Francisco S. N. Lobo

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.

When a star burns out and collapses under its own weight, the space around it crumples into a black hole. At the center, according to textbooks, lurks a singularity — a point where density becomes infinite and the laws of physics break down.

You can poke a pencil through a folded sheet of paper, and the path between two points becomes shorter. That's roughly how the idea of a wormhole works: a tunnel in space connecting distant regions.

A magnetic field can hold a star against complete collapse: that's the idea behind a new kind of black hole. Instead of the usual point of infinite density, inside there is a field that prevents space from crunching down to zero. It's like a spring: the harder you squeeze, the more it pushes back.

In 1973, Jacob Bekenstein proposed that black hole possess entropy — a measure of hidden disorder. Stephen Hawking later confirmed this by adding radiation, but the microscopic origin of entropy remained obscure.

Two cities with the same average population density. In one, a neat grid of blocks; in the other, a maze of narrow alleys and unexpected squares. On a global map they look like twins, but life inside flows quite differently.

A black hole is not a vacuum cleaner. By itself, it doesn't pull everything in more strongly than an ordinary star of the same mass. But if there's a magnetic field nearby and charged particles flying around, an interesting game begins.