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Quasar found 13 billion years away
Chalky wrote:
So, why wouldn't the thermal radiation from this known expanding cloud of hot transparent gas, after the surface of last scattering, produce, or, at least, contribute to, the observed CMB spectrum? If something re-absorbs that thermal radiation, why does it not simultaneously re-absorb the classically predicted CMBR, which we are taught was only released at this surface of last scattering? Possibly because most of the universe mass/energy at 1+z~1000, T~3000 was 'dark matter/energy' at temperature Td in equilibrium ~T/Td with CMBR at that time just as it is now ~T/Td at 1+z~1, T~3 Richard [Mod. note: four generations of quoted articles snipped -- please do this yourself -- mjh] |
#12
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Quasar found 13 billion years away
On Jun 27, 1:52 pm, "
wrote: On 26 Jun, 10:35, Chalky wrote: .... You have thus missed my real point, which is as follows: Closer to us than the surface of last scattering, we should 'see' successively closer shells of successively cooler gas, which should emit thermal radiation, according to temperature. However, if the temperature increases with redshift, and that radiation is, by definition, redshifted by that redshift, all successive shells should reinforce a black body 2.7K spectrum, when measured in the here and now. Rephrase it slightly - after correction for the red shift, more distant neutral hydrogen clouds, which were essentially in equilibrium with the apparent temperature of the CMBR to which they were exposed, should have higher temperatures. In fact that has been observed. I agree, as does Jonathan Thornberg, apparently, in his posting earlier. However, I doubt that neutral hydrogen is the only thing which obeys the basic rules of thermodynamics. Phillip Helbig's quoted dark matter "bricks" would, I expect, be at thermal equilibrium too. Interesting, this term thermal equilibrium. It means the matter (whatever it is) is emitting and absorbing thermal radiation in equal measure. Each lump of matter has the CMBR from the past, arriving from all directions. Each lump of matter must radiate as much as it absorbs, for thermal equilibrium to be maintained. So, is the theta and phi mapping of the CMBR a direct map of density fluctuations at z=1069? That seems hardly likely once the above described mechanism for maintaining thermal equilibrium in intergalactic space therebetween, is taken into account. Chalky. |
#13
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Quasar found 13 billion years away
In article ,
Chalky wrote: Closer to us than the surface of last scattering, we should 'see' successively closer shells of successively cooler gas, which should emit thermal radiation, according to temperature. I don't really want to get involved in this argument, since I have to moderate it, but here's a hint: since this 'cooler gas', after the epoch of recombination, will be neutral atomic hydrogen, by what emission process will it 'emit thermal radiation'? At what rest-frame wavelength will the radiation appear? At what wavelength would we see it now? 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 |
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Quasar found 13 billion years away
On Jun 28, 8:08 am, Richard Saam wrote:
Chalky wrote: So, why wouldn't the thermal radiation from this known expanding cloud of hot transparent gas, after the surface of last scattering, produce, or, at least, contribute to, the observed CMB spectrum? If something re-absorbs that thermal radiation, why does it not simultaneously re-absorb the classically predicted CMBR, which we are taught was only released at this surface of last scattering? Possibly because most of the universe mass/energy at 1+z~1000, T~3000 was 'dark matter/energy' at temperature Td in equilibrium ~T/Td with CMBR at that time just as it is now ~T/Td at 1+z~1, T~3 Richard Thermal equilibrium considerations (discussed in part with George Dishman) would seem to confirm that the microwave intensity detected now would be the same, either way, but that is not the point at issue. As far as I can tell, the intensity of that radiation released at ~ z=1069 has not been predicted to sufficient accuracy for any confirmatory measurement, in the here and now, to form the basis for justification of the concordance model. And this was certainly not the method employed to derive the WMAP compatible concordance model in practice. It might be of relevance to establish whether the more subtle effect hinted at by my current musings, was encompassed within that more subtle analysis, or not. Chalky |
