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-------------------- 2522 - SPACE - curved or flat?
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- The shape of the universe is one of the most important questions in cosmology, with far-reaching implications, up to and including the ultimate fate of the cosmos.
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- For decades, we've been measuring our universe to be geometrically flat, but a team of cosmologists are now reporting that our latest measurements actually prefer something rounder.
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- The surface of the Earth is curved. We know this because the tiles of geometry that you learned in high school don't always apply. For example, parallel lines don't always stay parallel on the Earth: lines of longitude intersect at the north and south poles, something that can never happen on a flat plain.
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- If you were to draw a triangle connecting three cities on the Earth, you would find that the angles inside that triangle add up to more than 180 degrees.
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- Astronomers are very curious about the ultimate curvature of the universe: how do parallel lines and triangles behave on the very largest scales? They care because the shape of the universe is intimately connected to its fate. Einstein's theory of general relativity, which we use to understand the cosmos, tells us that the contents of space-time affect its shape, and the shape tells the contents how to move.
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- A geometrically flat universe will just keep on expanding forever, while a "closed" one will eventually pull back in on itself, leading to the reverse of the Big Bang, something called the Big Crunch.
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- To test the geometry of space-time, we need to look at all sorts of distant sources and determine if the light from those sources has undergone any major deviations in its path to us. Light beams should stay on the straight and narrow over billions of years, so we can use distant probes to "smooth over" tiny little bumps and wiggles like those caused by galaxies and black holes, and look at the true, underlying geometry of the universe.
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- The cosmic microwave background (CMB) is a bath of light soaking the universe, left over from when our cosmos was just a baby, only 380,000 years old. That light has spent the past 13.8 billion years racing to us, so we can study features in the CMB to test our universe for flatness.
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- The Planck satellite was the latest effort to map the CMB across the whole sky. Planck did a really good job, measuring the CMB to the greatest level of precision yet, with its most recent data released in 2018.
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- If you look at the bare, raw, naked data of the CMB as recorded by Planck, it seems that our universe might just prefer to be closed. The measurement isn't significant enough to be considered ironclad, but it's still suggestive. This is intriguing because everything we know through our theory of the Big Bang suggests that instead our universe should be very, very flat.
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- Taking the Planck data hinting at a curved universe in isolation, we have two possible options:
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------------------ (1) Planck is telling the truth, and the universe just might be curved.
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------------------ (2) Planck is lying to us, and either something in the instrument itself or some other astronomical source (for example, pesky interstellar dust) is making the universe look curved when it really is flat.
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- The Planck Collaboration itself did a lot of analysis and checking, and came to the conclusion that our universe is really flat, but that some other contaminant is nudging the data to make it look curved.
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- But more recently, a trio of astronomers performed their own analysis and came to the opposite conclusion: Planck is not a liar, and the universe is indeed curved.
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- Ask any detective, and they'll tell you that eyewitness testimony is always shaky. You need multiple, unconnected people giving similar accounts of an incident before you can paint a reliable portrait. And so to determine if Planck is lying to us or not, we need to ask some other eyewitnesses.
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- Thankfully, cosmologists have a lot to draw from, with measures aplenty that inform us about the curvature of the universe.
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- The Planck team took a straightforward approach. The researchers combined the data from the Planck satellite with data from other observations, mixed them all together (in a statistically appropriate way) and asked the combined data set about the curvature of the universe. The answer? No curvature at all. Therefore we live in a flat cosmos.
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- In 2019 according to Planck team members, their own data aren't perfect trustworthy when it comes to curvature, and the measurements of the CMB have to be combined with other cosmological probes to get an accurate answer.
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- So is Planck lying to us or not? The Planck Collaboration says yes; the trio of astronomers (who also happen to be members of the Planck Collaboration) say no. While a curved universe seems very unlikely, only more data and more digging in will settle the controversy
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- How can space be curved? 2,200 years ago curvature was determined by plane geometry. Relativity showed us space was curved by mass and gravity. Today curvature in space tells us 96% is mysterious Dark Mass and Dark Energy.
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- The concept of curved space and time is challenging. Not easily digested. Most of the concept relies on mathematics to provide the descriptions, but, math is another language that has to be learned first.
