Chapter 7: The Quantum and the Cosmos

Introduction to Quantum Mechanics
Quantum mechanics studies subatomic particles’ strange behaviours. Unlike classical physics, outcomes are probabilistic.

Quantum mechanics is the branch of physics that explores the behaviour of matter and energy at the scale of atoms and subatomic particles. Unlike classical physics, where objects follow predictable paths, quantum mechanics reveals that at very small scales, nature operates in a fundamentally probabilistic way.

At its core, quantum mechanics introduces concepts such as wave-particle duality, where particles like electrons and photons can exhibit both wave-like and particle-like properties, depending on how they are observed. Another central idea is the superposition principle, which states that particles can exist in multiple states simultaneously until measured. For example, an electron in an atom does not travel in fixed orbits (as in Bohr’s classical model) but exists in orbitals-regions of probability where it is most likely to be found.

This probabilistic nature is captured mathematically through the wave function, introduced by Schrödinger, which provides the probability distribution of a particle’s position or momentum. Measurement in quantum mechanics collapses this wave function into a definite state, a process that has led to profound debates about the nature of reality.

Example: In the hydrogen atom, instead of revolving around the nucleus like a planet around the sun, the electron exists in a “cloud-like” orbital. Its exact location cannot be determined until it is observed, only the likelihood of where it may be found.