It is shown that the minimum wavelength is approximately equal to the Planck length. To prove the exact equality, it is necessary to find an analytical solution of a certain integral = 1 /(8*Pi)^2 . The calculations are based: on a previously obtained dependence of the temperature of zero oscillations on the maximum and minimum wavelengths of standing oscillations in the cavity; on the previously calculated fraction of thermal fluctuations in the critical energy density (1/4); and on the law of Stefan – Boltzmann. It is assumed that thermal and zero-point vibrations are held in the cavity by their own gravitational field, and the wavelength of these oscillations is quantized. The critical frequency is determined above which corrections arise associated with the quantization of the wavelength of oscillations. The corrections are obtained: the Rayleigh – Jeans law, the formula for the distribution of the energy density of zero-point vibrations over frequencies, the Planck formula, and the Stefan – Boltzmann law. It is shown that corrections that reduce the energy density of zero-point vibrations by 120 orders of magnitude are almost impossible to detect in laboratory experiments with thermal radiation. I apologize for spreading false information that the minimum wavelength is significantly greater than the Planck length. My attempts to find a solution by adjusting the parameters led to errors.