General relativity treats spacetime torsion induced by celestial spin as a purely near-region effect confined to the vicinity of the event horizon, with vacuum regions far from celestial bodies regarded as torsion-free flat spacetime. This paper constructs a decisive thought experiment: two widely separated black holes share a single symmetry axis, their intrinsic spins are opposite in handedness, each equipped with an accretion disk rotating synchronously with the black hole. Two observers stay in the local inertial frames attached near each horizon and observe each other along the common axis. Under the traditional geometric framework, there is no global torsion field between the two systems, and traveling along the axial coordinate path requires only conventional gravitational energy. However, from the perspective of spacetime fluid hypothesis, spin generates a long-range continuous torsion field penetrating the entire vacuum. The inertial manifold possesses intrinsic chiral topology. The transition from one local co-moving frame to the opposite-handed frame cannot be a uniform motion; the observer must undergo continuous non-uniform angular acceleration and consume large deformation energy to cross the topological barrier. Light, as a wave of spacetime fluid itself, naturally follows the gradual torsion of the background without additional energy cost, forming a fundamental distinction between massless radiation and massive material bodies. The whole model does not rely on existing astronomical observations, but serves strictly as a logical discriminant to compare conventional tensor geometry and fluid spacetime theory, providing a new path for exploring the origin of inertia and Mach’s principle.
Q Chen (Fri,) studied this question.