In the double-slit experiment, the act of observing a photon or any quantum particle can indeed affect its superposition and interfere with its wave-like behavior. This phenomenon is known as the "observer effect" or "measurement effect" in quantum mechanics.
When the double-slit experiment is conducted without any measurement or observation, a single photon can pass through both slits simultaneously, creating an interference pattern on the screen behind the slits. This interference pattern arises due to the constructive and destructive interference of the photon's wave-like nature.
However, when the photon's path is observed or measured to determine which slit it passes through, the interference pattern disappears. The act of measurement collapses the photon's wavefunction into a definite state, either passing through one slit or the other, destroying the interference pattern.
The observer effect is not dependent on the distance between the observer and the experimental setup. Whether the observer is near the double-slit apparatus or far away, the act of measurement will still collapse the photon's wavefunction and remove the interference pattern.
It's important to note that in the double-slit experiment, the observer effect is not caused by the physical interaction between the observer and the photon. Instead, it is a fundamental aspect of quantum mechanics related to the measurement process itself.
In some variations of the double-slit experiment, it is possible to perform a delayed-choice measurement, where the measurement is made after the photon has passed through the slits but before it reaches the detector screen. In such cases, the decision to observe or measure the photon's path can be made at a considerable distance from the slits. However, regardless of when or where the measurement is made, it will still collapse the photon's wavefunction and affect the interference pattern.
The observer effect is a fundamental aspect of quantum mechanics, and it is not limited by distance. The act of observation or measurement in quantum experiments has a profound impact on the behavior of quantum particles, including their superposition and interference patterns.