Picture Definition and 402 Threads

Which is closest to how you are most apt to think of the universe's timeline: bounded interval with definite beginning and end? half-bounded, with a definite beginning but no end? or with a definite end but no beginning? infinite in both directions, no beginning and no end?

Which of these comes closest to how you picture the expansion of space? As an explosion from a central point with galaxies flying away from the center of the explosion? As the 3D analog of the surface of a balloon? As the 3D analog of an infinite flat sheet of graph paper on which the...