P. Debye's theory of specific heat, based on observations conducted at Nernst's laboratory, challenges the assumption of uniform energy distribution in materials. Einstein initially proposed a formula for specific heat as a function of temperature, but it showed discrepancies with experimental data, especially at higher temperatures. Nernst and Lindemann modified Einstein's formula by introducing an additional harmonic frequency, but this did not provide a satisfactory explanation for the observed deviations. Debye's approach is more rigorous and considers the system of $3N$ degrees of freedom for a body composed of $N$ atoms. He derives a formula for specific heat that is consistent with experimental observations, showing that it is a universal function of the ratio $T/\Theta$, where $\Theta$ is a characteristic temperature. For sufficiently low temperatures, the specific heat is proportional to the cube of the absolute temperature, which is confirmed by experiments. Debye's theory also provides a method to calculate the characteristic temperature $\Theta$ from elastic constants, and it agrees well with experimental data for various materials. The theory supports the idea that specific heat is proportional to $T^3$ at low temperatures, and it offers a more accurate prediction of specific heat values compared to Einstein's and Nernst-Lindemann's formulas.P. Debye's theory of specific heat, based on observations conducted at Nernst's laboratory, challenges the assumption of uniform energy distribution in materials. Einstein initially proposed a formula for specific heat as a function of temperature, but it showed discrepancies with experimental data, especially at higher temperatures. Nernst and Lindemann modified Einstein's formula by introducing an additional harmonic frequency, but this did not provide a satisfactory explanation for the observed deviations. Debye's approach is more rigorous and considers the system of $3N$ degrees of freedom for a body composed of $N$ atoms. He derives a formula for specific heat that is consistent with experimental observations, showing that it is a universal function of the ratio $T/\Theta$, where $\Theta$ is a characteristic temperature. For sufficiently low temperatures, the specific heat is proportional to the cube of the absolute temperature, which is confirmed by experiments. Debye's theory also provides a method to calculate the characteristic temperature $\Theta$ from elastic constants, and it agrees well with experimental data for various materials. The theory supports the idea that specific heat is proportional to $T^3$ at low temperatures, and it offers a more accurate prediction of specific heat values compared to Einstein's and Nernst-Lindemann's formulas.