quantum bounce

A homogeneous, spherical cloud of cosmic dust begins to contract under its own gravity. At some point, by classical laws, it should collapse into a point of infinite density — a singularity.

In the far reaches of space, there exists a hypothetical object: an ultracold black hole. It is charged and resides in an expanding universe (de Sitter space). Its temperature hovers just above absolute zero — about one trillionth of a degree above it.

A classical black hole is a bottomless well: everything that falls past the horizon disappears into a point of infinite density. But in loop quantum gravity (one approach to quantum gravity), that point is replaced by a quantum 'bounce'—a sphere of finite size where spacetime doesn't tear but rearranges itself.

In a two-dimensional universe, a black hole looks like a funnel in spacetime. But the authors of the new work went further: they proposed that the space where particle momenta 'live' is also curved, like a saddle.

At the center of a classical black hole lurks a singularity — a point where the density and curvature of spacetime become infinite. Physics goes silent there.

In classical theory, a black hole is where matter collapses to a point of infinite density. Such a 'singularity' looks like an error in the equations: nature hardly tolerates infinities. Many physicists seek ways to 'smooth out' this flaw, and one idea is to modify the theory of gravity itself at small distances.

In the first moments of the universe's life, there was not even a hint of dark energy — the very force that today pushes galaxies apart ever faster. But if you look deeper, down to the Planck scale (billions upon billions of times smaller than an atomic nucleus), spacetime ceases to be smooth.

The universe hasn't always been expanding. In some models, it first contracted, nearly empty and flat, and then, upon reaching a limit, bounced back and started growing, like the world we know. This scenario is called bouncing cosmology.

A textbook black hole resembles a perfectly smooth sphere: everything outside it calmly flies off to infinity. However, quantum gravity paints a different picture. Recently, within loop quantum gravity, a solution was found — a 'Kruskal' black hole where spacetime beyond the horizon behaves differently.

A star contracts under its own gravity, and at some point its fate hangs on a razor-thin balance. Classical physics paints a grim picture: if the mass and the force of compression are tuned with terrifying precision, what emerges is not a black hole but a 'naked' singularity.

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.

An empty glass on the table seems reliable. But if there's a microcrack in the bottom, one day it will break — not with a crash, but quietly, spreading in a web of lines. So too with the vacuum: it may not be the true vacuum but a false one — temporarily stable, yet ready to transition to a deeper, real state.

Space is like a sheet of paper: gravity bends it, making lines converge toward the center. But if you bend too hard, the paper tears, just as space, under monstrous curvature, doesn't collapse into a point but forms a torn edge. That edge is the quantum boundary.

At the center of attention is a black hole with two points of no return: the outer and inner horizons. Beyond the outer horizon, space and time swap roles, but the journey is not over. Further in, at the inner horizon, gravity has another surprise in store.

In the quantum world, dark matter particles can merge into a single superfluid droplet — a state where matter flows without friction, like an ideal fluid. When near a black hole, this droplet doesn’t just disappear into it but twists into stable vortices, like water swirling around a rock in a stream.

Quantum objects live in a world of superpositions — being here and there at the same time, with one spin and another. But as soon as they gain enough mass, this magic fades. Roger Penrose suggested that gravity itself is to blame.

An ordinary kettle: you heat it up — temperature rises, molecular chaos grows, and steam shoots out. But in the lab, they've created a peculiar "kettle"—an analog black hole made from superconducting circuits cooled to the extreme.

A dying star is not just fading away. In its final moments, the core, starved of fuel, collapses into itself at colossal speed. Classical gravity leaves no choice: if the mass is large enough, a black hole is born — a region from which not even light can escape.

Holography is the idea that everything happening inside a volume can be encoded on its boundary, like an image on a hologram. In physics, this helps connect gravity to the quantum world. But sometimes, the holographic rules fail to assemble familiar spacetime, and scientists are looking for where exactly the mechanism breaks down.

