The interpretation of the double-slit experiment in quantum mechanics can be a subject of debate and different interpretations. The statement that "photons go through both slits" is often associated with the concept of wave-particle duality and the superposition principle in quantum mechanics.
In the double-slit experiment, when photons or particles are not observed, they exhibit an interference pattern, suggesting that they can behave as waves and interfere with themselves. This is what Feynman meant by saying that photons go through both slits. According to the principles of quantum mechanics, a particle can exist in a superposition of multiple states, meaning it can be in a combination of different possibilities simultaneously.
However, when a measurement or observation is made at the slits to determine which path the photon took, the interference pattern disappears. This is known as the "observer effect" or "measurement collapse," where the act of measurement disturbs the system and alters its behavior.
The interpretation of this phenomenon depends on the philosophical and theoretical framework one adopts. One interpretation is that the act of measurement forces the system to "choose" a definite path and loses its wave-like behavior, causing the interference pattern to vanish. This interpretation is often associated with the Copenhagen interpretation of quantum mechanics.
It's worth noting that there are alternative interpretations, such as the many-worlds interpretation or pilot-wave theory, which offer different explanations and ways to reconcile the observations. These interpretations propose that the interference pattern is still present, but in a different way or hidden from direct observation.
In summary, the statement that "photons go through both slits" is a conceptual framework to understand the behavior of particles in the double-slit experiment based on the principles of quantum mechanics. The observed disappearance of interference when making measurements is a manifestation of the measurement process itself and is subject to interpretation based on different philosophical and theoretical perspectives.