Schwinger effect

The quantum world is like a kitchen where particles suddenly appear out of "nothing." But you need a chef — a classical field acting as an external source. Glauber's theorem, long known in optics, has now been generalized: it shows exactly how the field "cooks up" particles, be they photons or gravitons.

In the first moments, the Universe expanded at an enormous rate. This process is called inflation, and its driving force is the inflaton field. Its energy pushed space apart, like yeast raising dough. But physicists suspect that the dough might have left 'bubbles'—superheavy particles born from the expansion itself.

In the first moments, the Universe expanded at an enormous rate. This process is called inflation, and its driving force is the inflaton field. Its energy pushed space apart, like yeast raising dough. But physicists suspect that the dough might have left 'bubbles'—superheavy particles born from the expansion itself.

A cloud of waves collapses under its own gravity. While it's loose, everything goes by the book: the field oscillates gently in nearly flat space, and approximate formulas work perfectly. But add just a bit more energy, and the picture changes. Physicists used a numerical model to catch the moment when simple calculations stop describing reality.

At the center of nearly every galaxy lurks a supermassive black hole. Its gravity is so strong that it warps space itself. But few stop to wonder: what does it do to the very fabric of reality — the fields that permeate the cosmos? One such field is the Higgs field.

A pale green crystal was placed in a magnetic field and cooled below one kelvin — almost to absolute zero. Inside it hide chains of copper atoms that behave like tiny magnetic needles. Usually their orientation is chaotic, but the strong field and cold make the needles align in a unified impulse, like soldiers on a parade ground.

Hot tea cools down, a pendulum comes to rest — nature loves equilibrium. But a charged black hole can reach a special, extreme state: the mass becomes minimal, and the temperature drops to zero.

Empty space is not as empty as it seems. According to quantum theory, the vacuum is filled with particles that constantly pop in and out of existence. In 1976, physicist Bill Unruh showed that if an observer moves with acceleration, this 'quantum soup' turns into a genuinely warm bath for them — the Unruh effect.

In a room, air touches the skin, and we feel its temperature. But if your body suddenly accelerated at a colossal rate, heat would come even from absolute emptiness. This is not fiction but a strict consequence of quantum field theory: for an accelerating observer, the vacuum becomes a warm bath.

If you accelerate an observer to near-light speed, the emptiness around them stops being cold. A thermal glow emerges — an effect predicted in 1976 and named after William Unruh. For earthly accelerations, this glow is vanishingly faint, like a whisper at a rock concert.

Quantum vacuum is not absolute emptiness. It is more like a taut membrane that constantly ripples from invisible particles popping in and out of existence. Even in total darkness, this membrane trembles. Physicists decided to see how it behaves around a thin spherical shell, inside which is ordinary flat space, like in our room.

In 1981, Alan Guth proposed a scenario of cosmological inflation — a lightning-fast expansion of space that stretched quantum fluctuations to the scale of entire galaxies. Since then, cosmologists, like archaeologists, have been excavating this event from the structures of the Universe.

A black hole is where the usual rules break down. At its center, according to classical physics, lurks a singularity: a point of infinite density where everything that falls in gets crushed. Quantum theory was supposed to soften this picture.

The quantum vacuum is not a dead void but a boiling cauldron of probabilities. In some theories, our Universe is frozen in a metastable state: like superheated water, it's ready to explode into steam at the slightest nudge.

A regular object moves along a predictable path, like a ball. In the quantum world, a particle is smeared into a probability cloud. To find order in this fog, scientists have recast Schrödinger's equation in the language of flowing water.

After the Big Bang, the universe may have been stuck in a false vacuum — a temporary state like a soap bubble ready to pop. A rare true vacuum bubble could then erupt, stretching space in the blink of an eye.

Quantum electrodynamics, or QED, describes how light interacts with charged particles — for example, electrons. It is one of the most precise theories in history: its predictions match experiment to the eleventh decimal place.

The vacuum is not as empty as it seems. If an observer moves with acceleration, the vacuum around them heats up: this was predicted by William Unruh back in the 1970s. The effect is akin to black hole radiation, but in flat space.

In the depths of a neutron star, the remnant of an exploded star, matter is compressed so tightly that a teaspoon would weigh billions of tons. Within this superdense material, a special kind of force might be at work, one that affects only muon and tau neutrinos.

In very dim light, photons arrive one by one, like drops from a leaky faucet — never in pairs. This effect, predicted by Roy Glauber and confirmed by Leonard Mandel, directly proves that light is made of particles.

