In the double-slit experiment, when using a light source that emits photons, such as a laser, it is not necessarily known with certainty that a single, discrete photon is emitted at a time. However, the experiment can be set up in a way that allows for the observation of the wave-particle duality of light.
When a light source, such as a laser, is used in the double-slit experiment, it emits a stream of photons. Each photon can be considered as a particle with wave-like properties. These photons pass through two slits, creating two separate coherent wavefronts that then interfere with each other as they propagate. The resulting pattern on the screen or detector behind the slits shows an interference pattern characteristic of waves.
The interference pattern indicates that each individual photon interacts with both slits and interferes with itself, which is a clear demonstration of the wave nature of light. This interference pattern builds up gradually as more and more photons are detected on the screen or detector. Over time, the pattern becomes more pronounced and consistent.
However, if one were to decrease the intensity of the light source to the point where only one photon is emitted at a time, it would be possible to observe the arrival of individual photons on the screen or detector. In this case, the interference pattern would still emerge over time as more photons are detected.
This experiment demonstrates the probabilistic nature of quantum mechanics. Although it is not known which specific slit each photon passes through, the overall pattern that emerges from the accumulation of many photons indicates the wave-like behavior and the interference phenomenon.
In summary, the knowledge that the emitter produces a single, discrete photon in the double-slit experiment is not known with certainty, but the experiment can be set up in a way that demonstrates the wave-particle duality of light and the interference phenomenon.