Spacetime dimensions

• How Can You Imagine Curled-Up Dimensions?
  Picture a curled-up dimension as a tiny circular direction at every point in space, like the cross-section of a hose seen from far away.
• What Is the Gravitational Constant in Higher Dimensions?
  In D spacetime dimensions, Newton’s constant has dimension-dependent units; compactifying extra dimensions relates it to the observed four-dimensional constant.