B Does the Big Bang model rule out an eternal universe?

[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