The interconnection between the surface tension and fluctuations within fine drops, bubbles, and their nuclei.
We consider the effect of surface tension upon fluctuations within the core of drops and bubbles. We also investigate the fluctuations of the substance density rho, volume V, and particle number N within the objects under study. It is demonstrated that cores of drops and bubbles are homogeneous when they contain several thousand nanoparticles (molecules, atoms). Fluctuations of particle number are very large within the nucleus core containing only a few nanoparticles. Therefore, the surface tension has a probabilistic character since there is no surface separating the nucleus substance from the surrounding medium, only a transitional zone whose radius fluctuates considerably in time. In this case, it is more correct to consider not the surface tension but a certain quantity that we named the quasi surface tension.