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


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#18 OceanBreeze

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Posted 26 April 2019 - 03:27 PM

I would agree there is more than one way of viewing radio waves. 

 

A minor correction electro magnetic radiation / radio waves consist of virtual photons, not photons. 

 

That’s an interesting point of view!

 

However, about the only place you will ever see virtual photons is on a Feynman diagram, as they only exist as force-carriers for the Electromagnetic force that exists directly between charged particles. So, they only exist in static fields and are not detectable nor do they have energy or momentum.

 

 

J5Qfx.gif

 

Obviously, radio waves must consist of real photons as they do carry energy and momentum and are detectable.


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#19 exchemist

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Posted 27 April 2019 - 02:36 AM

This complete map of CMB with detectable anisotropy of CBR, showing thermal variations in the order of 10^-4 Kelvin degrees.

(Wikipedia: All-sky mollweide map of the CMB, created from 9 years of WMAP data)

 

Read carefully these articles from Wikipedia and will understand what spherical armonics have to do with it (there are more sources if you search about it):

 

https://en.wikipedia...wave_background

 

https://en.wikipedia...ground_Explorer

 

 

 

800px-Ilc_9yr_moll4096.png

No, I'm not going on a wld goose chase through these articles to hunt for an answer to my own question.

 

You are the one claiming spherical harmonics have some connection with CMBR. So you can tell me, in your own words, what that connection is. Or alternatively you can quote the most relevant paragraph of the articles you are relying on, to give me an idea.   



#20 Flummoxed

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Posted 27 April 2019 - 03:25 AM

A photon is an oscillation in the electric and magnetic fields. 

 

 

You say a photon has momentum. Well that means it has a wavelength, given by p=h/λ, and thus it has a frequency. This is basic quantum theory. Why do you think this is wrong?  

 

Classically yes. But it does not have a electric or magnetic field that can be affected by other electric or magnetic fields. 

 

If a photon has momentum, does not mean it has a frequency, it is like saying a train has momentum therefore it has frequency. The definition of frequency might be 1 train / hour, or one photon / second. Those photons have momentum which is not neccesarily a periodic wave type frequency. I think it is very dodgy ground to ascribe a hypothetical frequency to an individual photon. 

 

 

That is untrue. Radio waves consist of real photons, as does any form of EM radiation. 

 

Er you might be right quoting wiki 

 

"

  •  Actual and virtual photons are mixed near an antenna, with the virtual photons responsible only for the "extra" magnetic-inductive and transient electric-dipole effects, which cause any imbalance between E and cB. As distance from the antenna grows, the near-field effects (as dipole fields) die out more quickly, and only the "radiative" effects that are due to actual photons remain as important effects. Although virtual effects extend to infinity, they drop off in field strength as 1/r2 rather than the field of EM waves composed of actual photons, which drop 1/r (the powers, respectively, decrease as 1/r4 and 1/r2). See near and far field for a more detailed discussion. See near field communication for practical communications applications of near fields.
  •  

"

 

Also the longer a virtual particle stays in existence, the more real it becomes. Do these virtual particles, that might not exist, maybe become real and are no longer influenced by the electromagnetic field creating them ?

 

 

That’s an interesting point of view!

 

However, about the only place you will ever see virtual photons is on a Feynman diagram, as they only exist as force-carriers for the Electromagnetic force that exists directly between charged particles. So, they only exist in static fields and are not detectable nor do they have energy or momentum.

 

 

J5Qfx.gif

 

Obviously, radio waves must consist of real photons as they do carry energy and momentum and are detectable.

 

Sort of agreed. But no it is not obvious how those photons appear from virtual particles around the antennae. Is it due to a near field effect due to virtual photons interacting with real photons.?

 

 

Ps thanks all for the answers. 



