In the late 19th century, many physicists believed that all phenomena in physics could be fully explained using Newtons laws of motion and the theory of electromagnetic waves, which describes light as part of the electromagnetic spectrum. 

However, this classical view of physics faced significant challenges when Albert Einstein introduced the concept of photons- discrete packets of energy that are particles of light- to explain the photoelectric effect. 

His groundbreaking work led to the realization that light has a dual nature, behaving as bot a wave and a particle depending on the circumstances. Nevertheless, reality is described neither by idealized waves nor by idealized particles; rather, these frameworks provide insight into different aspects of how things behave in the quantum realm.  

Schrödinger's wave function

Erwin Schrödinger later developed a wave equation to describe the motion of particles, which he initially envisioned as equation for electromagnetic waves. However, Schrödinger’s wave function turned out to describe not electromagnetic waves, but probability waves. The wave function gives the probability of finding a particle in a particular position or state.

Heisenberg's uncertainty principle

A key aspect of the wave- particle duality is Heisenbergs uncertainty principle, which states that it is fundamentally impossible to precisely know both position and velocity of a particle at the same time. The more accurately you know a particles position, the less certain you are about its velocity, and vice versa. 

For instance, if the velocity of a particle is known with absolute certainty, its position could be anywhere. 

This uncertainty has profound implications in quantum mechanics, including the phenomenon of vacuum fluctuations, where particles spontaneously appear and disappear within the quantum field (Quantum Field Theory).