Basic Particle Physics To Learn In Your Free Time

Light

In 1637, a man named Descartes put forward the first theory of light, stating that light was made of tiny particles called " corpuscles " which travel in a straight line and have kinetic energy. In 1672, Issac Newton further elaborated on this theory saying that it explained refraction. And soon, everyone believed in the corpuscular theory of light.

But then, in 1801, a man named Thomas Young set up what is known as the double-slit experiment. notice when there are ripples in a pond and if there is a bottleneck the ripple spread out after going through the bottleneck. Now imagine two bottlenecks. Two ripples are created simultaneously and sometimes the top/bottom of one wave coincides with the top/bottom of another wave. This is called being 'In phase' but there are some tops of waves that phases with the bottom, the waves cancel each other and this is called 'Out of phase'. If one were to place a surface in front of the bottlenecks, the water will hit the surface in a zebra pattern. Thomas Young attempted this experiment with light and two slits and the results showed a zebra pattern on the paper that the light hit after going through the double slits. Meaning, light was a wave.

This experiment got many confused. How could light be particles and waves at the same time? Light has a frequency. High frequency light include X-rays and Ultraviolet while low frequency light include Infrared. In 1873, two men whose names were Heinrich Hertz and  Wilhelm Hallwachs  found that metals could lose electrons if exposed to certain frequencies of radiation.

 Albert Einstein explained this by proposing that light was a wave AND a stream of particles containing energy carried in packets called 'quanta' which were later dubbed the term,'photons'.