#21 exchemist

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Posted 27 April 2019 - 04:00 AM

From

 

https://en.wikipedia...wave_background

 

Data reduction and analysis

Raw CMBR data, even from space vehicles such as WMAP or Planck, contain foreground effects that completely obscure the fine-scale structure of the cosmic microwave background. The fine-scale structure is superimposed on the raw CMBR data but is too small to be seen at the scale of the raw data. The most prominent of the foreground effects is the dipole anisotropy caused by the Sun's motion relative to the CMBR background. The dipole anisotropy and others due to Earth's annual motion relative to the Sun and numerous microwave sources in the galactic plane and elsewhere must be subtracted out to reveal the extremely tiny variations characterizing the fine-scale structure of the CMBR background.

 

The detailed analysis of CMBR data to produce maps, an angular power spectrum, and ultimately cosmological parameters is a complicated, computationally difficult problem. Although computing a power spectrum from a map is in principle a simple Fourier transform, decomposing the map of the sky into spherical harmonics, in practice it is hard to take the effects of noise and foreground sources into account. In particular, these foregrounds are dominated by galactic emissions such as Bremsstrahlung, synchrotron, and dust that emit in the microwave band; in practice, the galaxy has to be removed, resulting in a CMB map that is not a full-sky map. In addition, point sources like galaxies and clusters represent another source of foreground which must be removed so as not to distort the short scale structure of the CMB power spectrum.

 

Constraints on many cosmological parameters can be obtained from their effects on the power spectrum, and results are often calculated using Markov chain Monte Carlo sampling techniques.

 

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

 

With this, I'm done with this topic in our interaction.

Ah OK I see now, just about, why you bring in spherical harmonics. But can only be relevant to an angular Fourier transform decomposition of the signal. So, as I read it, they relate only to attempts to measure the angular anisotropies, not the CMBR signal itself. For that, you obviously do not need anything with the angular dependence characteristic of a spherical harmonic.

 

These anisotropies are very tiny indeed, corresponding to temperature variations of the order of 10⁻⁴ K, which is why it is a challenge to measure them, i.e. they are close to zero.  

 

So none of this calls in question the observation that the CMBR spectrum very accurately corresponds to a black body, which is why Planck's law is used to describe it.



#22 Flummoxed

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Posted 27 April 2019 - 04:18 AM

Classically yes. But it does not have a electric or magnetic field that can be affected by other electric or magnetic fields. 

 

If a photon has momentum, does not mean it has a frequency, it is like saying a train has momentum therefore it has frequency. The definition of frequency might be 1 train / hour, or one photon / second. Those photons have momentum which is not neccesarily a periodic wave type frequency. I think it is very dodgy ground to ascribe a hypothetical frequency to an individual photon. 

 

 

 

Er you might be right quoting wiki 

 

"

  •  Actual and virtual photons are mixed near an antenna, with the virtual photons responsible only for the "extra" magnetic-inductive and transient electric-dipole effects, which cause any imbalance between E and cB. As distance from the antenna grows, the near-field effects (as dipole fields) die out more quickly, and only the "radiative" effects that are due to actual photons remain as important effects. Although virtual effects extend to infinity, they drop off in field strength as 1/r2 rather than the field of EM waves composed of actual photons, which drop 1/r (the powers, respectively, decrease as 1/r4 and 1/r2). See near and far field for a more detailed discussion. See near field communication for practical communications applications of near fields.
  •  

"

 

Also the longer a virtual particle stays in existence, the more real it becomes. Do these virtual particles, that might not exist, maybe become real and are no longer influenced by the electromagnetic field creating them ?

 

 

 

Sort of agreed. But no it is not obvious how those photons appear from virtual particles around the antennae. Is it due to a near field effect due to virtual photons interacting with real photons.?

 

 

Virtual particle pairs appear all the time and disappear, could it be that the electromagnetic field around the antennae separates these virtual particles which become real and unstable so decay to photons, a bit like hawking radiation without the black hole gravity.?


Edited by Flummoxed, 27 April 2019 - 04:18 AM.


