The photoelectric effect is a process whereby light shining onto a material can cause electrons to be knocked loose from it. Before Albert Einstein’s research, there were two primary theories on how light behaved: as particles, or as most accepted, as waves. However, scientists noticed that while brighter light would not knock electrons free, light of different colors would. This anomaly of light behavior was known as the Ultraviolet Catastrophe. It was Max Planck who found that energy is instead emitted in tiny chunks. Einstein expounded on this and discovered (later confirmed by Robert Millikan) that light not only acts as a wave, but also like tiny particles of energy, each carrying with it a particular amount of energy depending on its wavelength.
The implications of this discovery are far reaching. Einstein’s work helped launch the field of quantum physics. We can see its application in all manner of technology, from solar panels to light sensors for digital cameras to medical imaging devices. It also opened the door to later inventions such as transistors and computer chips, essential for today’s electronics. But beyond technology, perhaps another legacy of the photoelectric breakthrough is how it changed science itself. It would show that even the most accepted ideas could be inaccurate or incomplete, and that new experimental evidence could completely reshape our understanding of nature and the universe.