In the early 20th century, scientists like Einstein proved that light (which was thought to be a wave) can act like a particle (photon). In 1924, a French physicist named Louis de Broglie asked a revolutionary question: If light waves can act like particles, can physical particles act like waves?
De Broglie was awarded the Nobel Prize in Physics in 1929 for this revolutionary theory.
His hypothesis was experimentally proven in 1927 by the Davisson-Germer experiment, which successfully showed electrons diffracting just like light waves.
This hypothesis laid the foundation for Quantum Mechanics and the invention of the Electron Microscope.
The de Broglie hypothesis states that all matter exhibits wave-like properties. According to his theory, moving particles (like electrons, protons, and even whole planets) have a wave associated with them. These are called Matter Waves. This established the concept of the 'Dual Nature of Matter'—meaning matter acts as both a solid particle and an invisible wave.
He provided a mathematical equation to calculate the wavelength of these matter waves. The formula is: $\lambda = \frac{h}{p}$ or $\lambda = \frac{h}{mv}$
Where:
If you throw a cricket ball, the formula says it has a wave. Why can't we see it? Because Planck's constant ($h$) is incredibly small, and the mass ($m$) of a cricket ball is relatively large. If you plug the numbers into the formula, the resulting wavelength is so infinitesimally small that it is impossible to detect. However, for an Electron (which has almost zero mass), the wavelength is large enough to be easily measured in a laboratory.
If a particle stops moving, its velocity (v) becomes zero. In the formula $\lambda = h/mv$, dividing by zero approaches infinity. Therefore, a stationary particle does not have a defined matter wave.
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