|
|
Thread Tools | Display Modes |
#21
|
|||
|
|||
New problems for current cosmology
In article ,
Robert L. Oldershaw wrote: Ok. When theorists tell us what happened within the first 10^-30 sec after the Big Bang, are they talking science, or are they talking something else. Does any modeling of what went on before recombination qualify as science? If so, where exactly is the line between untestable speculation and testable science? Of course they're talking science. We have ample evidence that the universe was hotter, denser and younger in the past, that galaxies and the CMB evolve, and so on. One can take the laws of physics known in the lab and say: what happens if we run the theory governing the evolution of the universe back from the current observational limits? What does that predict for the properties of the universe now? If the answer is that it predicts something that is not observed, something is wrong with the observations or the theory (either the local laws of physics don't apply or you are not doing the extrapolation correctly) and that is telling you something. Big Bang nucleosynthesis is a good example of this; there's no way of directly observing it happening but it must have done so if the BB model is correct, and the theoretical predictions for primordial elemental abundances agree well (on the whole) with reality, suggesting that (a) we understand the relevant local laws of physics and (b) the extrapolation to those times works well. Clearly as one extrapolates to earlier and earlier times there comes a point where we don't actually know the relevant fundamental physics very well from terrestrial observations, but it's still interesting to think about, because you might find that certain classes of model make predictions (say, 'the universe contains no matter') which are clearly at variance with observation, and then you have constrained fundamental physics without having to carry out an experiment at the required energy. Well.... don't other readers have thoughts on this question? I would really like to hear from people who accept the something-from-nothing beginning of the whole shebang. Surely these people are out there because it is the prevailing story one reads in Nature, Sci Amer., NYT, ..., and from all the luminaries who are dutifully quoted in the media. The sensible position, supported by the observations of the CMBR, of BBN and of the evolution of galaxies, is that the Universe went through a phase where all matter contained in the currently observable universe was extremely hot and dense and has been evolving from those initial conditions ever since. There is not, and I think there is never likely to be, any evidence to say for sure what happened before that. Whether it all sprang into being ex nihilo or not is therefore not a scientific question, so it's not one I personally lose any sleep over. (Note that people who say 'The universe *began* in the Big Bang' or '*began* in a phase where all matter was extremely hot and dense' are simply using a definition of 'began' to mean 'for practical purposes, began' rather than taking a side on this question. Creation ex nihilo is not assumed.) Martin -- Martin Hardcastle School of Physics, Astronomy and Mathematics, University of Hertfordshire, UK Please replace the xxx.xxx.xxx in the header with herts.ac.uk to mail me |
#22
|
|||
|
|||
New problems for current cosmology
Le 28/09/2015 05:10, Jos Bergervoet a écrit :
Well, at least the "soup of subatomic particles" phase did not take too much of the total time in this process, I would expect. In another message (in this same thread) I calculated that the CMB is too hot for star formation until z=20 at least, i.e. 180 million years. Since we already see galaxies at z=11 that leaves around 240 million years to form a galaxy so big that we can see it through 13.2 billion years!!! But this is no problem for BB theory OF COURSE! To see the problem please read: arXiv:1506.01377v1 [astro-ph.GA] 3 Jun 2015 THE IMPOSSIBLY EARLY GALAXY PROBLEM The authors try to justify BB theory for galaxies up to z=8. Now, with galaxies at z=11 the justifications falls down, but it is a good introduction to the problem you do not want to see. [[Mod. note -- I'm not confident that we understand star formation today, never mind star formation in the early universe, well enough to rule out stars forming before z=20. I am fairly confident that as of today, we have precisely zero (published) observations of star formation at z15 (for example). -- jt]] |
#23
|
|||
|
|||
New problems for current cosmology
In article ,
jacobnavia writes: arXiv:1506.01377v1 [astro-ph.GA] 3 Jun 2015 THE IMPOSSIBLY EARLY GALAXY PROBLEM A key phrase in the Abstract is "if halo mass to stellar mass ratios estimated at lower-redshift continue to $z \sim 6-8$...." That's certainly a reasonable assumption to start exploring, but I don't see why anyone would be surprised if it turns out to be false. I've mentioned http://xxx.lanl.gov/abs/1504.00005 here before. [[Mod. note -- lanl.gov urls for the arxiv have been obselete for many years now. The current url is http://arxiv.org/abs/1504.00005 and the paper is Finkelstein et al, "An Increasing Stellar Baryon Fraction in Bright Galaxies at High Redshift" -- jt]] -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#24