#23 Flummoxed

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Posted 27 April 2019 - 07:32 AM

This might be of interest on this thread ref sources of cosmic back ground radiation  https://phys.org/new...=daily-nwletter and https://journals.aps...Lett.122.161601

 

A sort of cherenkov radiation caused by magnetic fields around pulsars via interaction with virtual particles in space. If I read it correctly  :unsure:



#24 exchemist

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Posted 27 April 2019 - 08:06 AM

This might be of interest on this thread ref sources of cosmic back ground radiation  https://phys.org/new...=daily-nwletter and https://journals.aps...Lett.122.161601

 

A sort of cherenkov radiation caused by magnetic fields around pulsars via interaction with virtual particles in space. If I read it correctly  :unsure:

Yes, but this phenomenon is quite separate from the CMBR.

 

It is not black body radiation, is not part of the background and involves emission of far higher frequency radiation than the CMBR. 



#25 Flummoxed

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Posted 27 April 2019 - 12:04 PM

 Spherical harmonics is a mathematical tool used to analyze data of any kind at spherical surfaces, in spectral terms.

They are the equivalent to Fourier analysis for one-dimensional data.

 

A sphere is analyzed as being a bi-dimensional surface, which has a curvature. Because of that curvature, bi-dimensional

Fourier analysis can't be performed.

 

As CMB data is collected as broadband temporal information about power density over a dome, wich is the cap of the solid

angle at which the radio measurement is performed, THEN Spherical Harmonics DECOMPOSITION is applied over this

specific dome's reading by the antenna. The bi-dimensional information, captured as a single temporal data, HAS TO be

decomposed into spectral components in order TO UNDERSTAND what are the major components of this sample of the CBR.

 

The use of Spherical Harmonics decompose the signal as having components called n-poles. Then you have monopoles, dipoles,

quadrupoles, octupoles, etc.

 

You can analyze each sample of the solid angle that is captured the antenna either as one single value, which poses not so much

value, or decompose the sample and study the contribution of each part of the spectrum in the tridimensional space.

 

After you have the thousands of samples of CBR, solid angle per solid angle, UNTIL you complete the scanning of the

spherical perspective of the universe, you make complex computations over each single sample and make corrections

to: eliminate undesired sources of radiations (like the Milky Way, weird zones at space with nebular aspect, artifacts (noise)

of different types and as many other undesired influences). Once you have completed this, using spherical harmonics, you

can transform the power samples into temperature samples (by using the PLANCK'S FORMULA).

 

Then, with thousand of pieces at your disposal, you can create a single 2D projection, placing each sample at his correct place.

 

THEN, you have to perform a digital low SPATIAL FILTERING of the whole data, in order to eliminate ARTIFACTS that appears at

the edges of each sample, when they are placed togheter.

 

THEN, you have choice: 1) present the whole map, which is not a good idea; 2) present a differential map, substracting the cosmic

average temperature of the background noise (the most popular version for laymen); 3) analyze the source of anisotropies by

decomposing (AGAIN) the radiation in monopoles, dipoles,quadrupoles, etc., for the ENTIRE UNIVERSE and analyz the contributions

of each n-pole, trying to figure out the sources of anisotropies.

 

There is much more behind this work, which is far beyond the capability of this forum to publish,

 

Here you have the best simplified explanation about CBR spectrum, the use of Spheric Harmonics and more.

 

It worth the effort to read it:

 

An introduction to the CMB powerspectrum

 

http://folk.uio.no/h...5220_2_2011.pdf

 

That link is WRONG!!! inflation came before any hot big bang. (if it happened as theorized). The hot big bang singularity is complete !!!!!!!s (and leaves me indicating what nationality I have :)


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#26 exchemist

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Posted 27 April 2019 - 12:42 PM

 Spherical harmonics is a mathematical tool used to analyze data of any kind at spherical surfaces, in spectral terms.

They are the equivalent to Fourier analysis for one-dimensional data.

 

A sphere is analyzed as being a bi-dimensional surface, which has a curvature. Because of that curvature, bi-dimensional

Fourier analysis can't be performed.

 

As CMB data is collected as broadband temporal information about power density over a dome, wich is the cap of the solid

angle at which the radio measurement is performed, THEN Spherical Harmonics DECOMPOSITION is applied over this

specific dome's reading by the antenna. The bi-dimensional information, captured as a single temporal data, HAS TO be

decomposed into spectral components in order TO UNDERSTAND what are the major components of this sample of the CBR.

