I think you and the author are talking about different concepts. To your credit, for the author's 'real thing like an atom' here, the term real is ambiguous. T

I think you and the author are talking about different concepts. To your credit, for the author's 'real thing like an atom' here, the term real is ambiguous. The question the author is talking about isn't whether a particular theory is correct, or even whether a theory contains explanatory power. I believe the author is assuming general relativity for the sake of argument, and discussing the concept of existence within the general relativity theory's framework. For example, take the three-body problem [1]: does the _theory_ of general relativity require us to add initial conditions to the three body problem? In other words, are there more fundamental initial conditions not derivable that must be inserted as inputs into the equations when we use general relativity to solve the problem instead of say Newtonian mechanics? The answer is No. While the equations will change, the initial conditions (the degrees of freedom) do not. What does that mean? It demonstrates indivisible properties of the universe given a set of theories. With general relativity now 'energy' and 'mass' are interchangeable, but the existence of mass/energy isn't a fictitious force, it can't be explained away by coordinate transformations. Gravity can't either, but a gravity well points to an underlying reality of mass/energy, not the other way around. If it were the other way around, we would say gravity is the 'real' thing, and mass/energy are resulting effects. [1]: https://en.wikipedia.org/wiki/Three-body_problem https://en.wikipedia.org/wiki/Three-body_problem