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------------------------ - 1861 - How can space be curved?
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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. 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. 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 shrunk 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 that most of space is “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 an 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. 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 notice it. God only knows? It sure looks flat to me.
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- Request these Reviews to learn more:
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- #1831 - From Blackholes to empty space.
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- #1790 - Why space and 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. Believe me this defies all logic.
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--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
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- to: ------- jamesdetrick@comcast.net ------ “Jim Detrick” -----------
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----- 707-536-3272 ---------------- Friday, April 22, 2016 -----
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