“Propagation speed. An important feature of fields is that changes in their intensity do not propagate through space instantaneously but proceed, point by point, with a speed that is limited by a number in the equations. This number is about 300,000 km/sec (186,000 miles/sec) and, since light itself is a field, it's no coincidence that this number is the speed of light. If we imagine that an object suddenly appears in space, the gravitational field generated by that object will first appear near the object and then rapidly extend outward until all of space has acquired, to some extent, the attractive property created by that field. Similarly, if the object were suddenly to disappear, the field would continue to exist for some time afterward. If the earth were suddenly to disappear, the moon would continue in its orbit for another second and a half before the gravitational field in its vicinity vanished. If the sun were suddenly to disappear, earth would continue in its orbit for eight and a half minutes before heading off into space.”