Physics and Society physics.soc-ph

Picture a globe divided into cells: near the poles they shrink into narrow wedges, while at the equator they stretch into wide bands. If you connect random points on such a globe with lines, the compass arrows will lie: connections will point to where there are more cells, not where the flows actually go.

In February 2017, Lima, a city of over ten million people, was hit by El Niño: the warm current off Peru's coast brought torrential rains, floods, and landslides. More than a hundred people died, thousands of homes were destroyed, and roads turned into rivers. The city's economy, like a living organism, fell out of rhythm: shoppers visited stores less often, and their spending patterns shifted almost overnight.

Two people are talking at once, and by the loudness of their voices you can't tell who is answering whom. That's how climatologists have for decades searched for a link between warm water off the coast of Peru and droughts in Australia: they compared how synchronously ocean temperature and rainfall change in different parts of the planet.

Every summer, a giant atmospheric engine unfolds over India: moist ocean winds bring the rains that sustain crops and the lives of two billion people. But this engine sputters, and forecasting it a season ahead remains elusive. Models give only rough answers, and a monsoon forecast error can cost millions of tons of food.

Seventy-five years of weather observations in India, when plotted on a graph, resemble the cardiogram of a vast organism. Instead of a single steady pulse, there are fifteen different lines, each with its own rhythm. Somewhere the heartbeat is as steady as a sleeping person's, while elsewhere it falters, as if after a quick run.

In 2015, downpours in Chennai turned streets into rivers overnight. The city was caught unprepared: seasonal models offered only a vague warning. Yet the monsoon is not a whim of the sky; it is the pulse of a vast machine linking oceans and continents.

The train pulls into the station. Doors slide open, and the crowd spills onto the platform. From there, everyone goes their own way: some head for the bike racks, some dive into the underpass toward the bus, and some just walk to the exit. This final stretch, from the train door to the door of home or office, often decides whether people take the train at all.

A density of four people per square meter is the threshold beyond which a crowd ceases to be a sum of individual pedestrians and becomes something else. In Pamplona's Plaza Consistorial during the San Fermín festival, local density reached nine people per square meter.

The Social Laser theory describes society by borrowing the inner workings of a laser. People, like atoms in a crystal, absorb streams of information and become charged by it. When the number of those charged with a single idea outweighs the indifferent, even a weak signal (a post, a call to action) makes everyone act as one.

Science is a vast kitchen where scientist-cooks seek new recipes. Once, they sifted ingredients by hand; now artificial intelligence, a seasoned chef, lends a hand. AI memorizes millions of flavors and suggests surprising pairings: through information search, the algorithm uncovers hidden patterns.

A group of people searches for a lost item in a large park. Some get tired and leave, others join along the way. The number of searchers is constantly changing. How does this affect the search time? Until now, science had no clear answer. In a new study, a general model of such a process has been built. In it, independent participants randomly enter and leave the search.

An infection is spreading through a city, and residents are watching each other: some have already been vaccinated, others are hesitant. Every day, they update their decisions — whether to imitate neighbors or friends who support vaccination.

A translator who jumps at every rustle in the hall turns a one-hour meeting into two. It's the same in epidemic control: contact tracing teams try to reconstruct the chain of infections, but something always slips through. Someone forgets who they met, someone doesn't answer the phone, someone never even comes to the attention of health workers.

The bronze plates of a gamelan do not sound according to a single tuning standard: each orchestra on Java keeps its own tuning, and two neighboring ensembles may play the same melody in slightly different intervals.

Every time deuterium and tritium fuse in a fusion reactor, a fast neutron flies out. It can turn one substance into another — for example, create valuable isotopes for medicine. Today such neutrons cost a fortune, because there are few experimental facilities and they rarely operate.

Deep in the brain lies a tiny region called the suprachiasmatic nucleus. It's the conductor that sets the rhythm for the whole body: when to sleep, when to wake, when to release hormones. Scientists took the real connection map of this region from a mouse and made copies — one bigger, one smaller.

A customs officer can't take a suitcase apart to see what's inside. They shine X-rays through it and, from the shadows on the screen, tell: here's metal, here's organic matter. In much the same way, an inspector for future nuclear disarmament treaties should be able to check a warhead — without opening it or seeing its secret internals. Neutrons are better suited for this than X-rays.

A dense social network: everyone is connected to almost everyone else, and in this web it's hard to see who really matters. Too many threads — computers choke, simulations stall. Scientists have figured out how to prune such networks without losing what's essential. The idea is to remove connections that don't participate in shortest paths.

A Network That Decides When to Stop A crowd grows: each new person joins the group with a probability that depends on how large the group already is. If the group is small, joining is easy; if it is huge, people start to hesitate, and growth slows down. This mechanism, called feedback, changes the entire behavior of the network.

The fate of a civilization isn't just a matter of luck or disasters. Scientists simulated a thousand years of history under ten different scenarios, accounting for resource consumption, governance, and random shocks. The key metric turned out to be the 'activity coefficient' – the fraction of time when a civilization is technologically alive. At best, this fraction nears 100%; at worst, it drops to 38%.

