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Modern physics is the branch of physics that arose in the early 20th century, built upon a set of revolutionary theories that challenged and extended the principles of classical physics. While classical physics, which includes the work of Newton and Maxwell, successfully describes the world at everyday scales—from the motion of planets to the behavior of sound—it fails to explain phenomena at very high speeds, extremely large energies, or the atomic and subatomic levels. Modern physics fills this gap, providing a more comprehensive and accurate description of the universe.
The foundation of modern physics rests on two main pillars:
Quantum Mechanics: This theory revolutionized our understanding of the smallest particles of matter and energy. It postulates that energy is not continuous but is quantized, meaning it exists in discrete packets called quanta. Quantum mechanics introduced the radical idea of wave-particle duality, where particles like electrons and photons can exhibit both wave-like and particle-like properties. It also brought a probabilistic rather than deterministic view of the universe, suggesting that we can only predict the probability of a particle’s behavior, not its exact state. Key concepts include the Heisenberg Uncertainty Principle, which states that we cannot simultaneously know a particle’s exact position and momentum, and the Schrödinger equation, which describes the state of a quantum system.
- The Theory of Relativity: Developed by Albert Einstein, the theory of relativity fundamentally changed our understanding of space and time. His Special Theory of Relativity (1905) established two key postulates: that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum is constant for all observers, regardless of their motion. This led to profound and counter-intuitive conclusions, such as time dilation and length contraction, and the famous mass-energy equivalence formula, . His General Theory of Relativity (1915) extended this to include gravity, proposing that it is not a force but a curvature of spacetime caused by mass and energy.
- Together, quantum mechanics and relativity form the bedrock of modern physics, which has led to countless technological advancements and our current understanding of the cosmos. Concepts like particle physics, condensed matter physics, and cosmology all fall under this umbrella. While these two pillars remain the most fundamental, physicists continue to strive for a unified theory—a “theory of everything”—that can reconcile quantum mechanics and general relativity, which currently describe the universe on different scales and in different ways.
