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Why Planck's Formula For Black Body Radiation Is Used To Measure The Cbr?


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#35 Dubbelosix

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Posted 29 April 2019 - 06:18 AM

My wife might disagree, she thinks I am always right:) (normally) .

 

I am open to being educated, can you tell me what is wrong with what I wrote above.

 

 

You misunderstand friend, I was not implying you made an incorrect statement in the post you made, its just that we do tend to make mistakes, but we learn from them, just as I have made incorrect statements... as you eloquently put, call it the senior moments... we all have them.



#36 exchemist

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Posted 29 April 2019 - 07:42 AM

But no1 does, there are models which you can discuss which are used remove the signals from the galaxy. But if you do not you still get these images in the 5 WMAP bands:
https://wmap.gsfc.na...1082/index.html

which are indeed anisotropies starting from l=2 (monopole and dipole removed)

Sanctus, rhertz's issue seems not to be the anisotropies but something far more basic.

 

He or she refuses to accept that the CMBR follows the spectral distribution of a black body, because he or she thinks the universe (at the time of the surface of last scattering) cannot behave like a classical black body "cavity".  (Actually of course the pre-transparent early universe WAS an almost perfect black body cavity, but never mind that.) 

 

To bolster this idea, rhertz maintains that the widely used CMBR spectral profile is an artifact of computer-enhancement of the spectrum, designed to produce the result desired by Big Bang theorists - in effect, a collusion by scientists to create a myth.

 

Part of the confusion seems to be that rhertz attributes the computer enhancements that are done to identify the anisotropies (which are what cosmologists are interested in nowadays) with what is needed to record the basic CMBR spectral profile itself, which does not require any of this.

 

I've had a go at explaining this but I am not making much headway. I suspect there is some crank idea at the bottom of it which makes these misunderstandings essential to rhertz's stance.  



#37 Flummoxed

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Posted 29 April 2019 - 09:44 AM

 

 

HOW the COBE, WMAP and PLANCK satellites data is gathered, proccessed and presented.

 

 

Here is a recent pop science link on how data is collected highlighting some differences. A technical paper is linked to at the bottom.

 

https://phys.org/new...weekly-nwletter

 

"But the true explanation is still a mystery".

 

You clearly have a lot of knowledge, it is a little unclear as to where exactly you are headed with this thread. Do you have a series of questions, involving or supporting a newer or older theory ?  Please clarify ?

 

The level of proof required in astronomy is apparently (sigmas) less than that for particle physics. This suggests there is greater room for error. 

 

What level of error are you claiming will be observed if you are correct ref what you have researched? 1,2,3,4,5,6 sigma? 



#38 Dubbelosix

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Posted 29 April 2019 - 09:54 AM

Here is a recent pop science link on how data is collected highlighting some differences. A technical paper is linked to at the bottom.

 

https://phys.org/new...weekly-nwletter

 

"But the true explanation is still a mystery".

 

You clearly have a lot of knowledge, it is a little unclear as to where exactly you are headed with this thread. Do you have a series of questions, involving or supporting a newer or older theory ?  Please clarify ?

 

The level of proof required in astronomy is apparently (sigmas) less than that for particle physics. This suggests there is greater room for error. 

 

What level of error are you claiming will be observed if you are correct ref what you have researched? 1,2,3,4,5,6 sigma? 

 

Don't you just need a sigma 5 statistical significance?



#39 Flummoxed

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Posted 29 April 2019 - 10:17 AM

Don't you just need a sigma 5 statistical significance?

 

Nope :) sigma 5 is good in particle physics, but astronomy gets away with sigma 3. Astronomy includes a lot of assumptions, as you are aware. I wouldn't bet my life on a sigma 3 outcome, whereas I might on a sigma 5 or >

 

Edit, I was just wading into this link when, I noticed your response https://ned.ipac.cal...Page/Page4.html It is interesting so far, and I only got to page 4. However its beer OClock, and I am off for a tipple.


Edited by Flummoxed, 29 April 2019 - 10:20 AM.


