In the double-slit experiment, interference occurs when waves (such as light or matter waves) pass through two closely spaced slits and interfere with each other, creating an interference pattern on a screen placed behind the slits. The pattern consists of alternating bright and dark fringes.
The distance at which interference can be observed depends on the specific setup of the experiment and the characteristics of the particles or waves involved. In the case of light, which is commonly used in the double-slit experiment, interference patterns can be observed even at significant distances from the slits.
The key factor that determines the distance at which interference remains observable is the coherence length of the light source. Coherence refers to the property of light waves that determines the extent to which they maintain a fixed phase relationship with each other. For interference to occur, the waves from the two slits must maintain their phase coherence.
In practice, the coherence length of light sources can vary widely. Laser light, for example, is highly coherent and can produce interference patterns that extend over relatively long distances. In contrast, incoherent light sources, such as thermal light, have shorter coherence lengths and the interference pattern becomes less distinct as the distance from the slits increases.
It's worth noting that as the distance from the slits increases, the interference pattern becomes more spread out and the fringes become wider and less defined. Eventually, at very large distances, the interference pattern fades away, and the light or particles behave more like individual localized entities rather than waves exhibiting interference.
The specific distance at which interference becomes indiscernible depends on various factors such as the wavelength of the light or particles, the size of the slits, the distance between the slits, and the characteristics of the detection screen. It is typically determined experimentally for a given setup rather than having a fixed theoretical limit.
In summary, while interference patterns can be observed at varying distances from the slits, the precise distance depends on the coherence length of the light source and other experimental factors.