Astronomers occasionally spot interstellar objects — rocky chunks or comets from other star systems. Most look ordinary, but some puzzle us with their shape, speed, or shine. To stop guessing, scientists applied the Loeb scale: from 0 (plain rock) to 5 (technosignature — an artificial signal from space).

Every group has its unspoken trios: three friends who are always together. And there are pairs that exist on their own. It turns out that how much trios "contain" pairs determines how everything, from a virus to a new idea, spreads through the group. Scientists introduced a measure they call the nesting coefficient.

Physics often resembles the construction of a giant ship — the Universe. The physicist-engineers have yet to agree on the basic blueprints.

Two quantum particles are linked by an invisible thread: one loses energy, the other gains it, but the total remains unchanged. If you watch only the first, its oscillations don't fade — the rhythm is steady, like that of a cosmic pulsar, even though it seems that entropy and chaos are increasing.

A city is a living system: it consumes resources, produces waste, and its 'circulatory system'—the road network — delivers people and goods to their destinations. But while engineers design transport arteries as rigid geometry of straight lines, nature has spent millions of years perfecting ideal distribution networks.

A social network is like a city: there are giant neighborhoods and tiny alleys. When an algorithm looks for tight-knit groups, it often picks out a couple of huge clusters and many small fragments. But the client (say, a municipality) needs districts of roughly equal size to distribute clinics or schools evenly.

On a scorching afternoon, a stifling haze hangs over the city, and not a single cloud is on the horizon. Usually, in such weather, all you can do is wait for nature to take pity and send some cool relief. But what if shade and rain could be switched on schedule, like a light in a room?

A crowd at a metro station during rush hour. Some hurry toward the escalator, others slow down at the departure board, still others weave around a column. Each step is not merely a reaction to what's right in front of your nose. A person estimates in advance where a neighbor will be a second from now and adjusts their route accordingly. Physicists call this forward-looking behavior anticipatory.

Every year, the food we eat costs humanity tens of millions of years of life due to unhealthy diets. At the same time, a third of all greenhouse gases warming the planet are produced along the journey from farm to plate. It seems obvious: switch to healthier eating, and we'll save the climate and improve our health. But new research shows these two goals don't always go hand in hand.

A living organism is a machine that constantly channels energy through itself and converts it into heat. This internal cycle is called internal entropy production (a measure of energy dissipation). But about 2.5 million years ago, our ancestors switched on a second loop — an external one. They picked up a sharpened stone, and then a burning branch.

In the depths of the ocean, where light never reaches, a plan is taking shape to capture particles that barely interact with anything. Geoneutrinos, tiny messengers from the scorching mantle, are emitted during the decay of uranium and thorium. Their flux carries information about how much heat lies hidden beneath our feet.

A person reaches out to a stranger across town. That stranger will never return the favor: they'll never meet. So why help? Biologists call this indirect reciprocity: kindness comes back not from the person you helped, but from someone else, down the line. In a new study, two variants of this idea were pitted against each other.

In the web of life, predators and prey exchange carbon and water, and each act of eating slightly increases the universe's disorder. But the intrusion of disease turns this system into a giant seesaw. When a mid-level predator gets sick, its hunting abilities decline, and it becomes easy prey.

A perfume bottle is not just glass with liquid. It is a snapshot of its time, a frozen melody of fragrant notes. From 1900 to 2024, tens of thousands of such 'melodies' have accumulated, and now they can be studied as a single organism.

In 1888, Vincent van Gogh cut off his earlobe. Biographers and psychiatrists have been trying to explain this act ever since. But mathematicians approached the mystery differently: they measured how the artist's feelings changed in his letters and how the 'nervousness' of his brushstrokes grew, and they saw a clear signal of impending trouble. A swing that gets pushed usually swings and quickly calms down.

In an oven, as temperature rises, molecules move faster and disorder increases. With language models like ChatGPT, it's the opposite. When developers increase the 'temperature' parameter, the model gets access to a wider choice of words, but its long texts suddenly start looping. A team of researchers tested 11 different AIs by generating 12,000 text continuations.

A mail carrier delivers letters along one-way streets. As long as he only drives forward, the route is simple and predictable. But if U-turns are suddenly allowed, he'll start doubling back, crossing his own tracks, and the delivery pattern gets tangled. That's roughly how an infection behaves when people can get sick more than once.

Two people agree to meet, but each has their own things to do. One hesitates: what if the other doesn't come? And decides not to go. The other thinks the same. The meeting doesn't happen. That's the simple mechanism the authors dissect: a joint endeavor requires everyone to invest time, but the payoff depends on whether the partner participates. In the model, each person keeps a to-do list ordered by importance.

In March 2020, France emptied out: people stopped going to work, school, and cafés, and the streets filled with silence. Epidemiologists stared at the graphs and understood that the virus was not spreading on its own, but through handshakes, conversations, and metro rides. But how could they predict how many contacts a person would keep if the government announced new restrictions?