light cone

In the familiar picture of the world, an event is a point on the map of spacetime: 'here and now,' with no size or internal structure.

An ionic conductor resembles a crowded bus where passengers (ions) try to squeeze toward the exit. Previously, it was thought that fast exit could be achieved either by a gently swaying bus (soft lattice) or by passengers standing in chaotic order (geometric disorder). The new work shows these are not two different tricks but the same one.

Light cones are not about light; they are boundaries in spacetime that separate causes from effects. These cones are not rigid: a massive object curves them, like a heavy ball pressing into a stretched sheet.

Every computer model of a black hole runs into the same inconvenience. A machine's memory is not infinite — at some point you have to cut off the calculation, as if placing a solid wall across space.

A heavy ion beam in an accelerator is like a crowd of people shoving each other with elbows: the more people, the wider the crowd. Charged particles repel each other, and at currents above a few microamps the beam spreads and loses its shape.

Light consists of portions — photons. Max Planck was the first to understand that light is emitted in quanta. Today, we can guide single photons. When such a photon encounters a fast shutter, it cannot be sliced — half a photon doesn't exist. Instead, a quantum mixture of states with different photon numbers emerges: zero, one, two, three..

The clock on the kitchen wall ticks, and each tick relentlessly carries us from breakfast to lunch. This is so familiar that it seems like a law of nature, but physics says otherwise. In Einstein's equations, time is reversible: you can rewind the film, and no frame will give the trick away.