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. But what if an event could not just be marked, but given a shape, like a drop of water that gathers into a sphere or swirls into a vortex?
In nonlinear photonic crystals, where the medium's properties depend on light intensity, such objects have indeed been created. The crystal's special structure suppresses free wave propagation — a complete energy gap (a range of forbidden states) emerges. Within this gap, light cannot simply escape, and due to self-focusing, it gathers into a compact clump localized in both space and time. The result is not a point but a tiny cloud with its own geometry.
By varying the system's symmetry, the authors obtained two types of such 'events': multipolar ones, resembling a flower with field petals, and vortical ones, where the wave's phase twists around the center. The vortices turned out to be more complex and 'costlier' in terms of energy expenditure, but their internal structure reliably distinguishes them from multipoles. Calculations show that the transverse size of these objects is 30–60 micrometers, and their duration is 85–170 femtoseconds. This is comparable to the thickness of a human hair and the time it takes light to travel tens of microns.
This research opens a path to controlling light in media whose properties change rapidly over time. An event ceases to be just a mark on a clock: it becomes a wave object with controllable internal degrees of freedom. Where one once saw only a point, one can now create a tiny vortex.
The energy gap that traps light acts like a perfect mirror in a certain range, but only for light that travels in both space and time simultaneously.