The term "modern physics" isn't actually used to refer to all of physics. It's a specific area of physics that focuses on the study of phenomena that emerged in the late 19th and early 20th centuries, which challenged the classical physics of Newton and Maxwell.

Here's a breakdown:

* Classical Physics: This encompasses the well-established theories of mechanics, electromagnetism, thermodynamics, and optics, developed from the 17th to 19th centuries. It describes the world at everyday scales and speeds.

* Modern Physics: This term typically encompasses two major branches:

* Relativity: Developed by Albert Einstein, this theory revolutionized our understanding of space, time, gravity, and the very nature of the universe at very high speeds and massive scales.

* Quantum Mechanics: This theory describes the behavior of matter and energy at the atomic and subatomic level, where classical physics fails. It introduces concepts like quantization, wave-particle duality, and uncertainty.

So, "modern physics" is called that because it represents a significant departure from the classical physics that preceded it. It delves into realms beyond everyday experience and requires a whole new set of concepts and tools to understand the universe at its most fundamental levels.

Here's a table to summarize:

| Physics Branch | Focus | Key Developments |

|---|---|---|

| Classical Physics | Everyday scales and speeds | Newton's Laws of Motion, Maxwell's Equations, Thermodynamics |

| Modern Physics | Very high speeds, massive scales, atomic/subatomic level | Relativity, Quantum Mechanics |