Does the Big Bang model rule out an eternal universe?

[Varsha Verma]

If the universe is infinite then the space is infinite at the big bang and at all times. Whereas an observable part of the universe isn't point like but very tiny at the big bang. In this case the entire universe consists of infinite observable universes, as you can imagine infinite circles on the infinite rubber sheet. One of those observable universes is ours. There may be others where the same discussion happens.

So this is the 'multiverse' you are describing right??

Also, why he "if"?

Because isn't the current model of the universe spatially infinite?? So, why use 'if'??

Does not this mean space was infinite at the big bang also??

If space was infinite at the big bang then even I can understand the stuff.

 

[Dale]

We know that 'space' is a thing. We live in it.

We don’t live in space, we live in spacetime. We have length, width, height, and duration.

Space is a convention regarding how we partition spacetime into space and time. The Big Bang Model makes the assumption that there is a way to partition spacetime into space and time such that at every moment in time the corresponding space is homogeneous, it is the same everywhere (at large scales).

Does not this mean space was infinite at the big bang also??

According to our best estimates, yes. Note that our best estimates do not go all the way back to a singularity, as is often portrayed. That is an extrapolation beyond our best estimates.

 

[Varsha Verma]

We don’t live in space, we live in spacetime. We have length, width, height, and duration.

Space is a convention regarding how we partition spacetime into space and time. The Big Bang Model makes the assumption that there is a way to partition spacetime into space and time such that at every moment in time the corresponding space is homogeneous, it is the same everywhere (at large scales).

According to our best estimates, yes. Note that our best estimates do not go all the way back to a singularity, as is often portrayed. That is an extrapolation beyond our best estimates.

Can you confirm this please. Because this will make my understanding of this big bang subject much clear.

That is, 'space' was 'infinite' at the Big Bang also?

This is what was confusing me all along.

If you scientists say that 'space' was also infinite at the big bang, then even lay people like us can kind of understand it much better.

Just look at any video on Youtube. Almost every on them say that space was created by the big bang. So, that is what is confusing understanding this.

 

[Dale]

Can you confirm this please. Because this will make my understanding of this big bang subject much clear.

That is, 'space' was 'infinite' at the Big Bang also?

Yes, but there are a couple of caveats. First, that is according to our best current model, which does not include a singularity as is often portrayed. Second, the data is right on the edge of a critical point in the model, so future data could easily change the best model from infinite to finite.

Just look at any video on Youtube. Almost every on them say that space was created by the big bang.

This is why the standard on this forum is the scientific literature, not you tube videos

 

[bapowell]

Wouldn't assuming a closed universe contradict the evidence that it expands accelerated which supports a open universe?

No. Why do you think this?

 

[phinds]

Just look at any video on Youtube. Almost every on them say that space was created by the big bang. So, that is what is confusing understanding this.

Varsha, in this and in other posts, you have made it clear that you are getting your "physics" from pop-science and consequently misunderstand almost everything . I empathize with this greatly because that's exactly the way I started out some years back. The problem is that, as you point out in this instance, they ALL get it wrong. They are completely consistent which makes you think they must have it right since they all say the same thing. As you are learning in your posts here, pop science presentations actually have most of it completely wrong (or at best, they state things in very misleading ways).

As has been pointed out, if you want to actually learn science, you have to avoid the pop-science presentations. The TV shows and videos in particular are enjoyable to watch (for simpletons like me anyway) because they have great pictures and graphics and are easy to understand. They just don't represent actual science and you need to get clear on that.

 

[timmdeeg]

So this is the 'multiverse' you are describing right??

No.

Also, why he "if"?

Because the data don't disprove the possibility that the universe is finite, see posts #19 and #64.

Because isn't the current model of the universe spatially infinite?? So, why use 'if'??

See said posts.

Does not this mean space was infinite at the big bang also??

Yes, if the universe is spatially infinite now, it can't be finite at earlier times including the big bang.

If space was infinite at the big bang then even I can understand the stuff.

OK

 

[Dale]

The TV shows and videos in particular are enjoyable to watch

Exactly right. They are entertainment, not education. The pop sci books are also, but not quite to the extreme as the videos

 

[timmdeeg]

No. Why do you think this?

I thought a universe which expands accelerated and thus eternally should be open. Unfortunately only after @PeterDonis corrected that in #38 I remembered Peacock stating in "Cosmological Physics" page 38: "If $\Omega_m > 1$, recollaps is only avoided if $\Omega_v$ exceeds a critical value." According to equation (3.55). I should have known it. And I will look at the Friedmann equations, they should reveal that.

 

[PeterDonis]

We know that 'space' is a thing. We live in it.

Not according to relativity. In relativity, "space" depends on your choice of coordinates.

Btw, do you remember that I said, back in post #34, that you need to be more careful of the claims you make? This is an example. The statement quoted above looks obvious to you--but it's false. Lots of other things that look obvious to you are also false. So you need to stop assuming that anything that looks obvious to you must be true, and stating it as such.

So, are you saying that the 'spacetime' is also a 'thing', a real 'thing'?

