{"id":2724,"date":"2020-06-21T01:49:32","date_gmt":"2020-06-21T01:49:32","guid":{"rendered":"http:\/\/www.glionns.com\/?p=2724"},"modified":"2020-07-03T18:35:48","modified_gmt":"2020-07-03T18:35:48","slug":"2724","status":"publish","type":"post","link":"https:\/\/www.glionns.com\/en\/2020\/06\/21\/2724\/","title":{"rendered":"How to Understand Einstein’s Theory of Gravity"},"content":{"rendered":"\n

Einstein\u2019s general relativity may be complicated, but it\u2019s our best way of understanding the universe.
<\/p>\n\n\n\n

\"Einstein<\/figure>\n\n\n\n

A phenomenon known as an \u201cEinstein Ring\u201d created when light is bent by gravity around a large object. In this case, the large red galaxy in the middle is causing light from a much more distant blue galaxy directly behind it to be bent around into the shape of a ring. (Credit: ESA\/Hubble\/NASA)<\/p>\n\n\n\n

An astronaut wakes up in a spaceship, with no memory of how she got there. Sitting alone in a chair, she wonders: \u201cWhere in the universe am I?\u201d<\/p>\n\n\n\n

The ship has no windows. Its instruments are dead. The only clue is the push of the chair against her body. Phew, there\u2019s gravity, she thinks. Her vessel must still be on Earth.<\/p>\n\n\n\n

But then a second possibility occurs to her. The ship could be accelerating through space, pressing her into the seat like a race car picking up speed. From inside the vessel, there is \u2014 terrifyingly \u2014 no way to tell.<\/p>\n\n\n\n

This spacefarer\u2019s dilemma would have been familiar to Albert Einstein. His 1915 general theory of relativity built on the notion that gravity and acceleration are not just easily confused, but are one and the same. This equivalence, \u201cthe happiest thought\u201d of Einstein\u2019s life, was his starting point for redefining gravity.<\/p>\n\n\n\n

General relativity grew out of Einstein\u2019s theory of special relativity, which describes how the speed of light (in a vacuum) can always be constant.<\/p><\/blockquote>\n\n\n\n

According to relativity, anything that can happen inside of a box picking up speed \u2014 i.e., accelerating \u2014 also happens in the presence of gravity. Imagine, for example, a horizontal laser inside an elevator that\u2019s accelerating upward. As the light travels sideways, the elevator rises, causing the beam to strike a spot on the wall slightly lower than where it started. If the elevator accelerates quickly enough, the beam visibly bends toward the floor.<\/p>\n\n\n\n

Einstein showed the same thing happens to a beam inside a stationary elevator within a powerful gravitational field; the gravity bends the light. Similarly, he expected a beam of starlight should bend when passing through the sun\u2019s gravity. This prediction proved correct when the stars moved during the 1919 solar eclipse.<\/p>\n\n\n\n

Relativity describes why a clock on a satellite ticks a few dozen microseconds faster than a clock on Earth; without accounting for that discrepancy, GPS technologies wouldn\u2019t work.<\/p><\/blockquote>\n\n\n\n

To link acceleration and gravity in this way, Einstein overthrew one of his own heroes: Isaac Newton. You may have learned that Newton described gravity as a force, an invisible rubber band that pulls together objects with mass. Newton\u2019s math did a good job at predicting how everything from projectiles to planets moved \u2014 but it kept gravity separate from acceleration.<\/p>\n\n\n\n

Einstein argued that gravity isn\u2019t a force at all. He described it as a curvature of time and space caused by mass and energy. Confused? The German physicist was, too, and he struggled with the theory for nearly a decade. He got help from mathematician Marcel Grossmann, an old friend who shared his notes when a young Einstein skipped class.<\/p>\n\n\n\n

Their math, laid down in 10 equations, explained how gravity could move around objects via a warped reality, accelerating without ever feeling any mysterious Newtonian forces.<\/p>\n\n\n\n

\"Warp<\/figure>\n\n\n\n

An apple feeling no force usually stays in the same place (left). But when gravity curves space and time (right), as Einstein\u2019s general theory of relativity predicts, the fruit winds up on the ground without feeling a force. (Credit: Alison Mackey\/Discover; Collage elements: Envato Elements, Vanatchanan\/Shutterstock)<\/p>\n\n\n\n

The Relative Basics<\/h2>\n\n\n\n

The main takeaways behind Einstein\u2019s general theory of relativity:<\/p>\n\n\n\n

1.<\/strong>\u00a0Time and space are neither flat nor fixed; they are curved and distorted by mass and energy.<\/p>\n\n\n\n

2.<\/strong>\u00a0Gravity is not a force, but rather a distortion of time and space.<\/p>\n\n\n\n

3.\u00a0<\/strong>The effects of gravity are indistinguishable from the effects of acceleration, over a small space.<\/p>\n\n\n\n

\"Einstein<\/figure>\n\n\n\n

Einstein\u2019s inspiration for general relativity struck while he was a patent clerk in Switzerland in 1907. (Credit: Heritage Image Partnership Ltd\/Alamy Stock Photo)<\/p>\n\n\n\n

Einstein\u2019s Peculiar Predictions<\/h2>\n\n\n\n

Relativity makes numerous bizarre predictions, many of them experimentally verified. They only seem bizarre because we don\u2019t notice them in our daily lives \u2014 we live, for the most part, in Newton\u2019s reality. But beyond that lies Einstein\u2019s universe, where gravity bends space and time to its will. Here are some of the theory\u2019s strangest side effects:<\/p>\n\n\n\n

  • Gravity literally slows down time.<\/strong>\u00a0Waves of light emitted by stars stretch out because of this time bending, and objects closer to a massive object age more slowly. Super-precise clocks, which tick according to the vibrations of atoms, have verified that gravity alters time\u2019s flow.<\/li>
  • Satellites have shown that\u00a0rotating celestial bodies twirl the fabric of the cosmos around themselves,<\/strong>\u00a0like honey twisted by a spoon, affecting the motion of gyroscopes.<\/li>
  • One prediction solved a long-standing dilemma, a\u00a0weird wobble in Mercury\u2019s orbit<\/strong>\u00a0that Newton\u2019s math couldn\u2019t account for. (Astronomers had initially blamed a hidden planet called Vulcan.) Relativity explained the wonky orbit in terms of the warping of space by the sun\u2019s powerful gravity.<\/li>
  • Tiny ripples in reality,\u00a0<\/strong>caused by colliding black holes, have tripped sensors in highly sensitive instruments buried underground on Earth.<\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"

    Einstein\u2019s general relativity may be complicated, but it\u2019s our best way of understanding the universe. A phenomenon known as an \u201cEinstein Ring\u201d created when light is bent by gravity around a large object. In this case, the large red galaxy in the middle is causing light from a much more distant blue galaxy directly behind […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-2724","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/posts\/2724","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/comments?post=2724"}],"version-history":[{"count":10,"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/posts\/2724\/revisions"}],"predecessor-version":[{"id":4851,"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/posts\/2724\/revisions\/4851"}],"wp:attachment":[{"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/media?parent=2724"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/categories?post=2724"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.glionns.com\/en\/wp-json\/wp\/v2\/tags?post=2724"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}