 

The use of Spherical Harmonics decompose the signal as having components called n-poles. Then you have monopoles, dipoles,

quadrupoles, octupoles, etc.

 

You can analyze each sample of the solid angle that is captured the antenna either as one single value, which poses not so much

value, or decompose the sample and study the contribution of each part of the spectrum in the tridimensional space.

 

After you have the thousands of samples of CBR, solid angle per solid angle, UNTIL you complete the scanning of the

spherical perspective of the universe, you make complex computations over each single sample and make corrections

to: eliminate undesired sources of radiations (like the Milky Way, weird zones at space with nebular aspect, artifacts (noise)

of different types and as many other undesired influences). Once you have completed this, using spherical harmonics, you

can transform the power samples into temperature samples (by using the PLANCK'S FORMULA).

 

Then, with thousand of pieces at your disposal, you can create a single 2D projection, placing each sample at his correct place.

 

THEN, you have to perform a digital low SPATIAL FILTERING of the whole data, in order to eliminate ARTIFACTS that appears at

the edges of each sample, when they are placed togheter.

 

THEN, you have choice: 1) present the whole map, which is not a good idea; 2) present a differential map, substracting the cosmic

average temperature of the background noise (the most popular version for laymen); 3) analyze the source of anisotropies by

decomposing (AGAIN) the radiation in monopoles, dipoles,quadrupoles, etc., for the ENTIRE UNIVERSE and analyz the contributions

of each n-pole, trying to figure out the sources of anisotropies.

 

There is much more behind this work, which is far beyond the capability of this forum to publish,

 

Here you have the best simplified explanation about CBR spectrum, the use of Spheric Harmonics and more.

 

It worth the effort to read it:

 

An introduction to the CMB powerspectrum

 

http://folk.uio.no/h...5220_2_2011.pdf

Yes thanks. But if you read my post 30, you will see my understanding of the relevance of this is that it ONLY applies to analysis of the minute angular anisotropies of the CMBR, not the CMBR signal itself. 



#27 exchemist

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Posted 28 April 2019 - 02:48 AM

Well, your understanding of the relevance of spherical harmonics in the CBR analysis is just plain wrong.

 

I think that you like to argue just for the sake of it, and not for a valid scientific doubt. Also, I note that your

way to addressing to me is a little bit tilted to the downplaying game, to prove that you're the smartest child

in the block (you're far from being a child, of course).

 

So, this is mi final attempt to give you insights about the complex mechanisms behind the measurement of

the Cosmic Backgroud Radiation. I'll base this simple explanation on the final analysis of the data of COBE,

which was written by 18 scientists involved in the posterior evaluation of the data recopiled by COBE FIRAS.

 

As the final paper is heavily protected to readings by non-members, as it is in custody of the American

Astronomical Society, I've managed to get a link to a photographic copy at this link:

 

Measurements of the Cosmic Background Spectrum by the COBE FIRAS Instrument

 

http://adsbit.harvar...GIF&classic=YES

 

But also, I searched a copy of a derivate paper at this link, which is written by the same 18 scientists, and is

less protected (if you select PRINT to a virtual PDF printer will obtain the document):

 

Cosmic Background Dipole Spectrum Measured by the COBE FIRAS Instrument

 

http://adsabs.harvar...ApJ...420..445F

 

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

Some explanations to make it easier to understand:

 

1) The Universe was measured as a black body spherical cavity by COBE, 30 years ago,

    As the capabilities of FIRAS to make accurate measurements over small areas was low,

    scientists invented (specifically for COBE) the reduction of a sphere to a "cube), which

    was called: quadriteralized spherical cube.

 

    tutorial-image.jpg

 

 

This cube was decomposed into 6144 macropixels, to make average measurements over each one of them (they only could

measure 90% of the total).

