  Recent criticism of higher-dimensional extensions of Einstein's theory is
considered. This may have some justification as regards string theory, but is
misguided as applied to five-dimensional theories with a large extra dimension.
Such theories smoothly embed general relativity, ensuring recovery of the
latter's observational support. When the embedding of spacetime is carried out
in accordance with Campbell's theorem, the resulting 5D theory naturally
explains the origin of classical matter and vacuum energy. Also, constraints on
the equations of motion near a high-energy surface or membrane in the 5D
manifold lead to quantization and quantum uncertainty. These are major returns
on the modest investment of one extra dimension. Instead of fruitless bickering
about whether it is possible to "see" the fifth dimension, it is suggested that
it be treated on par with other concepts of physics, such as time. The main
criterion for the acceptance of a fifth dimension (or not) should be its
usefulness.
