An infinite and eternal universe

[MigL]

6 hours ago, ProximaCentauri said:

So no way the early universe in its hot, dense state at the very moment of the (supposed) Big Bang could have been infinite at a quantum level? (Eternal) inflation caused infinite expansion? Can you please elaborate?

The Big Bang is not a moment, but a model of the evolution since that 'moment'; the point at which we can no longer regress in time because our theories don't work anymore ( usually taken as the Planck era ).
We only have information about our observable universe, and know that it is finite.
What is outside is causally disconnected and cannot be known.
It could be infinite, and our 'universe' developed from a small part of an infinite, hot dense state. And from these small parts, infinitely many 'universes' developed.
But then all these small parts would not all be in causal contact with each other, could not share information, and might lead to totally different universes. But there are many other possibilities.
That was one of the purposes of the original inflationary model. Before inflation, all parts of it were in causal contact ( they are not now ) and so homogeneity and isotropy were ensured.

Edited April 9, 2020 by MigL

[Strange]

3 hours ago, MigL said:

The Big Bang is not a moment, but a model of the evolution since that 'moment'; the point at which we can no longer regress in time because our theories don't work anymore ( usually taken as the Planck era ).

Important point. The Big Bang is still happening; it was not an event in the past. And especially not the "creation" of the universe.

10 hours ago, ProximaCentauri said:

Though I am not a mathematician and will not pretend to understand any of the maths behind CCC , but I trust someone like Penrose when he says he never liked inflation

It just occurred to me: you do realise that inflation is not the same thing as expansion? It is a hypothesis added to the Big Bang model to address the horizon problem. There are alternative hypotheses (such as cyclic models) but inflation solves several other problems and so is favoured at the moment.

[beecee]

Can I add something here? The BB model of universal/spacetime evolution applies to the observable universe only. If the following is correct that is and I don't see any reason to doubt it......

http://www.astro.ucla.edu/~wright/infpoint.html

 

And of course as mentioned, the BB isn't about how the universe started, just how it evolved from a hot dense state at the quantum/Planck era at t+10-43 seconds.

In my layman's opinion, the biggest bit of evidence the BB has going for it, after the CMBR, is how it fits in nicely with GR. 

[Airbrush]

When I read the title of this discussion "An Infinite and Eternal Universe" the first thing I wonder is if the universe is the same as the big bang?  

The universe may be infinite and eternal, but only if there was something before the big bang. 

Is the big bang the entire universe?  Big bangs could be numerous, if not infinite in number, according to eternal inflation.

Edited January 9, 2021 by Airbrush

[martillo]

On 4/6/2020 at 8:30 PM, ProximaCentauri said:

The universe of dynamical equilibrium. The universe is not expanding. Redshift has been misunderstood - it is not down to the Doppler effect and Hubble himself never even stated that this was so, and treated that idea with skepticism/caution. The universe never had a beginning, it has always existed and always will (eternal) and is infinite in extent.

This second model you are considering must have an alternative explanation for the observed redshift in spite of the Doppler effect. Could it be that the physics' parameters like the "constants" in the fields equations like the electric and magnetic ones have changed through time? which are the considerations against this possibility?

[beecee]

On 4/7/2020 at 9:30 AM, ProximaCentauri said:

Two cosmological models involving the universe as never having had a beginning and never having an end (eternal), and having no boundaries (infinite) are really interesting me:

The Cyclic universe

The universe of dynamical equilibrium.

When I was at school in the fifties, there were three competing models of our universe. They were the BB, Steady State and Oscillating models.

If I remember correctly the BB only arose above the other two as more likely, by a serendipitious stroke of luck when Penzias and Wilson discovered the CMBR.

I also see the fact that science now accepts the BB as the most likely, [despite the religious/creationist connotations]  as a feather in its cap for science and the scientific methodology, in being impartial and going where the evidence took them, despite those connotations. I also believe that these creationists connotations may have been too much for an otherwise great scientist/astronomer in Fred Hoyle, and why he continued to push his Steady State model.

And beside the point I made before in that the BB applies to the observable universe, we also as far as I know, still do not have convincing evidence to show whether the universe as a whole, is infinite or finite.  

[beecee]

Can someone give me more info re the CC [Cosmological Constant] and its relationship with GR?

Was it always a part of GR ? Was Einstein's "greatest blunder" simply the act of giving it a particular value? Or was it just an additional term Einstein added to avoid what GR was telling him? [that is the universe was dynamic which went against the beliefs of the day and showed Albert was actually human] 

[StringJunky]

4 hours ago, beecee said:

Can someone give me more info re the CC [Cosmological Constant] and its relationship with GR?

Was it always a part of GR ? Was Einstein's "greatest blunder" simply the act of giving it a particular value? Or was it just an additional term Einstein added to avoid what GR was telling him? [that is the universe was dynamic which went against the beliefs of the day and showed Albert was actually human] 

AFAIK the CC was his way of preserving a static universe model, which he was comitted to at the time. His blunder was hanging on to his belief, contrary to the evidence: Hubble's work..

Edited January 19, 2021 by StringJunky

[Airbrush]

18 minutes ago, StringJunky said:

AFAIK the CC was his way of preserving a static universe model, which he was committed to at the time. His blunder was hanging on to his belief, contrary to the evidence: Hubble's work..

"Einstein abandoned the concept in 1931 after Hubble 's discovery of the expanding universe. From the 1930s until the late 1990s, most physicists assumed the cosmological constant to be equal to zero.

when did einstein learn cosmological constant was wrong - Bing

[StringJunky]

7 minutes ago, Airbrush said:

"Einstein abandoned the concept in 1931 after Hubble 's discovery of the expanding universe. From the 1930s until the late 1990s, most physicists assumed the cosmological constant to be equal to zero.

when did einstein learn cosmological constant was wrong - Bing

Yes, he conceived the CC to solve his own mathematical issue and abandoned it,  but I think it was later  found to be needed to solve another problem.

Edited January 19, 2021 by StringJunky

[beecee]

9 minutes ago, Airbrush said:

 most physicists assumed the cosmological constant to be equal to zero.

As in zero but still  part of GR as originally formulated?

 

4 minutes ago, StringJunky said:

  but I think it was later  found to be needed to solve another problem.

Dark Energy?