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What is quantum physics and how did it emerge?

So, what is quantum physics? In the simplest terms, it is the theoretical framework that explains how matter and light behave at atomic and subatomic scales. What makes this field difficult is that the intuitions that work in everyday life do not always apply at very small scales.

Max Planck opened the door to quantum thinking in 1900 by proposing that energy is absorbed and emitted in discrete packets. Albert Einstein then strengthened the physical meaning of this approach by explaining the photoelectric effect in 1905; he received the 1921 Nobel Prize in Physics for this work.

The birth of modern quantum mechanics is generally dated to June 1925. While Werner Heisenberg laid the foundations of matrix mechanics on the island of Helgoland, Erwin Schrödinger published the wave equation in 1926.

Because this milestone marks its 100th anniversary, the topic has also gained global attention. Following a decision process at UNESCO, the United Nations General Assembly declared 2025 the International Year of Quantum Science and Technology.

Reading the five core concepts through simple examples

Quantization: Energy does not always flow continuously

In an everyday analogy, it is like an elevator stopping only on certain floors: it cannot pause at every point in between. But the comparison has its limits; in the quantum world, which values are possible depends on the physical system being studied.

The starting point for this idea is Planck's quantum hypothesis. Einstein's explanation of the photoelectric effect is also one of the key examples that gave experimental support to the idea of light as packets of energy.

Wave-particle duality: One label is not enough

Labeling light or electrons only as “particles” or only as “waves” is often incomplete. Although everyday analogies can help, quantum objects reveal which property is dominant depending on the experimental setup.

For that reason, wave-particle duality is not about wearing two separate identities in turn, but about different aspects of a single quantum entity becoming visible in different experiments. Interference phenomena and the explanation of the photoelectric effect show why this framework is necessary.

Superposition: Carrying multiple possibilities at once

Superposition means that a quantum system can contain more than one possibility at the same time before measurement. It is sometimes easy to summarize this as “being in multiple states at once,” but that description carries a classical image too directly into the quantum world.

A more accurate explanation is that the system carries contributions from different possible outcomes together. The power of this idea can be understood through the wave-like nature of quantum mechanics and the interference behavior seen in experiments.

The uncertainty principle: A structural limit, not a measurement error

The uncertainty principle says that certain physical quantities cannot be determined with unlimited precision at the same time. This is not merely a technical problem caused by imperfect instruments; it is a fundamental limit built into the theory itself.

In everyday life, people use the analogy of a blurry photo, but the issue here is not just a loss of sharpness. Heisenberg's framework showed that, at the quantum level, measurement and state description work differently from classical physics.

Entanglement: The extraordinary bond of a shared quantum state

Entanglement is a special relationship in which the states of two or more particles cannot be written independently of one another. It is often compared to a pair of pre-matched gloves; however, in that example the outcome is known in advance, whereas entanglement involves a much deeper quantum structure.

The importance of this concept was reinforced by experiments showing violations of Bell inequalities. Alain Aspect, John Clauser and Anton Zeilinger shared the 2022 Nobel Prize in Physics for their work with entangled photons.

How do qubits and quantum computers connect to these concepts?

A qubit is not thought of only as 0 or 1, as in a classical bit; under suitable conditions, it can exhibit superposition and entanglement. For this reason, a quantum computer is not a machine that automatically does everything faster, but an approach that offers a different model of computation for certain types of problems.

  • Superposition allows multiple probability contributions to be processed together in computation.
  • Entanglement creates correlations between qubits that do not exist in classical systems.
  • The uncertainty principle and the measurement process determine how quantum information is read out.

The safest way to understand quantum physics is to separate the concepts from mystical associations and learn them through their experimental foundations. For beginners, these five concepts provide the strongest framework for both the language and the logic of the field.

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