Is light a particle or a wave?
From the farthest stars in the sky to the screen in front of your face, light is everywhere. But the way light travels has long puzzled scientists. One question in particular has troubled thinkers from Isaac Newton to Albert Einstein: Is light a particle or a wave?
“Whether light is a particle or a wave is a very old question,” Riccardo Sapienzaphysicist at Imperial College London, told Live Science. As a living species, we seem driven to understand the basic structure of the world around us, and this puzzle kept 19th century scientists busy.
Today, there is no doubt about the answer: Light is a particle and a wave. But how did scientists reach this mind-boggling conclusion?
The first thing was to distinguish scientifically between waves and particles. “You can describe something as a particle if you can identify it as a point in space,” Sapienza said. “A wave is something you don’t define as a point in space and you need to give the frequency of oscillation and the distance between maximum and minimum.”
The first concrete proof of the wave nature of light came in 1801, when Thomas Young performed his famous bisplitting experiment. He placed a screen with two slits in front of the light source and observed the behavior of the light after it passed through the slits. The light hitting the wall showed a complex pattern of bright and dark bands, known as interference fringes.
As the light waves passed through each hole, they produced semi-circular waves, which combined and increased or decreased the final power.
“If the light was a particle, you would have ended up with two bands on one side of the screen,” Sapienza said. “But we have interference, and we see light everywhere behind the screen, not just in the area of the holes. That’s proof that light is a wave.”
Eighty-six years later, Heinrich Hertz was the first to demonstrate the nature of light. He noticed that when ultraviolet light shines on metal, it produces a charge – a phenomenon called the photoelectric effect. However, the significance of his observations was not fully understood until many years later.
Related: What is the speed of light?
Atoms have electrons in fixed energy levels. Therefore, light shining on them is expected to energize the electrons and enable them to escape from the atom, with the bright light releasing the electrons quickly. But in the experiments following Hertz’s work, several strange ideas seemed to contradict this old understanding of physics.
It was Einstein who finally solved this problem, for which he was given a Nobel Prize in 1921. Instead of absorbing light continuously from the wave, atoms actually receive energy in packets of light called photons, which explains unusual phenomena such as the existence of choppy waves.
But what determines whether light acts as a wave or as a particle? According to Sapienza, this is not the right question to ask. “Light is sometimes a flash and sometimes a wave,” he said. “It’s always a wave and a particle. It’s just that we highlight one of the properties depending on what tests we’re doing.”
In everyday life, we often see light as a wave, and it is this type that physicists find useful to control.
“There is a whole field called metamaterials – by creating materials that have the same properties as light, we can improve the interaction of light with materials and control the waves,” said Sapienza. “For example, we can make solar devices that can absorb light more efficiently for energy generation or more efficient MRI devices.”
However, the dual nature of light, known as wave particle duality, is crucial to the existence of the world as we know it. This strange twin behavior also extends to other quantum particles, such as electrons.
“You wouldn’t have a stable atom if you didn’t have one quantum mechanics with electrons in certain places, “Sapienza said. “If you take away the fact that it is a particle, you take away the fact that it has a certain energy and life would not exist. “
#light #particle #wave