How Double-slit diffraction experiment is related to quantum theory

Double-slit diffraction is a classic experiment that not only demonstrates the phenomenon of diffraction but also played a pivotal role in the development of quantum theory, specifically the concept of wave-particle duality. Here's how it is connected to quantum theory:

1. Wave-Particle Duality:

   • The double-slit experiment involves firing particles, such as electrons or photons (particles of light), one at a time at a barrier with two closely spaced slits. On the other side of the barrier, there's a screen that records where these particles hit.

2. Classical Expectation:

   • In classical physics, particles are expected to behave as discrete entities. If you fire particles, you would expect them to pass through one of the slits and form two distinct bands on the screen opposite each slit.

3. Quantum Surprises:

   • However, when individual electrons or photons are fired through the double slit, something astonishing happens. Instead of forming just two bands, they produce an interference pattern, similar to what you'd expect for waves.
   • This interference pattern consists of alternating dark and light bands, with a central bright band. It suggests that the particles are behaving as if they were waves, with wavefunctions that interfere constructively and destructively.

4. Wavefunction:

   • In quantum theory, particles are described by wavefunctions, mathematical functions that represent the probability distribution of a particle's position and properties.
   • The interference pattern observed in the double-slit experiment implies that the particles have wave-like properties and exhibit interference, as if they were waves.

5. Wave-Particle Duality Explained:

   • This experiment led to the formulation of the concept of wave-particle duality, which suggests that particles like electrons and photons can exhibit both particle-like and wave-like properties depending on how they are observed or measured.
   • When observed or measured, they behave as particles with definite positions, but when not observed, their behavior is governed by wavefunctions and they exhibit interference patterns.

6. Quantum Superposition:

   • The key insight from the double-slit experiment is that particles can exist in a superposition of states. In other words, an electron, for example, can be in multiple positions or states simultaneously, represented by its wavefunction.

7. Uncertainty Principle:

   • This experiment also contributed to the development of Heisenberg's Uncertainty Principle, which states that the more precisely you know a particle's position, the less precisely you can know its momentum, and vice versa.