I see we come to this question from different directions, wether a sound is a stimulus, or the response to a stimulus. Allow me to quote the Standards of the Acoustical Society of America:Factually incorrect. Merriam-Webster:
Perception is inherent to all primary meanings. Otherwise, it's just acoustic energy.
Consider, a tree falls in the forest and only one deaf man is a witness. It doesn't make a sound.
The falling tree does make a sound, the deaf man is just not able to detect it. It all comes down to the question of Object Permanence, the understanding that whether an object can be sensed has no effect on whether it continues to exist.2.01 sound. (a) Oscillation in pressure, stress, particle displacement, particle velocity, etc., propagated in a medium with internal forces (e.g., elastic or viscous), or the superposition of such propagated oscillation. (b) Auditory sensation evoked by the oscillation described in (a).
Annotation 1 Not all sounds evoke an auditory sensation, e.g., ultrasound or infrasound. Not all auditory sensations are evoked by sound, e.g., tinnitus.
Again, factually incorrect. The universe is not locally real independent of observation. I don't need to point out that even the most technical definition that you quoted includes observation as part of its meaning.The falling tree does make a sound, the deaf man is just not able to detect it. It all comes down to the question of Object Permanence, the understanding that whether an object can be sensed has no effect on whether it continues to exist.
Consider: if a tree falls in the forest and there are more people around to hear it, does the tree make more noise?
The more complete interpretation -- them falling in love first and then crowning their relationship -- is favourable, because otherwise any intercourse would have sufficed.So this is a personal theory based on pure headcanon! Since the timeloop traps them as teenagers, it means they can never grow up. And "climbing the stairs to adulthood" is a euphemism for losing your virginity. Taking a deeper look, they are getting grimmer and more jaded the longer the loop goes on, and that's kind of like growing up too. So my theory is that "becoming an adult, aka having sex/maturing into a relationship" is the key to breaking the timeloop.
It's a thin theory based entirely on themes and making connections so I won't die on this hill or anything.