?

As with many experiments, some results are not so clear as others. Are the bubbles on this coffee evenly distributed or weighted to one side? How would you count them?

For the case of the experiment with the Aeropress, this remains an open question. Generally though, many experimentalists will aim to try to reduce conscious or unconscious biases by putting procedures in place to prevent them coming in. When Isaac Newton and John De Saguliers investigated the role of air resistance on falling masses from inside the dome of St Paul’s Cathedral, London, they dropped them from a trap door system. This meant that the masses (which in the first instance included glass balls filled with mercury) fell at the same time; the quiet suspicions of the experimentalist investigators could not influence the results. It created a mess on the floor of that great Cathedral, but it did eliminate this component of bias from the experiment. You can read more about their experiment here.

A need for peer review

Assuming that we are collecting data in a neutral way, what happens then? On the face of it, seeing if the bubbles appeared on the left hand side or the right hand side should be an easy question to answer. And in some cases, such as the pictures that I chose to illustrate my post about the results last week, the answer is clear. But are those photos representative of the whole data? And, for more ambiguous photos, such as the one shown here, how do you define which bubbles to count?

One problem here is that each photo is very slightly different. Either the angle is different, or there is steam on the lens, or the focus is not there. But even so, sometimes it is harder to see all the bubbles on an image. For this experiment I defined a minimum bubble size (which you can see as the white square in the image) which I used to decide which features on the surface of the coffee to ignore: after all, when viewing the image, it is not clear whether items smaller than this are bubbles or just a different colouration to the coffee crema.

You may notice that I did not mention this detail in last week’s post, but one of the images includes the square. This is one of those things that would (most likely) be picked up in what is known as ‘peer review’. When we write results up and submit it to a journal for publishing, the journal will typically send the paper out to 2 or 3 ‘referees’. These are people, who ideally work on similar experiments, who will read the paper and think “hang on a minute, what if it is not the bubbles but the bubble size that shows an effect, how have these authors counted the bubbles?” The example is admittedly a somewhat trite one, but the point is that the paper is read by someone who also does this sort of experiment and knows where problems can be encountered. The ideal is not to trip the authors up, or to show that they did anything wrong, but to see things from a new angle, a different set of obsessions and so ask the original authors to address points that improves the paper in the sense that we can all start to see what is going on*.

Look carefully at this image. Can you see the white square towards the top left? This was the minimum ‘bubble’ size counted in the initial experiment.

Peer review also of course helps to stop the publication of results that are wrong, or statistically invalid (see below). We therefore need some form of peer review in order that we can be collectively, as a society, happy that this science is being done robustly. So if you see a newspaper report that “the study, which has not yet been peer reviewed…” treat it with a very large pinch of salt and please don’t tweet it (unless you happen to also research that area and so can read the paper as if you are writing it).

Statistics…

We have attempted to eliminate our biases, we have been open and transparent about our methodology, what could possibly go wrong now? It is in not taking enough data. Say I made a coffee pouring from my right hand and the bubbles formed on the left, then with my left hand and the bubbles formed on the right, we can know that this is not enough to be sure that the bubbles ‘always’ form on the alternative side. For that bit of the experiment I made 22 coffees. Not enough to be statistically certain (more on that here), but probably enough for an observation on a coffee blog.

But the bit I want to focus on here is the part of the experiment where I counted the number of bubbles versus the bubble size. I was investigating any similarities with a study that measured thousands of bubbles over 225 images documenting 14 events. I counted the number of bubbles on one small portion of one coffee that may not be representative of the coffee generally. Can we accept that as a valid procedure?

