Is the unsolvability of the N-Body Problem equivalent to the Halting Problem
There is some (somewhat scattered) research into the undecidability of the N-body problem from physics (in line with general study of undecidable phenomena in classical and quantum physics), which asks about calculating future trajectories or orbits of objects all subject to $n^2$ gravitational interactions; it has been studied for centuries including by e.g. Newton and Gauss. It basically reduces to a large array of differential equations and such systems have been proven to contain undecidability scenarios. However, this is a somewhat unusual crosscutting area of physics and mathematics that is not widely cited in either field and there do not seem to be widely cited single references either.

See e.g. 


Church’s thesis meets the N-body problem / Smith
On an Undecidable Problem Related
to Difference Equations with Parameters / Abramov
Decidability and Undecidability in Dynamical Systems 2.2.2 n-body problem / Hainry