 

2) The measurements covered the band between 60 and 660 Ghz (THIS has to make your eyebrows to raise). It was

     EQUIVALENT to measure wavelengths between 0.2 mm and 2 mm.

 

    What was measure was a "fluctuating thermal radiation" using a wideband bolometer. The measurements were a total

    TEMPORAL AVERAGE per macro-pixel, and were stored (thousands of them) to further and heavy post-processing

    here, at Earth,

 

    And this is a KEY FACTOR. The Planck's formula is an SPECTRAL formula, not a TEMPORAL formula, and is based

    on statistical averages (Boltzmann, Planck).

 

    To obtain the SPECTRAL data of a macro-pixel, you HAVE TO make a spectrum transform of bidimensional order,

    But each macropixel is not a cartesian area, but a 2D representation of a 3D surface, so you HAVE TO apply

    spherical harmonics transforms to EACH macropixel (either to analyze power or to its derivate temperature, which is

    obtained FROM Planck's formula. Or Rayleigh's formula, as frequency is very low).

 

3) Having your thousands of samples per each of the 6144 pixels, you need to ELIMINATE distortions (galactic noise,

    cosmic noise - difficult to define, instrument's missbehaviors, glitches, etc).

 

    To do that, you use the spectral spherical decomposition in monopoles, dipoles, quadrupoles, etc., and HEAVILY

    DOCTOR the data to eliminate what you don't like.

 

4) Finally, you have to SHOW to the audience HOW GOOD is the job COBE did, by proving that CBR is fully compliant

    with Planck's law for a black body cavity,

 

    But you have A PROBLEM:

 

   Planck's formula is about DENSITY of thermal radiation that fills the cavity, wich is a volumetric measurement.

 

   But you only have 6000+ pieces of spectral data (heavily doctored) and you need to MAKE PUBLIC a single

   chart (measured radiation intensity that escapes from a small hole at the Planck's cavity versus wavelength).

 

   Then, what you do is A WEIGHTED SPECTRAL AVERAGE of 6000+ spectral data (with a wide range of wavelengths)

   and PRESENT IT as a SINGLE spectral formula, like Planck did.

 

   Then, when you fitted data to your target, you present it to the general audience, which cheers you and the mission

   and recover their faith on science and its reconciliation with history: Planck tell us that CBR is exactly as he predicted,

   He's the father of quantum physics, so the man knows and, also, the COBE results HAVE TO be true,

 

I end it here, as I'm sicked of this, But remember that I claimed for "petitio pricipii" sophistic mechanism behind COBE, WMAP

or Planck satellite; The calibrations of the antenna and the measurement instrument use not one, but two Black Body radiation

generators,

 

So, going back to this topic and my OP: "Why Planck's formula for black body radiation is used to measure the CBR?"

 

THE END

No, I think you've misunderstood this.

 

Here is a description of the detector used when the CMBR was originally measured in 1964.https://en.wikipedia...iometer#History

There is no reference here to Fourier transforms, still less to spherical harmonics. They just used a heterodyne method to convert the microwave frequency to a lower one they could put through a conventional amplifier. 

 

Oceanbreeze has told you he has detected the CMBR himself, for fun, on his research ship. He did not need to futz about with Fourier analysis and spherical harmonics to do that. 

 

I repeat: spherical harmonics can only be relevant to evaluating angular dependence of the signal. Whereas the CMBR can be - and was originally - detected just by looking in some direction and assessing the microwave background, without considering any angular variation. 

 

Anyway, you have my answer to your final (and original) question: Planck's formula is used because the radiation has a black body spectrum, i.e. it is black body radiation, so that is the appropriate formula to use.  


Edited by exchemist, 28 April 2019 - 02:54 AM.


#28 Flummoxed

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Posted 28 April 2019 - 10:09 AM

" Planck tell us that CBR is exactly as he predicted,

   He's the father of quantum physics, so the man knows and, also, the COBE results HAVE TO be true,"

 

PLanck was long dead before the COBE results were published. His information was not what we have today. How could he know, what the COBE results would predict? 