|
|||
|
|||
New problems for current cosmology
[[Mod. note -- I have manually rewrapped over-long lines. -- jt]]
On 10/4/15 10/4/15 12:08 PM, jacobnavia wrote: In another message (in this same thread) I calculated that the CMB is too hot for star formation until z=20 at least, i.e. 180 million years. Since we already see galaxies at z=11 that leaves around 240 million years to form a galaxy so big that we can see it through 13.2 billion years!!! But this is no problem for BB theory OF COURSE! To see the problem please read: arXiv:1506.01377v1 [astro-ph.GA] 3 Jun 2015 THE IMPOSSIBLY EARLY GALAXY PROBLEM The authors try to justify BB theory for galaxies up to z=8. Now, with galaxies at z=11 the justifications falls down, but it is a good introduction to the problem you do not want to see. [[Mod. note -- I'm not confident that we understand star formation today, never mind star formation in the early universe, well enough to rule out stars forming before z=20. I am fairly confident that as of today, we have precisely zero (published) observations of star formation at z15 (for example). -- jt]] Is there an implicit assumption that galaxies are formed by stars? It seems to me that galaxies are formed by mass, and aggregation on the galactic scale can proceed even while the gas that will form the stars has not yet done so. Tom Roberts |
#25
|
|||
|
|||
New problems for current cosmology
On Thursday, October 8, 2015 at 11:17:17 AM UTC-6, Tom Roberts wrote:
[[Mod. note -- I have manually rewrapped over-long lines. -- jt]] On 10/4/15 10/4/15 12:08 PM, jacobnavia wrote: In another message (in this same thread) I calculated that the CMB is too hot for star formation until z=20 at least, i.e. 180 million years. Since we already see galaxies at z=11 that leaves around 240 million years to form a galaxy so big that we can see it through 13.2 billion years!!! But this is no problem for BB theory OF COURSE! To see the problem please read: arXiv:1506.01377v1 [astro-ph.GA] 3 Jun 2015 THE IMPOSSIBLY EARLY GALAXY PROBLEM The authors try to justify BB theory for galaxies up to z=8. Now, with galaxies at z=11 the justifications falls down, but it is a good introduction to the problem you do not want to see. [[Mod. note -- I'm not confident that we understand star formation today, never mind star formation in the early universe, well enough to rule out stars forming before z=20. I am fairly confident that as of today, we have precisely zero (published) observations of star formation at z15 (for example). -- jt]] Is there an implicit assumption that galaxies are formed by stars? It seems to me that galaxies are formed by mass, and aggregation on the galactic scale can proceed even while the gas that will form the stars has not yet done so. Tom Roberts It appears that the Milky Way is about 9 Gyr old, but there are a few stars within it that are much older: http://phys.org/news/2007-05-galacti...ion-years.html http://www.cnn.com/2014/02/12/world/...tar/index.html http://adsabs.harvard.edu/abs/2013ApJ...765L..12B So some stars must have formed before galaxies. It appears that our galaxy grew from older star formations, but its original structure (as well as those it ate) may well have formed from an accretion disk. Gary |
#26
|
|||
|
|||
New problems for current cosmology
Le 08/10/2015 19:17, Tom Roberts a écrit :
Is there an implicit assumption that galaxies are formed by stars? It seems to me that galaxies are formed by mass, and aggregation on the galactic scale can proceed even while the gas that will form the stars has not yet done so. 1) Galaxies are formed by mass. We agree on that. 2) To be able to see a galaxy it must SHINE. I hope we agree with that too. 3) To be able to shine, a galaxy must have stars. So, if we see a galaxy at z=11, 420 Million years after the supposed big bang, that galaxy must shine, and shine considerably, since we are able to see it 13.200 million light years away... So, if that galaxy exists with so many stars that it can shine through all that distance it must have started to make stars EARLIER. If the CMB in the first 180 million years is too hot to form stars, (CMB temperature is bigger than 50 kelvins) that leaves 420-180 --240 million years to build that galaxy. You can start arguing that in those times stars would form somehow anyway at 100 million years after the supposed bang or even earlier, that makes you gain very little. Instead opf 240 Million years you could have 340, what is actually almost the same at this scales. |
#27
|
|||
|
|||
New problems for current cosmology
On 10/11/15 4:39 PM, jacobnavia wrote:
Le 08/10/2015 19:17, Tom Roberts a écrit : Is there an implicit assumption that galaxies are formed by stars? It seems to me that galaxies are formed by mass, and aggregation on the galactic scale can proceed even while the gas that will form the stars has not yet done so. 1) Galaxies are formed by mass. We agree on that. 2) To be able to see a galaxy it must SHINE. I hope we agree with that too. 3) To be able to shine, a galaxy must have stars. So, if we see a galaxy at z=11, 420 Million years after the supposed big bang, that galaxy must shine, and shine considerably, since we are able to see it 13.200 million light years away... So, if that galaxy exists with so many stars that it can shine through all that distance it must have started to make stars EARLIER. If the CMB in the first 180 million years is too hot to form stars, (CMB temperature is bigger than 50 kelvins) that leaves 420-180 --240 million years to build that galaxy. You can start arguing that in those times stars would form somehow anyway at 100 million years after the supposed bang or even earlier, that makes you gain very little. Instead opf 240 Million years you could have 340, what is actually almost the same at this scales. Logic dictates the possibility of a much colder phase than CMBR thermally distinct from CMBR as the source medium for galactic formation. |
#28
|
|||
|
|||
New problems for current cosmology
On 10/8/2015 12:17 PM, Tom Roberts wrote:
[[Mod. note -- I have manually rewrapped over-long lines. -- jt]] On 10/4/15 10/4/15 12:08 PM, jacobnavia wrote: In another message (in this same thread) I calculated that the CMB is too hot for star formation until z=20 at least, i.e. 180 million years. Since we already see galaxies at z=11 that leaves around 240 million years to form a galaxy so big that we can see it through 13.2 billion years!!! But this is no problem for BB theory OF COURSE! To see the problem please read: arXiv:1506.01377v1 [astro-ph.GA] 3 Jun 2015 THE IMPOSSIBLY EARLY GALAXY PROBLEM The authors try to justify BB theory for galaxies up to z=8. Now, with galaxies at z=11 the justifications falls down, but it is a good introduction to the problem you do not want to see. [[Mod. note -- I'm not confident that we understand star formation today, never mind star formation in the early universe, well enough to rule out stars forming before z=20. I am fairly confident that as of today, we have precisely zero (published) observations of star formation at z15 (for example). -- jt]] Is there an implicit assumption that galaxies are formed by stars? It seems to me that galaxies are formed by mass, and aggregation on the galactic scale can proceed even while the gas that will form the stars has not yet done so. Tom Roberts There appears to be some debate about which came first in galaxy formation ... the super massive black hole or the stars that form the structures we see today. If, in fact, the black holes came first then, it seems to me, the first galactic light would come from the accretion disk and not from stars. A quasar shining through the mass that will eventually form the stars of the galaxy. I'm not sure how visible that would be from here now but I can see how that might initiate a bulge forming starburst very quickly. |
#29
|
|||
|
|||
New problems for current cosmology
Le 13/10/2015 06:32, Richard D. Saam a écrit :
Logic dictates the possibility of a much colder phase than CMBR thermally distinct from CMBR as the source medium for galactic formation. I have turned this sentence in many ways but I can still not make much sense of it, sorry. How can a colder phase exist if the CMBR is by definition coming from all directions of space? How can this colder phase insulate itself from the CMBR radiation? Note that after the supposed bang there shouldn't be any dust around that could shield a portion of the universe from the CMBR. The condensation of the very first stars must have happened without the protection of dust clouds that cool the gas and favor condensation into stars. [[Mod. note -- I think the whole topic of a "much colder phase than the CMBR" falls under our newsgroup charter's prohibition on "excessively speculative" material, and henceforth I'm going to apply that prohibition rather more strictly than I have in the recent past. In particular, unless there are new and not-excessively-speculative ideas or data introduced, I think this posting is a good place to end the discussion of this topic. -- jt]] |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
current status of the horizon problem in cosmology | Phillip Helbig---undress to reply | Research | 8 | May 14th 11 07:34 PM |
CDM Cosmology (was formation of dwarf galaxies in CDM cosmology) | Nicolaas Vroom | Research | 3 | February 2nd 10 11:53 PM |
Problems with Problems With The Orion Spacecraft #9: Stress | bombardmentforce | History | 63 | November 1st 05 01:14 AM |
Problems with Problems With The Orion Spacecraft #6 - Air Force Funding | bombardmentforce | History | 40 | October 30th 05 01:20 AM |
Current Space Station Problems | ElleninLosAngeles | Space Shuttle | 0 | October 24th 03 05:21 AM |