Modern physics

Modern physics, however, is concerned with more extreme conditions, such as high velocities that are comparable to the speed of light (special relativity), small distances comparable to the atomic radius (quantum mechanics), and very high energies (relativity).

Modern physics is an effort to understand the underlying processes of the interactions of matter using the tools of science and engineering.

[1] However, since roughly 1890, new discoveries have caused significant paradigm shifts:[1] especially the advent of quantum mechanics (QM) and relativity (ER).

Quantum mechanical effects tend to appear when dealing with "lows" (low temperatures, small distances), while relativistic effects tend to appear when dealing with "highs" (high velocities, large distances), the "middles" being classical behavior.

For example, when analyzing the behavior of a gas at room temperature, most phenomena will involve the (classical) Maxwell–Boltzmann distribution.

Classical physics is usually concerned with everyday conditions: speeds are much lower than the speed of light , sizes are much greater than that of atoms, yet very small in astronomical terms. Modern physics, however, is concerned with high velocities, small distances, and very large energies.
Classical physics ( Rayleigh–Jeans law , black line) failed to explain black-body radiation – the so-called ultraviolet catastrophe . The quantum description ( Planck's law , colored lines) is said to be modern physics .