scale factor

Newton gave us a world where bodies move in a void and clocks tick the same for everyone. For three centuries, this picture worked flawlessly. But it relies on many invisible props: absolute position, the 'up-down' direction, and a single rhythm of time for the entire universe. We have never measured these directly — only through the relations between objects.

In a binary star system, one star pulls matter from its companion. Over centuries, this material settles onto the surface of a neutron star — the ultra-dense remnant of a dead star. This process, called accretion, usually proceeds smoothly. Gravity behaves as general relativity predicts, without surprises.

When the cooling cosmos, in the aftermath of the Big Bang, lost its primordial symmetry, tensions arose in the fields, like microcracks forming in solidifying glass. Global monopoles, predicted by Gerard 't Hooft and Polyakov, became such “scars” on the fabric of the universe. Each monopole is a tiny but incredibly massive knot of field.

Quantum tunneling — the ability of particles to pass through barriers forbidden by classical physics — powers stars with thermonuclear fusion, ignites primordial nucleosynthesis, and gives us flash memory.

The crumpled DNA thread in the cell nucleus is not a chaotic knot, but an intricate melody played on a polymer string. Modern experiments Hi-C, like highly sensitive microphones, capture the echo of contacts between distant genome regions, turning spatial organization into a two-dimensional probability matrix.

When two dark matter particles approach each other, they can attract more strongly than expected. This phenomenon is called Sommerfeld enhancement — it works like an invisible spring that compresses before impact. For a long time, it was believed that the spring compresses more strongly the slower the particles approach each other.

A wormhole is a tunnel connecting two distant regions of the universe. If such a wormhole existed and were traversable, a particle inside it would feel not only gravity but also a force from its own electric field. This force depends on how spacetime is curved around it.

A lump of sugar drops into hot tea, a spoon stirs a few times, and the sugar disappears. But how exactly does it spread through the churning liquid? Physicists have peered into this process with unprecedented detail: they simulated turbulence on a grid of 8192³ points. If you were to split every millimeter of the cup into a hundred cells, you'd get a similar resolution.

A guitar string decides for itself how tightly to stretch when a musician plays a chord in different octaves. That's roughly the picture physicists paint when they try to unite gravity, the weakest but most pervasive force, with the quirky laws of the microcosm.

A palm hovering over a hot stove feels the heat even when the surrounding air seems cool. Something similar happens to electrons in the Aharonov–Bohm effect: the particle senses an electric voltage even though it enters a region where the field has already been switched off.

The Universe is like an inflating balloon. Quantum mechanics forbids measuring exactly how big it is and how fast it's inflating at the same time. This principle permeates the cosmos: a new equation states that the Universe's expansion and its size are linked by a fundamental uncertainty.

If you drop an ice cube into a glass of water, it will float until it melts. But if you cool the water slowly, at some point it all freezes at once: that's a first-order phase transition: abrupt, with a clear boundary.

A balloon inflates on its own, even though no one is blowing it up. That's roughly how the accelerated expansion of the universe looks, and to explain it, scientists usually invoke dark energy, an invisible and poorly understood force. But what if the balloon expands because new air molecules are continuously appearing inside it?

A stone drops into a pond. Ripples spread, fade, and soon the surface is smooth again. But what if the pond has no shores, no bottom, and no characteristic ripple size? That is the world, a scale-free world, where quantum systems live when surrounded by an environment that picks out no particular length or energy.

An ultracold cloud of atoms trapped in laser light can 'breathe': it rhythmically contracts and expands, much like lungs. Physicists have long been able to observe this breathing, but only now have they realized that its amplitude is not just a pretty picture: it is a precise measure of hidden energy jitters inside the cloud.

Toss a handful of sand on the floor: there are few large grains, many medium ones, and even more tiny ones. This skew, where small events are common and large ones are rare, is described by a power law. It shows up in city sizes, earthquake magnitudes, and citation counts of scientific papers.

A tumor doesn't grow like a tree; it grows like a city: today's skyline is shaped by yesterday's construction and the fires of the day before. Standard tumor growth equations don't account for this: they only look at the current moment, as if the city were rebuilt from scratch every day. The authors added "memory" to the model: now the equation remembers what came before, and that changes the forecast.

A snowdrift grows by strict rules: falling snowflakes form bumps, those attract more snow, and the bumps amplify. The same mathematics describes city growth, patterns on bark, ripples on water, and clusters of cosmic dust. Physicists call this uniformity universality.

An attempt to suppress room background noise by adding anti-sound turns into speaker howl if the circuit has an error. A similar glitch occurred with a theory that set out to remove the main cosmic hum — the inexplicably weak dark energy.

The quantum world is full of surprises: even simply observing a particle changes its behavior. In a new study, physicists showed that continuously measuring energy can make quantum chaos more pronounced. They used a quantity that indicates how long a quantum state remains similar to itself under repeated measurements.

A stag beetle the size of a fingernail stands on the ground with its legs spread wider than its own height. An elephant as tall as a room, on the other hand, towers above the ground like a tower. Why is that? Both animals walk on the same ground, but they see it differently. For a beetle, each pebble is a boulder, while for an elephant, it's a grain of sand.

Neutrinos are the most elusive of all known particles. Every second, trillions of neutrinos from the Sun fly through your body, but you never notice: they barely interact with matter. To catch even one, physicists build giant detectors — pools of water or liquid argon deep underground.

A snowflake falling from a cloud chooses between a left-handed and a right-handed form. The difference between them is almost imperceptible, like a breath of wind, yet it is that very breath that decides which pattern will grow.