# B Do we still live in a Big Bang Singularity?

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1. Apr 18, 2017

### ivant6900

My question is very simple but it is something I have been thinking about for some time.

Every time a person needs to have the expansion of the Universe explained or the question "What does the Universe expand into?", people who know a bit about the topic answer that it expands into and onto itself. Then this is swiftly followed by the analogy of an expanding bread dough with raising representing galaxies or a balloon.
This is all good, however it also creates another notion, i.e.:

If the Universe or better said, the Big Bang occurred from a Singularity (i.e. an infinitely dense and small point) and if the expansion of the Universe is into and onto itself rather than outwards into yet another an ever larger space, does that mean that the Big Bang essentially happened within the singularity and as such the entire Universe, as it stands, is still existent only within such Singularity?

I realise that there are people who believe that the Big Bang was referring to the expansion of matter within a preexisting fabric of space. If you are one of those people, please do no bother answering my question. This is aimed at people who believe (as the data suggests) that the Big Bang was indeed about the expansion of space time including any kinds of matter, creating the expanding Universe as we know it.

So again, do we still exist within that initial Singularity? And if we do, how does that redefine our understanding of a singularity and their sizes?

2. Apr 18, 2017

### Staff: Mentor

The singularity did not occur at a single point. It arises because an infinite density is reached and the crucial thing to realize is that this infinite density is reached throughout the entire universe at the same time. So singularity doesn't refer to a single point in this case as it usually does.

No, because we don't exist within regions of space of infinite density.

3. Apr 19, 2017

### ivant6900

Singularity is singularity. The only difference is that in the case of a singularity, e.g. black hole, it is contained in the wider fabric of the spacetime (Universe). If the Universe is all there is, then the singularity that preceded the Big Bang was also all there ever was and essentially a single point.
I think you have misunderstood the point that I was making.

So let's try it again. If the Universe is all there ever has been and it all started with a Big Bang that had been preceded by a singularity that essentially contained everything that led to the current state of spacetime and when the Universe expands but not into another much larger space but itself, it must mean that although it expands into itself creating lawyers upon layers of new space, if it was possible to view it from outside, it would still look like a singularity, i.e. infinitely small....

If anyone has better ideas, please enlighten me

4. Apr 19, 2017

### Bandersnatch

The cosmological singularity is not a part of the big bang model in the same way that 0 is not a part of the interval $(0, 1]$.

5. Apr 19, 2017

### ivant6900

Thank you for your response, however if you reject my assumption with an alternative explanation, please elaborate rather than being vague.

6. Apr 19, 2017

### phinds

We reject your assumption because you do not seem to understand what "singularity" means and are instead taking it to mean something physical. The word "singularity" is just a placeholder for the phrase "the place where the math model breaks down and gives nonphysical results and we dont' know WHAT is/was going on"

7. Apr 19, 2017

### Staff: Mentor

As has already been pointed out, this is not what the actual Big Bang model says.

It isn't, because there is no "outside". It is pointless to make hypotheses that cannot be satisfied.

We're not rejecting your assumption with "an alternative explanation". We're rejecting your assumption as not properly capturing what the actual Big Bang model says.

8. Apr 19, 2017

### Staff: Mentor

A singularity doesn't contain anything. It's simply a discontinuity in the math that we use to calculate the curvature of spacetime. It means that geodesics, the equivalent of straight lines in curved space, abruptly end instead of being continuous. Viewing this as an indication that a singularity contained the entire universe is very problematic. Especially if you think the singularity is a single point. For one, if the universe is infinite in size, then you are trying to take an infinitely-sized space and condense it down to a single point. I know of no way of doing this. If we wind the clock backwards, we see that the density of the universe increases but the size does not (though the size of the observable universe certainly decreases). If I understand things correctly, at some finite time in the past the density goes to infinity while the size of the universe is still infinite.

I admit I'm not an expert in GR or cosmology, so my understanding of the details could be off.

No, I understand what you're saying. What I'm saying is that your view doesn't have anything to do with how scientists actually model the universe.

9. Apr 19, 2017

### acidmatic

There is no one who can tell you what it was before big bang or where its edge lays...

10. Apr 19, 2017

### Staff: Mentor

Assuming "it" means the state and properties of the universe, then yes, we know that.

There's no evidence at this time that any such edge exists.

11. Apr 19, 2017

### rbelli1

This is a very important point. Singularities don't exist as real things. They are simply where math says something meaningless or impossible therefore an indication that the math is incomplete.

Unfortunately pop-sci descriptions often explain these as if the meaningless or impossible stuff actually happens.

BoB

12. Apr 19, 2017

### rootone

We never did live in a big bang singularity.

13. Apr 20, 2017

### lifeonmercury

Do you mean the universe has physical edges?

14. Apr 20, 2017

### phinds

It doesn't matter if he meant that; as Drakkith has already pointed out, it's not true.

15. Apr 21, 2017

### Chronos

Assumes facts not in evidence. We have no observations to suggest a primordial singularity preceded the big event. It is a purely theoretical conjecture.