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4 minutes ago, andrew s said:

Yes the formation of neutral hydrogen let the CMB fee but it was sometime later that stars formed and their UV re-ionized the hydrogen.

Regards  Andrew 

So did re ionisation have any impact on subsequent star formation ?    The Horizon video is no longer available on the BBC iPlayer - odd clips are up on YouTube. It's a shame it was watchable albeit suffering from the  repetitive graphic style of the later Horizon documentaries. 

Jim  

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@Scotti G you have some major misunderstanding of galaxies , gravity and black holes. The spiral form of galaxies is not due to material falling into the centre. A black hole has the same gravita

Well, this thread has been a fascinating lunchtime read! It's also just cost me a bit of money - I've gone and bought a couple of the books mentioned! What an absolutely fascinating pursuit this

What came before the Big Bang? The Long Tick Tick Tick...

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26 minutes ago, saac said:

So did re ionisation have any impact on subsequent star formation ?    The Horizon video is no longer available on the BBC iPlayer - odd clips are up on YouTube. It's a shame it was watchable albeit suffering from the  repetitive graphic style of the later Horizon documentaries. 

Jim  

Simple answer is I don't  know. I will look into my extensive library.  I do know that real data from that era is sparse to say the least.

Regards Andrew 

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1 hour ago, saac said:

I thought that the CMB photons were able to travel unchecked before star formation - the thinning of the fog until it became transparent. Didn't stellar formation then follow ?

 

Yes unchecked, but the "fog" had already just cleared to allw the photons to be unchecked

My (limited and fallable) understanding :
that the time f , at approx. 380,000yrs is called the "time of last scattering" **    because it is when the universe became transparent to photons.  ie. they could travel freely across the universe without bumping into anything (being scatterd by anything) as they were doing in the "fog" of the plasma that existed throughout the universe before that time.

The CMB originated at that time f.
It, the CMB, is visible to us (and anyone else elsewhere !) across and throughout the universe because the photons that constitute it, that background 'noise', are free and able to travel.

ie. the "fog" had already cleared during e to f , just before f,  to allow the CMB to then  be 'seen'.
That CMB noise is thermal noise that started out at 3000K, at f , and has now cooled to 2.7K because of expansion.

** it is also called the "time of recombination" or "of decoupling"
I dont like recombination because that implies that stuff was combined once before and is re- doing it again !,  you see ?

The "dark ages" is the period from f  (well, poetically dark!,  not quite totally dark to human eyes as it still glowed at 3000K for a wee while :) ) until the first stars lit up at time g.

howzat ?

 

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As a deeply religious person I do not agree with this scientific nonsense of their being nothing and then all of a sudden there was a big bang and the universe was created from the void ....

 

Gospel dictates that there was nothing and then God said "let it be" and all of a sudden the universe was created from the void..

 

Er ! .... hold on a moment ?

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Are theory's of the Universe being nothing but a holographic projection still floating about as this would mean that space was never created and only time came out of the big bang and it is this that dictates what we observe?

Alan 

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1 hour ago, andrew s said:

Simple answer is I don't  know. I will look into my extensive library.  I do know that real data from that era is sparse to say the least.

Regards Andrew 

I picked up "At The Edge of Time - Exploring the Mysteries of Our Universe's First Seconds" by Dan Hooper - I think it was following a review in BBC Sky at Night .  Early days with it but so far I like the way the author doesn't just drop statements as received fact but makes a point to cite evidence.   He has an easy to follow style as well which always helps with this type of subject.  Only covers the first few second though - need to wait for the sequel to find out about stellar formation. :) 

Jim 

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3 hours ago, saac said:

So did re ionisation have any impact on subsequent star formation ?    The Horizon video is no longer available on the BBC iPlayer - odd clips are up on YouTube. It's a shame it was watchable albeit suffering from the  repetitive graphic style of the later Horizon documentaries. 

Jim  

This paper seems to show it does https://www.arxiv-vanity.com/papers/1405.5540/

To quote "Reionization heats the gas and drives it out of the shallow potential wells of low mass halos, affecting especially those below a sharp mass threshold that corresponds to a virial temperature of ∼2×104 K at zreion. The loss of baryons leads to a sharp decline in the star forming activity of early-collapsing systems, which, compounded by feedback from early star formation, empties halos of gas and leaves behind systems where a single old stellar component prevails."

Regards Andrew

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53 minutes ago, andrew s said:

This paper seems to show it does https://www.arxiv-vanity.com/papers/1405.5540/

To quote "Reionization heats the gas and drives it out of the shallow potential wells of low mass halos, affecting especially those below a sharp mass threshold that corresponds to a virial temperature of ∼2×104 K at zreion. The loss of baryons leads to a sharp decline in the star forming activity of early-collapsing systems, which, compounded by feedback from early star formation, empties halos of gas and leaves behind systems where a single old stellar component prevails."