#40 Dubbelosix

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Posted 29 April 2019 - 10:22 AM

Mmm... I may have to challenge this. A sigma 5 significance level is a measure of confidence that according to a scientist, that their results are indeed significant enough that it is [not] by a chance accident. If there exists a sigma 5 relative significance, the results could only be by a chance if it is repeated, something like 4 million times -  in other words, the likelihood of that being an accident, is vanishingly small. Of course, I am open to be corrected.



#41 Dubbelosix

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Posted 29 April 2019 - 10:28 AM

As for your statements on the issue of cosmology, I regretfully agree... there is too much hand wavy arguments concerning cosmology, including the evaluation of statistical significance, so I certainly agree in that issue. We still need sigma 5 to be significant in cosmology, in which case, I certainly agree.



#42 sanctus

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Posted 30 April 2019 - 04:22 AM

Well the papers I published where at 5 sigma. (Was too detect foregrounds in CMB-WMAP data, also applied to Planck later).

All this talk about anisotropies or not does not really make sense here (I mean in this context). l=0 is the isotropic signal, l=1 movement of earth etc. l>2 we call anisotropies.  So all it is, is a decomposition into spherical harmonics of the CMB signal.

Wrt CMB being the perfect black body or not, well so far this assumption is in agreement with the observations (but I admit I was on the statistcal analysis side in Cosmology, not so much into the theoretical side). So my aitional 2 cents is simply there are sooooo many people (from profs to master-students) who worked with the different CMB-data we have (CObe, WMAP, Planck,etc.) and the obtained power spectra of the anisotropies where always coherent with each other, at least till the multipoles they were comparable. And this also consodering that they were at different frequencies. So I find it very hard to believe:
1) It is just a statistical fluke
2) And in case it were, no1 has picked it up yet

I do agree though that the behind milky-way filling of data is of limited trustability, that is why when doing my anlises the galaxy was always masked out.


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#43 OceanBreeze

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Posted 30 April 2019 - 06:03 AM

I don’t understand what his main objection is. First, he seemed to be saying it is impossible to detect any signal at all, due to background noise, then he was objecting that Planck’s formula for BB radiation was used to analyze the data and finally he had some objection to the satellites having on board BB generators; that NASA and ESA were using to “fudge” the data! So, I count at least three objections in there and none of them make any sense to me.

 

I know, from personal experience, it is entirely possible to detect the CMB signal out of the cold sky noise. True, to do this the antenna cannot be on either the ecliptic plane nor the geostationary arc, in order to avoid galactic noise in the former and satellite signals in the latter. I also doubt that a standard-gain, small aperture backyard satellite dish antenna is suitable for the task, but the antenna I used is anything but standard. It is a high-gain shaped system with cryogenically cooled LNAs. It is probably better than the Holmdel horn antenna used by Penzias and Wilson, when they first accidentally stumbled on the CMB signal. As for Planck’s formula, it is only used for a comparison with the observed data; and the same goes for the satellite on-board BB generators. Scientists aren’t involved in some great “collusion” to fudge their data; that is an absurd idea.

 


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#44 sanctus

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Posted 30 April 2019 - 06:27 AM


I know, from personal experience, it is entirely possible to detect the CMB signal out of the cold sky noise. True, to do this the antenna cannot be on either the ecliptic plane nor the geostationary arc, in order to avoid galactic noise in the former and satellite signals in the latter.

That is way overkill :-)
Just use an old anlaog tv, but some reserach on the net showed no1 really knows how much of the noise is CMB.



#45 OceanBreeze

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Posted 30 April 2019 - 06:34 AM

I think I see it! :1drink:

 

hqdefault.jpg


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#46 exchemist

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Posted 30 April 2019 - 09:28 AM

I have tracked down the paper publishing the findings on the shape of the primary CMBR spectrum (.e. before they got into studying anisotropies)  from the FIRAS instrument aboard COBE: http://articles.adsa...T&filetype=.pdf

 

It is clear from this that there was no spherical harmonic analysis required (unless you count the dipole contribution). All they did, to get the most accurate spectral curve they could, was to subtract off the signal the effects of the galaxy, which they did by making a model of it by observations over 10 months, and also subtracting the "dipole" effect due to the Earth's proper motion. 

