For many years, a central question perplexed the scientific community: "What is light?" Two competing theories sought to answer this query. One, proposed by Newton, posited that light was composed of particles. The other, suggested by Huygens, asserted that it was a wave. The question appeared to be settled by a simple experiment conducted in 1801 by Thomas Young, known as the double-slit experiment.
In the double-slit experiment, a light beam is directed at a barrier with two openings. If light acted solely as particles, it should pass through one slit or the other. However, an interference pattern of light and dark bands is observed instead, indicating that light behaves like waves. Simply put, the waves of light from both slits mix, intensifying in some areas and cancelling out in others, forming the observed pattern.
Years later, in the 20th century, it was discovered that light is composed of very small particles called photons. Remarkably, when the double-slit experiment was conducted with individual photons, the same wave-like behavior was observed. This groundbreaking discovery led to the attribution of wave-particle duality to light and laid the foundation for modern quantum mechanics.
There's nothing like experimentation to get closer to the truth. And it is fascinating how, often are the simple experiments, like the double-slit, that lead to some of the most important discoveries of our time.
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