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 Significance of the CMB

The Cosmic Microwave Background is a critical issue for cosmology.

Astronomers have noted distant galaxies have large red shifts implying high velocities away from Earth. Those velocities imply a time and imply a great distance by Hubble's law which began as a red shift to distance scale but later became a velocity to distance scale.
Since this observation of recession is symmetric, the implication is these objects were propelled at such velocities from a primordial source which 'exploded' with the tremendous force to generate the initial motion.
This conclusion is the foundation of Big Bang cosmology, a subset of general cosmology, the topic of this Facebook group.

There are two basic unknowns for a big bang:
1) what was at this big bang event?

The proposed source is a singularity.
Why it exploded cannot be determined with certainty.

2) when was it?

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In physical cosmology, the age of the universe is the time elapsed since the Big Bang. The current measurement of the age of the universe is 13.799±0.021 billion (10^9) years within the Lambda-CDM concordance model. The uncertainty has been narrowed down to 21 million years, based on a number of studies which all gave extremely similar figures for the age. These include studies of the microwave background radiation, and measurements by the Planck spacecraft, the Wilkinson Microwave Anisotropy Probe and other probes. Measurements of the cosmic background radiation give the cooling time of the universe since the Big Bang, and measurements of the expansion rate of the universe can be used to calculate its approximate age by extrapolating backwards in time.
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We cannot use the distance to the furthest galaxies as a distance or time metric because this is limited by our imaging technology (the dimmest object at the greatest distance); future telescopes will observe objects previously too dim.


With Hubble's Law and using a red shift as velocity and H=70), a red shift of Z=11 results in a calculated distance of 153.8 billion light years.
Cosmologists bring that object's extreme distance within the 'observable universe.'

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In Big Bang cosmology, the observable universe is what, in theory, can be seen from Earth. That is light, or other signals, which has had time to reach the Earth since the beginning of the cosmological expansion. The observable universe is a spherical volume (a ball) centered on the observer, regardless of the shape of the universe as a whole.

The word observable does not depend on whether modern technology actually allows detection of radiation from an object in this region. It simply means that it is possible in principle for light or other signals from the object to reach an observer on Earth. In practice, there is much that we cannot see. We can see light only from as far back as when particles were first able to emit photons that were not quickly re-absorbed by other particles. Before then, the universe was filled with a plasma that was opaque to photons.

Sometimes astrophysicists distinguish between the visible universe, which includes only signals emitted since recombination—and the observable universe, which includes signals since the beginning of the cosmological expansion (that is, the end of the inflationary epoch in modern cosmology). The radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light years), about 2% larger.

The best estimate of the age of the universe as of 2013 is 13.798 ± 0.037 billion years. Due to the expansion of the universe humans are observing objects that were originally much closer but are now considerably farther away (as defined in terms of cosmological proper distance, which is equal to the comoving distance at the present time) than a static 13.8 billion light-years distance. The diameter of the observable universe is estimated at about 28 billion parsecs (93 billion light-years), putting the edge of the observable universe at about 46–47 billion light-years away.
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Therefore:
The observable universe is based on the age of the universe.
Both are based on the assumed expansion of the universe.

The CMB is considered the temperature of the universe at the time of an event soon after the big bang.

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The cosmic microwave background, in Big Bang cosmology, is electromagnetic radiation as a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination.
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The CMB is critical for two reasons.

1) its presence is a possible confirmation of the 'epoch of recombination.'

Without a confirmation of some event after the big bang a proposed big bang sequence of events is completely without confirmation, implying cosmologists have no basis for the entire sequence.

2) CMB is being used to establish the age of the universe, a critical value for calculations in an expanding universe.


Together CMB is the foundation of modern cosmology.
The analysis of CMB data is critical.
 
 Here is a 2014 dissection of CMB by a radiologist who works with signal to noise problems; he was on the team for the new 8 tesla MRI technology.

Perhaps not everyone will be convinced by this radiologist with numerous published papers on cosmology so then it is up to the reader to decide whether this critical review has merit.

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