interaction model

Light from a distant galaxy reaches us through its own dust. This dust is not a smooth haze but ragged clouds, like wisps of cotton. Old models treated it as a uniform mist, and then the galaxy didn't add up energetically: too much light disappeared in the ultraviolet and too little came back in the infrared. Astronomers did what a cook does when they dice a potato instead of tossing it in whole.

In 1929, Edwin Hubble pointed his telescope at distant galaxies and discovered they were receding. Ninety years later, two measurements of this recession rate, from ancient light and from nearby stars, stubbornly disagree. A 9% discrepancy cannot be chalked up to error. It is as if the Universe in its youth and in its maturity runs on different clocks.

The universe is a vast, dark ocean. We see only the glowing foam on its surface — stars and galaxies. But hidden in the depths are two invisible forces: dark matter, which with its gravity keeps galaxies from flying apart, and dark energy, which, on the contrary, pushes space itself apart, making the universe expand faster and faster.

Gravity is a remarkably weak force. A small magnet holds a paperclip against the pull of an entire planet. Physicists have long sought the reason for this weakness, and one guess leads us into hidden dimensions. Perhaps gravity 'leaks' into them, losing strength in our three-dimensional world.

Cosmology has landed in an interesting pickle. The two main ways to look back into the universe's past, via the early glow (the cosmic microwave background) and via later objects like supernovae, yield different numbers for the expansion rate (the Hubble constant) and for how clumpy matter is distributed.

At the dawn of time, the universe experienced a brief moment of frantic expansion — inflation. Tiny quantum jitters of spacetime stretched to cosmic scales. These jitters, primordial fluctuations, became the seeds from which galaxies and stars later grew.

Cosmic ripples begin with tiny clumps. 380,000 years after the Big Bang, the universe was nearly homogeneous — density fluctuations were only one part in 100,000. But gravity turned these weak ripples into galaxies, clusters, and giant voids.

Light from distant quasars, breaking through billions of years, leaves a pattern of dark absorption lines on the cosmic film — the spectroscopic Lyman-alpha forest. Each line is like a note in a grand score, written by the hydrogen of the intergalactic medium.

Ever since Edwin Hubble discovered the fleeing of galaxies, the law of expansion of the Universe — Hubble's Law — has been a cornerstone of cosmology.

A drama is brewing in cosmology: two principal musical instruments, the orchestra of the early Universe and the chamber ensemble of the modern cosmos, play the same symphony of expansion at different tempos.

The standard model of cosmology, based on the field equations proposed by Einstein, describes the Universe as a cocktail of dark matter (discovered thanks to Vera Rubin) and dark energy in roughly a 1:3 ratio.

Imagine a cosmic orchestra performing a symphony from the Big Bang to the present day. The conductor, dark energy, long seemed an impassive metronome: the cosmological constant Λ motionless, like a baton frozen in mid-air.

At the center of the Milky Way, where the supermassive black hole Sagittarius A* reigns supreme (its metric first derived by Karl Schwarzschild), star S4714 makes a dizzying voyage.

The Universe is an orchestra playing the symphony of the Big Bang. For a long time, the conductor was thought to be dark energy — an unwavering metronome setting the pace of expansion.

In a recent study, astrophysicists showed how pre-recombination physics, particularly early dark energy, affects the spectral running $$α_s$$ and, consequently, the viability of scenarios forming primordial black holes from an ultra-slow-roll (USR) phase during inflation.

A large underground tank of liquid xenon waits for a rare event — a nudge from a dark matter particle. Normally, gravity is too weak to notice such a nudge. But if space has hidden dimensions, everything changes: at tiny distances, gravity suddenly strengthens, and the chance of catching an elusive particle grows.

Since the late 20th century, astronomers have known that the recession of galaxies is accelerating, as if pushed by an invisible tailwind.

The cosmic vacuum is not emptiness but a living ocean: its energy swells and subsides, echoing the expansion. Like a lunar tide, vacuum density sensitively responds to Hubble’s tempo — the conductor’s baton of the universe.

Cosmologists staged a showdown between two kinds of cosmic explosions. Type Ia supernovae are stars that flare up with nearly identical brightness, making them reliable beacons for measuring distances across the universe.

A stone thrown into water leaves ripples. A satellite orbiting Earth also leaves a trace — not on water, but in the laws of physics. Its orbit is not a frozen line: it slowly rotates, like the hand of a giant clock.

