Quantum Gravity: A Dogma of Unification?

The dynamical approach to spin-2 gravity

“…Accordingly, all further philosophical observations also apply. In particular, given the more fundamental framework, the quantum spin-2 theory can be viewed as decisively supporting an ontological reduction of g. Also, since GR can be obtained independently as the classical limit, GR is arguably reduced to QFT (see Salimkhani (2018)) and may be viewed as non-fundamental, i.e., as an essentially phenomenological (albeit unique) theory for describing interactions at macroscopic distances and times. (Boulware and Deser, 1975, 230) It is particularly the quantum spin-2 approach that underlines and makes precise the effective field theory viewpoint of GR (see Donoghue (1994)).…”

“…Adopting this approach arguably brings with it the task of explaining-or, at least, making plausible-why the SEP should hold in the first place (see also Salimkhani (2018) and Weinberg (1972)). Otherwise the SEP is just a brute empirical fact; and explaining chronogeometricity by a brute fact might be considered just as dissatisfactory as GA-GR's essentialism (where the g field just has this property).…”

“…So, particle physics would be used as a continuity condition for our interpretation of GR. In fact, we may even argue that we already have a working quantum theory of gravity in terms of the quantum spin-2 approach (see Salimkhani (2018)). The problem, infamously, is that with respect to topology or causality.…”

“…This paper engages with the following closely related questions that have recently received some attention in the literature on the foundations and interpretation of relativity theory (e.g., Read et al (2018), Read (2018Read ( , 2019, Salimkhani (2018), and Lehmkuhl (2020)): (a) what is the status of the equivalence principle in general relativity (GR)? ; (b) how does the metric field obtain its property of being able to act as a metric that is surveyed by material rods and clocks?…”

“…Fang and Christian Frønsdal (1979), Richard Feynman (1995), Steven Weinberg (1964a;1964b;1972), Stanley Deser (1970;2010), Robert Wald (1986), and Brian Pitts and William Schieve (2001c;2007)-for a concise review see Preskill and Thorne (1995), for an extensive list of references see also Pitts (2016). In particular, it is suggested by Weinberg and others that the spin-2 approach to quantum gravity has a particularly significant feature: it is taken to provide an explanation for why the strong equivalence principle (SEP)-that is, the fact that locally all laws reduce to the laws of special relativity (SR)-holds (see Salimkhani (2018) for a sketch of the argument for a philosophical audience). I investigate these claims in sections 2 and 3.…”