No, I'm saying that, in relativity, spacetime is the "real thing", the thing that plays the same logical role that "space" does in pre-relativity physics.

I thought 'spacetime' was just a mathematical concept which was used to explain GR.

Then that's another thing you thought was true that is false.

You say that that the big bang is the 'earliest state' of the 'entire universe', not just the observable universe.

The earliest state for which we have good evidence. Not the earliest state period; as I have already said, we don't know what the "earliest state" was or even if there was one.

But you also say that 'space' was occupying a very small volume.

No, that's not what I said. I did say that something was occupying a very small volume at the big bang, but that thing was not "space". Go back and read my previous posts again, carefully. I have already stated the key distinction you are missing here several times. I'm not going to keep repeating it. You need to read more carefully.

 

[PeterDonis]

the big bang, the earliest observable state

The earliest state we currently have good evidence for. But our ability to collect evidence could improve in the future; we could get evidence for states earlier than the one we currently call the "big bang".

 

[Varsha Verma]

In order to complete the picture I need to know this.

So, at t=0 of the Big Bang, not T=0, that is the start of the universe, we have
(1.) Infinite space - We don't know how this space came to be. Maybe it was 'created' or was there all along.
(2.) Very dense hot point the size of a atom. Since it is 'dense' and 'hot' that means it is 'matter'. Since there is already 'space', this dense point of 'matter' the size of an atom resides inside 'space'.

So now the big bang or more correctly the big expansion occurs.
At ^{10 -33} after t=0 inflation starts and expands that atom size dense point of 'matter' to ^{10 26} times the volume at ^{10 -33} . So now that 'point' of dense hot point of 'matter' is humongous.

At ^{10 -6} protons form and then normal expansion continuous.

What I want to know is, that point like dense hot 'thing' was not 'space', right?? It was 'matter' right?

So, what happened is that a very dense hot point like bit of 'matter' expanded rapidly inside the 'space' (infinite 'space') and this is what we call the 'observable universe' now.

Did I get it right?

PS: I think now that not only the point size dense hot point of matter, but the entire universe started expanding and inflating?

 

[PeterDonis]

In order to complete the picture I need to know this.

Stop looking at pop science articles. The picture you gave does not give times according to our actual best current model. It gives times according to an idealized model that nobody actually uses, which are correlated to the actual best current model by using temperature values. In short, the picture you are using is misleading you. That's what comes of not using valid sources to learn science.

To point out just one big difference: the term "big bang", in our actual best current model, refers to the event marked as "cosmic inflation ends" in the picture. The white dot at the far left of the line in the picture does not correspond to anything in our actual best current model.

at t=0 of the Big Bang, not T=0, that is the start of the universe

No. There is no "start of the universe" in our best current model. As has already been pointed out several times in this thread, our best current model does not include a "beginning" of the universe because we don't know what happened at any such "beginning", or even if there was one: it is possible that the universe has always existed, and that the "big bang" was simply the event that started off the expansion of one particular region of the whole universe, the one we live in. (Note that this region, all by itself, is still not just our observable universe--it's an entire spacetime that is spatially infinite.)

Infinite space

The spacetime that includes our observable universe--what we can see--is spatially infinite according to our best current model, yes.

We don't know how this space came to be. Maybe it was 'created' or was there all along.

Thinking about "how this space came to be" isn't really a good way of thinking about it. "Space" isn't something that has to be "created". A better way to put it is that the spacetime that includes our observable universe might be the only spacetime there is, or it might not; there might be a larger spacetime that includes ours as a portion.

Very dense hot point the size of a atom.

Our observable universe was that size. But the entire universe is still spatially infinite at this time, and all of it is very hot and dense, the same temperature and density as our observable universe was.

Since it is 'dense' and 'hot' that means it is 'matter'.

It depends on what you mean by "matter". It includes all of the fields of the Standard Model of particle physics: not just quarks and leptons, but gluons, W and Z bosons, and photons.

Since there is already 'space', this dense point of 'matter' the size of an atom resides inside 'space'.

Sort of. See my comment above about the entire universe all being very hot and dense.

At 10 -33 after t=0 inflation starts

No. Cosmic inflation comes before the big bang, not after. See my comment above on what the term "big bang" actually refers to. As I said, the picture is misleading you.

and expands that atom size dense point of 'matter' to 10 26 times the volume

No. All of that occurred before the big bang. Our observable universe being the size of an atom, and very hot and dense, occurs after inflation ends.

So, what happened is that a very dense hot point like bit of 'matter' expanded rapidly inside the 'space' (infinite 'space')

No. See above.

 

[Varsha Verma]

No. Cosmic inflation comes before the big bang, not after. See my comment above on what the term "big bang" actually refers to. As I said, the picture is misleading you.
No. All of that occurred before the big bang. Our observable universe being the size of an atom, and very hot and dense, occurs after inflation ends.
No. See above.

Inflation happened BEFORE the big bang?
I am completely flummoxed.

 

[phinds]

I am completely flummoxed.

reread post #76

 

[PeterDonis]

Inflation happened BEFORE the big bang?

