Published in the Research School of Physics Event Horizon
Vol45 Issue12 23–27 March 2020

Research

Stability is always relative. It depends on how the system is perturbed.

The recent rigorous study by the international team lead by Prof. Akhmediev and published in Phys. Rev. A, 101, 023843 (2020) has shown that basic knowledge  in this regard is far from being complete.  Namely, the well known modulation instability attributed to Benjamin and Feir (1967) does not provide the full picture. After all, it is just a linear approximation.  Exact theory developed in the new work shows that waves are actually unstable beyond  the frequency range predicted nearly 50 years ago and presented in every textbook on  nonlinear dynamics. Thus, when we observe an instability that results in drastic outbreak from normal  (seemingly stable) conditions, we should not be surprised too much. We should look for perturbations that caused it.