A blacksmith forges a sword. With each hammer blow, the red-hot metal flattens, but the hammer, the anvil, and the surrounding air all warm up slightly. Part of the impact energy is irreversibly lost as heat — a trade-off familiar to anyone who has ever driven a nail, and it turns out to be the key to the biggest mysteries of the cosmos.

The universe is expanding, and its history features two puzzling episodes that don't fit into a simple picture. The first is a brief period in its youth when everything flew apart faster than expected, as if someone had floored the gas pedal. The second is today's acceleration, as if the same pedal were pressed again, but more gently.

Imagine a huge layered cake, where the layers of dough are space and the filling is a special region resembling an invisible wall. This wall is not made of bricks but of energy, and it could be as thick as the entire universe. If such a wall exists, it should stretch the dough layers differently: those lying along it spread apart faster, while those across it spread slower.

When a car on cruise control hits a bump, the speed jumps for a moment, but the engine runs smoothly. Something similar was recently noticed with dark energy — the force that makes the Universe expand faster and faster.

An architect checks the blueprint when building a house. For cosmologists, the blueprint is the Standard Model, and the measuring tape is the light from distant galaxies. Recently, a new 'tape measure,' the DESI instrument, measured distances to millions of galaxies with unprecedented precision. And the numbers didn't match the blueprint.

The Universe is a vast city. In it, dark matter is the invisible framework of buildings, and dark energy is the force stretching the streets. For a long time they were considered independent, but new research has caught them in secret communication.

In the 1920s, Edwin Hubble noticed galaxies were moving apart — thus discovering the expansion of the Universe.

It all started with a tiny clump that grew faster than light could cross it. Inside this inflating bubble, our future Universe, reigned unimaginable heat. But one field, called the inflaton (the engine of inflation), behaved like a conductor: it controlled both the expansion and how other particles behaved.

For a long time, dark energy, the mysterious force prodding the expansion of the Universe, was considered eternal and unchanging, like yeast that never loses its activity. But explaining such constancy through the laws of the microcosm proved impossible, and scientists began to suspect that the “leaven” might be going flat.

Imagine inflating a balloon. It expands quickly at first, then slows down, and then suddenly speeds up again, as if someone gave the pump another squeeze. That's what seems to be happening to our universe.

Two clocks tell different times. One sits on our desk, the other lies far in the past, in the glow left over from the Big Bang. The first, looking at nearby galaxies, ticks off the expansion rate of the universe — about 73 kilometers per second per megaparsec of distance. The second, peering into ancient light, gives a noticeably lower value — roughly 67.

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?

Imagine inflating a balloon. At first, it expands slowly; then someone gives a sharp blast of air, and it swells faster. But as the airflow weakens, the balloon's growth slows again. According to a new study, the Universe has behaved much the same way: after the Big Bang, it expanded, then suddenly accelerated, and now that acceleration is fading.

No one has ever seen dark matter, but every galaxy feels its pull. Usually, it's pictured as a sea of identical, silent particles. The new work paints a livelier picture: two kinds of particles, heavy and light, constantly exchanging between them.

Dark matter is invisible, but its gravity holds galaxies together. For a long time, it was thought that dark matter particles pass right through each other without noticing. However, in small galaxies, the density of dark matter in the center turns out to be lower than calculations predict.

In the mid-20th century, astronomer Vera Rubin discovered that stars on the outskirts of galaxies were moving too fast — held by an invisible mass. Thus the mystery of dark matter was born. It doesn’t emit light but reveals itself through gravity. The big question: why is there exactly as much as we see?

Galaxies are flying apart, but the expansion rate measured from the afterglow of the Big Bang and from supernova explosions doesn't match: this problem has been called the Hubble tension. It's like two dancers losing their rhythm because they can't feel each other.

The Universe is expanding faster and faster. We used to chalk that up to dark energy — a mysterious force working alone. But the latest measurements seem to have eavesdropped on a private conversation: it appears dark energy is not silent but whispering back and forth with dark matter.

The universe is expanding, and the rate of that expansion is a hot topic in cosmology. Nearly a century ago, Edwin Hubble discovered that galaxies are flying apart, but modern measurements of the Hubble constant, which characterizes the expansion rate, give conflicting values.

In the first moments, the Universe went through a brief but turbulent period — inflation, when it expanded at a colossal speed. This idea was proposed by Alan Guth. At the same time, particles of ordinary matter were born.