Particle or Wave? The Baffling Nature of Light
- Lulama Kagua
- Jun 27
- 3 min read
Gaborone, Botswana
Quantum physics is…strange. While most of us are used to the rules and regulations that encompass classical physics - like projectile motion, the behavior of waves and the laws of thermodynamics, the carefully built foundation classical physics rests upon starts to break down as we view nature at a more microscopic level. That’s where quantum physics comes in and that’s where things get interesting. Quantum physics examines matter and energy at its most fundamental level and in the world of the very small, things act differently from how one would expect--especially an itty bitty concept we call ‘light’.
In grade school, we learned that light is electromagnetic radiation that can be detected by the human eye. It’s responsible for important processes like warming the Earth and photosynthesis in plants, but what is light really? What is it made up of? How does it work? And how does it interact with the matter around us? Well, great minds, from Christian Huygens to Albert Einstein, grappled with these questions for a couple centuries until we came to the prospect of wave-particle duality.
It was in the 17th century when scientists really started to toy around with ideas relating to the properties and nature of light. Isaac Newton believed that light was composed of tiny particles whilst Christian Huygens suggested light took on a more wave-like construction, which would come to be known as the wave theory of light. The wave theory of light described light as wave energy that propagated perpendicularly to the direction of its motion. A more intuitive way to think about this form of energy is to imagine water waves and their movements, like how a rubber duckling would bounce up and down statically as energy continued to pass through a wave.
The wave theory explained quite a few phenomena experienced by light such as diffraction and interference, yet could not make sense when applied to the problem of the photoelectric effect. The photoelectric effect was first taken note of in the 19th century. It involves the emission of electrons from a material when struck by light. Crucially, the light in question had to be above a certain frequency to cause this emission. In the classical wave theory of light, the energy carried by light is directly proportional to the intensity of the light emitted. So, the idea was that the brighter the light shone, the more energy is supplied and accumulated to cause electron displacement. But accumulation seemed to be unlikely because electron emission was observed to be instantaneous, way too fast for any time period over which energy could be supplied by a bright light. Due to this, the wave theory was deemed unsuitable for the explanation of the photoelectric effect.
The breakthrough wasn’t until Einstein came up with a theory to this tricky situation, one that snagged him a 1921 Nobel Prize win. He took and compounded upon an idea first posed by Max Planck in the year 1900 suggesting that light was ‘quantized’ to form small packets of energy known as photons. Einstein proposed the existence of photons present in light. These photons carry energy equal to their frequency. So, if an electron is to interact with a photon above a certain frequency, then the electron is immediately knocked out of place by the photon without accumulation nor time delay. This theory proved light to be of a particle nature alongside its wave-like properties, opening up the flood gates to quantum physics and revolutionizing the field as we know it.
Works Cited
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“What Is Quantum Physics?” Caltech Science Exchange, scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-physics. Accessed 13 Jan. 2026.
Stark, and Glenn. “Light | Definition, Properties, Physics, Characteristics, Types, and Facts.”
Encyclopedia Britannica, 29 Dec. 2025, www.britannica.com/science/light.
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Helmenstine, Anne. “Photoelectric Effect.” Science Notes and Projects, 3 Sept. 2025, sciencenotes.org/photoelectric-effect.
Scienly. “Planck's Quantum Theory: Quantization of Energy - Scienly.” Scienly, 10 Mar. 2025, scienly.com/plancks-quantum-theory.
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