Is Light a Wave or a particle ?

     For centuries, scientists debated the nature of light. Some claimed that light was a wave, behaving like a ripple in a pool. The opposing view was that light was a particle, like the droplets of water that flow from a kitchen faucet. Just when a prevailing view gained momentum, evidence for the other caused confusion. Finally, in the early 20rh century, Albert Einstein called a tie: Light is both wave and particle.

    Those who believed in the particle theory of light followed Sir Isaac Newton. He described light as a series of particles, using a prism to prove his theory. To Newton, the clarity and sharpness of the prism shadows meant that light traveled as a shower of particles, each following a straight line until disturbed. 

    Those who opposed Newton's theory followed  scientist Christiaan  Huygens, who   cited   light's   diffraction   and inrerference as proof that it is a wave. Diffraction, the bending of light as it passes around an object, and interference, when waves combine to form greater or lesser amplitude, occur in other mediums with wave-like properties, such as sound and water. Astronomers studying moving galaxies proved that light follows the Doppler Effect, the name for the change in sound as waves from the source move closer or fanher away from you, elongating
as they move away and shortening as they   come closer. Visible light, as seen in the   colors of the rainbow, exhibits similar  properties, with longer wavelengths  appearing as a red shift and shorter  wavelengths as a blue shift. Until the turn  of the century, this overwhelming evidence  convinced most scientists that light was a  wave, until Albert Einstein settled the  score. 

  One thorn in the argument for light-is-  a-wave purisrs is a phenomenon called the  photoelectric effect. When light shines on a  metal surface, electrons fly out. But higher  intensity of light does not cause more  electrons to be released, as you would expect with the wave theory. Albert Einstein srudied this effect and came up with a compelling theory that stated light was both wave and particle. Light flows toward a metal surface as a' wave of particles, and eletrons release from the metal as an interaction with a single photon, or particle of light, rather than the wave as a whole. The energy from that photon transfers to a single electron, knocking it free from the metal. Einstein's declaration of wave-particle duality earned him the Nobel Prize in physics in 1921. 

   Since Einstein's discovery, physicists have embraced this theory. Einstein declared: "We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do." Understanding light as a wave Ied to the deveiopment of important technology, such as lasers. The discovery of photons made possible the  electron microscope.   

  And thanks to Albert Einstein, we can  stop the centuries-old debace and declare  everyone a winner.