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The dark ages



 
 
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  #1  
Old January 3rd 17, 07:03 AM posted to sci.astro.research
jacobnavia
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Posts: 105
Default The dark ages

After the big bang, the gas was too hot to form stars. A time must pass
to cool the universe so that the star formation could begin.

In that period of time there shouldn't be any stars, galaxies or
similar.

The length of time that the "dark ages" has been shrinking lately, in
the beginning of the century it was something like 500 My, but now it
has shrunk to 250-300.

As I have calculated in a previous message, a minimum time of 272
million years (z=12) seemed reasonable to me, to cool the stuff to 35.36
K. Note that temperature in star forming cocoons is only 10K. But big
bang proponents could argue from special conditions, whatever, so I
choose 3 times the temperature where stars can form.

Nobody objected to my previous post, so I can assume that there are no
big errors in those calculations.

So, the incompresible time of dark ages is 272 million years, is that
correct?

The discovery of any galaxy at z=11.8 or higher would definitely
disprove the big bang hypothesis. Is that correct?

Because we have a galaxy at z=11 approx. That is why the really
incompresible length of the dark ages becomes important.

If we wait till the universe cools to (say) 15 degrees the observations
contradict theory. We need too much time, so we can move the cursor till
272 million years but not more.

The whole becomes difficult to visualize with a galaxy of 1e9 solar
masses just after 127 My from the first stars.

And the star population of that galaxy should be really weird since no
star is older than 127 My. That time is very short compared to the life
span of normal stars.

OK we could assume that all stars are super-giant stars that last only a
few million years and explode, but then that population should give a
definite signature in the light of that galaxy.

Do we see that?

If we say that (taking the formation and condensation phase into
account) we have a generation after only 5 million years, that makes for
30 generations at most.

But those are secondary considerations. The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...

Thanks

  #2  
Old January 3rd 17, 07:55 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default The dark ages

In article , jacobnavia
writes:

The length of time that the "dark ages" has been shrinking lately, in
the beginning of the century it was something like 500 My, but now it
has shrunk to 250-300.


When he was an old man, Paul Erdos* said, when asked about his age, that
he was 2.5 billion years old, because when he was young, the age of the
Earth was 2 billion years, and when he was old, it was 4.5 billion.

As I have calculated in a previous message, a minimum time of 272
million years (z=3D12) seemed reasonable to me, to cool the stuff to 35.3=

6
K. Note that temperature in star forming cocoons is only 10K. But big
bang proponents could argue from special conditions, whatever, so I
choose 3 times the temperature where stars can form.

Nobody objected to my previous post, so I can assume that there are no
big errors in those calculations.


First, "seems reasonable to me" is not quantitative enough. Second, the
fact that no-one has contested a usenet post does not prove its
veracity.

So, the incompresible time of dark ages is 272 million years, is that
correct?

The discovery of any galaxy at z=3D11.8 or higher would definitely
disprove the big bang hypothesis. Is that correct?


What is the "big bang hypothesis"? It is the idea that the universe is
expanding from a hotter, denser state, approaching a singularity near
the beginning of the expansion. That's it. What you are talking about
is galaxy formation.

See if you can find an article by Martin Rees entitled "Understanding
the high-redshift universe", which appeared in the (sadly now defunct)
Quarterly Journal of the Royal Astronomical Society about a quarter of a
century ago. It is relevant to your questions.

If we wait till the universe cools to (say) 15 degrees the observations
contradict theory. We need too much time, so we can move the cursor till
272 million years but not more.


At worst, to contradict some theory of galaxy formation, not the idea of
the big bang itself.

But those are secondary considerations. The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...

  #3  
Old January 3rd 17, 07:56 PM posted to sci.astro.research
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Posts: n/a
Default The dark ages

On Tuesday, January 3, 2017 at 1:03:49 AM UTC-5, jacobnavia wrote:
{snip}
Nobody objected to my previous post, so I can assume that there are no
big errors in those calculations.


This is, I submit, a fallacy (the "X, so Y" part).

First, I'm sure many members were like me in spending a lot of time
over the past ~couple of weeks or so on IRL matters ... so it's
likely your previous post was not read by many.

Second, I skimmed that (rather long) post of yours, and just that
quick skim triggered quite a few questions; some of the answers to
those questions may point to "big errors in those calculations".
I'll try to get a chance in the next week or so to read your post
carefully, and write up some of the most pertinent questions I have.

