A missile is launched from its silo, below the surface of the earth. It reaches the surface and keeps going.
If the universe is like a sphere can something go beyond its boundary?
If the universe is expanding what is it expaninding into?
Imagine a two-dimensional universe - Flatland - there is no 'up' or 'down', only the four compass directions - objects in this universe have no height, only length and breadth. The property 'height' is meaningless - there is no direction in which to measure it.
That Flatland universe can be:
-Infinite and endless (it extends without end in all possible directions)
-Finite, with an end (it stops in one or more direction, in which case
something must exist beyond the end.
But also:
-Finite and endless. The fabric of the 2D universe itself is warped so as to represent the surface of a sphere or toroid - it's still only two-dimensional, as far as the inhabitants are concerned - they can't leave the 2D surface, or see outside of it, but if they travel far enough in one direction (which they experience as a straight lne) they return to the place they started.
That's not too hard to visualise, because we live in three spatial dimensions, so can easily picture a flat surface being warped into a spherical one - but our three-dimensional perspective also makes it difficult to visualise being limited to only two dimensions - we ask what is inside and outside the sphere - but for the inhabitants of WarpedFlatland, there simply isn't any such direction as
inside or
outside the sphere, because those directions equate to up and down, which don't exist in a 2D world.
OK, now, the same thing is logically possible with our own universe of three spatial dimensions - it could be warped so as to join back up with itself, but not warped through any of the three spatial dimensions we can experience. Finite in size, but boundless in that it has no edges we could ever encounter.
This idea isn't new, or even slightly controversial or provocative to cosmologists, and is bread and butter to mathematicians who know anything about topology. It might be a
wrong idea, but it isn't a strange one.