Debye's work on specific heat theory challenges the uniform energy distribution law by showing that experimental data on specific heat as a function of temperature do not align with Einstein's initial formula. While Einstein's formula qualitatively matches the observed behavior, quantitative discrepancies arise, especially at low temperatures. To address this, Nernst and Lindemann modified Einstein's formula by introducing a second vibrational frequency, v/2, though the physical basis for this adjustment remains unclear. Debye argues that the necessity of multiple vibrational frequencies is plausible due to the complex interactions between atoms, which prevent their motion from being purely periodic. This leads to the need for a more comprehensive model of vibrational modes, as proposed by Einstein. Debye's approach involves considering the body as a system of N atoms, each contributing to 3N degrees of freedom, and thus 3N vibrational modes. The specific heat of a body is then determined by summing the energies of these vibrational modes, each governed by Planck's formula. The energy distribution is calculated by determining the vibrational frequencies of the body, assigning energy to each mode, and summing over all modes. This leads to a formula for specific heat that depends on the temperature and the vibrational frequencies of the system. Debye also derives a formula for the acoustic spectrum of a body, which is essential for calculating the specific heat. The acoustic spectrum is characterized by a density of vibrational modes proportional to $v^2 dv$, a result that aligns with the Rayleigh-Jeans law for blackbody radiation. This implies that the specific heat of a body at low temperatures is proportional to $T^3$, a conclusion supported by experimental data. Debye's work also addresses the issue of the characteristic temperature $\Theta$, which is derived from the elastic constants of the material. This temperature is crucial for understanding the behavior of specific heat at different temperatures. The derived formula for specific heat as a function of temperature and $\Theta$ shows that the specific heat of monatomic solids is a universal function of the ratio $T/\Theta$, a result that has been validated by experimental data. The paper also compares Debye's formula with the Einstein and Nernst-Lindemann formulas, showing that Debye's approach provides a more accurate description of specific heat at low temperatures. The results are supported by experimental data on various materials, including diamond, aluminum, copper, silver, and lead, demonstrating the validity of the derived formulas. The specific heat of these materials at low temperatures is found to be proportional to $T^3$, confirming the theoretical predictions.Debye's work on specific heat theory challenges the uniform energy distribution law by showing that experimental data on specific heat as a function of temperature do not align with Einstein's initial formula. While Einstein's formula qualitatively matches the observed behavior, quantitative discrepancies arise, especially at low temperatures. To address this, Nernst and Lindemann modified Einstein's formula by introducing a second vibrational frequency, v/2, though the physical basis for this adjustment remains unclear. Debye argues that the necessity of multiple vibrational frequencies is plausible due to the complex interactions between atoms, which prevent their motion from being purely periodic. This leads to the need for a more comprehensive model of vibrational modes, as proposed by Einstein. Debye's approach involves considering the body as a system of N atoms, each contributing to 3N degrees of freedom, and thus 3N vibrational modes. The specific heat of a body is then determined by summing the energies of these vibrational modes, each governed by Planck's formula. The energy distribution is calculated by determining the vibrational frequencies of the body, assigning energy to each mode, and summing over all modes. This leads to a formula for specific heat that depends on the temperature and the vibrational frequencies of the system. Debye also derives a formula for the acoustic spectrum of a body, which is essential for calculating the specific heat. The acoustic spectrum is characterized by a density of vibrational modes proportional to $v^2 dv$, a result that aligns with the Rayleigh-Jeans law for blackbody radiation. This implies that the specific heat of a body at low temperatures is proportional to $T^3$, a conclusion supported by experimental data. Debye's work also addresses the issue of the characteristic temperature $\Theta$, which is derived from the elastic constants of the material. This temperature is crucial for understanding the behavior of specific heat at different temperatures. The derived formula for specific heat as a function of temperature and $\Theta$ shows that the specific heat of monatomic solids is a universal function of the ratio $T/\Theta$, a result that has been validated by experimental data. The paper also compares Debye's formula with the Einstein and Nernst-Lindemann formulas, showing that Debye's approach provides a more accurate description of specific heat at low temperatures. The results are supported by experimental data on various materials, including diamond, aluminum, copper, silver, and lead, demonstrating the validity of the derived formulas. The specific heat of these materials at low temperatures is found to be proportional to $T^3$, confirming the theoretical predictions.