By pushing on a membrane with light, scientists have 'broken' Newton's Third Law to make sound waves grow exponentially.
April 1, 2026
Original Paper
Radiation-pressure-induced non-Hermitian skin effect in elastic membranes
arXiv · 2603.29111
The Takeaway
Newton's Third Law states that every action has an equal and opposite reaction, but this experiment uses laser pressure to create a 'one-way' street for energy. This allows sound waves to travel and amplify in one direction without the usual resistance, creating a system where the fundamental rules of classical physics no longer apply.
From the abstract
We show that optical forces perpendicular to the direction of the incident light, generated on structures with asymmetric optical scattering, can manipulate longitudinal elastic waves traveling in that same perpendicular direction. When the radiation pressure acts unidirectionally, reciprocity and hence Newton's Third Law are effectively broken. As a result, the waves grow exponentially with position, an instance of the non-Hermitian skin effect. The effect can be enhanced by orders of magnitude