 

In Plancks day inflation was not considered, there was an assumed singularity and hot big bang, which today is considered ludicrous. Some of his ideas might have been incorporated into Quantum Mechanics, but he is not the father of those ideas. 

 

He had to stand on the house of cards constructed by his fathers, who did not have the measurements we have today. 


Edited by Flummoxed, 28 April 2019 - 10:11 AM.


#29 exchemist

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Posted 28 April 2019 - 11:36 AM

I agree that Planck is long dead, but his formulae (for frequency and wavelength) are the heart of the state of the art

radiometry today. The ubergenius Henri Poincaré proved in 1912, just before his death, that any approach to the

problem of thermal radiation inevitably conducts to the Planck's solution and to the quantification of EM energy in hf chunks.

 

At his 1901 paper (available for free download in English and German), Planck used the Part 3 to present his values of "h"

and "k" constants (Boltzmann's constant), with a precision that was higher not more than 3.5% of current values.

 

One is inclined to think that science, 120 years ago (even before widespread of AC energy, radio, atom and molecules

composition, etc.) was something primitive. But this was not the case.

 

Planck, Wien, Thiesen  and many other scientists between 1890 and 1910, used the experimental research conducted at

what was the most advanced laboratory in the world for physics: the PTR or Physical-Technical Reichsanstalt, at Berlin.

 

This link, devoted to the figure of one of the greatest experimental physicist at the PTR (Otto Lummer) is in german.

 

But if you place this link into Google Translation tool, Google will translate it to English very well. You'll be amazed to

read about the depth and accuracy of measurements on spectrometry and more.

 

http://www.otto-lumm...estrahlung.html

 

Lummer was just one of more than a dozen experimental physicists that, working there, made breakthrough discoveries.

Many of them were nominated for the Nobel Prize.

 

I've studied Planck's work and life very intensively, as well as developments around the 2nd. Principle of Thermodynamics,

which is a central piece in the theories about thermal radiation and black bodies since Kirchoff, in 1859, challenged his

colleagues to find the SPECTRAL formula for black body cavity radiation. It took 40 years, until Planck, and the results

remain undisputed until today.

 

I know that Planck would NEVER had accepted that his formula be used to prove that CBR is equivalent to that of a black

body radiation, because it violates the principles of the 2nd. Law of Thermodynamics, which Kirchoff stablished as

mandatory to verify with the solution of the spectral equation of BB radiation. Nor it would had been accepted by any other of the dozen

or more scientists involved, in the last decade of XIX century, in the black body problem.

 

It's just a matter of logic and common sense. Black body radiation involves emissivity and absorptivity of thermal radiation, and the main

postulate is that a PERFECT black body has to have an absorptivity equal to ONE for every wavelength under observation.

 

There is no way to assimilate the universe to a black body cavity just because it violates the principle of absorptivity. So, I don't

see possible that any physicist (even today) could agree to this license about the misuse of BBR. Only astrophysicists and

cosmologists need that this happens, because its compliance is THE MAIN SUPPORT behind the BB theory. As simple as that.

 

Thanks for your thoughtful comment.

 

Greetings,

 

Richard

But Planck's formula is NOT used to "prove" anything. 

 

Observation shows the spectral distribution to be that of a black body. 



#30 exchemist

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Posted 28 April 2019 - 12:17 PM

Planck's formula is the only, universally accepted for 119 years, that express

the spectral distribution of a perfect black body cavity.

 

There is no other formula, nor it will be.

 

"Planck" is inmediately related to "Black Body Cavity Radiation spectral formula".

 

Unless you want to use the FAILED Rayleigh-Jeans formula (1900-1905) which is

an approximation to Planck's formula for wavelengths bigger than 100 micrometers.

 

By the way, how are you doing with your obserbations. Have you or someone that

you know "observed" an atom?

 

I bet you'll say yes.

I'm afraid you are really not making much sense here. The spectral distribution is observed to be a curve that looks like this: 

https://upload.wikim...s/c/cd/Cmbr.svg

 

To a very high degree of accuracy, this fits exactly the curve for a theoretical black body. No formula is relied on to derive this curve. It is what is observed.