Two black holes circle in a slow dance, gradually drawing closer. Their motion perturbs spacetime itself, like two heavy balls rolling on a stretched sheet, making it tremble. These tremors are what we call gravitational waves.

Two floats on the waves. Throw a stone into water, and the ripples will spread, rocking both floats one after another — not simultaneously. In the quantum world, such rocking is called entanglement: particles, like floats, begin moving in sync.

The early universe expanded at an unimaginable rate — faster than light could cross it. In this boiling cauldron, any region of space resembled an open can of paint: its boundaries continuously captured new 'vapor' from outside, while some of its own contents irrevocably escaped.

Electrons and muons are tiny magnets. Their magnetism is slightly more than two (in special units), and this 'excess fraction' (anomalous magnetic moment) arises from constant ripples in the vacuum: particle pairs momentarily pop into existence and vanish.

A superconductor carries current without resistance, like water running through a pipe without friction. The secret lies in electron pairs: two electrons stick together as one, even though they normally repel. In an ordinary superconductor, the spins of the electrons in a pair point in opposite directions: this is the singlet state.

Gravity is the curvature of spacetime, not just an attraction, as Einstein showed. On such a curved "dance floor", even the hypothetical carriers of gravity — gravitons — move oddly.

Quantum nothingness resembles water in a pot just before boiling. From time to time, a bubble spontaneously swells up — but not of steam, but of an entire universe. Such a bubble doesn't collapse; instead, it inflates into spacetime, triggering its own Big Bang. The only question is how often this happens.

Stephen Hawking imagined that the universe was born not from an explosion, but by smoothly emerging from a quantum 'nothing.' In worlds with concave geometry (anti-de Sitter space), such a birth acquires a rim, like the hoop of a drum.

A stone falls into a pond — ripples spread across the water. If the stone doesn't fall but whizzes over the surface at tremendous speed, a straight wave runs along the water. When it hits a floating log, ripples spread out from the point of impact. That's roughly how gravity works in the new study.

The riddle of quantum gravity has troubled minds for nearly a century. A classical field that curves spacetime refuses to fit into the probabilistic world of superpositions. Can gravitation, while remaining macroscopic, give rise to microscopic entanglement?

In physics, there's an old ache. General relativity paints the beginning of the universe as a point — a singularity where equations break down and volume shrinks to zero. Quantum mechanics hints that at the most critical moment, something goes differently than classical physics predicts.

A massive nanodiamond inside a quantum interferometer splits in two, pulling itself into two realities. Its gravity — tiny, almost imperceptible — stirs the quantum field of the vacuum, giving rise to coherent clouds of gravitons. These are the gravitational shadows cast by each position of the mass.

A massive nanodiamond inside a quantum interferometer splits in two, pulling itself into two realities. Its gravity — tiny, almost imperceptible — stirs the quantum field of the vacuum, giving rise to coherent clouds of gravitons. These are the gravitational shadows cast by each position of the mass.

When an electric field reaches monstrous strength, emptiness ceases to be empty. Back in the mid-20th century, Julian Schwinger showed that the vacuum literally explodes with pairs of particle-antiparticle if the field is intense enough.

When an electric field reaches monstrous strength, emptiness ceases to be empty. Back in the mid-20th century, Julian Schwinger showed that the vacuum literally explodes with pairs of particle-antiparticle if the field is intense enough.

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 early universe resembled a rapidly inflating balloon: it expanded so fast that light couldn't keep up with its own edges. Then this frantic acceleration gave way to calm expansion. The balloon was no longer being blown up, and it began to slowly deflate. At the moment of the regime change, emptiness didn't stay empty: from it, as if from an overheated boiler, pairs of particles burst forth.

A handful of rice grains falls onto a hot skillet, and they start jumping. Each grain pushes its neighbors, and the whole pile stirs without any external hand. That's active matter: a multitude of particles that draw energy on their own and convert it into motion.

An invisible film, a quantum field, is stretched over a rubber bagel. While the bagel is small, the film stays taut and doesn't sag anywhere: the vacuum remains empty. But once you stretch the bagel to a certain size, a dent spontaneously appears in the film — the field starts to be felt at every point. This dent is not random.

Inside a neutron star, the density doesn't change smoothly but drops abruptly at sharp cliffs — density staircases. At these steps, the void suddenly births pairs: neutrinos and antineutrinos.