quantum cosmology

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.

The first three minutes after the birth of the world are a cosmic kitchen where nature cooked the lightest atomic nuclei. The recipe is set by gravity: it controls the cooling rate of the hot 'broth' of particles. If gravity worked differently than we are used to, the dish would have turned out different — with different amounts of helium and deuterium.

Photographing hummingbird wings with an ordinary camera gives a blurry smudge. For a sharp picture, you take many rapid shots from different angles and piece them together: that's how a quantum 'snapshot' is made. In the lab, scientists 'feel' the vibrations of a tiny mirror with a laser beam.

A quantum wave is like a long-exposure photograph: everything’s blurred, but the blur itself reveals motion. Usually these frozen waves are treated as convenient abstractions. Yet if at each point in the image you estimate, by brightness, the moment on the particle’s internal clock it landed there, flat space suddenly acquires curves.

From childhood, we're used to thinking of space as infinite and isotropic. But Einstein and Lemaître were already asking: could the Universe be closed in on itself, like a Möbius strip or a 3-torus?

A builder checks the strength of an arch not by running through all possible shapes in their head, but by mentally nudging it and seeing how much force is expended. That's essentially how the principle of virtual work works in mechanics. The authors of a new study have applied this approach to the very geometry of spacetime. They constructed a covariant framework of virtual work for the metric.

Since the end of the 20th century, we've known: the expansion of the Universe is accelerating — galaxies are flying apart faster and faster. The discovery brought a Nobel Prize to Adam Riess, Saul Perlmutter, and Brian Schmidt.

Quantum noise, like the hiss of an untuned radio, filled the infant Universe. Alan Guth showed that superfast expansion (inflation) caused this ripple to freeze, giving rise to clumps of matter — the seeds of galaxies. A new method extends this picture to any theory of gravity.

For almost a century, cosmologists have been grappling with the mystery: what makes the Universe expand ever faster? The standard answer — dark energy — creates a monstrous discrepancy between the theoretical vacuum density and observations. But there's another path, one that turns causality on its head.

The end of the Universe is not just the fading of light. If dark energy, the mysterious substance accelerating cosmic expansion, tears it apart in a Big Rip scenario, or if expansion reverses into a contraction that pulls everything back to a point like a big bang in reverse, a…

First thing that comes to mind when thinking about the birth of the Universe is an explosion. But modern cosmology paints a more refined picture: birth through the neck of a wine glass. This geometry is not a sommelier's fantasy, but a rigorous form of Euclidean wormhole that connects two anti-de Sitter worlds.

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

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.

The universe abhors monotony. A century ago, Edwin Hubble and Georges Lemaître gave us an elegant picture: an expanding cosmos, smooth as the surface of an inflated balloon.

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.

A rubber band stretched in different directions behaves differently from a whole sheet of paper. If you pull on an edge, the deformation does not spread evenly but seems to linger in certain spots.

You're inflating a balloon, but with each pump of the bulb, the rubber doesn't just stretch: it subtly changes its elasticity. Gravity works similarly in the new model: not as a rigid stage for the cosmic play, but as a living material that responds to every speck of matter.

The Universe is a colossal web of invisible dark matter and galaxies, stretched by the expansion of space. Neutrinos, nearly intangible ghost particles, barely cling to the threads, but their collective mass subtly shifts the tension of the entire network.

It all started with tiny quantum flickers on the primal canvas. Inflation — an avalanche-like expansion proposed by Alan Guth — stretched those brushstrokes to the scale of galaxies.

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.

In one hospital ward it's +40°C, in another +10°C, and on average it's +25°C. If temperature affected something nonlinearly (say, the rate of bacterial growth) the average would give a wrong prediction. The same problem arises when cosmologists describe a universe where galaxies are packed into clusters and voids yawn between them.

The universe is expanding, and scientists want to know how fast and what it's made of. To do that, they compare data from distant stellar explosions, sound waves in the early universe, and the faint glow left over from the Big Bang. Each dataset is like a piece of a mosaic, and the goal is to assemble them into a full picture.

Light from distant galaxies, passing through clusters of matter, gets distorted — much like the bottom of a pool breaks up into ripples of water. Astronomers measure these barely perceptible bends in shape and create a map of gravitational ‘ripples.’ This is weak lensing — a natural detector of invisible matter.

In the familiar world, we have three spatial dimensions. However, theoretical physics allows for additional, hidden directions — compactified, that is, curled up to microscopic sizes.

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.

The clock on the kitchen wall ticks, and each tick relentlessly carries us from breakfast to lunch. This is so familiar that it seems like a law of nature, but physics says otherwise. In Einstein's equations, time is reversible: you can rewind the film, and no frame will give the trick away.

At night, an astronomer points a telescope at the edge of the visible universe and sees not stars but ripples — the imprint of the first moments. He knows these ripples should obey statistics, like the heights of people in a crowd. But he has only one crowd, and nothing to compare it with. This is cosmic variance.