A stone falls into still water, and smooth rings spread across the surface. If the stone doesn't just fall but also spins, tiny whirlpools, vortices, appear on the surface. Light can do the same, only instead of water, it's space and time themselves.
Physicists have discovered that a light pulse, when it hits a simple obstacle, can twist itself into a spacetime vortex. The twist happens not only in the plane but also in time. Previously, this required complex devices that shaped the wave step by step. Now it turns out that simply letting the wave scatter is enough — vortices with controllable charge emerge naturally, like water eddies behind a boat.
Such vortices turn out to be surprisingly stable: they don't break apart as they move, unlike many other light structures. It's as if a smoke ring, once blown from a chimney, kept its perfect shape mile after mile.
The ability to create such structures without complex equipment is a universal key. It will be useful wherever light needs to be controlled at the microscopic level: from optical tweezers holding living cells to transmitting information through optical fibers. Light sculpts rings and whirlpools out of itself, just give it a reason.
Vortex rings in a fluid can pass through each other without breaking apart — much like two smoke rings passing through each other. Optical vortex rings behave the same way.
In Stanisław Lem's novel Solaris, the ocean creates complex spatial structures — possibly using similar vortex mechanisms.