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Uh, Oh: BICEP2 Results In Jeopardy?
In principle, suppose that I say:
The CMB is perfectly homogeneous, and all "imperfections" whatever is discovered is the effect of a foreground object. Not only BICEP2 but all those "wrinkles in the face of god" etc. All those are just foreground objects. The CMB is perfect. The perfect emission curve of a black body at around 2.7 K. All "wrinkles" are foreground objects. jacob [Mod. note: I charitably interpret this as asking 'why is this not true?' rather than stating 'this wisdom has been revealed to me'. --mjh] |
#2
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Uh, Oh: BICEP2 Results In Jeopardy?
In article , jacob navia
writes: In principle, suppose that I say: The CMB is perfectly homogeneous, and all "imperfections" whatever is discovered is the effect of a foreground object. This is simply not true. Essentially all of the features in the CMB spectrum were calculated theoretically before they were observed. Foreground contamination is only a small part. Add to this the fact that the cosmological parameters derived from fitting these theoretical predictions to the observed power spectrum results in the same cosmological parameters derived by other means and the case is very convincing. If you want to ascribe all observed features to foreground objects, then you have to explain the extraordinary coincidence that the shape of the power spectrum corresponds to theoretical expectations and also explain why the theoretical expectation is not expressed in your perfect CMB. |
#3
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Uh, Oh: BICEP2 Results In Jeopardy?
Le 18/05/2014 09:20, le moderateur a ecrit:
[Mod. note: I charitably interpret this as asking 'why is this not true?' rather than stating 'this wisdom has been revealed to me'. --mjh] In principle CMB is the light when the universe "become transparent", i.e. is the farthest light you will ever see. It is impossible to prove that ANY perturbation is not due to a foreground object since it is impossible to PROVE that there ISN'T some foreground object that could be incredibly far away from us! Basically it amounts to prove that you are sure of the composition of a line of sight up to the beginning of the universe, an impossible task. I thank you for your charity and I promise to make my best to avoid PRESSING THE SEND BUTTON TOO SOON!!! :-) |
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Uh, Oh: BICEP2 Results In Jeopardy?
In article , jacob navia
writes: In principle CMB is the light when the universe "become transparent", i.e. is the farthest light you will ever see. It is impossible to prove that ANY perturbation is not due to a foreground object since it is impossible to PROVE that there ISN'T some foreground object that could be incredibly far away from us! True. It is also possible that we are living inside some literal celestial sphere in a sort of cosmic Truman Show and everything we think we observe is actually cleverly crafted input on the part of our masters. It is possible that God and/or the Devil exists and has deceived us. It is possible that we are Boltzmann brains, or living in a simulation. It is possible that everything we see, including false memories, arose 1 second ago in a random fluctuation. It is possible that you are dreaming. The common theme he the usual interpretation is MUCH more probable. |
#5
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Uh, Oh: BICEP2 Results In Jeopardy?
In article ,
jacob navia wrote: In principle CMB is the light when the universe "become transparent", i.e. is the farthest light you will ever see. It is impossible to prove that ANY perturbation is not due to a foreground object since it is impossible to PROVE that there ISN'T some foreground object that could be incredibly far away from us! Proving a negative is notoriously difficult. But consider this: the first maximum in the power spectrum of the CMB is on scales of order one degree on the sky. There are very few objects that have this physical scale: basically a handful of nearby galaxies (and they are clearly not the foreground structures of interest, since the CMB structure would correlate with their position if they were). It is very, very hard to see how the large-scale structure in the CMB could be related to any known cosmological foreground object, so your conjecture can only be true if there are otherwise unknown, invisible, extremely large-scale foreground objects that affect the CMB via physical mechanisms that are not understood but that exactly mimic the expectations for primordial fluctuations in their power and frequency spectral properties. You need to ask yourself how probable this is. (By contrast, there *is* small-scale structure in the CMB that is known to be associated with foreground structures like clusters of galaxies via the Sunyaev-Zel'dovich effect. This is well understood, well observed, behaves spectrally in the expected way, and is taken account of in the power spectrum analysis.) Note that the BICEP2 result is rather different. They observed a small region of the sky (380 square degrees) and so it's possible that the polarized structure they see is due to polarized emission from dust in the particular part of the Milky Way they're looking through, which we don't understand very well. But that can't be true of the all-sky analysis of large-scale CMB anisotropies from COBE, WMAP or Planck, where you get the same result whether you're looking towards or away from our galaxy, once the emission from the galaxy itself is taken into account. 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 |
#6
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Uh, Oh: BICEP2 Results In Jeopardy?
