Comments about "Microwave Background radiation" in Wikipedia


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Cosmologists refer to the time period when neutral atoms first formed as the recombination epoch, and the event shortly afterwards when photons started to travel freely through space rather than constantly being scattered by electrons and protons in plasma is referred to as photon decoupling.
The question is if physical you can consider two periods: One period where the photons where scattered and one where they freely travelled through space?
I expect that there is also a mixed period where both happened simultaneous. The question is how long this period took.
The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time
Many of the photons disappeared because they where involved in the creation of the elements of the periodic table.

1 Features

In the Big Bang model for the formation of the universe, Inflationary Cosmology predicts that after about 10-37 seconds the nascent universe underwent exponential growth that smoothed out nearly all irregularities.
This is an assumption. In some sense this is pure speculation. Of course you can claim this and claim that it happens because we do not observe irregularities, but does that mean that such a process really happened? Where there irregularities in the first place? and what are the physical processes that caused inflation?
The remaining irregularities were caused by quantum fluctuations in the inflaton field that caused the inflation event.
Also this is an assumption and speculation. Fields are descriptions of some underlying physical reality, like the cause of an electric field are electrons. What is this cause of the inflation field?
Two of the greatest successes of the Big Bang theory are its prediction of the almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background.
The Big Bang theory and the inflation theory are two distinct physical concepts. The first is a more basic theory. The second a refinery which comes in many flavours.

2. History

The first peak in the anisotropy was tentatively detected by the Toco experiment and the result was confirmed by the BOOMERang and MAXIMA experiments.
These measurements demonstrated that the geometry of the Universe is approximately flat, rather than curved.
For the results of the Boomerang experiment read this: A Flat Universe from High-Resolution Maps of the Cosmic Microwave Background Radiation
The document shows detailed results of the power spectrum calculation in Figure 2.
Page 2 of this document reads:
Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature.
These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the universe.
Page 3 reads:
The existence of this peak strongly supports inflationary models for the early universe, and is consistent with a flat, Euclidean Universe.
A flat Euclidean Universe is basically a mathematical concept. The evolution of the Universe after the Big Bang are physical processes. Flat implies that the universe is not curved, compared to mathematical concepts open en closed.
IMO it seems strange that by observing the structure of the CMB radiation you can decide that the universe is mathematical flat and infinite. See also: "The Inflationary Universe book review" page 44.

For the results of the Maxima experiment read this: MAXIMA-1: A measurement of the Cosmic Microwave Background anisothropy on angular scales of 10' to 5 degrees. 26 January 2000

3. Relationship to the Big Bang

When it originated some 300,000 years after the Big Bang—this time is generally known as the "time of last scattering" or the period of recombination or decoupling—the temperature of the universe was about 3000 K.
The question is how do we know these two values.
The temperature Tr of the CMB as a function of redshift, z, can be shown to be proportional to the temperature of the CMB as observed in the present day (2.725 K or 0.235 meV):
Tr = 2.725(1 + z)
This is a wishful thinking equation.
This equation is a backwards in time. That means the present temperature is 2.725K and at z=1 it was 5.45 K.

