The study of the cosmos as a whole or cosmology has drastically changed within the last century. With the advent of the General Theory of Relativity and discoveries made by astronomers such as Edwin Hubble as early as 1920s, cosmology became a much more distinct science than astronomy.

Two important topics that revolutionized cosmology are inflationary cosmology and quantum cosmology (applying the laws of the quantum physics to understand the whole universe).

The standard models of cosmology — the big bang theory without the inflationary theory — had to suffer from the three problems, namely, the smoothness problem, the horizon problem and the flatness problem. The first problem asks why the matter is uniformly distributed in the universe. The second problem concerns the large-scale uniformity of the observable universe. Finally, the third problem asks why the universe is close to being spatially flat.

However, with the introduction of Inflationary Cosmology in 1970s, cosmologists were able to explain all of the three problems of the standard cosmology.

According to inflationary cosmology, the size of the universe expanded exponentially to an extremely huge number (10^{60}) of its original size. This happened in a very short time from 10^{-35} to 10^{-32} seconds after the big bang.

Today cosmologists work with some of the most interesting concepts such as black holes, wormholes, dark matter and dark energy. They also deal with some of the most intriguing and yet fundamental questions about the universe such as:

- What is the overall shape and size of the universe?
- How old is the universe?
- What is the fate of the universe?
- Can physics describe what was happening before the big bang?
- What happens to the notion of Space and Time before big bang?