 

The fact that Planck originally derived his formula, which fits any black body, and therefore fits this curve too, by considering oscillators inside a cavity, is neither here nor there. It is the formula for the radiation distribution of any black body. 


Edited by exchemist, 28 April 2019 - 12:18 PM.


#31 exchemist

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Posted 28 April 2019 - 03:05 PM

You really should be carefull writing wrong information.

 

There are two universal laws for black bodies:

 

1) Stefan's law for total surface radiation of PERFECT black bodies:

 

                            J = s.T4        (s= 5.67x10-8 Watt.m-2.K-4 and T in Kelvin degrees), which applies as W = A.J (A: area (real or equivalent) of the surface)

 

2) Planck's law for spectral density of PERFECT black body cavities.  This is the original formula, with variant f, at his 1901 paper,

about the density of radiation inside a perfect black body cavity:

                       

                        u = 8hc-3f3 (ehf/kT – 1)-1     (Joule.m-3.Hz-1)

 

or, derivated after his 1901 paper, as the spectral intensity of a perfect black body cavity radiation, as it is emitted

per steraradian within such a cavity.

 

                        I = u.(c/4)  = 2hc-2f3 (ehf/kT – 1)-1     (Watt.m-2.Hz-1.sr-1)

 

For lab measurements, and measuring at an angle normal to the wall of the cavity, through a small (non-perturbatory) hole,

this formula is used being multiplied by the solid angle of the aperture (in sr).

 

1 steradian = 1 rad2 = (180/π)2 square degrees = 3282.8 deg2 = 4.25 x 1010arcsec2

 

Current industrial black body cavity radiation generators (near perfect BB) are sold with an aperture wheel, which allows to

make measurements with different solid angles, like this portable instrument, manufactured by:

 

https://www.newport.com/p/67032

 

 

LS-pg5-35a_800w.jpg?1

 

 

 

This is the method used by COBE, WMAP and PLANCK satellites to scan the "apparent sphere" of the Universe, step by step:

 

20090703261309706.jpg

 

1989 COBE resolution: 7° (420 arcminute) per scan.

2001 WMAP resolution: 0.22° (13 arcminute) per scan.

2009 PLANCK resolution: better than 0.07° per scan (< 4 arcminute). Bandwith to be measured: 25-1000 GHz.

 

Use the conversions from above to obtain the solid angle aperture (sr.sr = sr2)

 

Time to complete an entire spherical scan (Planck satellite): 7.5 months (15 months doing two complete scans)

 

Source for Planck satellite:

https://frontline.th...03261309700.htm

 

 

Source for WMAP satellite:

https://lambda.gsfc....ct/map/current/

So what? Stefan's Law has nothing to do with spectral distribution, which is what I was talking about.  

 

All this guff you have posted about cavities is irrelevant. Planck's Law applies to ANY black body, from an oven with a hole, to a star, to the tungsten filament of a traditional light bulb. For what it is is worth the CMBR is the most perfect black body radiation curve ever seen in nature. https://en.wikipedia...wiki/Black_body. I quote:-

"The cosmic microwave background radiation observed today is "the most perfect black body ever measured in nature".[49] It has a nearly ideal Planck spectrum at a temperature of about 2.7 K. It departs from the perfect isotropy of true black-body radiation by an observed anisotropy that varies with angle on the sky only to about one part in 100,000."

 

Or...... are you trying to say you think Planck's law only applies to a black body that is a cavity? If that is what you are contending, please explain how you think the spectral distribution of a black body that is not a cavity differs, and what law if any governs its spectral distribution curve, according to you. 


Edited by exchemist, 28 April 2019 - 03:15 PM.


#32 Flummoxed

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Posted 29 April 2019 - 03:14 AM

 

This link, devoted to the figure of one of the greatest experimental physicist at the PTR (Otto Lummer) is in german.

 

But if you place this link into Google Translation tool, Google will translate it to English very well. You'll be amazed to

read about the depth and accuracy of measurements on spectrometry and more.