Regards Andrew

Thanks for the link Andrew; so it tapped the brakes so to speak :)   I had read that early star formation was aided by the formation of molecular hydrogen which acted to absorb heat giving gravity the leading edge in collapsing the gas clouds.  It's a fascinating subject for sure and relatively accessible but I guess hard won by those who led the way. 

Jim 

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What do people think of the various hologram/simulation hypotheses?  Personally I find them predictable and fatuous. They're predictable because they are just what you'd expect bright people who play too many video games to come up with. They're fatuous because they are not falsifiable in principle, because they throw us into an infinite regression (who made those who made the simulation?) and because they are utterly anthropomorphic.

I would far rather spend my time thinking about the implications of what fragments of reality we see being selected and edited into a narrative by the ways in which we see them.

Olly

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Hi @ollypenrice I agree with your position . It is interesting how the dominant ideas of the time impacts our model of the world. 

After the God controlled Universe  we had the clockwork one following Newtonian mechanics and on into the current field theory models triggered by Faraday and Maxwell.

The rise of information processing has led to serious speculation on informatics  as the basis with ideas about the entropy of a black hole being  related to its area and Archibald  Wheeler's "It from bit".

As for a simulation what does it bring? Only a return to an all powerful presence! It's not for me.

Regards Andrew 

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@andrew s

 

I have no doubt about the universe and its formation even with almost zero understanding.

A question that keeps popping in my mind is: if the big bang happened (I believe it did) what did it bang in? Has there been any progress made with this one?

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17 minutes ago, jetstream said:

@andrew s

 

I have no doubt about the universe and its formation even with almost zero understanding.

A question that keeps popping in my mind is: if the big bang happened (I believe it did) what did it bang in? Has there been any progress made with this one?

It did not bang in anything. The idea of it being an explosion in anything is mistaken.

It was in an initially very hot dense state and the "scale factor" has been increasing ever since causing it to cool and become less dense with time.  There is no external view in which to view the expansion. 

In the current state of the Universe the scale factor increase is seen as the Hubble expansion.  If you measure the distances  between galaxies today you get one number. If you do it again some time later you get a larger distance. It's as if your ruler got shorter but it has not the scale factor has got larger.

It a difficult concept I know but that's it.

Regards Andrew 

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Just now, andrew s said:

It was in an initially very hot dense state

I'm not even sure if my question makes sense- this very hot dense state, was it "everywhere"? or was it "in" anything? I remember Alan Guth saying we don't know what banged, where it banged or what it banged in.

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Got to remember that we can only speculate and theorise as what we are trying to fathom is something that we have had no part in, we think we as a human race know what we are talking about but if truth be known we are only guessing. 

SORCE: Stafford2020. 

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17 minutes ago, jetstream said:

I'm not even sure if my question makes sense- this very hot dense state, was it "everywhere"? or was it "in" anything? I remember Alan Guth saying we don't know what banged, where it banged or what it banged in.

The current model is that the Universe is and always has been spatially infinite (or very close to it). So yes the hot dense state was everywhere. 

Unfortunately,  even respected scientists make "popular" science comments that mislead. Nothing went bang. The term Big Bang was I tended as a put down.

It is correct to say, as discussed above, we cannot go back to t = 0 but we can get very close. Formally t  = 0 is outside our spacetime geometry as are the singularities in a Black Hole.

Regards Andrew 

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2 minutes ago, andrew s said:

t is correct to say, as discussed above, we cannot go back to t = 0 but we can get very close. Formally t  = 0 is outside our spacetime geometry as are the singularities in a Black Hole.

Yes a singularity was explained to me as point where the math breaks down. I guess my concept of infinity (in reference to the dense state) needs work- I think by framing it as an object I'm wrongly imposing spatial limits.

I sure like these threads thats for sure.

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1 minute ago, jetstream said:

Yes a singularity was explained to me as point where the math breaks down. I guess my concept of infinity (in reference to the dense state) needs work- I think by framing it as an object I'm wrongly imposing spatial limits.

I sure like these threads thats for sure.

If I was being pedantic that maths does not break down. The maths is quite comfortable with these points just like it is comfortable with open and closed intervals.

If you take the interval 0 to 1 on the real line you can chose to include 0 and 1 (closed interval) or exclude them (open interval) they has significant differences and no I am not going into them.

What scientists will say us that it is an indication the physical theory breaks down at these points. That is it loses it predictive power.

Regards Andrew 

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5 minutes ago, Macavity said:

Multiverse theory (of certain types) appears to allow multiple bangs (crunches):
https://en.wikipedia.org/wiki/Multiverse
Naievely,  I suppose "t-zero" for OUR bang might be after/before some others.
But I've no idea how... if "multiverse time" works outside our own universe... 😛

There us no evidence for any of these speculations.  When there is please post again.

Regards Andrew 

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