Monday, November 12, 2018

Cosmic Microwave Background



-  2164  -  The Universe is 13.8 billion years old.  We know how fast it has been expanding.  We know that the Universe is 31 % matter of which is only 5% is Ordinary Matter.  We know that the other 23% matter is invisible Dark Matter that we know is there but we do not understand what it is.  The rest is energy of some sort that remains another mystery that is creating and accelerating the expansion, we call it Dark Energy. 
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 ------------------  2164  -  CMB - What did it tell us?
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-  The Big Bang started the Universe with a unique signature.  Astronomical Probes are making measurements that unravel how our Universe began.  This Review will start with the conclusions and then look at how we learned from COBE, WMAP, and PLANCK  probes that did the exploring.
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-  About 380,000 years after the Big Bang started, the expansion cooled and expanded enough for electrons and protons to combine to form neutral atoms.  Seeing this today after 13.8 billion years of expansion is studying radiation energy that has expanded and cooled from 3,000 to 2.725 degrees Kelvin. 
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-  From the measurements collected astronomers have concluded that the Universe is 13.8 billion years old.  We know how fast it has been expanding.  We know that the Universe is 31 % matter of which is only 5% is Ordinary Matter.  The only ordinary stuff we think we know and understand.  We know that the other 23% matter is invisible Dark Matter that we know is there but we do not understand what it is.  The rest is energy of some sort that remains another mystery that is creating and accelerating the expansion, we call Dark Energy. 
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-  The Cosmic Microwave Background , CMB, is stretched out radiation wavelengths and lowest Kelvin temperature because it has been expanding and cooling for 13,800,000,000 years.  Much has been learned when we were able to study this microwave afterglow with precision instruments measuring down to the millionth of a degree. 
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-  The Universe started with a primordial soup of subatomic particles.  When the soup cooled after 380,000 years atomic nuclei of hydrogen and helium formed , with trace amounts of lithium. When the temperature had cooled to 3,000 Kelvin the free electrons latched on to the hydrogen nuclei to form the neutral atoms.
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-  When the Universe was mostly neutral hydrogen the light photons could escape from the still expanding soup.  The photons started out as gamma rays but have now stretched out to the microwave wavelengths.
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-  The COBE satellite measured the intensity of this microwave energy at wavelengths from 0.1 to 10 millimeters.  The measurements prove that the CMB had a very specific intensity signal peaked at 2 millimeters wavelength.  This wavelength corresponds to a temperature of 2.725 Kelvin.
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-  The wavelength of light is directly related to temperature.  The redder the light the less the energy.  The bluer the light the higher the temperature. 
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-  At first view the temperature would look like a solid color, with no variations.  But, when the resolution of the measurements could see down to 0.00002 Kelvin the hotter and cooler patchwork became "visible".  The COBE satellite could map these hot and cold spots to within 7 angular degrees across the sky. 
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-  Another satellite, the WMAP, could expand this resolution down to 0.5 angular degrees.  And the PLANCK satellite brought the resolution down to 0.16 angular degrees.  These two satellites swept their  measurements across the entire sky to map the Universe CMB in every direction.
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-  The signal strengths plotted across the sky revealed the Universe's age, its composition, its expansion rate, and even when the first stars lit up out of the atomic soup. 
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-  Computer models were created until the model results matched the measured data.  Calculations made to match the models were able to tell astronomers the composition of the Universe.  From this astronomers have a "standard model of cosmology".
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-  Students today are studying this model to explore and learn even more about the Universe they occupy.  There is plenty left to learn with nearly 95% of the Universe still remaining "unknown".
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-  We pickup only pebbles of knowledge on the beach with a whole ocean of unknown before us.
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-  November 12, 2018.             An Index of recent Reviews is available.
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 ---------------------   Monday, November 12, 2018         -------------------------
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