While I may not have counted enough bubbles here, one experiment (that can involve coffee) where there certainly were enough objects counted was in the determination of the mechanism behind Brownian motion. Brownian motion is the phenomenon by which small particles of dust or bits of coffee move in random directions on the surface of your cup. It happens because the molecules within the water of the coffee hit against the dust and impart a small momentum to the particles. Because there are many molecules moving in all sorts of directions, the resultant movement appears random. If we look through a microscope we can see the particles moving but there is no way that we could see the molecules that move them. Back in the nineteenth century this became an exceedingly controversial topic: could you form a scientific theory for a phenomenon (such as Brownian motion) which relied on assuming an underlying reality (molecules) that you could not hope to see or measure directly? The question was (partly) resolved only in the early twentieth century with the very careful experiments of Jean Perrin (you can read more about Perrin’s experiments and their relation to coffee here). When Perrin summarised his results he wrote:

View of St Paul's Cathedral London
St Paul’s Cathedral in London. The site of an
experiment by Isaac Newton and John de Saguliers in 1710.

“I have counted about 11, 000 granules in different regions of different preparations to obtain the figure 21.2 of the first column.”

Which is slightly more than the number of bubbles I counted last week.

A way forward – truth and integrity

What does this mean for science and how science is done and reported, especially in this era of rapid research and in which everyone has an opinion? Is science discredited by the fact that we are humans, and not fully dissociated and objective, when we do it?

Although I ran out of space to discuss Michael Polanyi’s comments on statistics and pattern recognition, he does have something extremely relevant to say about the progress of science. For Polanyi, how we do science and how we behave as a society were (and are) intimately linked. He considered that for science to prosper, we needed “fairness and tolerance” in discussion. By fairness he meant the requirement to state your case, your experimental result or theory, openly, separating fact, from opinion and emotional involvement and openly allowing them each to be critiqued. By tolerance he meant that we needed to listen to the other, even while we disagree, in order to see where they may have a point. He linked this behaviour within science to the behaviour required of the public in listening (and sharing) science. As he said:

“Fairness and tolerance can hardly be maintained in a public contest unless its audience appreciates candour and moderation and can resist false oratory. A judicious public with a quick ear for insincerity of argument is therefore an essential partner in the practise of free controversy…“

Science and society move together.

An invitation

And so an invitation. Keeping in mind the idea of Polanyi about honesty and integrity in discussion, I would like to invite any reader of this blog to become a peer reviewer of the experiment reported last week. Please go and enjoy a coffee, carefully preparing and noticing your brewing technique and then work out how you would have made the experiment and tested any results. Perhaps you have a different theory that would require a slightly different counting method than the one chosen? Perhaps you think that more experiments are necessary? Become my peer reviewer! Feel free to comment below, or on Facebook or Twitter. Or, if you would prefer, email me through the contact form here. Bear in mind I am human, and so I will react to your report. But if you and I keep can Polanyi’s warning in focus, perhaps we can together improve our understanding of the science behind bubbles in an Aeropress. And, by extension, improve our understanding of how science, and society, can work.

I genuinely do look forward to reading your comments.

*I have worked in academia long enough to know that this is not always how the peer review process works in practise. There are many cases where peer review falls short of the ideal, for all sorts of reasons. But it remains a necessary part of the publication process as many referees (and authors) do try to approach the process in this way. Obviously emotion gets in the way when we receive the referee’s report initially, or, on the other side, if we think that the authors have seriously misunderstood their experiment, but if we take a few days to sit with the report/paper, we do try to get towards the ideal.

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Coffee whispering

coffee and cassette tape in Batch and Co
What does listening to your coffee tell you? Would a long black sound different to an Americano?

How does your coffee sound? Does an espresso sound different to a latte? Could you deduce how the milk had been frothed, or what milk had been used, by listening to your coffee before you drank it?

To see why there may be an effect, it’s worth thinking about your coffee for a moment. The tiny bubbles in the crema of an espresso are different from the larger bubbles of a milk froth made of semi-skimmed milk in a cappuccino. Bubbles of non-dairy milks may be different too, particularly if the initial small bubbles have combined to form larger bubbles as the froth ages. Indeed, sound is used as a characteristic of coffee: think about the sounds made by a steaming wand in milk. Somehow the environment of a café would not be the same without the constant hiss and whistle of a cappuccino being made. But can we use it to experience our coffee more fully? Not just the aroma, taste, sight and feel but also, can we start to listen to our coffee?