 

Planck's Law does not feature in any of this until we get to the discussion of the results, by which time it has been established, purely by observation, that the radiation spectrum is  - very accurately - that of a theoretical black body. 


Edited by exchemist, 30 April 2019 - 09:29 AM.


#47 sanctus

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Posted 30 April 2019 - 09:40 AM

Wrt to your point 3:

I do not really know how COBE measurements were done. But as I said above, in WMAP most of data analysis is done with masking of the galaxy. Here is an example of such a mask comparing WMAP7 and WMAP9:
https://lambda.gsfc....d/cb9_f17_M.png

 

 

Wrt 2) and 4):
Why is composite a problem?



#48 sanctus

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Posted 30 April 2019 - 11:27 AM

No, not a problem at all!

 

It's the proper way to do it.

 

But 1 post before you said:


Then, due to points 2) and 3), I find that the curve presented at the COBE's report, claiming

full compliance with Planck's formula is just plain and simple BS.



Seems a contradiction to me
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#49 exchemist

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Posted 02 May 2019 - 09:42 AM

Well, I'll make a last try, using Planck's and Wien's formulae, and some definitions:

 

Monochromatic Irradiance or Spectral Flux Density at the aperture in the cavity: Radiance of a surface per unit frequency or wavelength per unit solid angle. A directional quantity and differs from Planck's formula by (c/4). This is sometimes confusingly called "spectral intensity". (Note: I use L instead of the symbol for Lambda)

 

Le(L,T) = (c/4).We(L,T) = 2hc2L-5(ech/kLT-1)-1    [unitsWatt.m-2.m -1.sr-1]

 

Using Le(L,T) for a single measurement at COBE (or WMAP or PLANCK), and assuming that the measured value is X, then:

 

X = 2hc2L-5(ech/kLT-1)-1

 

Extracting T (the temperature that is derived from Planck's formula), you have:

 

T(L)  = (kL/ch) ln [1 + (2hc2L-5) X-1 , in Kelvin degrees

 

In this way temperatures from 6,144 spots (COBE), 234,541 spots (WMAP) and 703,524 spots (PLANCK), is calculated. With this data, average temperature of the CBR is calculated, and a differential map (after filtering anomalies) is presented.

 

Using Wien's displacement law, and assuming that the average temperature obtained is about 2.73 Kelving deg,

 

Lmax = b/T   , being b = 2900 m.K-1

you have

 

Lmax = 1.067 mm

 

at peak frequency

 

f(max ) = 282.4 GHz

 

----------------------------------------------------------------------------------------------------------------------------------------------

 

I hope that the above explanation can help to understand HOW thermal radiation temperature is CALCULATED,

and is only by using a derivation of Planck's formula.

 

As you can see, Planck's formula is everywhere, when it is about CBR measurements.

 

To my understanding, there is not any other formula used, as Planck's formula is the ultimate expression

for thermal radiation density WITHIN a Black Body Cavity, as the Universe is assumed to be.

 

These formulae also prove why Planck's BBR generators are VITAL for instruments calibration.

 

And if you wonder HOW did I obtain the amount of spots (actually reduction of domes to small plane areas),

I obtained it from NASA's Planck details, and NASA's WMAP and ESA's PLANCK deails from ESA sources.

 

I don't know what else to do to probe the usage of Planck's formula everywhere, whithin the BB cavity that

the Universe was assumed for these projects.

 

My original question at the topic stands, because I strongly dissagree that the Universe be interpreted as

a Black Body Cavity.

 

And if you wonder the role of the BBRG on board, think with an analogy.

 

Suppose that you are at a MIT lab, and you are measuring a voltage with your 8 digits

state of the art voltmeter, and have to measure the accuracy of a third order reference

of 1.0000000 volts.

 

But you read 0.9347581 volts.

 

Then you use your first order voltage reference for 1 volt (with 10^-10 accuracy), and

it results that you recalibrate your voltmeter to have a 1.000000 volts reading.

 

But, for whatever be the cause, your premium reference has shifted to a value 5% lower

and you don't know about this error.

 

Your's voltmeter calibration will render a measurement of 1.000000 volts, but actually the

true value is 0.950000 volts.