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- And, even space itself is a hard concept. It is impossible to leave space. It holds everything. Like time keeps everything from happening all at once, space keeps everything from being in the same place.
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- If we study space we have to study it from the inside. A corollary might be how early humans discovered that the Earth was not flat, it was not seen as a giant sphere not totally visible until thousands of years later.
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- Math was used by an Egyptian, Eratosthenes, 2,200 years ago to show the Earth was a sphere and we could calculate its circumference. He used plane geometry. He used camel drives to gage the distance between two cities, Syene and Alexandria.
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- He assumed the Sun’s rays were parallel lines. At noon in Syene he saw the Sun light directly overhead reach the bottom of a well. At noon in Alexandria, 5,000 stadice away, the Sun rays were at an angle of 1/50 of a circle ( 7 degrees, 12 arc-seconds) A full circle would be 50 * 5,000 stadice, or 35,000 miles for the circumference. The Earth is 24,901 miles circumference. He was 29% to high. The camels must have been taking shorter steps that day.
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- Using geometry on curved surfaces did not arrive until 1818 when Carl Gauss showed that for curved surfaces the laws of geometry were different. The shortest distance between two points is not a direct line. The shortest path is always a geodesic, a curved arc with the center at the center of the Earth in the case of our sphere.
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- Euclid decided that not only the Earth’s surface was curved, but, space itself was curved. The tracers for the geodesics are rays of light. Light always takes the shortest path in empty space. Gravitational lensing uses the fact that light bends passing through curved space created by a massive object.
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- It was not until 1916 that the General Theory of Relativity showed us the math for curved space. Space curves in response to mass. Arthur Eddington first demonstrated how star light bends around a solar eclipse.
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- So, if we can measure how much mass bends light we can calculate how much mass is there. The biggest effect occurs around galaxy clusters, the most massive objects in the Universe. Clusters contain thousands of galaxies and billions of stars.
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- The surprising result measuring bending starlight ( actually quasars) was that cluster contain more mass than can be seen. This missing mass is known as Dark Matter and we have yet to discover what it actually is. It is affected by gravity but not electromagnetism.
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- Astronomers are using this technique on the Cosmic Microwave Background radiation, light that has been redshifted into the microwave spectrum after 13 billion lightyears traveling through expanding space. The “ hotspots” in the fabric of the CMB are magnified or shrink from actual size. If we can determine the true size we can calculate the magnification and the average curvature of space.
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- The result: On average the curvature of space is flat. And, the density of mass is on average 10^-29 grams per cubic centimeter. With that small a number it is obvious the most of space of “empty” of mass. But, add up all the mass in the Universe and it reaches only 30% of the calculated result using this density.
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- Where is the missing 70% of the universe? It has been given the name “ Dark Energy”. Remember, energy and mass are the same thing. Mass is concentrated energy according to E=mc^2.
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- What we model as “ space” today is resembling and old picnic table. Full of chips and scratches you can see up close. But, from a distance the table top looks perfectly smooth and flat. The chips and scratches correspond to small regions of strong space curvature due to the gravity from individual stars and galaxies.
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- These stars and galaxies account for only 4% of the mass-energy in the Universe. The other 96% is the missing matter and energy.
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- We have come a long way from plane geometry in understanding the Universe. With 96% left we have a long way to go.
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- Maybe the Universe appears flat because it is so big even if it is curved we can not ever be able to notice it.
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------------------------- Other Reviews available about space:
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- 2475 - space is not nothing
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- 2404 - the vacuum of space. Also lists 8 more Reviews about space.
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- 2279 - inventions for earthlings.
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- 2252 - what did we learn in space?
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- 2243 - what is space really? Also lists 5 more Reviews about space.
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- 2074 - much todo about nothing.
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- 2049 - the expanding space.
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- 2029 - dust is outer space. Lists 11 more Reviews about space.
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- 1986 - space is what separates things. Time is what keeps everything from happening all at once.
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- 1831 - from Blackholes to empty space.
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- 1790 - why space ant time must change as we approach the speed of light.
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- 1773 - the size of space depends on how fast you are moving.
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- 1407 - space is in constant motion.-
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- 1241 - At the smallest levels things remain connected. Even though they are separated in space.
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- December 3, 2019 2522 1861
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--------------------- Tuesday, December 3, 2019 --------------------
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