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In the Bible, creation begins with light, which inaugurates the universe by separating day from night. It is what allows us to see the world and yet it is almost impossible to visualize its true nature. As if that weren’t enough, it has such strange and contradictory properties that it baffles even the most experienced physicists.
Until the beginning of the 20th century, everything indicated that light was nothing more than a wave. Just like the sound or movement of the sea, it is reflected when it encounters something like a mirror and is interfered with when it crosses with other light waves. The difference is that luminosity propagates in a vacuum and does not need to be conducted through a medium such as water or air.
But the conception of light as a wave could not explain certain phenomena, such as the so-called photoelectric effect: when light is emitted against certain metals, it is observed that their surface releases electrons. The puzzle began to unravel in 1900, when German physicist Max Planck published the first study of what would come to be known as quantum physics. He discovered that atoms do not emit energy continuously, but in tiny particles called quanta. In 1905,
Albert Einstein decided to apply this theory to light and realized that, if we consider that it is also made of particles (later called photons), the photoelectric effect would be explained. Quantum physics shocked the entire scientific community by proposing that light is simultaneously wave and particle, vibration and matter – an ambiguity considered absurd, incoherent, impossible. Planck and Einstein’s theory has already been proven several times in the laboratory. But the question still remains: after all, is light a wave or a particle? Physics has embraced mystery. “Whoever says that it is a wave is right and whoever says that it is a particle is also right.
According to the experiment, light has characteristics of one or the other”, says physicist Adriano Natale, from the São Paulo State University (Unesp). “We don’t need to solve the riddle. Light works with its own logic, different from what we are used to”, says Amir Caldeira, also a physicist, from the State University of Campinas (Unicamp).