Mass and the Curvature of Space
First consider case with little mass (little
curvature)
Ant (in 2-d world) can move in straight line
from point A to point B.
Add mass to create curvature in extra
dimension invisible to the ant.
   In trying to go from point A to
   point B, fastest path is curved one
   which avoids the deepest part of the
   well.
  Ant will be delayed by the extra
  motion in the hidden third
  dimension.
Both effects verified in sending photons past
the sun:
  Bending of starlight during solar eclipse
  Delay in signals from spacecraft on
  opposite side of the sun