In 1965, Penrose unleashed a mathematical thunderbolt on physics: any sufficiently massive star, shrinking under its own weight, inevitably collapses into a singularity — a region where spacetime curvature becomes infinite and the laws of physics break down.

You can picture a black hole as a whirlpool in a river: it has an edge, the event horizon, beyond which the current drags everything in irreversibly. At the center lurks the singularity, a point where the familiar laws break down.

A star that has exhausted its fuel falls into itself. Its outer layers fly apart, while the core compresses to unimaginable densities. It was once thought that this process ends in a point — a singularity where the laws of physics break down. New work shows that just before the very end, something strange happens inside the future black hole.

Classical general relativity predicts: a singularity hides inside every black hole. In this region, spacetime curvature skyrockets to infinity, and Einstein's equations lose meaning.

The standard picture of black hole evaporation, painted by Hawking, long seemed reassuring: quantum fluctuations near the horizon produce thermal radiation, the hole slowly melts away, and the spacetime behind it remains smooth.

A pencil dropped on the floor hits with its entire surface at once. But if the floor were quantum, made of countless vibrating grains of sand, the pencil would never touch a single point.

Usually, the story of the universe goes like this: there was nothing, then a bang, and ever since everything has been flying apart. But what if there was no 'nothing'? A group of physicists has shown that the universe could have existed forever: it just sometimes contracts and then expands again, like a spring.

A thrown stone arcs along a clean trajectory, but an electron's position in an atom is smeared out like fog. The transition from one to the other is a puzzle. New work shows that the fuzziness disappears not because of an observer, but because of the particle's own gravity.

When stars at the edges of galaxies rotate faster than calculations based on visible mass predict, standard cosmology invokes the hypothesis of hidden dark matter — invisible substance that reveals itself only through gravity. A new study offers an alternative that requires no new particles.

The equations of Einstein and the model of Lemaître led to the conclusion that the Universe began from an infinitely dense point — the singularity of the Big Bang. At that point, familiar physics broke down, leaving the mystery of the first moment.

In the first moments, the Universe was squeezed to tiny sizes. What keeps it from collapsing entirely into a point? One answer comes from quantum mechanics: the wave function describes all possible states, and particles move along hidden trajectories that depend on the shape of this wave.

The standard cosmological model describes the birth of the universe as an explosion from a singularity — a point of infinite density and spacetime curvature.

Picture a black hole as a funnel in a taut sheet — the classic analogy for spacetime curvature caused by a massive body. But if a fifth dimension exists, this simple picture gets complicated: the sheet gains hidden springs.

When two black holes merge, the newborn hole should ring like a bell, emitting gravitational waves — ripples in space. Yet before the ring, a silence can fall: the black hole gets caught in a phantom trap, as if an invisible hand grips the bell’s clapper.

The universe can behave like a spring: compressing to microscopic sizes and then expanding again. In this cycle of contraction and bounce, black holes and dark matter are born.

Traditional cosmology begins with the Big Bang — the idea of Georges Lemaître. However, a new approach, inspired by the work of Stephen Hawking, bypasses the mystery of the initial moment.

The third law of black hole mechanics, proposed by Stephen Hawking, forbids a hole from spinning up to its limit in finite time — much like a whirlpool would need an eternity to reach absolute speed. Yet numerical simulations in five dimensions break this rule.

Modern telescopes see distant galaxies flying apart faster and faster. The cause is called dark energy, but its nature has been a mystery. On top of that, calculations of the expansion rate in the early and late Universe don't match. The answer might lie in an event much like a falling pencil.

In the quantum world, an object can be in several places at once. Yet in everyday life we see things strictly in their places. The reason is gravity. A massive star under its own weight inevitably collapses into a black hole or a neutron star, but it can't be both at the same time.

The early universe was far from perfect: some regions stretched faster than others, creating folds and warps. But a quantum bounce — the transition from contraction to expansion, driven by the laws of the microworld — fixes everything.