<p>Krotanix : nobody really knows the answer to this. We have good evidence that the universe is expanding, and we extrapolate this back to the big bang. Then some people say the universe was once the size of a grapefruit. See for example <a href="http://www.physicsoftheuniverse.com/topics_bigbang_timeline.html" rel="nofollow">this</a>. Since WMAP evidence in 2013 suggested the universe is flat, some people have started saying the <em>observable</em> universe was once the size of a grapefruit. And that the universe was always infinite. But this is a non-sequitur, and a non-answer. </p>

<p>Yes,  it looks as if 13.8 billion years space had a much higher density and started expanding. And it may have had a certain volume, so space may have already existed. But nobody knows for sure.</p>

<p>Re your follow-on question, nobody has discovered hollowness or emptiness anywhere in the centre of the universe. The expansion is thought to be like that of a <a href="https://www.google.co.uk/#q=raisin+cake+analogy" rel="nofollow">raisin cake</a> rising in an oven. There's no big hole in the middle.   </p>

CC BY-SA 3.0
2016-01-11T08:14:34.473Z
2016-01-11T08:14:34.473Z
John Duffield
<p>You're right; space did exist. In fact, the universe was infinite in size at the moment of the Big Bang, and it still is. This is because a common misconception is wrong: <a href="https://physics.stackexchange.com/questions/136860/did-the-big-bang-happen-at-a-point">The Big Bang did not happen at a point</a>. Thinking of it like an explosion isn't correct.</p>

<p>You asked in a comment about the multiverse. This is speculative, to say the least. There are some theories involving objects called branes that posit that we are on the surface of some object floating through a higher dimensional "bulk". However, these theories of so-called large extra dimensions have yet to be supported by experimental evidence.</p>

CC BY-SA 3.0
2016-01-04T01:11:16.947Z
Thanks, I'll solve it at some point of my life, If I find a moment to have a coffee and spend an afternoon thinking about it! XD
Felix L.
CC BY-SA 3.0
2016-01-11T08:06:41.160Z
We do not know that _the universe was infinite in size at the moment of the Big Bang, and it still is_. This idea is not supported by experimental evidence.
John Duffield
CC BY-SA 3.0
2016-01-11T21:26:05.023Z
@JohnDuffield The curvature of the universe is nearly zero, and the added assumption of homogeneity means that there can't really be an edge. Put the two together, and evidence shows that if we don't live in an infinite universe, it's certainly very big.
HDE 226868
CC BY-SA 3.0
2016-01-12T13:28:14.310Z
@HDE 226868 : it's an _assumption_ of homogeneity and isotropy. For all you know some guy 46 billion light years away is looking up at the clear night sky wondering why one half is black, or a mirror-version of the other, or something else. We just don't have any evidence for a universe that's a lot bigger than the observable universe, or an infinite universe.
John Duffield
CC BY-SA 3.0
2016-01-04T01:07:02.983Z
2016-01-04T01:07:02.983Z
HDE 226868
<p>Big bang is not an explosion, but an expansion of space and time. Universe had almost infinite density... wait a moment. If it had ALMOST infinite density, it had a certain volume, and thus, space already existed. 
Am I commiting a mistake?</p>

<p><a href="https://astronomy.stackexchange.com/questions/669/what-is-in-the-center-of-the-universe">I had this question after reading this post.</a></p>

CC BY-SA 3.0
2016-01-03T19:31:07.037Z
Very high density does not imply a finite volume. Is that what you're asking about?
HDE 226868
CC BY-SA 3.0
2016-01-03T21:33:13.313Z
Yes. Well as far as I know, density = mass / volume. If density and mass are not infinite, volume must be different from zero
Felix L.
CC BY-SA 3.0
2016-01-03T22:36:48.817Z
Yes, [the Big Bang did not happen at a point](https://physics.stackexchange.com/questions/136860/did-the-big-bang-happen-at-a-point).
HDE 226868
CC BY-SA 3.0
2016-01-04T01:03:37.923Z
Well thanks, now I see! If you could write your last comment as an answer I would accept it :) One last question: may it be (and it might be just speculative) that our universe is a subset of a higher dimensional space? Well I'm pretty sure I am not the first to think about it. Multiverse theory? Just wondering...
Felix L.
CC BY-SA 3.0
2016-01-04T05:02:17.817Z
So let's rewind time a bit, say roughly 1 billion years ago every galaxies and stars must be very close to one another. This time let's rewind the clock all the way... I'll throw in some random number say 14 billion years ago there must be a location in the pre-spacetime that current spacetime is born... Of course pre-spacetime or whatever it is called cannot be detected or can it?
user6760
<big-bang-theory><space-time>
Center of the universe
Felix L.
# Center of the universe

