data storage

Imagine a book with latches on its pages: you can only flip a page if you know how to click its edge. That is roughly how the mechanical metamaterial we are about to discuss works. Each cell is a small mass inside a larger one, connected by an elastic beam. The beam can sit in two stable positions, like a switch.

A person hunting for keys mentally runs through places where they might be. A bird that tucked hundreds of seeds into crevices in autumn retrieves them flawlessly in winter. How can a brain hold so many addresses when all birds have roughly the same number of neurons? The answer lies in geometry.

A magnetic film just tens of atoms thick stores information in tiny magnetic vortices. But you can't look inside and see these vortices directly: the instrument only senses the weak magnetic field around the film. Reconstructing the magnetization pattern from such a field is like guessing the shape of an invisible relief from its shadow on a wall.

In a tiny magnet, information is encoded not in which way the arrow points, but in how the directions of its atoms alternate. In antiferromagnets, these arrows cancel each other out, so the material appears non-magnetic from the outside. The data is there, but you can't read it the usual way: the state is like a note written in invisible ink.

A white dwarf is what remains of a star like the Sun after it sheds its outer layers. What's left is a hot core the size of Earth but with a mass close to that of the Sun. A teaspoon of this material would weigh as much as a truck. Some of these stars have extremely strong magnetic fields — a billion times stronger than Earth's.

Inside a magnet, there are regions where all the atomic magnets point in the same direction. Between such regions lies a narrow transition zone where the magnetization direction gradually rotates. This zone is called a domain wall. Previously, it was considered massless: give it a push, and it stops immediately.

A hawk soars over a field, its wings tracing an intricate dance. Each flap, each tilt is not random but a combination of simple motions that can be broken down into components. Collective behavior in the air may seem intuitive, but behind it lies strict mechanics. Scientists recorded the hawks' movements using cameras that track the position of every point on the wing and tail.

The brain is like a sprawling city: districts-regions communicate via streets-neural pathways. If traffic lights at an intersection fail, traffic grinds to a halt. Similarly, in the brain, when bundles of nerve fibers (white matter) malfunction, distant regions stop working in concert, and thought stalls.

In a pot of boiling soup, small bubbles churn, but gradually large-scale flows come to dominate. Something similar happens in cosmic plasma, where magnetic fields behave like tangled threads.