Have you ever wondered ,where did our Universe come from?, what it may look like?, Millions of stars galaxies, where does it end?,even if we imagine that Universe have a boundry what lies outside this boundry? To answer all these or to atleast get a glimpse of idea about the world around us , first we need to know some of the basic concepts of astrophysics.
The most important one is “Principle of cosmology”. Its just an idea that states that on a very large scale, ‘universe is both isotropic and homogeneus’. These two terms have a special meaning to cosmology. Isotropy means there is no special direction in the universe and homogeneous means there is no special place in the universe. Even though these two definations sound same, they describe very different properties of the universe.For example isotropic universe means when veiwed on large scale, universe looks the same in all direction by a particular observer and homogeneity means average density of matter is same in all places and universe is fairly smooth on large scale.
Notice that it is clearly not applied for the smaller scales like size of earth , our solar systems or even on the scale of our galaxies. this principle is true only on the scales of millions of light years in size. Not only the universe ,bigger than the portion we could see , it is bigger than the portion we can ever see. So it is hardly possible for us to have an exact proof of this principle , but based on many observable data homogeneity and isotropy of universe is beleived by everyone.
One of the best implication of this principle is that it gives the idea of centreless universe.It means that there is no centre to the universe. So where is the place of birth of the universe? Since universe has no centre there is no particular place at which bigbang may have occured, it might have occured anywhere in the universe. Empedocles says the same in a best way , that is “God is an infinite sphere ,whose centre is everywhere and circumference nowhere”.
Corollory to the cosmological principle is that physical laws are same everywhere in the universe, that is laws which are applied here on Earth , same can be applied anywhere else in our universe.We have known alot about our universe, but one of the fascinating cosmic riddle of all time is that , is there any edge to the universe? By defination , all the charecteristics of universe must face the fact that universe has to contain the properties of everything .Thus the term edge says that there exist something which is not contained in the universe and invoking the different laws to this outside universe is inconsistent. From this we can say that Universe is boundless. Although this is the simplest solution, it still remains as a mystery!