For now, just one comment on what you wrote in this new thread:

The discovery of any galaxy at z=3D11.8 or higher would definitely
disprove the big bang hypothesis. Is that correct?


No, it is not correct.

For starters, we are in the domain of science, not mathematics;
"proof" has no place in science (outside its use of mathematics).
Of course, "disprove" is quicker and easier to write than something
like "robustly shown, quantitatively, to be extremely inconsistent
with all relevant observations and experiments"!

Second, the physical processes which turned a fairly homogeneous
soup of (mostly) dark matter, protons, electrons, hydrogen atoms,
and helium atoms (at z~1100) into a gravitationally bound system
of dark matter, stars, gas, and dust (at z~10) are not yet well
understood, much less accurately modeled.

From my own reading of the relevant literature, I get the impression
that one curious thing is the many possible ways the fairly homogeneous
state at z~1100 could become very inhomogeneous by z~10.
  #4  
Old January 3rd 17, 11:57 PM posted to sci.astro.research
jacobnavia
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Posts: 105
Default The dark ages

Thanks for your answer (and patience) Mr Helbig.

My answers to your remarks below:

Le 03/01/2017 =E0 19:55, Phillip Helbig (undress to reply) a =E9crit :
In article , jacobnavia
writes:


[small snip]

As I have calculated in a previous message, a minimum time of 272
million years (z=3D12) seemed reasonable to me, to cool the stuff to

35.3= 6

[[Mod. note -- Some characters got garbled on the previous few lines. -- jt]]

K. Note that temperature in star forming cocoons is only 10K. But big
bang proponents could argue from special conditions, whatever, so I
choose 3 times the temperature where stars can form.

Nobody objected to my previous post, so I can assume that there are no
big errors in those calculations.


First, "seems reasonable to me" is not quantitative enough. Second, the
fact that no-one has contested a usenet post does not prove its
veracity.


Sure. It was New year's eve and I understand :-)

So, the incompresible time of dark ages is 272 million years, is that
correct?

The discovery of any galaxy at z=3D11.8 or higher would definitely

[[Mod. note -- Garbled characters on the previous line, too. -- jt]]
disprove the big bang hypothesis. Is that correct?


What is the "big bang hypothesis"? It is the idea that the universe is
expanding from a hotter, denser state, approaching a singularity near
the beginning of the expansion. That's it. What you are talking about
is galaxy formation.


Both are very closely related. If there was a "dark ages" period, as big
bang theory supposes, no galaxy can exist during that period.

See if you can find an article by Martin Rees entitled "Understanding
the high-redshift universe", which appeared in the (sadly now defunct)
Quarterly Journal of the Royal Astronomical Society about a quarter of a
century ago. It is relevant to your questions.


Yes, interesting article. He says:
quote
Quasars observers should have a strong motive to push out to still
larger redshifts and thereby constrain and embarrass the theorists more.
end quote

At that time (1993) the most distant quasars were at z approx 5. What
would he say now to a quasar at z=11 ???

More relevant (I think) is this ESA press release:
(http://sci.esa.int/planck/58193-firs...ously-thought/)
quote
In 2015, the Planck Collaboration provided new data to tackle the
problem, moving the reionisation epoch even later in cosmic history and
revealing that this process was about half-way through when the Universe
was around 550 million years old. The result was based on Planck's first
all-sky maps of the CMB polarisation, obtained with its Low-Frequency
Instrument (LFI).
Now, a new analysis of data from Planck's other detector, the
High-Frequency Instrument (HFI), which is more sensitive to this
phenomenon than any other so far, shows that reionisation started even
later =96 much later than any previous data have suggested.
"The highly sensitive measurements from HFI have clearly demonstrated
that reionisation was a very quick process, starting fairly late in
cosmic history and having half-reionised the Universe by the time it was
about 700 million years old," says Jean-Loup Puget from Institut
d'Astrophysique Spatiale in Orsay, France, principal investigator of
Planck's HFI.
end quote

This galaxy at 400 My is then REALLY exceptional...
This galaxy wasn't known in 2015, nobody thought it could exist.


If we wait till the universe cools to (say) 15 degrees the observations
contradict theory. We need too much time, so we can move the cursor till
272 million years but not more.


At worst, to contradict some theory of galaxy formation, not the idea of
the big bang itself.


