a portable telephone). The electric field gives rise to conduction currents with the energy dissipation rate $\sigma \,E^2/2$, where $\sigma $ is a conduction constant. In turn it leads to the temperature rising. The second step is the solution of the respective heat conduction equation (or more precisely, bioheat equation [@WF]) with found local heat sources $\sigma \,E^2/2$ and with allowance for all the possible heat currents. Hence, for this method the distribution of electric field inside the head is of primary importance. The spatial behaviour of the eigenfunctions characterize the system as a whole, and these properties cannot be taken into account by local methods for calculating the solution to partial differential equations (in our case, to the Maxwell equations).

Conclusion
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We have shown that such different, at first glance, notions as quasi-normal modes in black hole physics, Gamov states in quantum mechanics, and quasi-bound states in the theory of open electromagnetic resonators [@Vaynstayn] have the same origin, namely, all these are the eigenmodes of oscillating unbounded domains. By making use of a simple but physically motivated example of electromagnetic oscillations outside a perfectly conducting sphere, which admits analytical treatment, we have easily shown the main features of 