Quantum mechanics provides a framework for understanding the behavior of particles and waves at the microscopic level, including light. The nature of light has been a subject of scientific inquiry for centuries, and through various experiments and observations, it has been established that light exhibits both wave-like and particle-like properties, a phenomenon known as wave-particle duality.
In the early 20th century, experiments such as the double-slit experiment played a crucial role in demonstrating the wave-like behavior of light. In this experiment, a beam of light is directed at a barrier with two slits, and an interference pattern is observed on a screen placed behind the slits. This interference pattern is characteristic of waves, where peaks and troughs interact constructively and destructively to form bright and dark regions, respectively.
On the other hand, the photoelectric effect, which was extensively studied by Albert Einstein and for which he received the Nobel Prize in 1921, provided evidence for the particle-like behavior of light. The photoelectric effect occurs when light shines on a material surface and ejects electrons from it. The observation that the kinetic energy of the ejected electrons depends on the frequency of light but not its intensity implies that light consists of discrete particles, now called photons.
Quantum mechanics reconciles these seemingly contradictory observations by describing light as having both wave-like and particle-like characteristics, depending on the experimental setup and the specific observation being made. This duality is a fundamental aspect of quantum mechanics, and it applies not only to light but to other elementary particles as well.
In summary, quantum mechanics does not provide a definitive answer to whether light is a wave or a particle. Instead, it demonstrates that light exhibits properties of both waves and particles, and the specific behavior observed depends on the experimental context.