The logic is very simple he

t=0 Bang (13,700 million years ago)

t= 400 000 years: CMB

Dark ages (no stars)
From t=400000 years to t=XXX

t = 400 My: Full blown bright galaxy with 1e9 stars.

How much is this time "XXX" ?

I thought that it must be around z=12 with a CMB Temperature of around
36K. Please tell me where do you place the cursor.

But those are secondary considerations. The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...


Yeah, you did not answer that question!
  #5  
Old January 4th 17, 09:19 PM posted to sci.astro.research
jacobnavia
external usenet poster
 
Posts: 105
Default The dark ages

Thanks for your answer.
I reply below

Le 03/01/2017 à 19:56, a écrit :
On Tuesday, January 3, 2017 at 1:03:49 AM UTC-5, jacobnavia wrote:
{snip}
Nobody objected to my previous post, so I can assume that there are no
big errors in those calculations.


This is, I submit, a fallacy (the "X, so Y" part).

First, I'm sure many members were like me in spending a lot of time
over the past ~couple of weeks or so on IRL matters ... so it's
likely your previous post was not read by many.


Yeah, I did not think about Christmas/New year stuff. Sorry.

Second, I skimmed that (rather long) post of yours, and just that
quick skim triggered quite a few questions; some of the answers to
those questions may point to "big errors in those calculations".
I'll try to get a chance in the next week or so to read your post
carefully, and write up some of the most pertinent questions I have.


Thank you. It would be interesting to see where those calculations could
be wrong. I used standard formulas, that can't be "as such" wrong, but
maybe I can't use them in this context, I do not know. Those
calculations look correct "to me" of course.

For now, just one comment on what you wrote in this new thread:

The discovery of any galaxy at z=11.8 or higher would definitely
disprove the big bang hypothesis. Is that correct?


No, it is not correct.

For starters, we are in the domain of science, not mathematics;
"proof" has no place in science (outside its use of mathematics).
Of course, "disprove" is quicker and easier to write than something
like "robustly shown, quantitatively, to be extremely inconsistent
with all relevant observations and experiments"!


If a galaxy is found at t262 My it would mean that galaxy formation was
extremely quick, so extremely quick that it is impossible to believe,
excuse me. If a galaxy is found at t=262 My, then star formation must be
pushed even earlier, at a CMB temperature that doesn't allow for star
formation!

Second, the physical processes which turned a fairly homogeneous
soup of (mostly) dark matter, protons, electrons, hydrogen atoms,
and helium atoms (at z~1100) into a gravitationally bound system
of dark matter, stars, gas, and dust (at z~10) are not yet well
understood, much less accurately modeled.


Sure, but you will agree that we can derive the CMB temperature from the
"z" parameter, and arrive at a conclusion about when the gas would be
cold enough to condense into stars. Note that we are NOT in the realm of
"unknown physics" when the universe had only a few planck times age...

From my own reading of the relevant literature, I get the impression
that one curious thing is the many possible ways the fairly homogeneous
state at z~1100 could become very inhomogeneous by z~10.


Sure but that TAKES TIME. Time to cool down the searing hot big bang
gases and time to let the expansion cool the universe to allow star
formation.

My thesis here since several years is that there is NO TIME to build
galaxies in just 137 million years.

Again, thanks for your post.

  #6  
Old January 4th 17, 10:10 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default The dark ages

In article , jacobnavia
writes:

What is the "big bang hypothesis"? It is the idea that the universe is
expanding from a hotter, denser state, approaching a singularity near
the beginning of the expansion. That's it. What you are talking about
is galaxy formation.


Both are very closely related. If there was a "dark ages" period, as big
bang theory supposes, no galaxy can exist during that period.


That's why I suggested the Rees article. People use "big bang" to mean
different things. Does it include nucleosynthesis? Galaxy formation?
A problem is that if some speculative aspect which SOME people consider
to be part of the big-bang paradigm turns out to be not true, some
(usually other) people assume that that somehow invalidates the whole
idea. A somewhat similar example: it now seems that Homo sapiens
sapiens and Neanderthal people interbred; this was previously believed
not to be the case. This is a revision of an idea, but in no way
questions the idea of evolution.

See if you can find an article by Martin Rees entitled "Understanding
the high-redshift universe", which appeared in the (sadly now defunct)
Quarterly Journal of the Royal Astronomical Society about a quarter of a
century ago. It is relevant to your questions.


