WAVE PARTICLE DUALITY

wave particle duality

What if I tell you, that you are a wave? Or that every single entity is a wave and a particle, and that too at the same time!! This is the statement of one of the most important principle of quantum mechanics, the wave particle duality. Quantum mechanics has wrapped away the old concept of wave and particles being entirely opposite entities, and incorporated them in such a way, that both of them are now actually one thing.

 HISTORY OF WAVE PARTICLE NATURE OF LIGHT

Humans have been trying to understand the nature of light from the very start of our existence. It was Greeks who first studied light in a scientifical way. Democritus stated that light is made up of subcomponents. Euclid gave the mechanism for certain phenomena of light. In 11th century , Arabic scientist Ibn al-Haytham wrote the first comprehensive Book of optics describing reflectionrefraction, and the operation of a pinhole lens via rays of light traveling from the point of emission to the eye.Isaac Newton championed the corpuscular nature of light . On the other hand Robert hook and Huygens developed the wave viewpoint of light .

Thomas young , through his famous double slit experiment, proved the wave nature of light. Maxwell developed his famous equation for light as an electromagnetic radiation.

Then , in 19th century , Max plank gave ideas of photons through experiments on black body radiation. Elbert Einstein took this idea to photoelectric effect and showed the particle like nature of light.

nature of light

THE DE BROGLIE’S HYPOTHESIS ON WAVE PARTICLE DUALITY

The scientifical world was spilt in two sides, one believing light to be wave and other believing it to be particles (photons). In 1924 , De Broglie proposed his hypothesis in his PHD thesis :

Electrons as well as all matter have both the wave and particle nature. The wavelength of wave associated with a particle is related to its momentum by the following relation:

λ = h/p = h/mv

where, λ is wavelength

h is planks constant, having value of 6.626176 x 10-34 joule-seconds.

m is mass of the object

v is the velocity  

According to this equation every object has a wavelength, but massive and slower (relative to speed of light) has wavelength so small that it is not observable.

de broglie hypothesis

Wavelength of a man

Suppose a 60 kg man is moving with a speed of 20 m/s. Then his wavelength would be:

Λ = (6.626176 x 10-34) / (60×20) = 5.52 × 10-37 m

This wavelength is too small to be observed. So, we don’t usually notice wave effects of massive objects.

Wavelength of an electron

 Now consider an electron of mass 9.1 × 10-31 kg moving with a speed of 5.93 × 106 m/s .The be Broglie wavelength comes out to be

Λ= = (6.626176 x 10-34) / (9.1 × 10-31 ×   5.93 × 106) = 1.22 × 10-10 m

This is in order of nanometer and can be observed.

wave particle nature of electron

EXPERIMENTAL EVIDENCE

In 1927 at Bell Labs, Clinton Davisson and Lester Germer fired slow-moving electrons at a crystalline nickel target. The angular dependence of the diffracted electron intensity was measured, and was determined to have the same diffraction pattern as those predicted by Bragg for x-rays. After this experiment , the de Broglie equation has been shown to apply to elementary particles, neutral atoms, and molecules as heavy as Buckyball’s .

A picture containing room
experiment 
Description automatically generated

BOTTOM LINE

As confusing as it seems, quantum physics has helped us to see the reality in a completely different way. wave nature duality is yet another surprising idea that sort of defies our mind but understanding this idea will help us to gain a better knowledge of physics and ultimately a better knowledge of reality of the universe.