Physics Question:
What key principle of quantum mechanics does the double-slit experiment demonstrate?
Answer:
The double-slit experiment powerfully demonstrates the core principles of quantum mechanics, specifically:
- Wave–Particle Duality
- Quantum Superposition
- Effect of Measurement (Observer Effect)
Wave–Particle Duality
When particles such as electrons or photons are emitted toward a barrier with two open slits, they create an interference pattern on the detection screen behind the slits—even when sent one at a time.
This pattern is typical of wave behavior, even though the entities involved are particles. Hence, the experiment reveals that quantum particles behave both like waves and particles.
Quantum Superposition
If we do not observe which slit the particle passes through, the particle exists in a superposition of states, meaning it effectively goes through both slits simultaneously.
The resulting interference pattern arises from the interference of probability amplitudes—a purely quantum effect that has no classical equivalent.
Measurement and Collapse of the Wave Function
When a measurement is made to detect which slit the particle goes through, the interference pattern disappears.
This happens because the act of observation collapses the wave function, forcing the particle into a definite state. The experiment highlights the critical role of measurement in quantum theory.
Conclusion:
The double-slit experiment is a profound demonstration of the principles of quantum mechanics. It shows that:
- Particles exhibit both wave-like and particle-like behavior.
- Quantum systems exist in superposition until measured.
- Observation collapses the wave function and changes outcomes.
These insights are foundational to understanding modern quantum physics.