On Sunday, May 18, 2014 10:03:15 AM UTC-4, jacob navia wrote:
In principle CMB is the light when the universe "become transparent", i.e. is the farthest light you will ever see. The CMB was generated many thousands of years after the putative inflationary era. Given that we are dealing with a high-energy and very turbulent Big Bang event, how can we claim that the imprints of hypothetical inflationary era phenomena are preserved without a high degree of modification after many thousands of years in a high-energy, turbulent event? This has always troubled me. Using distortions in the CMB to infer what was going on many thousands of years before its advent seems far-fetched and pseudo-scientific. Are we doing science or reading tea leaves? [Mod. note: attributions corrected -- mjh] |
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Uh, Oh: BICEP2 Results In Jeopardy?
In article , "Robert L.
Oldershaw" writes: The CMB was generated many thousands of years after the putative inflationary era. Given that we are dealing with a high-energy and very turbulent Big Bang event, It was not turbulent. In fact, one of the biggest puzzles in cosmology is understanding why it was so smooth. how can we claim that the imprints of hypothetical inflationary era phenomena are preserved without a high degree of modification after many thousands of years in a high-energy, turbulent event? No-one "claims" this. Rather, it is the result of using known physics to follow the growth of perturbations. There are literally thousands of papers on this. Someone once said that we know more about the centre of the Sun than the centre of the Earth. Some things which are far away and/or last a long time are nevertheless better understood than more familiar things. This has always troubled me. Using distortions in the CMB to infer what was going on many thousands of years before its advent seems far-fetched and pseudo-scientific. Are we doing science or reading tea leaves? The former. Actually, it would be hard to find an example where theory (your definitive, prior, unmodifiable, unique predictions) was more spectacularly confirmed by observation, long after the theory was mature. IIRC, in your view an ideal scientific theory can essentially predict everything, so what is the problem with thousands of years? |
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Uh, Oh: BICEP2 Results In Jeopardy?
On Sunday, May 18, 2014 10:03:15 AM UTC-4, jacob navia wrote:
It is impossible to prove that ANY perturbation is not due to a foreground object since it is impossible to PROVE that there ISN'T some foreground object that could be incredibly far away from us! Beside the spatial properties of the CMB mentioned by Martin Hardcastle, its spectral properties also provide an extremely strong limits on any foreground contamination. Any foreground object that differed by more than a millikelvin from T = 2.725 degrees would be recognized as such from multi-wavelength observations (e.g. the 5 bandpasses on WMAP or 9 bandpasses on Planck). So yes, the CMB fluctuations could be due to mysterious foreground objects at exactly T = 2.725 degrees which are located at regular intervals across the entire sky. But at some point Occam's Razor takes effect. --Wayne P.S. The BICEP2 polarization results were only taken at one wavelength, which is why everyone is eagerly awaiting the multi-wavelength Planck results. |
#9
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Uh, Oh: BICEP2 Results In Jeopardy?
On Monday, May 19, 2014 3:00:49 PM UTC-4, Phillip Helbig---undress to reply wrote:
papers on this. Someone once said that we know more about the centre of the Sun than the centre of the Earth. (1) If we understood the center of the Sun, we could explain the 22-year solar cycle, but it remains a mystery that we have not yet understood. (2) When I look at the cosmos and all of its structure on all the different scales, I would not call it "smooth". It is inhomogeneous right up to the largest reliably observable scales. To me a "smooth" and non-turbulent BB is a Platonic fiction I do not think we understand the details of the Big Bang event any better than we understand the center of the Sun, stellar formation, or especially galaxy formation. Just-so stories don't count as explanations. And I still doubt the preservation fine details about what was going on at 10^-30 sec after eons of time and what I believe to be turbulent expansion. Look at the detailed structure of a typical supernova remnant, then compare it with the detailed structure of the vast filamentary cosmic web, which is definitely not smooth. See any self-similarity? I see lots of that. |
#10
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Uh, Oh: BICEP2 Results In Jeopardy?
Le 19/05/2014 22:11, wlandsman a écrit :
On Sunday, May 18, 2014 10:03:15 AM UTC-4, jacob navia wrote: It is impossible to prove that ANY perturbation is not due to a foreground object since it is impossible to PROVE that there ISN'T some foreground object that could be incredibly far away from us! Beside the spatial properties of the CMB mentioned by Martin Hardcastle, its spectral properties also provide an extremely strong limits on any foreground contamination. Any foreground object that differed by more than a millikelvin from T = 2.725 degrees would be recognized as such from multi-wavelength observations (e.g. the 5 bandpasses on WMAP or 9 bandpasses on Planck). Yes. That would completely destroy my argument. You have a reference where I could take a deeper look at that? Or the whole issue of foreground object contamination when studying the CMB? Thanks |
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