Full Idea
Four-dimensionalism may be formulated as the claim that, necessarily, each spatiotemporal object has a temporal part at every moment at which it exists.
Gist of Idea
4D says each spatiotemporal object must have a temporal part at every moment at which it exists
Source
Theodore Sider (Four Dimensionalism [2001], 3.2)
Book Reference
Sider,Theodore: 'Four Dimensionalism' [OUP 2003], p.59
A Reaction
If there were tiny quantum gaps between temporal parts, that would presumably ruin the story. On this view an object has to be a 'worm', to be the thing which has the parts.