The double-slit experiment reveals the strange and counter-intuitive nature of quantum mechanics, challenging our understanding of reality. The experiment was originally conducted by Thomas Young in the early 19th century to demonstrate the nature of light, the experiment has since become a cornerstone in quantum physics, showing that particles such as electrons and photons exhibit both wave-like and particle-like properties, depending on how they are observed.
The Classical Experiment
In its classical form, the double-slit experiment involves shining a beam of light at a barrier with two parallel slits. If light were made of particles, one would expect two distinct bands of light on a screen placed behind the slit, corresponding to the area where the particles pass through. However, what actually appears is an interference pattern, where multiple bright and dark bands alternate with each other, suggesting that light behaves like a wave, with peaks and drops interfering with each other constructively and destructively. This was one of the earliest pieces of evidence supporting the wave theory of light, opposing the particle theory proposed by Isaac Newton.
The Quantum Version
The real mystery of the double-slit experiment emerges when it is performed with individual particles, such as electrons. If electrons are fired one at a time through the slits, one would expect each electron to land in a pattern corresponding to two distinct region behind the slits, as if they were small particles traveling straight through. However, over time, the same interference pattern appears, suggesting that each electron behaves as a wave and somehow “interferes with itself.” The puzzle deepens when scientists attempt to determine which slit an electron passes through. If a measuring device is placed at the slits to observe the electron’s path, the interference pattern disappears, and the electrons behave like particles again, forming two distinct bands. This suggests that the act of measurement collapses the wave-like nature of the electron, forcing it to behave like a particle.
Wave-Particle Duality
The double-slit experiment is a direct demonstration of wave-particle duality, a fundamental concept in quantum mechanics. Particles at the quantum level do not exist in definite states until they are observed. Instead, they exist as a probability wave, described by Schrödinger’s wave equation. The wave function represents the likelihood of finding a particle at a particular location, and it collapses into a definite state upon measurement. The Copenhagen interpretation, proposed by Niels Bohr and Werner Heisenberg, suggests that quantum systems exist in superposition until observed. Other interpretations, such as the many-worlds hypothesis, propose that each possible outcome exists in a separate parallel universe.
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https://plus.maths.org/content/physics-minute-double-slit-experiment-0
https://www.imperial.ac.uk/news/244037/double-slit-experiment-that-proved-wave-nature/
https://www.discovery.com/science/Double-Slit-Experiment
https://www.nature.com/articles/s41598-020-68181-1
https://www.techtarget.com/whatis/definition/double-slit-experiment
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