From a physics perspective, "observation" (such as looking at the cat) is just a series of interactions between photons, electrons, ions, and all the different molecules that make up our eyes and brains.

So if we are talking about a real cat in a box, opening the box and looking into it would not change some "quantum wave function of the cat" or something like that, right? The quantum state of everything in the box is what it is regardless of wether we open it or not.

If an atom has decayed, and emitted a particle (alpha/beta/gamma), and this particle has interacted with something, then whatever wave function of this decay must already have collapsed. The particle can not have both interacted and not interacted.

The wikipedia article on Schrödinger's cat (under "Copenhagen interpretation") says

Analysis of an actual experiment found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement.

But any interaction should be pretty much the same as a measurement, should it not?