(Asked by: username_0 on 2016-01-03)

Big bang is not an explosion, but an expansion of space and time. Universe had almost infinite density... wait a moment. If it had ALMOST infinite density, it had a certain volume, and thus, space already existed.
Am I commiting a mistake?

[I had this question after reading this post.](https://astronomy.stackexchange.com/questions/669/what-is-in-the-center-of-the-universe)

**Tags:** big-bang-theory, space-time
> **Comments:**
> **username_1**: Very high density does not imply a finite volume. Is that what you're asking about?  
> **username_0**: Yes. Well as far as I know, density = mass / volume. If density and mass are not infinite, volume must be different from zero  
> **username_1**: Yes, [the Big Bang did not happen at a point](https://physics.stackexchange.com/questions/136860/did-the-big-bang-happen-at-a-point).  
> **username_0**: Well thanks, now I see! If you could write your last comment as an answer I would accept it :) One last question: may it be (and it might be just speculative) that our universe is a subset of a higher dimensional space? Well I'm pretty sure I am not the first to think about it. Multiverse theory? Just wondering...  
> **username_2**: So let's rewind time a bit, say roughly 1 billion years ago every galaxies and stars must be very close to one another. This time let's rewind the clock all the way... I'll throw in some random number say 14 billion years ago there must be a location in the pre-spacetime that current spacetime is born... Of course pre-spacetime or whatever it is called cannot be detected or can it?  

---

## 2 answers

### Answer by username_3 on 2016-01-11. Score: 1

Krotanix : nobody really knows the answer to this. We have good evidence that the universe is expanding, and we extrapolate this back to the big bang. Then some people say the universe was once the size of a grapefruit. See for example [this](http://www.physicsoftheuniverse.com/topics_bigbang_timeline.html). Since WMAP evidence in 2013 suggested the universe is flat, some people have started saying the *observable* universe was once the size of a grapefruit. And that the universe was always infinite. But this is a non-sequitur, and a non-answer.

Yes, it looks as if 13.8 billion years space had a much higher density and started expanding. And it may have had a certain volume, so space may have already existed. But nobody knows for sure.

Re your follow-on question, nobody has discovered hollowness or emptiness anywhere in the centre of the universe. The expansion is thought to be like that of a [raisin cake](https://www.google.co.uk/#q=raisin+cake+analogy) rising in an oven. There's no big hole in the middle.


---

### Answer by username_1 on 2016-01-04. Score: 0

You're right; space did exist. In fact, the universe was infinite in size at the moment of the Big Bang, and it still is. This is because a common misconception is wrong: [The Big Bang did not happen at a point](https://physics.stackexchange.com/questions/136860/did-the-big-bang-happen-at-a-point). Thinking of it like an explosion isn't correct.

You asked in a comment about the multiverse. This is speculative, to say the least. There are some theories involving objects called branes that posit that we are on the surface of some object floating through a higher dimensional "bulk". However, these theories of so-called large extra dimensions have yet to be supported by experimental evidence.

> **Comments:**
> **username_0**: Thanks, I'll solve it at some point of my life, If I find a moment to have a coffee and spend an afternoon thinking about it! XD  
> **username_3**: We do not know that _the universe was infinite in size at the moment of the Big Bang, and it still is_. This idea is not supported by experimental evidence.  
> **username_1**: @JohnDuffield The curvature of the universe is nearly zero, and the added assumption of homogeneity means that there can't really be an edge. Put the two together, and evidence shows that if we don't live in an infinite universe, it's certainly very big.  
> **username_3**: @HDE 226868 : it's an _assumption_ of homogeneity and isotropy. For all you know some guy 46 billion light years away is looking up at the clear night sky wondering why one half is black, or a mirror-version of the other, or something else. We just don't have any evidence for a universe that's a lot bigger than the observable universe, or an infinite universe.  

---

