Theoretically, the universe is a sphere surrounded by an incomprehensible field of non-existence.

The universe as we know it is supposed to be infinite. It may be hard to get your head around, but there really can't be a brick wall somewhere, because what would be on the other side of that brick wall. Personally, I believe that the universal boundaries have something to do with dark matter and/or black holes. Many physicists think there might be more than one universe- the concept is called the multi-verse. Maybe black holes or dark matter represent some connection between universes.

i think its not infinate but its circular.....

i dont no, but my personal theory, with no proof besides that ever other answer comes up with anoying unanswerable questions wihch them selves are infinate "whats out side of that", is that the universe is a 4th dimaentional version of a sphere, if uve watched plesant vill, its like how they go to the end of the street and they end right back were they were (sorry about spelling), so if u kept goin ude end up right back here, because the way i see it the only way u can travle in a straight line infinatly on any dimention (without it going into infinate annoying questions) is on a sphericle shape from the dimention above the one it is on, kind of fall in place of ienstiens theory that space is curved, and i imagine a 1 dementional line, traveling along a a 2 dimentional circle, or some 1 drawing a line on a sphere ball. but like i said i have no proof, besides its not an annoying answer (besides what does a 4th dimentional sphere look like... which u cant make in a 3rd dimentional space) i wish sum 1 super smart would figure it out for real, and if im right, atleast make a math equasion for it, because understanding this fully (weather im right or not) would be a huge leap towards teleportation and also if time travel is posible or not

If there was a brick wall,how thick would the brick wall be and where would it end.The answer is the universe is infinite.