gravitational decoherence

An ordinary mirror swaps left and right. Many laws of physics don't notice the swap: they are mirror-symmetric. But some phenomena, like the weak interaction, break this symmetry. Until now, it was thought that gravity and light each break mirror symmetry in their own independent way.

In the first instants after the Big Bang, the universe expanded faster than light could cross it. Like an inflating balloon, but instead of rubber, it was space itself. On this balloon, ripples inevitably formed — tiny compressions and rarefactions from which all galaxies and stars later grew.

A stone drops into a pond, and ripples spread across the water. In the same way, massive bodies generate gravitational waves, except it's space itself that ripples. So far, these waves have been caught by giant detectors that barely flinch as a wave passes through. But what happens on the microscopic scale, inside a tiny piece of matter?

Quantum mechanics allows a particle to be in two places at once: this is called superposition. But massive objects, like a dust grain or a ball, don't behave that way: their position is always definite. Why? One idea is that it's an illusion: the particle is constantly "jittering" from random environmental kicks, and the blurred picture averages out.

Two massive bodies frozen in a quantum superposition resemble a pair of dancers trying to keep a single rhythm while an orchestra blares around them. Each gravitational wave is a musician throwing them off beat.

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.

A choir where every singer hits the notes precisely sounds louder than you'd expect from a simple sum of voices. A hundred singers aren't just a hundred times louder than one: they're ten thousand times louder. In the world of atoms, something similar happens. In collective behavior discovered by Robert H.

A quantum particle can be a wave, and pass through two paths at once. But if something 'peeks' at which path it took, the wave disappears. This effect is called loss of interference. Usually, photons or air molecules do the peeking.

A mosaic of squares and triangles covers the floor without gaps, yet it never settles into a simple repeating pattern. Such a pattern is a quasicrystal — a solid where atoms are arranged not periodically but according to a pattern of several waves of different lengths. These waves are incommensurate with each other, and together they create long-range order.

The quantum world loves balance. When a massive particle is forced to split, to go down two paths at once, something must give way in response. That "something" turns out to be the very apparatus that split the particle.

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.

The Universe doesn't just expand — it resonates. After the Big Bang, stretched strings remained in its fabric — thin as a proton, yet heavy as a mountain range. Their oscillations give birth to gravitational waves, and in this radiation, like in a musical score, the history of fundamental symmetries is encoded.

A single particle can be in two places at once — that's superposition. But any interaction, like a shout, instantly 'collapses' this uncertainty. It was long thought that even gravity could interfere.

An old mechanical alarm clock ticks on the shelf. You hear the steady sound, see the hands moving, and you're certain time is passing. But if you take the clock apart, you won't find a single part labeled "time." Only springs and gears.

A quantum particle can be in two states at once, like a coin spinning, both heads and tails. Near a black hole, the event horizon, where spacetime curvature bends space and time to the extreme, acts as a one-way gate.

A single graviton, a quantum of spacetime, is incredibly weak. For detectors like LIGO, built by Rainer Weiss and colleagues, quantum effects are suppressed by a factor of 10⁻³⁸: it's like trying to hear a grain of sand changing the wind's direction in a hurricane.

A coffee whirlpool can span two spots in a cup — a blur of swirling liquid. Quantum particles behave similarly: a spacetime whirlpool where they exist in two places at once. But gravity acts as the spoon that stirs the fabric of space and time.

Two parallel streams of atoms, released from Bose condensates, begin their journey in free fall. In the classical picture, their separation remains unchanged — like two skiers gliding down a perfectly smooth slope. But if spacetime is not frozen snow, but a living, rippling membrane, then every tremble of it is transmitted to matter.

Toss a dozen coins on a table. The number of heads-and-tails combinations is just over a thousand. For two dozen coins, it's already a million. The number grows as 2 to the power of the number of coins, and that's fast. But quantum systems are far richer. Each particle here is not a coin with two sides but an arrow that can point in any direction.

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.

Drop a stone into a pond — the ripples spread evenly and then fade. Gravitational waves born from black hole mergers behave differently: even after the main wave passes, a faint 'tail' remains. It's as if, after the ripples on the water, a tremor persists for a long time, caused not by the stone itself but by how the water 'remembers' the impact.

Schrödinger's cat, according to quantum rules, can be both alive and dead at once. But a table can't pull that off. When a massive object tries to be in two places, its mass curves spacetime so drastically that instead of two points, a single deep depression forms, and the object rolls into it.

Time flows slower near the ground than on the roof: this was predicted by Einstein in his theory of relativity. To spot the tiny difference, physicists propose using a pair of photons, linked like voices in a duet.

The Sun’s gravity creates an invisible goblet, in which dark matter of a special kind — ultralight — doesn’t splash around chaotically, but occupies strict energy steps, like transparent layers of liquid. So around the Sun, a natural spectroscope emerges, sorting the invisible substance into levels, just like electrons in an atom.

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.

A quantum particle can be in two places at once, but large objects never are. Is it noise that creates chaos and increases entropy? Or does nature itself forbid quantum tricks in the macroworld? One hypothesis suggests that quantum 'fuzziness' disappears on its own, and the heavier the object, the faster it goes.

Two massive spheres in the cosmic void. Push one, and the second will feel the push only after a moment: gravitational influence travels, like an echo of a shout in the mountains, with inevitable delay. This is how curved space transmits signals locally, step by step — predicted by Einstein long ago.

In the first moments after the Big Bang, space expanded at an incredible rate. A tiny quantum ripple, embedded in the uncertainty principle itself, pushed matter apart more strongly than any known force. This ripple is the generalized uncertainty principle, or GUP.

Two vessels of water at different temperatures are separated by a thin partition. As long as the partition is intact, each vessel lives its own life: in one, the water is hot; in the other, it's icy. But once the partition is removed, the temperatures begin to equalize, and eventually both vessels reach the same state.