Yes. Again, stop reading pop science sources and looking at pop science pictures and watching pop science videos. Any textbook on cosmology will explain our actual best current model properly and will give you the proper definition of the term "big bang".

I understand you might not feel ready to tackle a textbook on cosmology. But that doesn't change the fact that pop science sources are not good sources from which to learn the actual science. If you aren't ready to learn the actual science, then you just need to accept that you aren't yet ready to learn the right answers and be patient until you are. Going to the wrong sources and seeking out wrong answers won't help.

 

[Varsha Verma]

Please see this video of Alan Guth the 'father' of inflation:


I swear I hear Alan Guth say at the beginning that "inflation is a PREQUEL.. ", meaning that it happened 'before'.

But look at the diagram he shows after that. It clearly indicates that that inflation is happening AFTER the big bang.

Surely you can't call 'this' pop science because this is from the horses mouth, the guy who invented inflation.

What is going on here?

 

[nikkkom]

At ^{10 -33} after t=0 inflation starts and expands that atom size dense point of 'matter' to ^{10 26} times the volume at ^{10 -33} . So now that 'point' of dense hot point of 'matter' is humongous.

I think the point when matter was in a form of quark-gluon plasma is the earliest time for which our predictions are semi-accurate.

Before that, the conditions quickly become such that our experiments did not test them yet. Therefore, a depiction of what was happening before "~10^-12 s after BB", and for how long it was happening, is theory-dependent. For example, there could have been quite a bit more time than 10^-12 seconds. Eternal inflation theories, for example, have infinite amounts of time before that.

 

[bapowell]

That's not Alan Guth's diagram, but credits to NASA. He's using the diagram in a popular setting; no cosmologist takes it seriously. The words he uses are what you quoted: "prequel", which is what it is.

Your time would be better spent learning from an intro cosmology textbook rather than debating with experts on this forum.

 

[Varsha Verma]

That's not Alan Guth's diagram, but credits to NASA. He's using the diagram in a popular setting; no cosmologist takes it seriously. The words he uses are what you quoted: "prequel", which is what it is.

Your time would be better spent learning from an intro cosmology textbook rather than debating with experts on this forum.

I am not trying to debate. I am trying understand this stuff.

I am bit shocked that somebody like Alan Guth did not correct the diagram.

 

[Bandersnatch]

I swear I hear Alan Guth say at the beginning that "inflation is a PREQUEL.. ", meaning that it happened 'before'.

But look at the diagram he shows after that. It clearly indicates that that inflation is happening AFTER the big bang.

Surely you can't call 'this' pop science because this is from the horses mouth, the guy who invented inflation.

What is going on here?

There are two meanings of 'big bang' in use. This is an example of the second use of the term 'big bang'.

One use describes expansion from a hot dense state (that's the use @PeterDonis was referring to in his posts).

The other use of big bang refers to the singularity you get if you extrapolate the model of the expanding universe backwards in time far enough. This big bang (singularity) is a feature in the model. It is likely unphysical - i.e. just an artefact of the idealised model - which is why physicsts don't find it terribly interesting, unlike big bang in the first meaning.

Now, one of the things about inflation is that while it describes evolution of the universe in the time before the time described by the big bang phase, it still ends in the same kind of singularity.
So, depending on which meaning of the expression 'big bang' is in use, you can either place it before inflation (the singularity) or after inflation (the expansion from a hot and dense state).
And to make matters more confusing, some people include inflation in the big bang phase.

On this forum, and as far as I'm aware in the academic context in general, the singularity meaning is rarely used. I think this preference is flipped in popular contexts, which is likely what causes the whole confusion.
In any case, it's good to be always aware of which one is being talked about. The context usually makes this clear, once you know to pay attention to it. If you want to be 100% sure everybody understands which one you're talking about, just use the whole phrases: either 'big bang phase' of 'big bang singularity'.

There's a bit more written about the two uses in this blog post:
http://www.einstein-online.info/spotlights/big_bangs.1.html

 

[PeterDonis]

Please see this video of Alan Guth the 'father' of inflation

Since you have refused to heed my repeated advice to stop looking at pop science sources, I have banned you from further posts in this thread.

I am not trying to debate. I am trying understand this stuff.

And you have already been told, multiple times, that the right way to understand this stuff is to stop looking at pop science and start looking at actual textbooks and peer-reviewed papers. Yet you continue to try to gain understanding from pop science and asking questions about it. That is a waste of other people's time.

I am bit shocked that somebody like Alan Guth did not correct the diagram.

You shouldn't be. It is quite common for scientists, in pop science sources, to not exercise the same care that they do in textbooks or peer-reviewed papers, where other experts are checking their work. If you were previously unaware of that, now you know.

 

[Chronos]

The big bang is often confused with describing the beginning of the universe, for which it was never intended. It only represents the beginning of our ability to describe the universe.

 

[Dale]

I am completely flummoxed.

That is a common side effect of skipping the prerequisites.

 

[rootone]

Bring on the ghost of Fred Hoyle. All of this 'big bang' stuff started because of a joke he made