In the double-slit experiment, the behavior of photons (or any other particles) depends on how they are observed or measured, regardless of whether it is by human eyes or scientific apparatus. This phenomenon is known as the observer effect or wave-particle duality.
When photons are not observed or measured, they exhibit wave-like properties and can interfere with each other, producing an interference pattern on a screen behind the slits. This is characteristic of their wave nature.
However, when an attempt is made to determine through which slit a photon passes, such as by placing a measuring device at one of the slits or using detectors to observe the photons, the interference pattern disappears. The photons start behaving more like particles, as they can only pass through one slit or the other, and they no longer exhibit interference.
The important point to note is that the act of observation or measurement, regardless of whether it is by a human observer or scientific apparatus, disturbs the system and alters the behavior of the photons. It is not specifically related to the human eyes but rather to the interaction between the measuring apparatus and the photons.
This behavior is a fundamental aspect of quantum mechanics and has been experimentally verified in numerous experiments, including the double-slit experiment. The exact interpretation and implications of this behavior are still subject to debate and ongoing research in the field of quantum physics.