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Quasar found 13 billion years away
On Jun 28, 10:10 am, Martin Hardcastle
wrote: In article , Chalky wrote: Closer to us than the surface of last scattering, we should 'see' successively closer shells of successively cooler gas, which should emit thermal radiation, according to temperature. I don't really want to get involved in this argument, since I have to moderate it, but here's a hint: since this 'cooler gas', after the epoch of recombination, will be neutral atomic hydrogen, Actually, if the concordance model is correct, it is mostly dark matter. by what emission process will it 'emit thermal radiation'? Since the term "dark", as applied to both energy and matter, is as much a reflection of our lack of contemporary understanding as anything else, the answer to this question must necessarily be speculative. However, if dark matter does not obey the rules of thermodynamics, by emitting thermal radiation, the term "cold dark matter" would be an oxymoron (given initial conditions). At what rest-frame wavelength will the radiation appear? What do you mean by rest frame? The possibilities are infinite. At what wavelength would we see it now? From thermodynamic and logic considerations, black body spectrum. (You can't get any darker than black). From observation, this is centred around a 2.7K black body emission peak. Chalky. |
#16
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Quasar found 13 billion years away
In article ,
Chalky wrote: On Jun 28, 10:10 am, Martin Hardcastle wrote: In article , Chalky wrote: Closer to us than the surface of last scattering, we should 'see' successively closer shells of successively cooler gas, which should emit thermal radiation, according to temperature. I don't really want to get involved in this argument, since I have to moderate it, but here's a hint: since this 'cooler gas', after the epoch of recombination, will be neutral atomic hydrogen, Actually, if the concordance model is correct, it is mostly dark matter. We're talking about the material that might radiate, or affect radiation. That's normal baryonic matter, mostly neutral hydrogen. Non-baryonic dark matter does not directly interact with radiation, practically by definition. However, if dark matter does not obey the rules of thermodynamics, by emitting thermal radiation, the term "cold dark matter" would be an oxymoron (given initial conditions). There's no 'rule of thermodynamics' that says that material -- baryonic or non-baryonic -- has to radiate or interact with radiation. `cold dark matter' vs `hot dark matter' refers to the energy of the (putative) dark matter particles. At what rest-frame wavelength will the radiation appear? What do you mean by rest frame? The possibilities are infinite. `rest frame' is used by physicists to mean `a frame in which the body under discussion is at rest'. From thermodynamic and logic considerations, black body spectrum. (You can't get any darker than black). A black-body spectrum is produced only if radiation is in thermal equilibrium with matter. (There's a common misconception, which can sometimes even persist past undergraduate level, that `thermal radiation' = `black-body radiation' but that's not so.) Since being in thermal equilibrium with radiation requires the material to be optically thick, it's not true of baryonic matter after the epoch of recombination and it's essentially never true of dark matter. So, given this, what contribution would you expect the baryonic matter post-recombination to make to the observed background radiation? Again, you should try to think about the process by which this matter might radiate. 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 |
#17
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Quasar found 13 billion years away
On 28 Jun, 08:10, Chalky wrote:
On Jun 27, 1:52 pm, " wrote: On 26 Jun, 10:35, Chalky wrote: .... You have thus missed my real point, which is as follows: Closer to us than the surface of last scattering, we should 'see' successively closer shells of successively cooler gas, which should emit thermal radiation, according to temperature. However, if the temperature increases with redshift, and that radiation is, by definition, redshifted by that redshift, all successive shells should reinforce a black body 2.7K spectrum, when measured in the here and now. Rephrase it slightly - after correction for the red shift, more distant neutral hydrogen clouds, which were essentially in equilibrium with the apparent temperature of the CMBR to which they were exposed, should have higher temperatures. In fact that has been observed. I agree, as does Jonathan Thornberg, apparently, in his posting earlier. OK, so I think that answers