Modern physics

Modern physics is an effort to understand the underlying processes of the interactions of matter utilizing the tools of science & engineering. It implies that nineteenth century descriptions of phenomena are not sufficient to describe nature as observed with modern instruments. It is generally assumed that a consistent description of these observations will incorporate elements of quantum mechanics & relativity.

Small velocities and large distances is usually the realm of classical physics. Modern physics often involves extreme conditions; in practice, quantum effects typically involve distances comparable to atoms (roughly 10⁻⁹ m), while relativistic effects typically involve velocities comparable to the speed of light (roughly 10⁸ m/s).

Overview

In a literal sense, the term modern physics, means up-to-date physics. In this sense, a significant portion of so-called classical physics is modern. However, since roughly 1890, new discoveries have caused significant paradigm shifts: the advent of quantum mechanics (QM), and of Einsteinian relativity (ER). Physics that incorporates elements of either QM or ER (or both) is said to be modern physics. It is in this latter sense that the term is generally used.