Quantum physics is a branch of physics that studies matter and energy at the most fundamental level. It aims to understand the properties and behaviors of the very building blocks of nature, the particles that make up matter and the forces that govern how they interact.
There isn't a single quantum theory that governs all of quantum physics. There is the mathematical framework that underpins it all, known as quantum mechanics. But to understand the nature of the world, quantum mechanics must be combined with other fields of physics to create what are known as quantum field theories. Three different quantum field theories explain three of the four fundamental forces of nature: electromagnetism, the strong nuclear force, and the weak nuclear force. These three theories are brought together in the "Standard Model," a theory of particle physics that consists of 17 fundamental particles, split into two groups: 12 fermions that make up matter and 5 bosons responsible for the interactions between matter.
Quantum discoveries inform our foundational understanding of materials, chemistry, biology, and astronomy. Quantum physics has led to the invention of new devices (e.g., transistors, lasers) and innovative fields, such as quantum computing and quantum technology.
Many experimental observations in quantum physics do not make intuitive sense given the context of classical physics. These include the realization that matter and energy can be described as discrete packets, or quanta, that have a minimum value associated with them. Quantum physics has transformed our conceptualization of the atom, consisting of a positively charged nucleus surrounded by negatively charged electrons. Early models depicted electrons orbiting the nucleus, similar to how planets orbit the sun. Quantum physics instead shows electrons are distributed in orbitals described by wave functions that represent the probability of an electron's existence at a location within a given time range. Electrons jump from one orbital to another as they gain or lose energy but cannot exist in between.
Other concepts central to quantum physics include the following:
- Wave-particle duality—light and matter have the properties of particles or waves, depending on how they were measured. Quantum physics shows that these different forms of energy are actually neither particles nor waves. They are distinct quantum objects that we cannot easily conceptualize.
- Superposition—a term used to describe an object as a combination of multiple possible states at the same time. In a mathematical sense, an object in superposition can be represented by an equation that has more than one solution or outcome.
- Uncertainty principle—a mathematical concept that represents a trade-off between complementary points of view. In physics, this means that two properties of an object, such as its position and velocity, cannot both be precisely known at the same time. If we precisely measure the position of an electron, for example, we will be limited in how precisely we can know its speed.
- Entanglement—a phenomenon that occurs when two or more objects are connected in such a way that they can be thought of as a single system, even if they are very far apart. The state of one object in that system can't be fully described without information on the state of the other object. Likewise, learning information about one object automatically tells you something about the other and vice versa.
