Quantum Light Swimmer Moves Upstream, Breaking Newton's Third Law

Physicists report an artificial swimmer built from quantum light that can travel against the direction of a flowing light stream. According to New Scientist, the swimmer's motion appears to break Newton's third law, which states that every action has an equal and opposite reaction.

Under ordinary conditions, a swimmer moves by pushing against its surroundings, and the surrounding fluid pushes back. In this quantum case, the swimmer moves upstream without the usual paired reaction, allowing it to move in a way that would not be possible in a classical fluid.

The demonstration provides a concrete example of non-reciprocal behavior at the quantum level. Because there is only one source, no conflicting findings are reported, but the result is still described as a striking violation of a foundational classical principle.