The vector nature of magnetic fields and the geometrical interpretation of
gravity introduced by general relativity guarantee a special coupling betwe
en magnetism and spacetime curvature. This magneto-geometrical interaction
effectively transfers the tension properties of the field into the spacetim
e fabric, triggering a variety of effects with profound implications. Given
the ubiquity of magnetic fields in the universe, these effects could prove
critical. We discuss the nature of the magnetic-field-curvature: coupling
and illustrate some of its potential implications for cosmology.