your question above. However, I doubt that neutral hydrogen is the only thing which obeys the basic rules of thermodynamics. Phillip Helbig's quoted dark matter "bricks" would, I expect, be at thermal equilibrium too. Interesting, this term thermal equilibrium. It means the matter (whatever it is) is emitting and absorbing thermal radiation in equal measure. Yes, that relates to another of your posts too. Each lump of matter has the CMBR from the past, arriving from all directions. Each lump of matter must radiate as much as it absorbs, for thermal equilibrium to be maintained. So, is the theta and phi mapping of the CMBR a direct map of density fluctuations at z=1069? That seems hardly likely once the above described mechanism for maintaining thermal equilibrium in intergalactic space therebetween, is taken into account. What we see is specific nebulae in front of the microwave background but of course it takes some care to remove such foreground features and there is always going to be some contamination. The question is to what degree foreground artefacts pollute the measurement. George |
#18
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Quasar found 13 billion years away
On Jun 28, 8:08 am, Richard Saam wrote:
Chalky wrote: So, why wouldn't the thermal radiation from this known expanding cloud of hot transparent gas, after the surface of last scattering, produce, or, at least, contribute to, the observed CMB spectrum? If something re-absorbs that thermal radiation, why does it not simultaneously re-absorb the classically predicted CMBR, which we are taught was only released at this surface of last scattering? Possibly because most of the universe mass/energy at 1+z~1000, T~3000 was 'dark matter/energy' at temperature Td in equilibrium ~T/Td with CMBR at that time just as it is now ~T/Td at 1+z~1, T~3 Interesting point. So the CMB would have precisely the same temperature now, no matter when it originated. C. |
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One final point on CMBR
On Jun 28, 8:08 am, Richard Saam wrote:
Chalky wrote: So, why wouldn't the thermal radiation from this known expanding cloud of hot transparent gas, after the surface of last scattering, produce, or, at least, contribute to, the observed CMB spectrum? If something re-absorbs that thermal radiation, why does it not simultaneously re-absorb the classically predicted CMBR, which we are taught was only released at this surface of last scattering? Possibly because most of the universe mass/energy at 1+z~1000, T~3000 was 'dark matter/energy' at temperature Td in equilibrium ~T/Td with CMBR at that time just as it is now ~T/Td at 1+z~1, T~3 One final point on this subject: George Dishman pointed out some time ago that all radio telescopes radiate heat to the night sky, until thermal equilibrium is reached. Many respondents, including George, have pointed out that any efficient radiator is also an equally efficient absorber, at the same wavelength. Ergo, a microwave dish capable of detecting black body radiation at 2.7 K, is also a 2.7 K black body radiator, whose own radiation is in thermal equilibrium with its own matter. Therefore, we cannot say with any certainty where, and, more importantly, when, the observed CMB came from. |
#20
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One final point on CMBR
In article , Chalky
writes: One final point on this subject: ^^^^^ ??? George Dishman pointed out some time ago that all radio telescopes radiate heat to the night sky, until thermal equilibrium is reached. Everything radiates heat to everything, until thermal equilibrium is reached (in which case it still radiates, but absorbs just as much). Ergo, a microwave dish capable of detecting black body radiation at 2.7 K, is also a 2.7 K black body radiator, whose own radiation is in thermal equilibrium with its own matter. The conclusion doesn't follow from the premises. Assume I have something which is COLDER than the surroundings. It can absorb heat, but is not in thermal equilibrium. Therefore, we cannot say with any certainty where, and, more importantly, when, the observed CMB came from. Are you seriously suggesting this? There are four interesting things about the CMB. First, there is a strong dipole, which is consistent with our motion relative to the bulk of the unuiverse. Second, when the dipole is removed, one is left with a very exact black-body spectrum. Third, the signal is the same from every direction. Fourth, at a very low level, there are inhomogeneities consistent with theoretical predictions. Any alternative model would have to explain ALL four points without any ad-hoc hypotheses. |
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