We know that fusion is a very common process that inevitably happens to even the simplest elements if you just make them hot enough, we just don't know how to do that in a controlled manner. We don't really know what intelligence is, how it came about, or how we would ever recreate it artificially or if that's possible. LLMs are some pretty convincing tricks though but that's on the level of making some loud noises behind a curtain and calling it fusion.