If the Big Bang theory suggests that the Universe is "expanding" then what is it expanding INTO? I am a software engineer and not an astrophysicist but I want to know if anyone is working on sorting out what exists outside the universe?
So what about outside spacetime? what is there? or shall I assume there are infinite galaxies? and even that is not a satisfying answer. 
I know this question might get closed soon ... but guys please tell me what is there outside the space as we know it? since childhood I have wondered about this. 
Its really a simple question. If we say that we live "inside" a Universe ... then we are objectively saying that there IS something "outside" the universe as well? Am I crazy? What exists there? Is it just empty space? Or what? 
 A: you are not crazy. its a very good (and deep) question but current physical theories don't have any compelling evidence to work about what sort of space, space-time itself would be embedded on, or if such a embedding space could have any physical consequences on our space-time. There is brane-world scenarios where such models are studied, but no evidence  to support anything of this sort so far
from the current factual perspective, current General Relativity assumes space-time is curved due to gravity sources, but to understand curvature mathematically you don't need to assume any outer space, so an expanding space-time in itself is a totally consistent idea mathematically. There is no requirement to postulate an outside, ambient space
A: There exists a mathematical space into which our universe is embedded, but it is mathematical because nothing as we know it can get out of the universe or enter the universe.
After the  big bang the universe is expanding in three dimensions analogous to the way that the surface of a balloon expands in two dimensions: all points on the balloon surface recede from each other and the surface gets large. The balloon surface is not expanding into anything, as far as the points on the balloon go.  In three dimensions all points in our universe recede from each other, having all started from the one point of the big bang.
