Quantum physics, also known as quantum mechanics, is the branch of physics that explores how matter and energy behave on the smallest possible scales—typically at the level of atoms and subatomic particles. Unlike classical physics, which works well in explaining large-scale phenomena (such as gravity and motion), quantum physics reveals a strange, counterintuitive world that defies our everyday expectations.

At the heart of quantum physics is the idea that particles can behave both like particles and like waves—a concept known as wave-particle duality. For example, electrons and photons (particles of light) exhibit properties of both particles and waves, depending on how they are observed. This duality was famously demonstrated in the double-slit experiment, which showed that particles can interfere with themselves like waves when not being observed, but act like solid particles when measured.

One of the most important concepts in quantum physics is the quantization of energy. Unlike in classical physics, where energy can vary continuously, quantum systems can only exist in specific energy levels. Electrons in atoms, for instance, occupy discrete energy states. They can jump from one level to another by absorbing or emitting energy in fixed amounts called quanta—a concept introduced by Max Planck and expanded by Albert Einstein in his explanation of the photoelectric effect.

Quantum mechanics also introduces the idea of superposition, where particles can exist in multiple states at once until they are observed. This leads to phenomena like quantum entanglement, where two or more particles become linked in such a way that the state of one instantly affects the state of the other, regardless of the distance between them. This phenomenon puzzled even Einstein, who famously called it “spooky action at a distance.”

Mathematically, quantum systems are described using wave functions, which represent the probabilities of finding particles in particular places or states. The famous Heisenberg Uncertainty Principle states that there is a fundamental limit to how precisely we can know both the position and momentum of a particle at the same time.

Quantum physics has had profound implications not only for our understanding of the universe but also for practical technologies. It underlies much of modern electronics, including semiconductors, lasers, and MRI machines. It also forms the foundation of emerging fields such as quantum computing, quantum cryptography, and quantum teleportation.

Despite its strangeness, quantum mechanics has been tested extensively and is one of the most accurate and successful theories in science. It challenges our intuitions about reality but provides a powerful framework for understanding the fundamental nature of matter and energy.