The Demon at Door Nine
On the way to the Royal Albert Hall last night I walked up Exhibition Road, past Imperial College’s Dyson School of Design Engineering, named for Sir James Dyson of vacuum cleaner fame. At the Hall my seat was upgraded. Door 9, Stalls L, row 11, seat 122. A small piece of luck. I knew nobody among the five thousand people around me. Yet somewhere in that hall, very probably, two people were discovering that they knew each other: a former colleague from another continent, a neighbour from a childhood town, a face last seen at a conference in another hemisphere. It happens every day, everywhere. And every time we reach for the same phrase. Small world.
It is not a small world. It is a well mixed one, and the difference matters more than it sounds.
The concert itself was about scale. The Royal Philharmonic Orchestra opened with Eric Whitacre’s Deep Field, set to the Hubble image that found thousands of galaxies in a patch of sky most of us would have called empty. After the interval came The Moonwalkers, Tom Hanks narrating, Anne Nikitin’s score played live for the first time beneath footage from the Apollo missions that put twelve men on the Moon. The universe on the screen was unimaginably large. The coincidences playing out among the seats were intimate. Physics says the two are connected.
In 1827 the Scottish botanist Robert Brown watched tiny particles released from pollen grains jitter about in water under his microscope. He could not explain it. In 1905 Albert Einstein did. Invisible molecules strike the particles from every side, at random, and they wander without intention. A particle on a random walk goes nowhere in particular and yet, given time, goes almost everywhere. The air in the Albert Hall tonight is doing the same thing, each molecule colliding with others billions of times every second. Nobody organises it. Gases mix by themselves. Mixing is simply what the universe does when it is left alone.
People mix the same way, and the arithmetic of chance is kinder to coincidence than intuition is. Put 23 people in a room and the odds are better than even that two share a birthday. Names mix too. The physicist Freeman Dyson, a different Dyson entirely, did the sum for miracles, building on the Cambridge mathematician J.E. Littlewood: register one event a second for eight waking hours a day and you clock up a million events in about five weeks. Something with a chance of one in a million should therefore turn up roughly once a month.
In 1967 Stanley Milgram asked people in Nebraska and Kansas to pass a letter, through acquaintances, to a stranger near Boston. The chains that arrived took about six steps. Six years later Mark Granovetter explained why. It is our weak ties, the former colleague, the old student, the friend of a friend, that bridge distant clusters. The person you bump into abroad is rarely your closest friend. It is almost always a weak tie, and weak ties carry jobs, news, ideas and trust.
The building has a lesson of its own. Queen Victoria opened the Royal Albert Hall in March 1871. That same year James Clerk Maxwell was describing, in a letter to Lord Rayleigh, an idea he had first sketched for his friend Peter Tait in 1867, and his Theory of Heat, whose first edition bears the date 1871, put it before the public. It was a tiny imagined being stationed at a door between two chambers of gas. It opens the door only for fast molecules, sorting hot from cold without apparent effort and seeming to defeat the second law of thermodynamics. It became known as Maxwell’s demon, and physicists spent more than a century proving it could not work for free. Leo Szilard, a Hungarian Jewish physicist, showed in 1929 that the demon must pay for what it knows. Rolf Landauer later put a price on forgetting it. The conclusion is simple. Mixing is spontaneous. Sorting costs energy.
That is a lesson the world is now relearning. For a generation after the Cold War the mixing ran fast: cheap flights, easier visas, and hub cities like Dubai, where I live, in which anyone might collide with anyone at a departure gate. Today there are demons at more and more doors. Sanctions lists, visa regimes, closed airspace, tariff walls and travel warnings all sort the particles. Some of these doors genuinely need guarding. But none of them is free. Every wall reduces collisions, and fewer collisions mean fewer flukes, fewer weak ties and fewer of the accidents from which trust is built.
Israelis understand both sides of this better than most. Jewish geography, the game of discovering within minutes that you share a cousin, a classmate or a commanding officer with a stranger, is what intense mixing looks like in a small and densely connected network. Young Israelis finishing army service turn up in Manali and Cusco and keep running into one another. The Abraham Accords of 2020 opened a door that had been shut for decades, and within months Israelis and Emiratis were colliding in Dubai malls and boardrooms. Since 7 October many doors have swung shut again, and the list of places Israelis are warned to avoid has grown longer.
The country’s strengths, its startups, its scientists, its alliances and its diaspora, have always depended on collisions: the chance conversation at a conference, the weak tie who makes an introduction. Israel can guard its doors. It cannot afford to be unmixed. It is fitting that Einstein, whose work on Brownian motion gave us the statistics of mixing, lectured on Mount Scopus in 1923 and left his papers to the Hebrew University. The man who explained diffusion chose a home for his ideas at one of the world’s most contested crossroads.
The Albert Hall once had an echo so notorious that in 1969 large fibreglass discs, nicknamed mushrooms, were hung beneath the dome to break it up. Properly, they are diffusers. The room was cured by scattering.
When the orchestra finishes tonight, five thousand people will pour out through the numbered doors into Kensington Gore, towards the Tube, the buses, the airports and the other hemisphere. Within an hour the hall will be empty, the diffusers hanging over silent Stalls. Somewhere out in the London night, two people who met by fluke will already be drifting apart again, perfectly mixed.
Door 9 will stand open. There is no demon at it.