# Thomson opacity (split from I finally found an accurate article on the speed of universal expansion)

## Recommended Posts

Can I ask, if anyone has considered, the Thomson opacity of the IGM, between earth and distant SNe Ia ?

Yes, the CMB limits the opacity to a few percent at most, but even that would have non-trivial impact on calculated distances (and, so, indirectly, on the best-fit cosmological parameters, as compared to the "completely clear skies" benchmark Cosmology) ?

##### Share on other sites

The interstellar medium can be accounted for as the medium affects different wavelengths of light differently depending on the composition. Through this we can compensate for any interstellar reddening by examining the response to different frequencies.

Stars will appear to be redder than actual as shorter wavelengths are more easily scattered than longer wavelengths. (This is not the same as redshift) this reddening is also distinctive from redshift.

Galactic redshift affects all wavelengths as opposed to selected frequencies of extinction reddening. So by using spectronomy one can readily avoid any affect the IGM will have on distance measures.

The 21 cm line when measuring hydrogen is a long enough wavelength that it the IGM is transparent and is essentially unaffected. ( As one example) however blue wavelengths will often suffer scattering.

Edited by Mordred
##### Share on other sites

Thomson opacity, of the IGM, is "gray" ?

##### Share on other sites

7 hours ago, TEFLing said:

Thomson opacity, of the IGM, is "gray" ?

Fair question. Myself I take the acronym to mean InterGalactic Medium. But who am I to try to educate someone who is TEFL 🤭.

##### Share on other sites

4 minutes ago, taeto said:

Fair question. Myself I take the acronym to mean InterGalactic Medium. But who am I to try to educate someone who is TEFL 🤭.

Am I allowed to mention that I made a numerical model of this "gray plasma"?

In very round numbers, the optical depth is about 1% per Z, say 2% at red shift 2. So you need to choose new cosmological parameters. Which. Bring supernovae closer to Earth for the same red shift. So that while they would appear brighter. If the Cosmos was completely empty. When you add the Thomson Opacity back in it reduces the observed brightnesses back down to observations.

I find that that it is actually possible to choose slightly modified cosmological parameters, slightly more total matter for example which has the effect of reducing distances to supernovae, which then still match actual observations at every red shift, with the opacity turned on

##### Share on other sites

If it's a personal model you can mention it with your mathematics in our Speculation forum. This grey your referring to isn't mainstream physics. This forum is reserved to strictly mainstream physics. However we don't rely strictly on redshift to determine distance particularly in the Z ranges you mentioned but also employ interstellar parallax.

Edited by Mordred
##### Share on other sites

8 hours ago, TEFLing said:

Thomson opacity, of the IGM, is "gray" ?

What do you mean by gray, and are you asking or proclaiming this?

##### Share on other sites

Side note if this grey is comprised of some form of medium then it would affect different wavelengths of light differently as the IGM does. The principle would be the same.

##### Share on other sites

19 minutes ago, Mordred said:

Side note if this grey is comprised of some form of medium then it would affect different wavelengths of light differently as the IGM does. The principle would be the same.

Thomson opacity affects all wavelengths equally?  Hence "gray"?

##### Share on other sites

If what you refer to as Thompson opacity involves Thompson scattering it would not.

See here for reference on opacity due to Thompson scattering

##### Share on other sites

14 minutes ago, TEFLing said:

Thomson opacity affects all wavelengths equally?  Hence "gray"?

Still have this issue of your use of question marks. Are you asking this?

10 minutes ago, Mordred said:

If what you refer to as Thompson opacity involves Thompson scattering it would not.

Cross section is independent of wavelength, according to https://en.wikipedia.org/wiki/Thomson_scattering

———

The article also mentions how the CMB is polarized as a result of this scattering, which raises the issue of why one might think that the process is not already included in our cosmological models.

##### Share on other sites

I will have to go through this after work on Thompson scattering is employed in astronomy applications.

In particular how it is employed to measure the composition of a plasma.

Edited by Mordred
##### Share on other sites

Here is the pertinent details in this Arxiv article and how this applies to the Lymann alpha forest

##### Share on other sites

13 hours ago, swansont said:

Still have this issue of your use of question marks. Are you asking this?

Cross section is independent of wavelength, according to https://en.wikipedia.org/wiki/Thomson_scattering

———

The article also mentions how the CMB is polarized as a result of this scattering, which raises the issue of why one might think that the process is not already included in our cosmological models.

What that particular link doesn't mention is the frequency dependency of when you apply Thompson  vs Compton scattering. This is given by the Klein Nishina formula

Though you were correct in correcting me on Thompson scattering. (I had confused it with Compton scattering)

The non relativistic assumption breaks down $hv=m_ec^2\sim 0.51 Mev$ when $hv\ge m_e c^2 Mev$ you are now dealing with Compton scattering. Which must be dealt with quantum mechanically

The inverse Compton scattering is particularly applicable to

So in essence we use both Compton and Thompson scattering with our cosmological models but which scattering to apply depends on the circumstance.