Take the example of the sound of a dripping tap: each drop of water falling into a bowl of water left under the tap ready for washing up later. Each “plink” is telling you something about the size of the drop coming from the tap. Intuitively, or perhaps from experience, we know that small drops produce a higher pitch, a higher frequency, than large drops: small drops ‘plink’, large drops ‘plonk’. But there is something wrong with this example, because, despite what we may think, we are not hearing the drops at all, only a consequence of the drops.

Drops on a coffee can reveal a lot, but this time we’re interested in the sound that they make.

As the drop falls, it creates a hole in the surface of the water, a dent that grows and then closes in on itself, so that the drop of water has formed a bubble of air under the water surface. As this bubble is unstable, it pulsates under the water just before it collapses and it is this pulsation that we hear. As the frequency of the pulsation will depend on the radius of the bubble, air cavities of different sizes will produce different sounds. And because a larger drop will generally produce a larger hole under the water, the larger drop will generate deeper sounds: plonks rather thank plinks.

How does this relate to the sounds made by your coffee? Well, it turns out that the sound of a bubble bursting reveals a lot about the surface tension and the size of the bubble. A recent study published in Physical Review Letters measured the sounds made by bursting soap bubbles through 24 microphones placed around each bubble. Analysing the sounds, the group found that not only could they ‘hear’ how the air escaped the bubble, by analysing the sounds recorded in the microphones they could determine, quantitatively, the movement and forces of the bubble ‘skin’ as it retreated back and the bubble burst. They suggested that listening to bubbles and liquid surfaces could be a complementary tool to high speed photography for understanding the forces on a liquid. This may prove useful for example when thinking about how a pond skater moves on the surface of the water.

To think about what this may mean for coffee, take the Aeropresses I’ve been making recently. First, I wet the grounds and allow a first stage of de-gassing to start. The sound here is of an almost continuous hiss, not entirely dissimilar to the sound you hear when you put an empty seashell to your ear.

latte art, hot chocolate art, soya art
Could we detect a difference between a semi-skimmed milk latte and an oat milk hot chocolate by the sound that they make? Some people listen to their bread in order to know when it is cooked. What does listening to coffee reveal?

At this point it was hard to know whether what I was hearing were the grinds or the ‘sound’ of the Aeropress ‘shell’. Topping up the chamber with water, the bubbles on the surface of the coffee became larger, and of a different form. And they sounded different too! A few pops, and a hiss.

Did I learn anything (apart from that putting one’s ear to the top of an Aeropress does get quite hot and a steamed ear is a strange experience)? I learned that there was much more to my coffee than I had appreciated, that there is always more to discover. It was almost as the author of the 1933 paper about determining the size of bubbles in water by the sound said:

“As a matter of fact we know very little about the murmur of the brook, the roar of the cataract, or the humming of the sea.”

What will you hear in your coffee? Do let me know, in the comments below, on Twitter or over on Facebook.

Categories
Coffee cup science General Home experiments Observations Science history

Telling the time with an Aeropress?

Aeropress bloom, coffee in an Aeropress
The first stage of making coffee with an Aeropress is to immerse the coffee grind in the water. Here, the plunger is at the bottom of the coffee.

On occasion, it takes a change in our routine for us to re-see our world in a slightly different way. And so it was that when there was an opportunity to borrow an Aeropress together with a hand grinder, I jumped at it. Each morning presented a meditative time for grinding the beans before the ritual of preparing the coffee by a different brew method. Each day became an opportunity to think about something new.

Perhaps it is not as immediately eye catching as the method of a slow pour of water from a swan necked kettle of a V60, and yet making coffee using the Aeropress offers a tremendously rich set of connections that we could ponder and contemplate if we would but notice them. And it starts with the seal. For those who may not be familiar with the Aeropress, a cylindrical ‘plunger’ with a seal tightly fits into a plastic cylinder (brew guide here). The first stage of making a coffee with the Aeropress is to use the cylinder to brew an ‘immersion’ type coffee, exactly as with the French Press (but here, the plunger is on the floor of the coffee maker). Then, after screwing a filter paper and plastic colander to the top of the cylinder and leaving the coffee to brew for a certain amount of time, the whole system is ‘inverted’ onto a mug where some coffee drips through the filter before the rest is forced out using the plunger to push the liquid through the coffee grind.

