# Difference: Outer Space, Observable Universe, Universe, and Cosmos

### Outer Space

To understand Outer Space, let us first understand and decipher the word space. In Layman’s terms, Space is like a huge seemingly-endless container that engulfs everything and anything that we can see and touch. In short, everything which has physical existence is either a part of space or covered by space around it.

In professional terms, astronomers define space as the finite extension of a three-dimensional region in which ‘all matter’ exists. Now, let’s roll back to outer space again. So, when does space becomes ‘outer’?

Well, Outer Space is just the space which is not under Earth’s influence. Now, where does the influence of Earth Ends?

Although nature is not bound to human-made bounds, restrictions, and limits, we have tried to make a clear distinction of where Earth’s space or Geospace ends. Geospace gradually merges with space outside of it (or outer space). But, for easy distinction between the two, scientists have accepted that outer space begins at about 100 km above the Earth’s surface. This boundary is called the Karman Line.

Outer space is something that exists within or inside the universe.

### Observable Universe

This one is a little confusing. The observable universe is the region of the universe comprising of the matter that can be observed by us. It encompasses the part of the universe from which electromagnetic radiation has had enough time to reach us since the beginning of Cosmological expansion. As the universe is widely believed to be isotropic in nature, distance to the edge of the universe is virtually the same in any direction.

### Universe

This is perhaps the most simple one to comprehend. If I were to make a formula-related analogy for this, I would say, Universe = Observable Universe + Unobservable Universe. But, stick with me, it gets really interesting. As the universe is expanding every passing second, each second we lose a tiny part of our observable universe to the unobservable universe as the edge thrusts out from the ever-mysterious realm.

### Cosmos

Cosmos can be defined in multiple ways. Different people adhering to different beliefs and faith can define Cosmos in surprisingly different ways. Cosmos is much bigger and greater than reality and physicality. The Cosmos we generally use in astronomy and cosmology is the Physical Cosmos, which deals with the physical nature of the Cosmos, and its study is called Physical Cosmology.

Religious Cosmology is the study and body of beliefs that defines cosmos in a mythological, eschatological and religious fashion.

Philosophical Cosmology is the study of the Cosmos in a metaphysical or non-physical sense. It is, conceivably, the broadest kind of cosmology in terms of its scope, and ironically the least explored and understood cosmology of all too.