- 3109 - CMB - measuring the Cosmic Microwave Background. We have a Universe with 5% normal matter, 27% dark matter, and 68% dark energy. At last, we can state, with extraordinary confidence, what the Universe is made of. The curvature of the Universe is no greater than 1-part-in-1000, indicating that the Universe is indistinguishable from perfectly flat. Where have I heard that before? Christopher Columbus did not believe it either.
----------------- 3109 - CMB - measuring the Cosmic Microwave Background.
- When God made the Universe he left 95% of it to be a mystery, We only know 5% that we call Ordinary Matter and that makes up the world and life that we understand. But, with that 5% we have built satellites that made the measurements that bring us to this conclusion. We are using 3 satellites, COBE, WMAP, and PLANCK.
This is their story :
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- It's been more than 50 years since humanity discovered a uniform bath of low-energy, microwave radiation originating from all regions of the sky. It doesn't come from the Earth, the Sun, or even the galaxy; it originates beyond every star or galaxy we've ever observed. It is the CMB theoretical leftover glow from the Big Bang.
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- The cosmic microwave background (CMB), has had its properties measured extensively. The most advanced observatory to ever measure its properties is the European Space Agency's Planck satellite, launched in 2009. The satellite took its full suite of data over many years. Here's how it's measurements changed our view of the Universe forever.
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- The leftover glow from the Big Bang, the CMB, isn't uniform, but has tiny imperfections and temperature fluctuations on the scale of a few hundred microkelvin temperature. The Universe's temperature is only non-uniform at a level that's less than 0.01%. Planck has detected and measured these fluctuations to better precision than ever before.
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- This baby picture of the Universe measures light that was emitted when the Universe was only 380,000 years old. In the early 1990s, the COBE satellite gave us the first precision, all-sky map of the cosmic microwave background, down to a resolution of about 7 degrees.
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- About a decade ago, WMAP managed to get that down to about half-a-degree resolution. Planck measured all the way down to just 5 arcminutes (0.07°) in nine different frequency bands.
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- Planck has measured this radiation and its fluctuations in more frequency bands than any satellite that came before. COBE had four (only three were useful), and WMAP had five.
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- COBE could measure temperature fluctuations that were approximately 70 microkelvin in magnitude; Planck can get down to precisions of around 5 µK. The high resolution and the multiple frequency bands have enabled us to understand, measure, and subtract out the effects of dust in our galaxy better than ever before.
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- A complete dust map of the Milky Way, provided by Planck, showcases a lower-resolution, 2D map of what our galaxy's dust distribution looks like. This 'noise' needs to be subtracted out to reconstruct the background, primordial, cosmic signature that Planck gives us.
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- Using the temperature fluctuations on large, intermediate, and small scales we were able to figure out:
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-------------------- How much normal matter, dark matter, and dark energy are in the Universe,
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-------------------- What the initial distribution and spectrum of density fluctuations were
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-------------------- What the shape or curvature of the Universe is.
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- The magnitudes of the hot and cold spots, as well as their scales, indicate the curvature of the Universe. To the best of our capabilities, we measure it to be perfectly flat. Baryon acoustic oscillations and the CMB, together, provide the best methods of constraining this, down to a combined precision of 0.1%.:
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- We have learned:
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-------------------- When the Universe became reionized (and, therefore, when star formation reached a certain threshold),
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-------------------- If there are fluctuations on scales larger than the horizon,
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-------------------- Whether we can see the effects of gravitational waves,
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-------------------- What the number and temperature of neutrinos were back then,
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- The Universe has more matter and is expanding more slowly than we previously thought. Before Planck, we thought the Universe was about 26% matter and 74% dark energy, with an expansion rate in units of 73 km/s/Mpc.
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- ( km/s/Mpc = kilometers per second per megaparsec. A megaparsec is equivalent to 3.3 million lightyears distance).
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- The Planck measurements put the Universe with 31.5% matter, that is 4.9% is normal matter and 26.6 % dark matter. 68.5% is dark energy creating a Hubble expansion rate today of 67.4 km/s/Mpc.
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. The Planck results definitively point to only 3 species of light neutrino. And , that the mass of any individual neutrino species can be no more than 0.04 eV/c2 which is more than 10 million times less massive than that of an electron.
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- We also know that these neutrinos had a cosmic temperature that would correspond to 72% of the temperature or kinetic energy that the CMB photons have; if they were massless, the temperature would be just 2 K today, not 2.73K.
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- Other quantities have changed mildly. The Universe is a little older at 13.8 instead of 13.7 billion years that we previously thought. The distance to the edge of the observable Universe is a lit
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- So, with all the data in:
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-------------------- Yes to inflation, no to gravitational waves created by inflation.
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-------------------- Yes to three very light, standard-model neutrinos, no to any extras.
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-------------------- Yes to a slightly slower-expanding, older Universe, no to any evidence for spatial curvature.
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-------------------- Yes to a little bit more dark matter and normal matter, yes also to a little less dark energy.
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-------------------- No to changing dark energy; no to the Big Rip or the Big Crunch.
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- We have a Universe with 5% normal matter, 27% dark matter, and 68% dark energy. At last, we can state, with extraordinary confidence, what the Universe is made of. Ok, now I can have a drink of wine my job is done here.
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- Ok I have had my glass of wine. So now let's do some math. The CMB picture shows light and dark patches across the sky when we magnify it by 100,000 times. We assumes these more dense and less dense patches are the early formation of galaxies. How big are they?
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- A typical dark patch is 1/2 millimeter in diameter when the photo is magnified to be 160 millimeters width. The photo spans 45 degrees of arc or 1 millimeter per 0.28 degrees. 1/2 millimeter would be 0.14 arc degrees, and that is about the size of the smaller spots.
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- 45 arc degrees / 160 millimeters = 0.28 arc degrees per millimeter.
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- To get a feel of this size across the sky think of the Full Moon which is 0.5 arc degrees diameter. Therefore the CMB spots are about 1/3 the size of the Full Moon.
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- The scale at that distance to reach the CMB is 62 parsecs per arc second.
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- A parsec is an early astronomer's definition for units of great distances. It is the distance of one astronomical unit that subtends an angle of one arc second. It is equal to 3.26 light years distance, which is equal to 19 trillion miles. Ok, an astronomical unit is the distance between the Earth and the Sun, about 93 million miles.
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- ( The earlier astronomers had their own way of doing things. We live with their definitions today.) 1 degree is 3,600 arc seconds.
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- That would put the small dark spots in the CMB at 0.14 degrees * 3600 arc seconds / degree * 62 parsecs / arc second = 35,000 parsecs .
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- So the dark spot on the CMB is 35,000 parsecs x 3.26 lightyears / parsec = 114,000 lightyears.
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- The Milky Way Galaxy is 100,000 lightyears across. So, these dark spots in the CMB are about the size of our Milky Way galaxy today. Our Galaxy is about 13.51 billion years old. The age of the Earth is 4.543 billion years. See what a glass of wine will do?
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- March 23, 2021 CMB - Cosmic Microwave Background. 2167 3101
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