clepsydra creative commons license British Museum
A 4th century BC Ptolemaic clepsydra in the British Museum collection. Image © Trustees of the British Museum

Immediately perhaps your mind could jump to water clocks where water was allowed to drip out of two holes at the bottom of a device at a rate that allowed people to time certain intervals. It is even suggested that Galileo used such a “clepsydra” to time falling bodies (though I prefer the idea that he sang in order to time his pendulums). With many holes in the bottom of the device and an uneven coffee grind through which the water (coffee) flows, the Aeropress is perhaps not the best clock available to us now. However there is another connection between the Aeropress and the clepsydra that would take us to a whole new area of physics and speculation.

When the medieval thinker Adelard of Bath was considering the issue of whether nature could sustain a vacuum, he thought about the issue of the clepsydra¹. With two holes at the bottom and holes at the top for air, the clepsydra would drip the water through the clock at an even rate. Unless of course the holes at the top were blocked, in which case the water stopped dripping, (a similar thing can be observed when sealing the top of a straw). What kept the water in the jar when the top hole was blocked? What kept it from following its natural path of flowing downwards? (gravity was not understood at that point either). Adelard argued that it was not ‘magic’ that kept the water in when no air could go through, something else was at work.

What could be the explanation? Adelard argued that the universe was full of the four elements (air, water, fire, earth) which are “so closely bound together by natural affection, that just as none of them would exist without the other, so no place is empty of them. Hence it happens, that as soon as one of them leaves its position, another immediately takes its place… When, therefore, the entrance is closed to that which is to come in, it will be all in vain that you open an exit for the water, unless you give an entrance to the air….”²

inverted Aeropress and coffee stain
The Aeropress inverted onto a coffee cup before the plunger is pushed down. Complete with coffee stain behind the cup where the inversion process went awry.

Now, we would argue that whether the water flows down and out of the Aeropress, or not, depends on the balance of forces pushing the water down and those pushing it up. The forces pushing the water down and out of the clepsydra, or Aeropress, are gravity and the air pressure above the water in the cylinder. Pushing it up, it is only the air pressure from below. Ordinarily, the air pressure above and that below the water in the Aeropress are quite similar, gravity wins the tug of war and the water flows out. In an enclosed system however (if the holes at the top are blocked), were the water to flow out of the bottom, the air pressure above the coffee space would reduce. This makes sense because, if no new air gets in, the same amount of air that we had before now occupies a larger volume as the water has left it, the pressure exerted by that air will have to be less than before. A reduced air pressure means a reduced force on the water pushing it down through the filter and so the force pushing the water down can now be perfectly balanced by the force (from the surrounding air) pushing the water up: the water remains in the Aeropress. The only way we get the coffee out is to change the balance of forces on the water which means pushing down the plunger.

But perhaps it is worth stepping back and imagining what the consequences could be of having the idea that the universe was just full of something that had to be continuous. You may find it quite reasonable for example to consider that vortices would form behind and around the planets as they travelled in their circular orbits through this ‘something’*. Such vortices could explain some of the effects of gravity that we observe and so there would perhaps be no urgency to develop a gravitational theory such as the one we have. There would be other consequences, the world of vacuum physics and consequently of electronics would be significantly set back. In his lecture for the Carl Sagan Prize for Excellence in Public Communication in Planetary Science, The Director of the Vatican Observatory, Br Guy Consolmagno SJ explored previous scientific ideas that were almost right, which “is to say wrong” (You can see his lecture “Discarded Worlds: Astronomical Worlds that were almost correct” here) If it is true that so many scientific theories lasted so long (because they were almost correct) but were in fact wrong, how many of our scientific ideas today are ‘almost correct’ too?

It makes you wonder how our preconceptions of the world affect our ability to investigate it. And for that matter, how our ability to contemplate the world is affected by our practise of doing so. They say that beauty is in the eye of the beholder. For that to be true, the beholder has to open their eyes, look, contemplate and be prepared to be shown wrong in their preconceptions.