I question the Z range mentioned above as there is in essence no free electrons for Thompson scattering at z=1 and Z=2. If memory serves correct one must apply Compton scattering to an atom taking into account the Compton wavelength of the atom.

This is one of the reasons why the CMB is referred to as the surface of last scattering as it refers to the transition stage when Thompson scattering no longer applies Ie the transition from an opaque universe to a transparent universe. There are stages at different Z as per the Lynmam Alpha papers I linked but you will note they do not apply at z=2 or z=1.

Edited by Mordred
##### Share on other sites

On 3/1/2020 at 10:21 AM, TEFLing said:

Can I ask, if anyone has considered, the Thomson opacity of the IGM, between earth and distant SNe Ia ?

Yes, the CMB limits the opacity to a few percent at most, but even that would have non-trivial impact on calculated distances (and, so, indirectly, on the best-fit cosmological parameters, as compared to the "completely clear skies" benchmark Cosmology) ?

Even from SNe 1a to Earth I don't see how there would be Thompson scattering however given the range of wavelengths emitted ? I'm still looking at the luminosity range only certain frequencies would be affected.

lol it is am interesting question that makes one want to research closer...So I've been looking at the SNe 1a data. Currently looking at the Compton and Klien Nimishi scattering due to processes involved in the composition of the SNE 1a. It definetely  emits xRays which wouldn't apply Thompson scattering.

Edited by Mordred
##### Share on other sites

9 hours ago, Mordred said:

no free electrons for Thompson scattering at z=1 and Z=2

Reionization was complete by z~6, evidenced by the disappearance of Gunn-Peterson Troughs in quasar spectra below that

The IGM has been virtually 100.0000% ionized ever since (neutral fraction of order PPM at most)

14 hours ago, Mordred said:

Here is the pertinent details in this Arxiv article and how this applies to the Lymann alpha forest

Yes, reionization was significant by z~11, and equation (6) is the appropriate one to use (with the presumed "Benchmark Cosmology") to compute the integrated optical depth

##### Share on other sites

Yes that is correct, however another side consideration is that cosmology doesn't rely on any one methodology to measure distances. It's well documented that due to not fully understanding the processes of the SNe 1a. That one cannot rely to heavily on that method.

Secondly no method handles all ranges accurately so we employ the numerous methods of the cosmic distance ladder for validation.  If I recall correctly there is also a certain range near z=6 where other adjustments must be made for angular diameter distance.

When you get down to the nitty gritty the SNe 1a just gives us a reasonable ballpark that further research of other methods then fine tune.

The inherent problem with redshift is that emitter frequencies must be well known. After equation 6 that link mentions some of the considerations that must further addressed. Though not all the considerations are mentioned. For example the typical textbook redshift equation must be adjusted for the non linearity past Hubble horizon.

Edited by Mordred
##### Share on other sites

There are researchers attempting to duplicate the successes of SNe Ia with QSOs, extending the distance ladder up to z~6

SN Ia themselves currently extend only to z~2, so that the IGM is virtually fully ionized, and essentially primordial in composition (X=3/4), and SNIa distance moduli involve a K-correction, indicating reliance on visible / IR wavelengths, such that Thomson opacity is valid

All distance ladder estimates can be improved with improved models, researchers have tried "gray dust" but for some reason have shied away from the "gray plasma" the CMB crew has already accounted for

Equation (6) can also be generalized for non-flat cosmologies with the Curvature term, that extra degree of freedom enables matching a modified cosmology with opacity to the benchmark cosmology without Thomson, I found (M=0.27,L=0.73) --> (M=.3, L=.76) maintaining the benchmark cosmology (B=0.036) for the IGM (total baryons without stars)

##### Share on other sites

Equation (6) is trivially integrated for the "Benchmark Cosmology" giving an optical depth of almost 1% at z=2

##### Share on other sites

That formula only applies to regions where Thompson scattering occurs. You need to prove that free electrons would be available at the range you described and if you run through the BBN calculations you will find the limit where free electrons are available.

One of the more accurate methodologies is the Saha equation for that.

Simply applying the equation to any region isn't sufficient in itself. Thompson scattering will not apply to atoms. However when it comes to scattering with neutral hydrogen atoms you need to apply the Lyman limit which will correspond to the Gunn Peterson trough.

For neutral hydrogen scattering you can apply Compton scattering or Ramen and Rayleigh. Not Thompson scattering however those formulas do apply Thompson scattering for the free electron basis.

I would like you to consider the following. With CMB measurements Thompson scattering is anisotropic as it has dependence on observer orientation. It is one of the key sources for intensity and polarization anisotropies in the CMB. In essence it causes blurring and measurable distortions. This is the bsZ effect as well as the ksZ effect.

