When Bean Thinking started, it was always going to be about coffee and yet, Katsute 100 is definitely a tea place. Not only that, but the idea was to see how the physics that we use to describe our universe is mirrored by the physics of the coffee and in a cafe, the physics of the every-day. On the other hand, the whole point of Schrodinger’s cat is to demonstrate how aspects of quantum mechanics are absolutely unlike our everyday experience: a cat both (and neither) dead and alive? And yet, without giving too much away, today’s cafe-physics review is absolutely this – a review of a tea house that features the famous thought experiment. How far Bean Thinking has moved!
Katsute 100 is a welcoming, and peaceful, Japanese tea place in Angel. With a full tea menu and some really great desserts, it is definitely a good place to spend half an hour, maybe more, watching the coming and going and exploring the tea. And there is certainly a lot of tea to explore, different tasting notes revealing themselves as the tea cools, the carefully placed tea pot and tray adding to the experience.
The shop itself is fairly narrow, decorated in sympathy with the Georgian age of the shop itself and with a view into a garden at the back. Japanese tea making equipment is displayed (and for sale) on the various wooden cabinets around the shop. My tea had been buttery (exactly as it had been described in the tasting notes) and the Ichigo Daifuku I had had with it was a fascinating exploration of texture. There were some Japanese art works on the wall and it was then that I saw my first one: a cat. Not a real one of course but one of several decorative cats that are, almost hiding, around the shop. The word “Katsute” has nothing to do with cats apparently meaning “once”, but nonetheless, a few cats do pop up here and there. And even where cats don’t pop up, there are drawers in the wooden cupboards that seem much like boxes, is there a cat there in the box? Is it dead, alive, both, neither? What does this even mean? And is it connected to Katsute, “once”, after all?
Looking carefully at my teapot, three grooves were carved into the spout allowing the tea to flow out. Each stream of complex flow interferes with the neighbouring stream to present an aesthetic of flowing liquid to match the sound and flavour of the tea. And of course it is reminiscent of an experiment that is key to the unfamiliarity of quantum physics: the double slit experiment.
When light (of a single wavelength, such as from a laser) is shone at a sheet with two holes in it, the light that has travelled through shows interference fringes and patterns. Indeed, it is one of the experiments that went to establishing the theory that light was a wave (and not, as Newton among others had thought, a stream of particles). The situation is quite different if you tried to pass particles through two slits, imagine a sieve with two holes and a stream of coffee beans travelling towards it, we’d expect each bean to go through one hole or the other, not both. In classical physics that’s what we would expect too and yet, when sub-atomic particles (such as electrons) were aimed at two slits and made to travel through them they interfered with each other, as if they were not particles but waves. But other experiments had shown conclusively that they were also particles and indeed, when each individually hit the detector it did so as a single spot, as a particle. Particles and waves? What was going on?
In fact it was a result that had been predicted: Louis de Broglie had shown, theoretically in 1923, that all particles should have wave-like properties and simultaneously, that all waves should have particle-like properties. We should expect that under certain circumstances, light, electrons, neutrons etc, even atoms, should behave as particles and under certain other circumstances (such as the double slit experiment) as waves. But there was an important catch. The electron travelling through a double slit will behave as if it is a wave, passing through both slits and interfering with itself to produce the characteristic “diffraction pattern” of a wave but only if we do not try to look at it to see which slit it really passed through. If we try to detect which slit the particle has travelled through, we can indeed find that some of the electrons travel through one slit and some through the other but when we look at the resulting interference pattern it is gone! What we are left with is the (classically expected) pattern of two particles going through two slits exactly as if they had been very small coffee beans. (You can see a video of Jim Al-Khalili explaining this peculiar result here).
What is going on? To a certain extent, this question is part of the reason that quantum mechanics can seem so strange. We can’t really ask what is going on, or rather, if we ask, we cannot expect to get an answer! We can describe what happens and we can make predictions based on the mathematics that we use to describe the processes. Our technology and our understanding of physics has developed hugely because we can describe how things will behave. But we will stumble if we try to understand what is really going on behind these processes. As Feynman said in lectures he gave to physics undergraduates:
“We cannot make the mystery go away by ‘explaining’ how it works. We will just tell you how it works. In telling you how it works we will have told you about the basic peculiarities of all quantum mechanics.”§
And so things remain enigmatic. Questions that appear to show paradoxes such as the problem of Schrodinger’s cat* continue to puzzle and intrigue us. Is the cat dead or alive? Can the cat be both? Is the cat an observer and what role does the observer have in physical measurements? What does this imply for the fabric of reality? And is there a connection back to the name of this cafe, “once”?
You perhaps should not expect to find any answers in Katsute 100, but pondering these things with a good cup of tea may help advance your understanding. It will certainly help advance your mood if you are in need of some peaceful, thoughtful, time out.
Katsute 100 is at 100 Islington High St, N1 8EG
§ Feynman Lectures on Physics Volume III, 1965
*The story of Schrodinger’s cat is that a cat is placed in a box together with a small amount of radioactive source material. The box is then closed and we cannot see inside. The amount of radioactive material is such that in one hour it has a 50:50 chance of decay. If the material decays radioactively, it triggers the release of a vial of poisonous gas which would kill the cat. Our mathematical models of quantum mechanics suggest that, until it is measured, the radioactive material is in a ‘superposition of states’: it has both decayed and not decayed; the cat is both dead and alive. Only when we open the box after an hour and thereby measure the state of the radioactive material does the cat, at that point, ‘collapse’ into a state that is either dead or alive.