Question

The detector emits a signal to a speaker if it detects the particle and the speaker emits an audible sound, my understanding is that the wave function would collapse - we measured the outcome. However, what if we left the detector doing its thing, but turned off the speaker so that we didn't know? Would this still be considered measurement or does measurement require recording/knowledge (future included) of the outcome?

Answer 1

Even without conscious observation or recording, the act of detection by the apparatus constitutes a measurement in quantum mechanics, leading to the collapse of the wave function, as per the Copenhagen interpretation and the Heisenberg Uncertainty Principle.

Step-by-step explanation:

In quantum mechanics, a measurement is defined as an interaction between the quantum system and a measurement apparatus that leads to a collapse of the wave function, regardless of whether the outcome is consciously observed or recorded. Thus, even if the speaker is turned off, the detection still constitutes a measurement, as the apparatus has interacted with and affected the system, causing collapse. The essence of the Copenhagen interpretation emphasizes that the act of measurement itself—not the act of a conscious observer perceiving the outcome—collapses the wave function.

This is consistent with the Heisenberg Uncertainty Principle, which reflects the fundamental limit on our ability to know certain properties of quantum systems precisely. Any measurement disturbs the system and influences the properties being measured. This principle ties deeply into the core understanding of quantum mechanics and the peculiarities of wave-particle duality.