I would just like to ask a very elegant question.
What is the shape of the universe?
I believe most cosmologist think it's spatially flat. Also the universe could as well be spherical shaped.
But see Shape of the Universe
(The present Wilipedia article to which I have given a permanent link looks reasonable enough)
Nexus555 is correct, the present opinion within the community is the WMAP data is consistent with a flat universe, although there is a statistical preference for a slight over-closure-density, which would make it just spherical.
The basic answer is that nobody knows. The universe appears to be locally flat, but on scales much larger than the horizon size, it could have any of a large number of shapes.
What I think is that, the universe started with a big bang right? Now, let us take the big bang to be similar to a normal explosion. Then, after the big bang, the matter and energy(or for that matter the universe) would have spread out symmetrical about every axis through the point of big bang singularity, thus giving the universe the shape of a sphere, which is now expanding.
Not a normal explosion
As any good cosmology book, even popular ones, will tell you: the big bang cannot be similar to a normal explosion! So forget that notion, it will only lead you further from understanding. Rather study what the current accumulated wisdom says.
unless some other force limits a given direction
all directions should be equal
so it should be round unless something is changeing it!
And that would be "round" in how many dimensions? Can you still call it a sphere if it has 11 dimensions?
And there's no rule that says the scale of those dimensions are the same.
You may perhaps call our observable universe "approximately round", but it is only speculation as to what lurks far beyond that observable horizon!
Depends which dimension you are looking in.
3 dimensions: Sphere
4 dimensions of movement : (Feels more like a flat plane)
That only works if you assume the BB occured inside some sort of preexisting space. According to the mainstream model, the BB created not just energy and mass, it also created all the spacetime dimensions as well. Without an external point of reference, shape is a meaningless concept.
"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the drug store, but that's just peanuts to space."
from The Hitchhiker's Guide to the Galaxy, Douglas Adams
What is flat is not the space but the space-time!
Space-time can be seem as a sphere with positive or negative curvature and flat, just to speak of the most popular space-time geometries.
Actually, it is space that is flat. In other words, ordinary Euclidean geometry should work in the universe, even on horizon scales. Spacetime is necessarily curved in general relativistic big bang models.
Right! I just wanted to point out the meaning of a flat universe. Flat doesn t mean that the shape of the universe is a flat disc.
Quite right. It can be confusing, since our usual notion of flat is in two dimensions.
It looks like the question was about the SHAPE of the universe but everybody here is discussing its GEOMETRY. The flat geometry can be attributed to different shapes. For example, a sphere of infinite radius has a flat geometry, but still it is a sphere (inlike a torus or a tea pot)
This is still geometry - it's just not Euclidean geometry.
I thought that geometry and topology are concerned with different questions. Of course, the geometry of the universe might be Euclidean or non-Euclidean but this does not liberate us from the question about its shape.
I'm a retired mathematician. In my whole life I never heard of a "sphere of infinite radius"
You are using words in a confusing way. There is no such thing as a sphere of infinite radius---such a thing would not be a sphere
You can define a limit as R -> infty, but the limit is not a sphere.
I see no clear distinction between discussing the geometry of space and discussing the shape.
In NEITHER case would one be merely discussing the topology. If you simply want to talk about the topology of space, then please don't call it the "shape".
that is another confusing use of words and will just muddy the discussion
You seem to be slinging words around without a clear understanding. When one asks about the geometry of space one is not asking "Is it Euclidean or non-Euclidean?"
there are a vast range of different geometries, each defined by a metric (a distance function).
when one asks about the geometry (which is the same as asking about the shape) one is asking about the METRIC.
It is not as if there were just two geometries "Euclidean and non-Euclidean"
Separate names with a comma.