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Uh, Oh: BICEP2 Results In Jeopardy?



 
 
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  #1  
Old May 18th 14, 08:20 AM posted to sci.astro.research
jacob navia[_5_]
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Default 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  
Old May 18th 14, 03:00 PM posted to sci.astro.research
Phillip Helbig---undress to reply
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Default 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  
Old May 18th 14, 03:03 PM posted to sci.astro.research
jacob navia[_5_]
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Default 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!!!

:-)
  #4  
Old May 19th 14, 08:38 AM posted to sci.astro.research
Phillip Helbig---undress to reply
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Default 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  
Old May 19th 14, 08:44 AM posted to sci.astro.research
Martin Hardcastle
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Default 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  
Old May 19th 14, 08:45 AM posted to sci.astro.research
Robert L. Oldershaw
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Default 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]
  #7  
Old May 19th 14, 08:00 PM posted to sci.astro.research
Phillip Helbig---undress to reply
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Default 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?
  #8  
Old May 19th 14, 09:11 PM posted to sci.astro.research
wlandsman
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Default 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  
Old May 20th 14, 07:28 AM posted to sci.astro.research
Robert L. Oldershaw
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Default 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  
Old May 20th 14, 07:29 AM posted to sci.astro.research
jacob navia[_5_]
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Default 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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