 

http://www.otto-lumm...estrahlung.html

 

 

I've studied Planck's work and life very intensively, as well as developments around the 2nd. Principle of Thermodynamics,

which is a central piece in the theories about thermal radiation and black bodies since Kirchoff, in 1859, challenged his

colleagues to find the SPECTRAL formula for black body cavity radiation. It took 40 years, until Planck, and the results

remain undisputed until today.

 

I know that Planck would NEVER had accepted that his formula be used to prove that CBR is equivalent to that of a black

body radiation, because it violates the principles of the 2nd. Law of Thermodynamics, which Kirchoff stablished as

mandatory to verify with the solution of the spectral equation of BB radiation. Nor it would had been accepted by any other of the dozen

or more scientists involved, in the last decade of XIX century, in the black body problem.

 

 

 

I still need to find time to read your link. Ich sprechen nein deutch

 

But it is a well known fact that the 2nd law of thermodynamics can be violated momentarily in Quantum mechanics, why would Planck not accept that the 2nd law of thermodynamics can be violated, if he invented quantum mechanics. 


Edited by Flummoxed, 29 April 2019 - 03:14 AM.


#33 exchemist

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Posted 29 April 2019 - 03:19 AM

And again:

 

No, and it's not my word. It's about Kirchoff's and Planck's words: The universal law of radiation density INSIDE a perfect black body cavity of any arbitrary form.... is: Planck's formula.

 

If the cavity IS NOT PERFECT, like being opaque or imperfectly black, then Kirchoff's law applies, affecting the density's formula by spectral emissivity and spectral absorptivity. In perfect black bodies, spectral absorptivity is 100%, under thermal equilibrium.

 

Now, cutting to the chase: YOU give me an example where Planck's formula for radiation density is not applied in black body cavities.

 

You have to be aware that there are two partially valid laws that can be derived from Planck's formula:

 

1) Wien's formula for perfect black body, valid only as an approximation for frequencies above short infrared frequencies (just below visible light, in the THz region)

 

2) Rayleigh-Jeans formula for perfect black body cavities, valid only for low frequencies (as microwave or long infrared), also an approximation.

 

This, unless you want to apply the modified Bose-Einstein approximation to Planck's formula, using photons instead of electromagnetic waves.

 

 

Pyrometers and several other instruments used in open enviroments to measure temperatures at a distance, or color equivalence of radiative

power of NON REFLECTING surfaces, like those covered with coating, use a derivation of Stefan's law, applied for measurements at an arbitrary angle different that the angle normal to the surface. And these instruments are based on the assumption of a NOT PERFECT black body surface or volume.

 

Planck is another world, as it is demonstrated by the hyphotesis and experimental proofs on cavities. It's all about the internal radiation equilibrium within a CLOSED enviroment and its dependance on wavelength and temperature.

 

WHAT IS YOUR PROBLEM WITH THIS THEORY? DO YOU REALLY UNDERSTAND IT?

 

If so, explain it to me as if I were a child, and write about practical uses of WHAT YOU'RE SAYING.

A black body does not have to be a physical cavity. It simply has to consist of a physical system in which matter and radiation are in thermal equilibrium and in which there are no specific line or band absorptions/emissions (i.e. it has to be "black"). It was first modelled by Planck as a cavity with "oscillators", because QM obviously did not exist at that time. However now that we have quantum theory, it can be seen as a consequence of Bose-Einstein statistics, applied to photons in thermal equilibrium. I quote Wiki:

 

"Planck's law arises as a limit of the Bose–Einstein distribution, the energy distribution describing non-interactive bosons in thermodynamic equilibrium. In the case of massless bosons such as photons and gluons, the chemical potential is zero and the Bose–Einstein distribution reduces to the Planck distribution."

 

(From this article: https://en.wikipedia...i/Planck's_law)



#34 sanctus

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Posted 29 April 2019 - 06:10 AM


Plus, if you read my former posts on this thread, I consider IMPOSSIBLE to rescue

background noise right behind Milky Way radiation. Impossible.

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)

 


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