  The 19th century Aether died with Special Relativity but was resurrected by
General Relativity in the form of dark energy; a tensile material with tension
equal to its energy density. Such a material is provided by the D-branes of
string-theory; these can support the fields of supersymmetric particle-physics,
although their energy density is cancelled by orientifold singularities upon
compactification. Dark energy can still arise from supersymmetry-breaking
anti-D-branes but it is probably time-dependent. Recent results on
time-dependent compactifications to an FLRW universe with late-time accelerated
expansion are reviewed.
