Space time and motion

From The Elegant Universe by Brian Greene:-

Einstein proclaimed that all objects in the universe are always traveling through space time at one speed--that of light. We are presently talking about an object's combined speed through all four dimensions--three space and one time--and it is the object's speed in this generalized sense that is equal to that of light.

This one fixed speed can be shared between the different dimensions--different space and time dimensions, that is. If an object is sitting still (relative to us) and consequently does not move through space at all, then all of the object's motion is used to travel in one dimension--in this case the time dimension.

Moreover, all objects that are at rest relative to us and to each other move through time--they age--at exactly the same rate or speed. If an object does move through space, however, this means that some of the previous motion through time must be diverted. This sharing of motion implies that the object will travel more slowly through time than its stationery counterparts, since some of its motion is now being used to move through space. That is, its clock will tick more slowly if it moves through space.

We now see that time slows down when an object moves through space relative to us because this diverts some of its motion through time into motion through space. The speed of an object through space is thus merely a reflection of how much of its motion through time is diverted.

Rambling hippies and string theorists. Can you tell them apart?