Wave-particle duality: Hugen's and Newton's thoery of the nature of light

Introduction

In the past, our understanding towards light was not very thorough and different theories were proposed by different scientist on what light actually was. Huygen’s and Newton’s theories were compared since they described waves in two entirely different forms — wave and particles. After the theories were proposed, more experiments were done for the theories, providing us a more complete understanding towards the nature of light.

What was Huygen’s theory of the nature of light?

Huygens’ principle was proposed in 1678 by the physicist Christian Huygen. In his work, he suggested that the wavefront of a propagating wave of light at any instant conforms to the envelope of spherical wavelets emanating from every point on the wavefront at the prior instant.[1] This principle was based on his observation of diffraction of light and the interference patterns he saw, proposing the nature of light consists of wave. However, due to lack of evidence and valid experimental proof, Newton’s theory was generally more accepted by the public than Huygen’s theory.

Figure 1“ Huygens' Principle,” MathPages,

What was Newton’s theory of the nature of light?

Meanwhile, Newton proposed corpuscular theory of light in which it states that light is made up of small discrete particles called ‘corpuscles’ which travel in straight line at a finite speed. He did not think light can be diffracted, saying that ‘We can hear sound from behind an obstacle, but we don’t see light’.[2] He also argued that light can pass through in a vacuum unlike sound waves since all the waves previously known required a medium to travel. Newton’s theory sounds very different from the understanding general public but he was not completely wrong providing the discovery of photon at a later stage.

Why was Young’s double slit experiment important?

In 1801, the wave property of light was displayed by an experiment carried by Thomas Young using visible light known as the Young’s double slit experiment.[3] For a modern version, this experiment is usually carried with a monochromatic laser in a school laboratory.[4] This experiment was a very significant discovery and also very strong evidence to support Huygen’s argument. In this experiment, bright and dark fringes were observed forming an interference pattern, which was caused by the superposition of wavefronts. The dark fringes were created by destructive interference while the bright fringes were created by constructive interference. The effect of diffraction suggested that light is formed by wave, similar to what Huygen suggested.

Figure 2“Young's Double-Slit Experiment,” Encyclopædia Britannica (Encyclopædia Britannica, inc.)

 

However, in 1927, this experiment was repeated using electrons instead of laser by Davisson and Germer, in which a small particle also demonstrated similar pattern as the previously done experiments. Scientists also discovered that this effect can also happen on a much larger molecule in more recent times suggesting the fact that light can also have properties of particles,[5] and this is known as wave-particle duality.

Conclusion

Light demonstrates both properties of wave and particles showing that Huygen and Newton are both correct. However, Huygen’s prediction was more accurate as it is very clear that the diffraction pattern is shown and Newton clearly did not agree with that. For a more complete understanding towards the nature of light, more experiments of diffraction pattern based on different size of molecules or types of light should be done to support the wave-particle duality.

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[1] “ Huygens' Principle,” MathPages, accessed April 28, 2023, https://www.mathpages.com/home/kmath242/kmath242.htm.

[2] “Newton's VS Huygens' Models of Light – HSC Physics,” Science Ready, accessed April 28, 2023, https://scienceready.com.au/pages/particle-and-wave-model-of-light#:~:text=Newton's%20model%20of%20light%20proposes,human%20eye%2C%20obey%20Newtonian%20physics.

[3] “Double-Slit Experiment,” Wikipedia (Wikimedia Foundation, April 28, 2023), https://en.wikipedia.org/wiki/Double-slit_experiment#cite_note-The_Bakerian_lecture-1.

[4] “Young's Double-Slit Experiment,” Encyclopædia Britannica (Encyclopædia Britannica, inc.), accessed April 29, 2023, https://www.britannica.com/science/light/Youngs-double-slit-experiment.

[5] The Physics arXiv Blog, “Physicists Smash Record for Wave-Particle Duality ,” Medium (The Physics arXiv Blog, November 8, 2013), https://medium.com/the-physics-arxiv-blog/physicists-smash-record-for-wave-particle-duality-462c39db8e7b.