  In this paper we analyzed the open problems in the physics of
ultra-low-frequency electromagnetic waves Pc1, which also known as the "pearls"
(frequency range 0.2 -5 Hz). A number of theoretical problems arose because the
standard model of excitation and propagation of waves in the magnetosphere, the
foundations of which were laid half a century ago, is unable to explain
observable properties of Pc1. In this article the problems are formulated and
discussed in context of the general physics of geoelectromagnetic waves. In
addition, one problem of experimental character is considered. The essence of
the problem is that the observations testify in favor of the idea of some human
impact on the Pc1 oscillation mode, but difficulties in interpreting of
observations indicate the need for further experimental research.
