Mantle Viscosity Inferred from Post-Glacial Rebound Relaxation

This study computes post-glacial rebound viscosity from stated inputs and places the result against both the published observational value and the density ceiling of Einstein-Cartan torsion gravity, in which spin-sourced torsion caps the effective density of neutron matter near 9.72e57 kilograms per cubic metre. The computation gives: inferred mantle viscosity 1.11e+21 Pa s; predicted present uplift 10.0 mm per year; observed Hudson Bay uplift about 10 mm per year; relaxation time used 5000 years. The standard geophysical account reproduces the measured behaviour of the formerly glaciated shields within the uncertainty of its inputs, and the largest correction the ceiling could contribute at terrestrial densities is far below the precision of the observations, so the measurement is consistent with the frame while also naming the threshold at which it would cease to be. Rebound remains the most direct measurement of mantle viscosity on geological timescales, and its value controls everything from sea-level projections near formerly glaciated coasts to the interpretation of the gravity field's longest wavelengths, so the simple inversion is worth redoing carefully rather than quoting by habit. The study is a computation from stated assumptions, not a new measurement.