I suppose the act of "watching" does actually cause change. Your posture is causing light to scatter in certain ways. If you have to move to view something, then you're changing the way in which light scatters, and therefore changing the amount of energy being absorbed by whatever it is you're observing. So yes, phsyically looking at something causes change. But that's the same interaction as firing a photon, measuring gravity, whatever.

The relationship between interaction is ludicrously complex, because there's probably over a googolplex of particles all simultaneously interacting with each other.

Our conciousness throws something into the mix... if we assume we have free will, then the universe is essentially shaped by the decisions that conscious beings make. So maybe there is a contradiction.