 

So, obeying your reference, you adjust your equipment and measure a wrong value.

 

This is what happens with the on-board BBRG calibrations. You follow the master reference

and, doing so, you are following Planck's law.

 

And this is a "petitio principii" fallacy. Of course that your values will follow exactly Planck's formula.

 

You've forced the whole system to follow the indications of the BBRG calibrator.

They measured differences from Planck's law.  This is described in the paper I linked to in post 67.


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#50 OceanBreeze

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Posted 02 May 2019 - 10:31 AM

 

 

My original question at the topic stands, because I strongly dissagree that the Universe be interpreted as

a Black Body Cavity.

 

And if you wonder the role of the BBRG on board, think with an analogy.

 

Suppose that you are at a MIT lab, and you are measuring a voltage with your 8 digits

state of the art voltmeter, and have to measure the accuracy of a third order reference

of 1.0000000 volts.

 

But you read 0.9347581 volts.

 

Then you use your first order voltage reference for 1 volt (with 10^-10 accuracy), and

it results that you recalibrate your voltmeter to have a 1.000000 volts reading.

 

But, for whatever be the cause, your premium reference has shifted to a value 5% lower

and you don't know about this error.

 

Your's voltmeter calibration will render a measurement of 1.000000 volts, but actually the

true value is 0.950000 volts.

 

So, obeying your reference, you adjust your equipment and measure a wrong value.

 

This is what happens with the on-board BBRG calibrations. You follow the master reference

and, doing so, you are following Planck's law.

 

And this is a "petitio principii" fallacy. Of course that your values will follow exactly Planck's formula.

 

You've forced the whole system to follow the indications of the BBRG calibrator.

 

 

Now I cannot take you seriously. Nobody in their right mind recalibrates their instrument according to a random measurement. Surely, as a retired “electronic engineer” you should know that! I should not even need to explain that the BB generators are used as the reference for calibration and then when the Input was switched to the CMBR no significant difference could be seen. To use your analogy, the multimeter is calibrated to a known reference of 1 Volt and when the unknown voltage is measured no difference is seen. Nobody calibrated the instrument to the unknown CMBR! The calibration was done to the known BB generator.

 

Here is an explanation that contradicts what you are claiming:

 

"The FIRAS instrument on COBE had a large conical horn for collecting the cosmic microwave background. There was only a small hole in the end of the horn to let the radiation into the instrument. But FIRAS also carried a microwave absorber, the external calibrator or XCAL, that could be inserted into the horn like a trumpet mute, and heaters that could make the whole horn+plus absorber cavity isothermal.

 

When the XCAL was in the horn FIRAS observed a very good blackbody cavity, but when the XCAL was out FIRAS observed the CMB. No signifcant difference could be seen. The CMB is very close to a blackbody with temperature 2.725 K. The FIRAS results are shown below in units of intensity (power per unit area per unit frequency per unit solid angle) vs. frequency and/or wavelength."

 

CMBspect.gif

 

 

 

"Eric Adelberger would like me to point out that the fundamental FIRAS measurement is the residual plot at the bottom. This is what FIRAS actually measured: the difference between the CMB and the best fitting blackbody. The plot at top shows this residual added to the theoretical blackbody spectrum at the best fitting XCAL temperature, based on the function derived by Planck in 1900. The three curves in the bottom correspond to three fairly likely non-blackbody spectra: the grey curve shows a body with a reflectivity of 100 parts per million instead of zero, and the red and blue curves show the effect of hot electrons adding an excess 60 parts per million of energy to the CMB either before (blue) or after (red) 1000 years after the Big Bang. These curves show the maximum distortions allowed by the FIRAS data."


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#51 exchemist

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Posted 03 May 2019 - 10:04 AM

Hi, I've searching for alternate theories about the origin of the CBR.

 

Please, take this with care as I'm not proposing any theory here. Just pure and simple

research over the Internet about people or groups which have a different proposal

than the currently accepted.

 

To be clear. and as far as I know (source:Dear Professor Dyson: Twenty Years of Correspondence

Between Freeman Dyson):

 

1) CBR was proposed in 1948 by Alpher and Herman, who estimated a 5 ºK as the

    average temperature of an expanding universe, originated in a Big Bang.

