In the double-slit experiment and similar quantum experiments, the act of observation or measurement does indeed have a significant impact on the quantum system being observed. This phenomenon is known as wavefunction collapse or the measurement problem in quantum mechanics.
Before an observation is made, the particle is typically described by a quantum superposition, where it exists in multiple possible states simultaneously. In the case of the double-slit experiment, the particle can be in a superposition of passing through both slits simultaneously, resulting in an interference pattern on the detection screen.
However, when an observation is made to determine through which slit the particle passes, the superposition collapses, and the particle is found to have a definite position corresponding to one of the slits. This collapse of the wavefunction occurs at the moment of measurement, and it is often said that the particle "chooses" a definite path.
The introduction of time in this context is a complex topic in quantum mechanics. Time is treated differently in quantum theory than in classical physics, and the precise relationship between time and the wavefunction collapse is still a subject of debate and ongoing research.
One interpretation is that the act of measurement introduces an interaction between the quantum system and the measurement apparatus, leading to entanglement between the two. This entanglement causes the wavefunction collapse, effectively selecting one outcome from the superposition.
It's important to note that various interpretations exist to explain the nature of wavefunction collapse and the role of measurement in quantum mechanics, such as the Copenhagen interpretation, the many-worlds interpretation, and others. These interpretations provide different perspectives on the underlying mechanisms and philosophical implications of quantum measurement.
In summary, the act of observation or measurement in the double-slit experiment does introduce a collapse of the quantum superposition, determining the particle's behavior. The exact relationship between observation, time, and the collapse of the wavefunction is a subject of ongoing research and interpretation within the field of quantum mechanics.