You can google how this relates to the Sache-Wolfe effect. In essence Thompson scattering has polarization terms. Here is one relevant Arxiv.

One primary detail your not looking at is density variations has polarization effects with regards to all scatterings.

Edited by Mordred
##### Share on other sites

It is well known that the IGM is (virtually) fully ionized from z=0 to z=11 (although Gunn-Peterson Troughs in Quasar Spectra reveal pockets of neutral material down to z=6)

For SNe Ia observed in the range 0<z<2, the IGM is fully ionized, and so Thomson opacity applies

yes?

##### Share on other sites

24 minutes ago, TEFLing said:

It is well known that the IGM is (virtually) fully ionized from z=0 to z=11 (although Gunn-Peterson Troughs in Quasar Spectra reveal pockets of neutral material down to z=6)

For SNe Ia observed in the range 0<z<2, the IGM is fully ionized, and so Thomson opacity applies

yes?

If this is true and it is "well known" then it will be taken into account in measurements of supernova apparent brightness and therefore distance. (My guess is that the effect is much smaller than the uncertainty in the absolute brightness, but I don't have any data to support that at the moment.)

I know that light absorption is taken into account when Cepheid variables are used as standard candles. So I see no reason to doubt the same is true (or, at least that it has been considered) for supernovae.

##### Share on other sites

10 hours ago, Strange said:

If this is true and it is "well known" then it will be taken into account in measurements of supernova apparent brightness and therefore distance. (My guess is that the effect is much smaller than the uncertainty in the absolute brightness, but I don't have any data to support that at the moment.)

I know that light absorption is taken into account when Cepheid variables are used as standard candles. So I see no reason to doubt the same is true (or, at least that it has been considered) for supernovae.

that would seem to be a reasonable assumption

but it's not true in this case

researchers have considered "gray dust" as an alternative to "dark energy", but no one has considered "gray plasma" as a (slight) addition

If they had, I would just be reading what they wrote, yes?

If there is an obscure article out there behind a pay wall, then please LMK

Otherwise, "gray plasma" could have as much as a <1% effect on the choice of optimal parameters (M,L 0.27,0.73) --> (0.28,0.72) say

On the evidence available to me, once researchers realized that "gray scatterers" could not explain away "dark energy" altogether... they stopped considering them entirely...

but they still have a non-trivial if lower-order effect

CMB folks consider it -- so why not SNe Ia folks as well?

##### Share on other sites

Consider the fact that Thompson scattering has completely different observation effects than the cosmological constant. You keep ignoring the other facts that have been presented by peer review articles I have posted.

Scattering has polarity effects that lead to distortions. If anything this would mean that the methodology of determining the curvature of spacetimne itself would be invalid.

The CMB distortions was a major determining factor in this via the WMAP, COBE and Planck measurements.

We can measure scatterrings via spectronomy due to the polarity shifts. We do this all the time when measuring plasma including our own Sun. The reason you will never find any papers concerning scatterrings below the ranges in those papers posted us that any scatterrings below that range are next to non existent.

It would not affect just SNe 1a but all observations including other galaxies. We can measure the scatterrings near quasars. The quasars has processes that heat up the surrounding temperature sufficient to allow the scatterrings to occur. With this tool we can measure the temperature anistropies.

All scatterrings are a primary tool used in astronomy research. Were quite versed in its applications.

Edited by Mordred
##### Share on other sites

For example the polarization cross section for Thompson scatterrings is

$\frac{d\sigma_T}{d\Omega}\propto|\hat{\epsilon}\cdot\acute{\hat{\epsilon}}|$ where the two epsilons are the scatterring angles. The linear polarizations intensity would be 90 degree phase shifted. The CMB temperature anistropies lead to quadrupolar anistropies. You also get the quadrupolar in plasma such as our sun or quasars etc.

Now these polarization angles depend upon observer location by viewing the same object from different orbit locations ie as the Earth rotates around the sun. Those angles will change.

This is nothing like redshift and nothing like the cosmological constant.

Now you might think 1 % is miniscule at z=1 however that becomes a major factor if you extend the curve you graphed to z=1100.

You wouldn't even be able to measure the CMB at that range.

So no your application is wrong plain and simple. If you want proof extend that graph to 100 percent opacity. You would reach that far sooner than z=1100. I seriously doubt you even get to the range of the Hubble horizon. As the curve is non linear your maximum range would be less than Z=100. You wouldn't be able to see over a quarter of the current observable universe. The Z scale is also non linear it is only approximately linear to the Hubble horizon that is when you must apply a different cosmological redshift formula to allow for the nonlinearity.

Not that opacity has anything to do with cosmological redshift. Those two terms describe completely different processes.

The other fact your either not aware of is that the temperature of the universe evolves with the expansion of the universe. If the universe radius is smaller the temperature would be higher. This is another piece of evidence that corresponds to expansion rate.

Edited by Mordred

## Create an account

Register a new account