3.1 Primary anisotropy

The anisotropy of the cosmic microwave background is divided into two types:
  • primary anisotropy, due to effects which occur at the last scattering surface and before;
  • and secondary anisotropy, due to effects such as interactions of the background radiation with hot gas or gravitational potentials, which occur between the last scattering surface and the observer.
The fact that there is anisotropy seems logical. The opposite is isotropy which implies identical properties.
When you study documentation the photons travelled in a straight line towards us implying that there is no anisotropy.
To assume that light did not travel in straight lines seems much more realistic.
The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping
The state of the universe 300000 years after the BB was like a huge pot filled with boiling magna of extreme temperature. The picture that emerges is that globally the universe is uniform but locally not. Locally you have 3D disturbances. The issue is to what extend those 3D disturbances create structures like 3D oscillations.
But more important to what extend tell these disturbances something about the total composition and the evolution of the universe, because its that that the power spectrum does.
What is also important those disturbances are always there. During the evolution of the universe the composition changes but disturbances are always there: the universe becomes never totally uniform.
The acoustic oscillations arise because of a conflict in the photon–baryon plasma in the early universe.
The word "conflict" is not very scientific. Physics has nothing to do with conflicts. The issue is to what extend the universe as a whole was rather static or more dynamic implying baryonic type 3D density waves in its interior.
Oscillations (density fluctuations) are in conflict with the concept that the universe is uniform.
The pressure of the photons tends to erase anisotropies, whereas the gravitational attraction of the baryons—moving at speeds much slower than light—makes them tend to collapse to form dense haloes.
How can photons cause pressure ?
This sentence is not clear. See for example Acoustic Signatures in the Cosmic Microwave Background Chapter 2 Physical Processes Page 5:
Since Coulomb interactions couple the electrons to the baryons, we refer to the system as a photon-baryon fluid.
Photon pressure in the fluid resists gravitational compression and sets up acoustic waves in the system.
What you have is a 3D sphere filled, as a matter of speaking, with a fluid. Normally waves exists between a boundary of different densities (Water and air). How can you envision waves within such a fluid?
These two effects compete to create acoustic oscillations which give the microwave background its characteristic peak structure.
The strings of a violin can show acoustic vibrations.
See also this:
The reader is advised to study the original Wikipedia document and in particular the simulations 69, 70 by Wayne Hu.
The problem is that the simulations are very convincing, but that does not mean that the mathematics behind the simulations is correct.
The problem behind the third peak is that how can you simulate the influence of dark matter when you do not know what it is?

3.2 Late time anisotropy

4 Polarization

The cosmic microwave background is polarized at the level of a few microkelvin.

4.1 E-modes

4.2 B-modes

4.2.1 Primordial gravitational waves

Primordial gravitational waves are gravitational waves that could be observed in the polarisation of the cosmic microwave background and having their origin in the early universe.
Gravitational waves are linked with rotating heavy binary objects. They cause fluctuations in the movement of for example rotating objects around these heavy objects. That such rotating objects also influence the CMB radiation does not seem very likely.
Models of cosmic inflation predict that such gravitational waves should appear; thus, their detection supports the theory of inflation, and their strength can confirm and exclude different models of inflation.
Gravitational waves have nothing to do with the expansion of the Universe nor with the inflation theory.

4.2.2 Gravitational lensing

5 Microwave background observations

6 Data reduction and analysis

6.1 CMBR dipole anisotropy

6.2 Low multipoles and other anomalies

7 Future evolution

8 Timeline of prediction, discovery and interpretation

8.1 Thermal (non-microwave background) temperature predictions

8.2 Microwave background radiation predictions and measurements

9 In popular culture

10. See also

Following is a list with "Comments in Wikipedia" about related subjects

Reflection 1 - First peak

The position of the first peak is discussed in document "Cosmic Microwave Background Anisotropies" by Wayne Hu and Scott Dobelson 2002
at page 4 of this document:
For the ordinary matter or baryons, Omega(baryon) = 0.02h^-2 (wb=0) with statistical uncertainties at about the ten percent level determined through studies of the light element abundances (for reviews, see Boesgaard & Steigman 1985; Schramm & Turner 1998; Tytler et al 2000). This value is in strikingly good agreement with that implied by the CMB anisotropies themselves as we shall see. There is very strong evidence that there is also substantial non-baryonic dark matter. (*)
This dark matter must be close to cold (wm=0) for the gravitational instability paradigm to work (Peebles 1982) and when added to the baryons gives a total in non-relativistic matter of Omega(m) = 1/3. Since the Universe appears to be flat, the total Omega(total) must be equal to one. Thus, there is a missing component to the inventory, dubbed dark energy, with Omega(Lambda) = 2/3
The problem is all what is written above requires a detailed explanation. Specific the sentence with (*). Do they mean in the universe or in a galaxy ?
at page 13:
To get a feel for where these features should appear, note that in a flat matter dominated universe eta is proportional t0 (1 +z)^-1/2 so that etas/eta0 = 1/30 = 2 degrees. Equivalently l1 = 200.
and at page 14:
3.2 Initial Conditions
As suggested above, observations of the location of the first peak strongly point to a flat universe.
The question to answer is how do you know that the equations to calculate the curvature are correct ? See also : "The Inflationary Universe book review" page 44.

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Created: 5 September 2014

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