> as physics almost by definition allows for multiple, completely equivalent descriptions of reality
> it's very hard to use physics to show what something fundamentally is.
There's no such thing as fundamental nature of existence. We just have mental models (like quantum mechanics) to describe the patterns of our observations. The idea that there is some fundamental underlying matter makes no sense, we only have perceptions and mental models do describe them. Like you said, there might be multiple physical models, as long as they give the same predictions, they're all correct.
When people say "fundamental" they usually mean "the basic elements of which everything else is made of". The ancient Greeks thought those basic pieces existed and called them atoms, but it is not clear that reality has such indivisible basic elements.
> as physics almost by definition allows for multiple, completely equivalent descriptions of reality
> it's very hard to use physics to show what something fundamentally is.
There's no such thing as fundamental nature of existence. We just have mental models (like quantum mechanics) to describe the patterns of our observations. The idea that there is some fundamental underlying matter makes no sense, we only have perceptions and mental models do describe them. Like you said, there might be multiple physical models, as long as they give the same predictions, they're all correct.