Gravity with spin excludes fermionic strings Abstract: The existence of intrinsic spin of matter requires the metric-affine formulation of gravity, in which the affine connection is not constrained to be symmetric and its antisymmetric part (torsion tensor) is a dynamical variable. We show that the cyclic identity for the curvature tensor in the metric-affine formulation forbids fermions represented by Dirac spinors to form point or string configurations. Consequently, fermionic strings contradict the gravitational field equations in the presence of spin. Superstring theory is therefore incorrect. From Page 7: Superstring theory, or supersymmetric string theory, assumes that all elementary fermions are oscillating, one-dimensional strings whose length is on the order of the Planck length. Although that theory lacks predictive power, it has become the most popular contender for a theory of everything. The results of this paper show that one-dimensional fermionic strings contradict the cyclic identity for the curvature tensor in the metric-affineformulation of gravity which is required in the presence of intrinsic spin. In addition, the simplest (ECSK) gravity withspin requires fermions to be spatially extended on the order of their Cartan lengths which are much greater than the Planck length. Consequently, fermionic strings contradict two combined physical phenomena that are well-established by experiment and observation: the geometric nature of the gravitational field and the existence of spin. Fermionic strings are thus unphysical and superstring theory is incorrect.