Yes, interesting article. He says:
quote
Quasars observers should have a strong motive to push out to still
larger redshifts and thereby constrain and embarrass the theorists more.
end quote

At that time (1993) the most distant quasars were at z approx 5. What
would he say now to a quasar at z=11 ???


He's still around, and he hasn't given up on the big-bang theory.

"The highly sensitive measurements from HFI have clearly demonstrated
that reionisation was a very quick process, starting fairly late in
cosmic history and having half-reionised the Universe by the time it was
about 700 million years old," says Jean-Loup Puget from Institut
d'Astrophysique Spatiale in Orsay, France, principal investigator of
Planck's HFI.


Doesn't question the big-bang theory, though; it revises ideas about
reionization.

This galaxy at 400 My is then REALLY exceptional...
This galaxy wasn't known in 2015,


Nothing was known before it was discovered.

nobody thought it could exist.


Can you point me to a refereed-journal paper which says "no galaxy could
exist at 400 My"? Even if you can, it doesn't mean that there is
something wrong with the big-bang theory. If there were nothing new to
be learned, there would be no point in doing science.

The logic is very simple he

t=0 Bang (13,700 million years ago)

t= 400 000 years: CMB

Dark ages (no stars)
From t=400000 years to t=XXX

t = 400 My: Full blown bright galaxy with 1e9 stars.

How much is this time "XXX" ?

I thought that it must be around z=12 with a CMB Temperature of around
36K. Please tell me where do you place the cursor.

But those are secondary considerations. The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...


Yeah, you did not answer that question!


I am not an expert on this. :-| But the answer is, the dark ages are
as long as they are observed to be. I don't think anyone claims to be
able to predict their length from first principles.
  #7  
Old January 4th 17, 10:11 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 273
Default The dark ages

In article , jacobnavia
writes:

If a galaxy is found at t=262 My it would mean that galaxy formation was
extremely quick, so extremely quick that it is impossible to believe,
excuse me. If a galaxy is found at t=262 My, then star formation must be
pushed even earlier, at a CMB temperature that doesn't allow for star
formation!


I don't think anyone has an intuitive grasp of such long time scales nor
of star formation. So, saying that it seems quick to you isn't enough.

Sure, but you will agree that we can derive the CMB temperature from the
"z" parameter,


Yes.

and arrive at a conclusion about when the gas would be
cold enough to condense into stars. Note that we are NOT in the realm of
"unknown physics" when the universe had only a few planck times age...


Right. Still, the exact mechanism by which the first stars formed is
not understood. On what basis do you claim that stars can't form above
a certain CMB temperature?

Sure but that TAKES TIME. Time to cool down the searing hot big bang
gases and time to let the expansion cool the universe to allow star
formation.


Right, but how long, exactly, and based on what? "It seems quick to me"
just doesn't cut it.

My thesis here since several years is that there is NO TIME to build
galaxies in just 137 million years.


Yes, you keep repeating it, but have yet to offer any evidence that
galaxy formation requires some minimum time greater than this.
  #8  
Old January 23rd 17, 04:50 AM posted to sci.astro.research
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Posts: n/a
Default The dark ages

On Monday, January 2, 2017 at 10:03:49 PM UTC-8, jacobnavia wrote:
After the big bang, the gas was too hot to form stars. A time must pass
to cool the universe so that the star formation could begin.=20


The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...=20


It doesn't seem relevant or perhaps even important to me what the
number is. The Big Bang is an idea that the universe explosively
began. But the idea that it originated from a tiny point basically
suggests that our universe originated (if correct) from the interior
of a black hole that breached confinement. Call it a singularity
or whatever, things exploded out of a tiny volume.

But the Big Bang doesn't posit what existed outside of that
singularity. There could have been an entire universe around a
black hole that breached confinement for all we know.

The point is to do the studies and search for the galaxies in the
oldest parts of the universe. And if we can find a bunch of them
in places they should not be able to be, then we will need to ponder
how to modify the big bang to include the new findings.

It's entirely possible that one region of the universe was cooler
than another so that stars and a galaxy could form unusually early.
It's possible a wave of star formation ripped through an entire
cloud of gas, fully forming a massive galaxy within a short period
of time.

