Tiny objects swimming in a superfluid of light move against the flow

Superfluids are intriguing states of matter in which particles behave like a giant collective wave, allowing them to flow without any friction.

When this fluid flows past a fixed obstacle at a velocity below a specific threshold, it moves around it without slowing down or exerting any drag.

Above this critical velocity, however, the superfluid state starts to break down, and the energy from the flow dissipates in the form of ripples and vortices in the fluid. ...