The Shear Threshold at the Aldred Limit: How Much Anisotropy a Spin-Torsion Bounce Can Survive

In a homogeneous but anisotropic collapse of Bianchi I type, shear acts as an additional positive energy density and competes with the negative spin-torsion term that produces the Aldred Limit bounce. This paper computes the largest shear the bounce can survive. Writing the shear as an equivalent mass density rho_sigma = sigma squared divided by (16 pi G c squared), the turnaround requires rho_sigma to stay below the maximum of rho(1 - rho/rho_A), which is rho_A/4. For neutron matter at the headline bound rho_A = 9.72e+54 g per cubic centimetre, the critical shear is sigma = 8.559e+32 per second. Set against the Planck-scale shear of 3.942e+52 per second obtained from the same formula at the Planck density, the bounce occupies only a fraction 2.171e-20 of the available shear range in amplitude, or 4.713e-40 in shear energy density. Across the published prescription band the critical shear runs from 4.279e+32 to 8.559e+32 per second. The result is a sharp, checkable statement: any simulation that claims a spin-torsion turnaround must keep its shear below the computed threshold near the turnaround density. All results are computed from stated assumptions, not measured.