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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
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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
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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
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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! |
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The dark ages
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#6
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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
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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. |
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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
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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
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The dark ages
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