What connections do you make to your coffee brew each morning? I’d love to know, here in the comments, on Twitter or over on Facebook.

 

* Does a connection between this and stirring your freshly brewed Aeropress coffee with a teaspoon trailing vortices stretch the connectivity a bit too far?

¹ “Much Ado about Nothing: Theories of space and vacuum from the Middle Ages to the Scientific Revolution”, Edward Grant, Cambridge University Press, (1981)

² Quoted from Adelard of Bath’s “Quaestiones Naturales” taken from Much Ado about nothing, page 67.

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Coffee review Coffee Roasters Observations Science history slow

Waiting for a green light at Alchemy, St Pauls

8 Ludgate Broadway, St Pauls
Alchemy Coffee

Alchemy, “a seemingly magical process of transformation, creation or combination”, is certainly a cafe that lives up to the dictionary definition of its name. The branch, on Ludgate Broadway near St Pauls, is the outlet that ‘showcases’ the coffee of Alchemy Roasters. On walking into this cafe, I was presented with a menu of two types of beans for espresso based drinks or two different beans for filter/aeropress. Both sets of coffees came with tasting notes. After a brief chat with the friendly barista I went for the San Sebastian with aeropress. Notes about the origins of the coffee are dotted around this superbly sited cafe (its location is ideal for people watching). The coffee is directly traded (where possible) and, if lattes or cappuccinos are your thing, there are also details about the farm that produces the milk.

Although there were cakes on the counter, I had just had lunch and so had to pass on what looked to be a good selection of edibles. The coffee though was certainly very good and definitely an experience to be savoured. As, perhaps I should have expected, when the coffee arrived it came in a beaker reminiscent of chemistry laboratories. From my chair in the corner, I could watch the preparation of the coffee behind the counter, the people coming into the shop to order their coffee and the crowds passing by outside.

E=mc2 Einstein relativity in a cafe
Scales at Alchemy. Weights on one side, chocolate on the other, it can only mean one thing: energy-mass equivalence

Close to where I was sitting was an old style set of measuring scales. This see-saw balance had weights on one side and chocolate on the other. Perhaps this connection seems tenuous, but for me weights on one side of the scales and an energy bar (chocolate) on the other side could only mean one thing:

E=mc²

The equation relating energy and mass for a particle at rest derived, and made famous by Einstein. The equation comes from Einstein’s theory of special relativity which states that nothing can be accelerated to faster than the speed of light (in a vacuum). First set down in 1905, the theory has some very odd predictions, among which the best known is probably the twin paradox (details here). The idea is that a moving clock will be observed to run slowly by a stationary observer, a prediction that has been confirmed several times by experiments using atomic clocks (here).

San Sebastian via Aeropress
Coffee is served at Alchemy

Moreover, the equation states that mass and energy are equivalent and that a small amount of mass can produce an awful lot of energy, (details here). A detail which will bring this story of a cafe-physics review nicely back to the Alchemy cafe, to London and to the importance of slowing down. The connection is through a set of traffic lights in Bloomsbury. Back in 1933, Leo Szilard was waiting to cross the road at the traffic lights at the intersection of Russell Square with Southampton Row. Szilard had recently escaped from Nazi Germany and was spending his time as a refugee in London pondering different aspects of physics†. That September day, Szilard was thinking about a newspaper article featuring Ernest Rutherford that he had read earlier. In 1901  Ernest Rutherford, together with Frederick Soddy, had discovered that radioactive thorium decayed into radium. The changing of one element into another could be considered a type of modern day alchemy. However Rutherford did not believe that there could ever be a way of harnessing this nuclear energy. In the article read by Szilard in The Times, Rutherford had dismissed any such ideas as “moonshine”. Szilard was forced to pause his walk as he waited for the traffic lights to change. Those few moments of pause must have helped clear Szilard’s mind because as the light went green and Szilard was able to cross the road, a thought hit him: If every neutron hitting an element released two neutrons (as one element was transmuted into another), a chain reaction could be started. As part of the mass of the decaying atom was released as energy, it would mean that, feasibly, we could harness vast amounts of energy; E=mc².

