Understanding wave-particle duality is like uncovering an exciting story in physics. It all began in the early 1900s when scientists noticed something strange about light and matter. Let’s explore some important experiments that helped shape this interesting idea.

1. Double-Slit Experiment (1801):

   • This famous experiment was done by Thomas Young. When light passed through two tiny slits close together, it created a pattern of bright and dark stripes on a screen. This suggested that light acts like a wave.
   • But here’s where it gets interesting! When scientists sent individual particles of light (called photons) through the slits one at a time, they still saw the same bright and dark pattern over time. This meant that photons, which seemed like little particles, could act like waves when no one was looking! It made people wonder: can particles also act like waves?

2. Photoelectric Effect (1905):

   • Albert Einstein took this idea further. He explained the photoelectric effect, which showed that light is made of particles called photons. When light strikes a metal surface, it can free electrons, but only if the light has enough energy. This couldn’t be explained if light were just a wave. It showed that light has certain energy levels.
   • Einstein’s work helped to prove that light can be both a particle and a wave, showing that these two ideas fit together.

3. De Broglie Wavelength (1924):

   • Louis de Broglie suggested something really bold: if light can act like a particle, then matter (like electrons) should act like a wave too. He came up with the idea of a wavelength for particles using an equation:

   $\lambda = \frac{h}{p}$

   Here, $h$ is a special number called Planck's constant, and $p$ is the momentum of the particle. This was a new idea that suggested that even tiny particles like electrons might behave like waves.

4. Electron Diffraction (1927):

   • Experiments with electrons showed that they could create patterns similar to light waves. This supported de Broglie's idea that matter can also show wave-like behavior. It was a big deal because it showed that particles can act like waves.

In summary, these experiments showed that light and matter can't just be categorized as waves or particles. Instead, they have a dual nature that depends on how we look at them. This wave-particle duality helps us understand the basic behaviors of the universe. It’s a key part of quantum physics and sparks more curiosity about the nature of reality!