AlbertE said:
... given that galaxies are moving away from each other - then there is an overall outer edge shape created by these galaxies.
Albert if you want to gradually get to understand standard expansion cosmology I susect you first need to get rid of the highlighted idea. I don't want to say it's WRONG (today's models are not final and can always be revised, they are just the most reliable accurate picture we've been able to construct so far) but it is a misconception from the standpoint of modern cosmology. It has nothing to do with the way working cosmologists think.
Current models they use to fit observational data to are not that of an explosion outward from some point in empty space.
AlbertE said:
... which of my options would it most look like at this point in time - today - if I were able to hold all the matter in my hand in the shape it had come to form.
Since matter is not supposed to be traveling outwards into empty space, away from some central point, there would not be any "overall edge shape" that it had "come to form".
So you are asking about something that is simply not part of our conception of the universe.
The question is based on a false premise and does not make sense.
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There are ANALOGIES that people use to illustrate expansion with one-dimensional or two-dimensional toy models. They can be very helpful but analogies tend to be imperfect and require care.
One analogy is a CIRCULAR RING with no surrounding space. All existence concentrated in this infinitely thin ring. Galaxies and stars are one-dimensional, little dots and dashes specklend along this ring.
As the ring expands it describes a flaring cone-shape, or a bell shape. The ring represents SPACE and the bell which it describes as it expands is SPACETIME, in this toy analog picture.
that particular analogy doesn't appeal to me personally, but you see picturesque versions of it around and about. Some NASA outreach documents use it as a kind of impressionistic illustration.
Another analogy is where today's space and the galaxies in it are infinitely thin
two-dimensional, like all existence (all space all matter) concentrated in the surface of a spherical balloon.
In cosmology we do not assume there is any "space around space" or any "boundary" or border to space, or any "central point" from which things spread out.
Therefore to get the good from this analogy we must imagine no inside or outside of the balloon. There is no surrounding 3D space, and therefore of course no center. Only the pure infinitely thin surface of the balloon exists. The mental concentration involved in thinking the balloon analogy can take some time to get used to.
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Those are just lower dimensional ("infinitely thin") analogies, that may or may not help you.
The goal is to be able to think of edgeless boundaryless THREE-dimensional space, with no "space outside of space"---i.e. all existence concentrated in this full-bodied 3D space that we experience.
And no center from which it is expanding. And since there is no "outside" it can have no shape as seen from the outside. No person looking from the outside, or "holding it in my hand" as you said.
We experience the expansion and the curvature of this 3D space INTERNALLY, by witnessing large triangles that do not add up to 180 degrees (as they would in a zero curvature space).
We do not stand outside to view the curvature, it is something experienced by creatures within the space. Likewise expansion. We witness it in several ways, not only in the enlargement of wavelengths of light and the cooling of background temperature but also in the curious fact that beyond a certain distance objects actually look LARGER (take up wider angle in the sky) the farther away.
this strange beautiful optical effect of expansion is something to understand. It is as if the ancient sky was smaller and so objects of a given size (e.g. compression waves in a cloud of gas) took up a wider sector of the sky. and so they look bigger than more recent objects the same size would look.
I'm telling you to think of "shape" that is geometry as something experienced from the inside, from within the space that realizes that geometry, that curvature, that expansion.
Geometry and the change it undergoes are not something to visualize from the outside, because there is no outside.
(according to the normal cosmic model that folks use, and fit their observational data to.)
(of course as I think you know there are those more speculative models in which there is a higher-dimensional outside surrounding our space but they aren't needed to fit data to and aren't used in normal everyday cosmology.)
