If two detectors are placed in front of the double slit, they will indeed be able to observe different paths taken by the electrons. However, the act of placing detectors at the slits fundamentally alters the experiment and introduces a measurement apparatus, which affects the interference pattern that would otherwise be observed.
In the classic double-slit experiment, when no detectors are present, electrons exhibit wave-like behavior and create an interference pattern on a screen behind the slits. This pattern arises from the constructive and destructive interference of the electron waves passing through the two slits.
However, if detectors are introduced to observe which path each electron takes, the act of measurement collapses the wave function, and the interference pattern disappears. The presence of detectors forces the electrons to behave as particles with well-defined paths, rather than exhibiting wave-like behavior.
If two detectors are placed at the slits, they will register which path each electron takes. One detector will detect electrons passing through one slit, and the other detector will detect electrons passing through the other slit. This way, they can observe different paths taken by the electrons.
It's important to note that once the detection is introduced, the wave-like interference pattern is lost, and the experiment becomes more akin to a particle-like behavior, where the electrons behave as individual entities with definite trajectories.