Waves overlap, creating an interference pattern of light and dark fringes (constructive and destructive interference).
This phenomenon is well-known and studied since the early 19th century.
Particles vs. Waves
If grains of sand are used, they behave like particles, showing two peaks beneath the slits (particle-like behavior).
When using atoms, the same setup produces an interference pattern, similar to the wave behavior of light.
Key Observations
Atoms Individually:
When sending atoms through one at a time, they still create the interference pattern.
This suggests that each atom behaves like a wave, contributing to the overall wave-like pattern.
Localized Behavior:
Atoms arrive at specific locations on the screen, indicating they are localized particles.
The pattern formed implies that atoms somehow know about both slits and can interfere with themselves.
Measurement and Observation
Detecting Slit Passage
If a detector is placed to observe which slit the atom goes through, the interference pattern disappears.
Each atom is detected as going through only one slit.
Unplugging the Detector
If the detector is unplugged (but atoms think it's still active), the interference pattern reappears.
This suggests that the act of measurement affects the behavior of particles.
Conclusion
The two-slit experiment illustrates fundamental principles of quantum mechanics, such as wave-particle duality and the impact of observation on quantum systems.
Quantum entanglement indicates particles remain interconnected regardless of distance, maintaining awareness of each other's existence.