But observing and establishing whatever in fact happened, is what
science is all about. For a galaxy to be found prior to some age
of the universe may be suggestive, but that's not proof without a
lot of evidence. =20

Water freezes at 0C. But under high pressure, it requires a lower
temp to freeze. It's possible that star formation in highly
compressed regions could have taken place at higher T than your
estimate.

Time ought to shine some light on all these ideas.

rt
  #9  
Old January 23rd 17, 10:33 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default The dark ages

In article ,
writes:

On Monday, January 2, 2017 at 10:03:49 PM UTC-8, jacobnavia wrote:
After the big bang, the gas was too hot to form stars. A time must pass
to cool the universe so that the star formation could begin.


The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...


It doesn't seem relevant or perhaps even important to me what the
number is. The Big Bang is an idea that the universe explosively
began. But the idea that it originated from a tiny point


Not necessarily; an infinite universe was always infinite, even at the
big bang.

basically
suggests that our universe originated (if correct) from the interior
of a black hole that breached confinement.


What does "breach confinement" mean?

A black hole is a static solution in an asymptotically flat spacetime.
The solutions of the Einstein equation describing the universe are
rather different. There are some superficial similarities, some of
which are basically due to dimensional analysis, but the universe did
not arise from a black hole in any meaningful sense.

Call it a singularity
or whatever, things exploded out of a tiny volume.


That's the main point. Or, more precisely, a given volume today becomes
arbitrarily small looking into the past.

But the Big Bang doesn't posit what existed outside of that
singularity. There could have been an entire universe around a
black hole that breached confinement for all we know.


See above.
  #10  
Old January 24th 17, 10:18 PM posted to sci.astro.research
Martin Brown
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Posts: 1,707
Default The dark ages

On 23/01/2017 03:50, wrote:
On Monday, January 2, 2017 at 10:03:49 PM UTC-8, jacobnavia wrote:
After the big bang, the gas was too hot to form stars. A time must pass
to cool the universe so that the star formation could begin.=20


The important thing is to kindly
tell me if that time (262 My) is correct for the length of the dark
ages...=20


It doesn't seem relevant or perhaps even important to me what the
number is. The Big Bang is an idea that the universe explosively
began. But the idea that it originated from a tiny point basically
suggests that our universe originated (if correct) from the interior
of a black hole that breached confinement. Call it a singularity
or whatever, things exploded out of a tiny volume.


The phrase "Big Bang" was a derogatory term coined by Fred Hoyle to
ridicule the expanding universe hypothesis then supported by Hubble's
observations, early radioastronomy and Einstein-Lemaitre's mathematics.

But the Big Bang doesn't posit what existed outside of that
singularity. There could have been an entire universe around a
black hole that breached confinement for all we know.


There doesn't need to be anything outside though. You are imagining a
spacetime with nothing in it apart from a dense proto universe. The
mathematics of GR permits a solution where at the singularity there is
nothing - no space *OR* time and no "before" either. This is in the
realm of metaphysics since there is no way we could test it. Quantum
effects means that this is almost certainly wrong for sizes less than
the Planck length but we have no testable theories for that era.

I am entrigued by the cyclic possibilities of the Steinhardt-Turok
ekpyrotic (sp?) model of the universe which might yet be validated by
observations and would circumvent the need for Guth's inflation.

The point is to do the studies and search for the galaxies in the
oldest parts of the universe. And if we can find a bunch of them
in places they should not be able to be, then we will need to ponder
how to modify the big bang to include the new findings.


I don't think we are likely to see anything that alters present models
that way. We can already see the relics of the Big Bang back to the
surface of last scattering when the universe first became transparent
and just how very nearly uniform it was at that stage.

It's entirely possible that one region of the universe was cooler
than another so that stars and a galaxy could form unusually early.
It's possible a wave of star formation ripped through an entire
cloud of gas, fully forming a massive galaxy within a short period
of time.


No it isn't. That is already ruled out observationally. The cosmic
microwave background is very uniform - embarrassingly so with only tiny
fluctuations of temperature and density visible in WMAP.

Water freezes at 0C. But under high pressure, it requires a lower
temp to freeze. It's possible that star formation in highly
compressed regions could have taken place at higher T than your
estimate.


Compressing a region of gas without raising its temperature and pressure
is the trick though. There is a limit to how quickly a star can form
given an ambient background temperature. The current models might be
imperfect but they are not likely to be hugely wrong.

--
Regards,
Martin Brown

 




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