This idea, a consequence of spending five minutes waiting for a traffic light rather than checking Twitter (not yet invented in 1933), proved to underpin both the nuclear fission which we use in electricity generation and the nuclear fission that we’ve used to develop weaponry. It makes me wonder what alchemy we could conjure in our minds if we stopped to enjoy the transformations of the coffee beans at Alchemy.

 

Alchemy (cafe) is at 8 Ludgate Broadway, EC4V 6DU

† A book that some may find entertaining is:

“Hitler’s Scientists”, John Cornwell, Penguin Group publishers, 2003. The book contains this anecdote about Szilard: As Szilard was of Hungarian-Jewish descent, he fled Germany to Britain via Austria on a train a few days after the Reichstag fire of 1933. On the day he left, the train was empty. One day later, the same train was overcrowded and the people leaving Germany were stopped at the border and interrogated.  An event that prompted him, a few years later, to reflect “This just goes to show that if you want to succeed in this world you don’t have to be much cleverer than other people, you just have to be one day earlier than most people.” Something to reflect on in today’s refugee crisis perhaps.

Categories
Coffee review Home experiments Observations

Sugar castles at Iris and June, Victoria

Iris and June, Victoria, coffee in Victoria
The exterior of Iris and June

This post has been a long time coming. Over the past few months I’ve been popping into Iris&June to get take away coffee now and then and have got quite fond of the friendly service and good coffee. What I have not really had the opportunity to do (until recently) was sit and enjoy a coffee inside. Fortunately that’s now changed and I can add Iris&June to the Daily Grind.

So, how is I+J? Well, it is a 5 minute walk from Victoria train station and a welcome break for good coffee. They serve Ozone based espresso, with a brew bar which features guest roasts (also from Ozone) made with the V60 or Aeropress. There are a good looking selection of cakes on offer, though sadly, on the day that I could sit inside with my drink, they all had nuts in them. Hopefully another time.

Sugar jar, I&J, I+J
A jar of sugar at Iris and June

I took a seat on the cushioned bench near the wall and started to look at what was going on. It is the sort of place that is very good for people watching. My eye though was drawn to what was on my table: a jar of sugar. It is not that I take sugar in my coffee, it is that I was reminded of a tutorial I once had as a student. I cannot remember the exact conversation but it concerned piles of sand. My tutor (a theoretical physicist) had said something along the lines “Ah yes, well, of course, everyone knew the maximum angle that a pile of sand could make before it became unstable and then how it started to collapse…. Until of course someone measured it.” [laughed] “We’d got it entirely wrong.”

This ability to laugh at what we do not know, (or what we assume we do know and then measure it and find out that in fact we do not)  is one of the pleasures of physics. We are trying to understand the world we live in, we have not yet got there. Sometimes it is the smallest things that are not yet understood, such as how and why (dry) sand forms avalanches as it is piled up. Yet these small things can turn out to have big consequences (as was also the case for the understanding of coffee stains). In this case, the experiment had tested the way that a pile of sand collapsed in response to different shaped grains of ‘sand’. It had relevance then (and continues to have relevance now) not only in terms of granular dynamics: how do we predict landslides/avalanches? But also in terms of crucial theoretical models about how these processes behave. Theoretical models that are applied to systems as diverse as knowing how electrical devices (resistors) work to understanding the noise on the luminosity of stars. Realising that we were wrong enabled us to probe the question more deeply and thereby to understand it more.

There are similarities between sugar and sand, but also key differences. Although it was tempting to start building sugar castles in the sugar jars on the tables at Iris and June, I was aware of the impression that I may have made to those who go to I+J to people watch (see above). I will therefore leave it as a home experiment. How steep a sugar castle do you think you can make? And how steep can you in fact make it, what is the role of water in building sand castles?

Please leave any reports of experimental results for how steep you can make a pile of sugar in the comments section below and feel free to send me your sugar-castle pictures.

Iris and June is at No 1 Howick Place, SW1P 1WG