A Brief History of Ideas About Light

Waves and particles are distinct concepts.

Waves can be reflected, diffracted – to spread out as the pass obstacles, refracted – change direction – as they pass from one material to another, or experience interference, so that waves can add to give a bigger wave, or cancel each other to produce no wave.

Particles can bounce off each other, deflect each other, damage each other. When particles hit other particles, we picture them as hard little things like tiny snooker balls, obeying the ordinary laws of physics like conservation of momentum and energy.

The Greeks were speculating about light around 500 BC. Pythagoras thought that he could see an object because it produced a stream of particles called corpuscles – particles - which travelled to the eyes.

Two thousand and two hundred years later Isaac Newton carried out a series of experiments that showed that light had properties of waves – the could be refracted and dispersed by a prism. Despite this, Newton supported the coscle theory.

A contemporary of Newton, Christian Huygens suggested light behaved as waves. He showed that the laws of reflection could be deduced from a general wave property – that all points of a wavefront can be considered as a source of waves.

In 1801, Thomas You showed that light could be diffracted. Diffraction is a wave property and this seemed conclusive evidence for the wave model of light.

That man Einstein showed that light behaved as a particle when interacting with electrons – the photoelectric effect.

The birth of quantum physics however changed everything. It was not necessary to choose between the wave and corpuscle model of light. Light could be both waves and corpuscles at the same time. Today we call light particles photons. To complete the confusion, ordinary particle matter, like atoms and even large things likes cars, planes and planets could be treated as waves, though for most purposes the wave properties are hidden from us.

Add comment

Security code