The difference between a double-slit experiment with observation and one without is primarily related to the role of measurement and observation in quantum mechanics.
In a traditional double-slit experiment, a beam of particles, such as electrons or photons, is directed toward a barrier with two small slits. Behind the barrier, a screen or detector is placed to record the pattern formed by the particles that pass through the slits. When the experiment is conducted without any additional measurement or observation, an interference pattern emerges on the screen, indicating that the particles exhibit wave-like behavior and interfere with themselves.
However, if one attempts to determine which slit a particle passes through by placing detectors or introducing any form of measurement, the interference pattern disappears, and instead, two distinct patterns corresponding to the slits appear. This is known as the "collapse of the wavefunction" or "wavefunction collapse." The act of measurement or observation disturbs the delicate superposition of states, causing the particles to behave more like classical particles with well-defined trajectories.
In summary, the difference between a double-slit experiment with observation and one without is that observation or measurement disrupts the interference pattern, and the particles behave more like classical particles with defined paths through the slits. Without observation, the particles exhibit wave-like behavior and create an interference pattern on the screen, indicating the presence of wave interference. This phenomenon highlights the inherent wave-particle duality of quantum objects.