Quantum mechanics is the study of the properties of subatomic particles and their interactions with energy. Quantum mechanics describes characteristics of both particles and waves, becoming a “wave-particle duality”. This is the third article in our “Intro to Quantum Mechanics” series, and we will now explore the concept of wave-particle duality.
Actor Cillian Murphy famously said: “Is light made up of particles or waves? Quantum mechanics says it’s both,” in the movie Oppenheimer. In reality, light comprises particles and waves, and this logic-defying phenomenon is called wave-particle duality.
Wave-particle duality is the concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave. With this characteristic in mind, this theory defies classical physics, where a particle or a wave is used to fully describe the behavior of quantum objects, such as photons and electrons.
Waves and particles
Fundamentally, waves and particles behave in different physical ways:
Classical waves obey the wave equation (v=λf), having many points in space with continuous values. The spatial aspect varies with time due to diffraction, displaying wave interference.
Classical particles obey classical mechanics, with some having a center of mass. Particles follow velocity, and time which are characteristics of different trajectories. However, particles do not exhibit interference.
Examples and Ways of Experimenting
The wave-particle duality theory applies to all subatomic particles, most notably electrons and photons.
Electrons were generally thought to behave as particles until their wave properties were discovered, showing that electrons can be both particles and waves.
The electron double-slit experiment is a famous demonstration of the phenomenon. Electrons hit the wall with two thin slits. These arrive at masks behind the slits which will expose the electrons to either slit. With either slit open shows a smooth intensity variation due to diffraction. When both slits are open and oscillate, this is a characteristic of wave interference. However, when the electron intensity is lowered to show 1 to 2 spots per second, these show individual particles, proving that electrons can also behave as single particles.
On the other hand, photons were thought to behave only as waves initially. Through the same double-slit experiment setup, photons also show characteristics of wave behavior passing through the slits (as seen in the diagram on the right), as well as individual particles as demonstrated (as seen in the diagram on the left).
The double slit experiment shows that these subatomic particles have both particle and wave-like characteristics, proving that the wave-particle duality is real.
Significance and Applications
The discovery of the wave-particle duality phenomenon is significant in the world of physics. This has led to a deeper understanding of the physical behaviors and properties of subatomic particles, such as electrons and photons, further developing quantum mechanics as a discipline. The phenomenon has also led to the discovery of quantum entanglement, optics, tunneling, and field theory.
Fun Facts
Not only is the wave-particle duality phenomenon applicable to electrons and photons, it is also applicable to atoms, molecules, and larger objects.
The discovery of the wave-particle duality phenomenon has led to the development of semiconductors, allowing faster computations.
In quantum computing, qubits are particles known to have both wave and particle-like properties, allowing for superposition and entanglement.
Works Cited
Arndt, M. and Hornberger, K. (2014). Testing the limits of quantum mechanical superpositions. Nature Physics, 10(4), pp.271–277. doi:https://doi.org/10.1038/nphys2863.
byjus.com. (2023). State and explain wave-particle duality. [online] Available at: https://byjus.com/question-answer/state-and-explain-wave-particle-duality/.
Hamamatsu Photonics K.K. (2014). The wave-particle duality of photons | Photon terrace. [online] Photon terrace. Available at: https://photonterrace.net/en/photon/duality/.
Peeler, A. (2024). 10 Intriguing Facts About Wave-Particle Duality. [online] Facts.net. Available at: https://facts.net/science/physics/10-intriguing-facts-about-wave-particle-duality/.
The Organic Chemistry Tutor (2022). Wave Particle Duality - Basic Introduction. [online] www.youtube.com. Available at: https://www.youtube.com/watch?app=desktop&v=TX_4r76RppM [Accessed 5 Feb. 2024].
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