Light beam 'swims' upstream through a quantum fluid by violating Newton's third law
Physicists have demonstrated a method for light beams to move upstream in a quantum fluid by breaking Newton's third law. This is achieved through non-reciprocal interactions that allow particles to generate net momentum.
Why it matters
This discovery challenges fundamental physical assumptions and could lead to new advancements in quantum-like systems and light-based technologies.
edited by Gaby Clark , reviewed by Robert Egan
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Add as preferred source Experimental results of upstream and downstream motion. Credit: Physical Review A (2026). DOI: 10.1103/lwyj-7m5f 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.
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