I have googled for the "meaning of universe" where I found the following: "all existing matter and space considered as a whole; the cosmos. The universe is believed to be at least 10 billion light years in diameter and contains a vast number of galaxies; it has been expanding since its creation in the Big Bang about 13 billion years ago."

Now,I have heard about big bang theory which tells that universe was initially a point of infinite density .But in the above definition I see space is also included in the universe. so if the universe was initially a point then what was outside that point? And how this point is expanding if there is nothing outside it? That is why I don't understand the balloon analogy also which is expanding in space. But here the universe itself contains the space according the google definition.

Probably I have this question in my mind because I couldn't visualize how the space meets on itself in 3 dimension like earth's surface does on 2 dimension.


marked as duplicate by jinawee, Kyle Kanos, Brandon Enright, John Rennie, Abhimanyu Pallavi Sudhir Feb 11 '14 at 9:49

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Regarding the meaning of "universe":

Unqualified, the Universe is all there is, was, and will be. In other words, there is nothing that is outside of, independent of, stands apart from, the Universe.

The Universe is commonly defined as the totality of existence

However, it is often the case that "universe" is short for "observable universe":

The observable universe consists of the galaxies and other matter that can, in principle, be observed from Earth in the present day because light (or other signals) from those objects has had time to reach the Earth since the beginning of the cosmological expansion.


Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from us, although many credible theories require a total universe much larger than the observable universe.

Regarding the Big Bang, you ask: so if the universe was initially a point then what was outside that point?

This is a common question and the answer takes some getting used to. The metric expansion of space does not require that there be something 'outside' within which space is expanding.

Regardless of the overall shape of the universe, the question of what the universe is expanding into is one which does not require an answer according to the theories which describe the expansion; the way we define space in our universe in no way requires additional exterior space into which it can expand since an expansion of an infinite expanse can happen without changing the infinite extent of the expanse. All that is certain is that the manifold of space in which we live simply has the property that the distances between objects are getting larger as time goes on. This only implies the simple observational consequences associated with the metric expansion explored below. No "outside" or embedding in hyperspace is required for an expansion to occur. The visualizations often seen of the universe growing as a bubble into nothingness are misleading in that respect. There is no reason to believe there is anything "outside" of the expanding universe into which the universe expands.


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