    They considered that the whole universe should be filled with Planck's radiation in

    the microwave region (Watt/m3), as rests of the original explosion and that this could

    be measured at present day, heavily red-shifted due to the Hubble constant (it was larger by then).

    There was no interest in cosmology by then, even when they tried for 15 years to convince

    astronomers, but they thought this radiation couldn't be measured.

 

2) In 1948, Hoyle, Gold and Bondi proposed an alternative: The steady Universe.

    They didn't like the Big Bang, the CBR and the primordial singularity. Their model was based on

    the constant number of galaxies per volume and an unexplained model for matter creation as

    the universe was expanding (they accepted that, due to Hubble's constant).

 

3) In a radio program, in 1950, Hoyle and Gamow were discussing about cosmology. At this program,

    Boyle introduced the term "Big Bang", mocking about Gamow's position.The name stuck.

 

4) In 1964, Penzias and WIlson discovered, accidentally, a steady low level radiation everywhere at

    the observed sky, while playing with an antenna given to them for spatial explorations in radioastronomy.

 

5) Everything slowly expanded around the CBR and the Universe's average temperature since then.

 

6) 25 years after Penzias-Wilson, and with many experiment around the CBR (on Earth, balloons, etc.),

    the COBE (Cosmick Background Noise Explorer) was launched in 1989. WMAP followed in 2001, with

    more advanced technology and finally PLANCK was launched in 2009 with the most advanced tech

    available by then. Since 2009, there is no other plan for an observatory after Planck satellite, and,

    since 2014, the original teams (WMAP and PLANCK) were dismembered, without explanations.

 

    Members of each of the three teams had to get a new job at other areas.

 

    It seemed that Planck's anisotropies were insuficient to explain the rol of galaxies in the creation

    of new matter, as well as the roles of the dark matter and dark energy. Now, the subject is in suspended

    state.

 

This is a simplified history of the perception of the CBR as Planck's radiation. It was born in 1948.

 

The CBR is out there, even when some people doesn't believe in the isotropy of the radiation, nor

about its origin. This persons, as the Hoyle's team did think, believe that that there was no Big Bang,

BUT they accept that the CBR exists (one way or another).

 

This is a link to one of these theories, and is based on the Oort Cloud, which is understood as an

spherical shell that encloses the solar system and that could be capable of produce something like the CBR:

 

They, apparently, believe that such an spherical shell could have the properties of a Planck's cavity and follow

the values of the Planck radiation.

 

http://aoi.com.au/OortSoup/index.htm

 

I don't believe nor deny this possibility, as I know very little about the Oort thing. But I know that scientists know

very little about this Oort shell, also.

 

It has been rather ignored by the astronomer's community.

 

I stop here. I'll keep searching for alternate explanations,which tipically are originated by not-believers of the Big Bang.

 

I, for many reasons, don't believe in the BBT either. But, even with several doubts that a initial singularity creates, it

seems that the BBT is adopted by consensus, like herd's behavior, just to stay "on" in the community. The BBT also

fails explaining several major doubts about acceleration of expansion, calculations about real amount of matter (which

forced the invention of dark matter and dark energy) and the future of the universe, among others.

Well it is something that you acknowledge the CMBR is real, at any rate.

 

On your difficulty accepting that the early universe behaved like a black body cavity, I should have thought that would not be too difficult to accept. According to the theory, the early universe was small and filled with plasma, until 380,000yrs after the big bang. During that phase it was a closed system in which matter and radiation were in thermal equilibrium. This is just what a black body cavity is.

 

The CMBR, according to the theory, comes from the "surface of last scattering", which was the point at which the plasma condensed into atoms, which only absorb and emit at certain frequencies, thus uncoupling the radiation flux from matter for the first time. The effective temperature of the radiation has dropped as the universe has expanded further.

 

This "herd" stuff is rather unfair. After all, the big bang model is quite successful so far. But it is only a model and can always be overturned by someone with convincing evidence against it. Have you researched the evidence against it and can you summarise any of that here for us?