Unruh effect

A quantum detector is like a sensitive pendulum suspended in empty space. If a sharp gravitational wave passes by, you might expect the pendulum to swing. But the calculation shows otherwise: the wave doesn't swing it: it damps any existing oscillations.

A black hole pulls in anything that gets too close. But if you toss in not one object but a pair, one of them can fly back out, carrying off some of the hole's rotational energy. This trick, devised by Roger Penrose in 1969, works only because a black hole has a horizon — a boundary beyond which nothing returns. Now it turns out the horizon isn't necessary.

The Kerr-NUT black hole is not just a cosmic vacuum cleaner. It's a solution to Einstein's equations where the hole has mass, rotation, and a strange NUT parameter. This parameter behaves like a magnetic charge for gravity: seemingly invisible, yet it alters the properties of surrounding space.

The early Universe was like a tightly coiled spring. In the first moments, it expanded at an unimaginable rate — a phase called inflation. Usually, this is attributed to a special field, but there's another idea: spacetime itself twists like a spring, and this twisting (in physics, torsion) becomes the engine of expansion.

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 pot of boiling water is covered with two lids — an inner and an outer one. The thermometer under each shows its own temperature, but their harmonic mean (a special averaging method where you add the reciprocals) always remains unchanged. Heat seems to obey an invisible rule.

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.

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.

A black hole cooled to nearly absolute zero resembles a musical instrument with only a limited set of possible notes. Strike it, and it will respond not with any sound, but only with a strictly defined set of frequencies.

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.

A black hole is not eternal. Even in a perfect vacuum, it slowly loses energy — a process known as Hawking radiation. Quantum effects near the event horizon create pairs of particles, one of which escapes, carrying away some of the black hole's mass.

The universe cooled like a giant bathtub after a hot start. At 400 000 years after the Big Bang, hydrogen was ready to recombine — protons capturing electrons to become neutral atoms. But somewhere in this dark water, a tap kept dripping.

A translator gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. That's roughly how thermal noise disrupts quantum teleportation: the carrier particles lose synchronization, and the message gets corrupted.

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.

A light ray passing by a massive body gets deflected: this is the effect of gravitational lensing, familiar from images of distant galaxies. The astrophysicists started with a rotating black hole (Kerr spacetime) and added a tiny correction to how light itself propagates.

Dark matter is invisible to telescopes, but its gravity was revealed half a century ago by Vera Rubin. Since then, physicists have explored dozens of hypotheses, and one of the most elegant is primordial black holes, formed in the first moments after the Big Bang.

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.

The Mpemba effect is a mystery where hot вода sometimes freezes faster than warm water. Usually this is attributed to how вода loses heat and энтропию (a measure of disorder). But in a glass of water, chaos prevents a precise model. Physicists built a quantum model: a particle in a well with two depressions separated by a barrier.

Gas passing through a narrow valve can heat up or cool down: this is the Joule–Thomson effect, which powers refrigerators and air liquefiers. It turns out black holes can do the same.

At the centers of many galaxies lurk supermassive black holes. One of them, Sagittarius A* at the heart of the Milky Way, has become a testing ground for a new idea. The authors of the work took Einsteinian gravity and added an unusual electromagnetic field to it.

A black hole is like a perfectly dark room: from outside, you can't see what's inside, and anyone crossing the threshold seems to vanish from the outside world. But what does the falling observer feel? In classical physics, nothing special: the event horizon isn't marked by any signpost.

The cosmic microwave background is not just a faint glow with a temperature of 2.7 K. It's a snapshot of the Universe 380,000 years after the Big Bang, when the primordial plasma finally became transparent to light. But for theoretical physicists, what came before is far more interesting.

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.

Observations by James Webb showed: already 500 million years after the Big Bang (at redshifts z~10), the Universe was aglow with black holes with masses of billions of solar masses. This baffles theories of gradual growth: matter would not have time to 'feed' the seeds at the required rate.

The story began with a missing mass. In the 1930s, Fritz Zwicky, measuring velocities in galaxy clusters, first suspected the presence of invisible matter. Later, Vera Rubin showed that the outskirts of spiral galaxies rotate too fast for the visible matter.

The void is never truly empty. In curved spacetime (for instance, in an expanding universe or near a black hole) the vacuum heats up. This is reminiscent of how acceleration makes particles appear seemingly out of nowhere: a phenomenon known as thermal vacuum radiation.

The universe as painted in Einstein’s textbooks is a smooth four-dimensional canvas. But string theory adds a frame of extra dimensions — invisible, yet tangible to gravity. Imagine our universe as a membrane that trembles under the pressure of hidden layers.

Dark matter is the invisible scaffold that holds galaxies together. But how did it come to be? The standard answer: particles of dark matter once stopped colliding and "froze out" in the amount we see today. However, there's a trickier path — UFO, or ultra-fast freeze-out. Here, everything is like coffee that cools down and then heats up again as you carry it through a cold corridor.

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.

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.

A bonfire doesn't burn out all at once. If you glance at the flames at a random moment, all you see is a jumble of fire tongues, and you can never tell what exactly burned: a wet branch, an old magazine, or an armful of dry grass. But if you watch the fire hour after hour, rhythms emerge in its dance: a burst of heat, a lull, a change in color. These rhythms tell the story of what was thrown into the flames.

An ordinary black hole is like a stove that heats up more as its mass shrinks. A tiny hole should glow at unimaginable temperatures and evaporate in an instant. But that scenario ignores quantum corrections — what happens when the very fabric of spacetime begins to tremble.

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.

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.

Tea in a cup cools quietly on the table. But if you zoom past at near-light speed, the thermometer will read higher — even though no one heated the tea. Calculations confirm: the needle will creep up. A century ago, physicists split into three camps.

A light beam approaches a black hole not head-on, but at a glancing angle. If the angle is just right, the light neither falls in nor escapes: it starts looping around, like a figure skater circling the rim of a funnel. This narrow track is the photon ring. It acts like a lens, repeatedly reflecting the image of everything that falls into the hole.

Two antennas in a soundproof room pick up only noise. But if you spin them, especially in opposite directions, a common signal emerges from the static. Quantum sensors in a vacuum work similarly: acceleration helps them pull quantum entanglement out of the void — an invisible link akin to what forms near the horizon of a black hole.

A black hole is a cosmic pocket into which everything, even light, falls. But the pioneering work of John Wheeler, Stephen Hawking, and Roger Penrose showed: sometimes, due to the colossal spacetime curvature, the pocket turns inside out.

If you accelerate one of four entangled particles to enormous speed, their quantum entanglement doesn't just melt away: it first weakens, then strengthens again. Physicists discovered this unexpected twist while studying the behavior of a special state called the Dicke state in a world governed by the laws of relativity.

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.