Time is only a measurement. It radiates into space. Generally, the space is all of space, but it could theoretically be contained to, say, the size of a bubble, for instance. So if you are in this bubble traveling through time, maybe the chunk of earth that you are standing on and some of the air around you goes with you.  Someone has to clean up the mess from all of the people from the future leaving little bits of the present all over the past – these chucks of earth and clouds of air and bits of flotsam are referred to, not ignorantly, as Presents.