Cosmological observations show that the universe is very uniform on the maximally large scale accessible to our telescopes, and the same laws of physics operate in all of its parts that we can see now. The best theoretical explanation of the uniformity of our world was provided by inflationary theory, which was proposed 30 years ago.
Rather paradoxically, inflationary theory also predicts that on a very large scale, much greater than what we can see now, the world may look totally different. Instead of being a single spherically symmetric balloon, our universe may look as a "multiverse", a collection of many different exponentially large balloons ("universes") with different laws of physics operating in each of them.
In the beginning, this picture looked more like a piece of science fiction rather than a scientific theory. However, recent developments in inflationary cosmology, particle physics, and string theory provided strong evidence supporting the new cosmological paradigm. It changes the standard views on the origin and the global structure of the universe and on our own place in the world.