Light beam 'swims' upstream through a quantum fluid by violating Newton's third law

Just as a leaf drifts along with a stream, objects in other moving fluids normally drift along with the flow. That is, unless they exert energy to move against it. Although it may be less intuitive, light waves or photons work similarly. To move against a stream of light, an object or particle, like a photon, must either have an external force acting on it or actively use energy to move upstream.

Read it at Phys.org ↗

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