All of us know Isaac Newton, the famous self-centric British scientist. He insisted that light consist of very small basic particles. Everyone believed him, who could say no to Newton?
Almost two hundred years later came another English theoretician not as famous, called Thomas Young. He produced credible
experimental evidence that light consists of waves.

(see the two-slit experiment).
Then Maxwell and Herz confirmed that light consists indeed of oscillations of electromagnetic waves.
However Einstein who believed in the light wave theory, grabbed the scientific community’s attention to the particle nature of light as he showed it in the photoelectric effect (for which he received the Nobel Prize).

Now how is it that light be both particles and waves? These two concepts seem irrevocably opposed!
Not really...

 

Then came the French prince Louis-Victor de Broglie, a French physicist, who proposed in his 1923 doctoral thesis that all matter and radiation have both particle-,and wavelike characteristics. Until the emergence of the quantum theory, physicists had assumed that matter was distinct from energy and followed different laws: energy radiation was waves and matter was particulate. Planck’s theory was the first to propose that radiation have characteristics of both waves and particles. Believing in the symmetry of nature, Broglie ended the wave-particle dichotomy by applying Einstein ‘s mass-energy famous formula along with Planck’s principle:

E = mc˛ = hf

Using the old-fashioned word corpuscles for particles, Broglie wrote: ”For both matter and radiation, light in particular, it is necessary to introduce the corpuscle concept and the wave concept at the same time. In other words, the existence of corpuscles accompanied by waves has to be assumed in all cases.”

Broglie’s conception was an inspired one,. However his examiners regarded this aspect of his thesis as more of a clever mathematical trick than anything of practical value. Still he was awarded the doctorate, and his thesis supervisor, Paul Langevin, sent a copy of the work to Einstein. It was Einstein who spotted at once the value of the work and its implications and who passed news of it on to other researchers.

De Broglie was duly awarded the 1929 Nobel Prize in Physics. By then it was clear that all “waves” have to be treated as “particles” and that all “particles” have to be treated as “waves”. The confusion doesn’t arise in everyday life, for objects big enough to see, or for waves on the ocean and ripples on the pond. But it is crucial to an understanding of atoms and subatomic phenomena. The physicists of the late 1920s were happy to have a consistent theory of the atom at last, even if the price they had to pay included some strange ideas about wave-particle duality. However this strange aspect of atomic reality was almost the least of the strangeness of the quantum word that was then unfolding before their astonished gaze.