General Relativity Explained simply & visually
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Published 2020-06-20
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3D gravity animation courtesy of: 1ucasvb.tumblr.com/
Albert Einstein was ridiculed when he first published his theory. People thought it was too weird and radical to be real. Einstein wasn’t satisfied with his theory either, because the theory did not apply if Gravity was present or if the observer was accelerating. One day, while observing a window washer on a ladder near his patent office, he had a thought experiments.
He imagined what would happen if the worker were to fall. He put himself in the window washer’s perspective, and imagined what he would experience as he was falling. He realized that if he was falling, gravity would be the only force acting on him. He would be accelerating towards the ground, but since the ground would not be pushing up on his body, he would feel no weight. And this would be no different than being weightless in space.
In a way gravity and acceleration were different ways to describe the same thing. The way to connect gravity in the theory of relativity was through the idea of acceleration, and this became the basis of general relativity.
Einstein imagined being in a room with no windows, and a bathroom scale. It would weigh 80 Kgs, What if the room was on a space ship accelerating in an upward direction at 9.8 m/s/s. He would feel the same weight. There would be no difference
He imagined what would happen if he took a flashlight and pointed it from one side of the room to the other, as the space ship was accelerating upwards. If he had a ruler, he could measure the height of the light on the other side of the room. He realized that the height measured on the wall would be lower than the source of the light, because the floor of the room would be rushing upwards at ever faster speeds, as the light was propagating across the room. The light beam would appear to curve downward.
However, If you were on earth, and you measured the two heights, you may think that there should be no difference. That light should go straight to the other side of the room. Einstein thought it can’t be because it would violate the principle of equivalence. Acceleration of the room on a space should be no different than the room under the influence of gravity on earth. He realized that this meant light must bend in the presence of a gravitational field.
But light should be going on the shortest path. Then he realized, maybe the shortest path between two points is not a straight line but a curved line near gravity.
This was the key insight that Einstein had about gravity. But in order to express this mathematically, it required very complicated mathematics that even a genius like Einstein could not easily figure out. He contacted an old buddy from his college days, mathematician Marcel Grossman.
It’s important to note that the trampoline analogy you normally see on TV shows and youtube videos like this is a 2D plane used for visualization purposes only, but it is really in 3D.
In order for this theory to really be taken seriously, it had to make a prediction that could be tested, which was confirmed by the fact that it explained Mercury’s orbit which had been a mystery for decades because it had a precession. General relativity predicted exactly the precession that Mercury actually has.
But many skeptics still remained. The most fool proof confirmation came 4 years after he published it,when a team led English Astronomer, Arthur Eddington. in 1919, photographed stars near the sun during a total solar eclipse. He found that light passed near the sun was bent by the curvature of space due to its gravity. This is the moment Einstein became a celebrity.
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Why is this not just a distortion of space but also of time?...because special relativity says that light always moves at the same speed regardless of perspective or reference frame. This means that light will have the same speed in an accelerating reference frame as it will in a resting reference frame. But since the distance traveled by the beam of light in a gravitational field is longer due the curving of space, in order for the speed of light to remain constant, time itself must pass slower in the gravitational field relative to time in empty space.
General relativity does not answer everything. Although it tells us how gravity works, it doesn’t really tell us what exactly it is.
All Comments (20)
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Now I know how my dog feels when I'm talking to it.
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When you see it, it's like oh cool. But when you actually start thinking about it, it's so insane.
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Stuff like this is so interesting to me. I’m a 16 year old who doesn’t like school, and yet my science teacher was passionate enough about physics and astronomy/cosmology that it got me so invested in it to the point where I go out of my way to look up things like this just because it’s so mind-blowing!
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watched this video 2 years ago while i was in high school, and it just triggered a big interest in physics for me, so a started to dig deeper in the wonderful world of youtube physics content. Now i am studying physics at the university and pursueing my passion, and all of it started with this video i clicked on when i was bored. Keep up the great work!
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Shout out to the window washer. Without him this video would not exist.
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Imagine being that window washer and living your whole life completely oblivious to the fact that you helped Albert Einstein figure out how the entire universe worked.
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Damn! This guy really breaks it down because he understands it properly. Not a single other video online can simplify it like he could. Kudos Arvin, you're amazing!
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Watching videos like this at 3:00 a.m. instead of sleeping just hits different
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sometimes a 14-minute video does more justice than those 14 years at school!
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Im a clerk. And also discovered a theory of relatively of time. Time slowdowns on monday. And speeds up on payroll day.
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The explanation around 10:50 was a perfect summary of how time can be affected by gravity. I never fully got it until hearing that.
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Really beautifully explained. I especially appreciate the reminder that distortion in the spacetime fabric occurs in three dimensions, not just in the 2 dimensions we are often shown in graphics. Mr Ash is wonderfully skilled in presenting this material.
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And yet there are people who still believe in flat earth
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This guy is a genius for making it so easy to understand
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Thanks. I'm getting closer to being less confused about special relativity thanks to this video. The more it's simplified the clearer the complexities come into focus. Keep up the good work with these videos.
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Great video. Thank you for this simplified version of a complex theory. What I learned from this video: 1. Gravity is caused by massive objects in space. How these massive objects cause gravity is unknown till date. (Understood) 2. Gravity curves light as it takes the shortest path between two points. (Understood) 3. Gravity also curves time and so the time near the source of gravity passes slower. (Confusing concept; need to research more) 4. Gravity curves space as well that result in objects moving around the massive objects. (Understood) 4. Gravity concept in actual is a 3d model showed in this video. (Confusing concept; need to research more). If you guys can create additional bullets for us noobs to understand gravity, it would be appreciated.
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2 things that make those videos great : 1. The animations 2. The quality of the questions he asks. It's like he's in your head. I hate it so much when people pretend to explain a concept and leave obvious questions unanswered. Thank you Arvin Ash.
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"Time is not absolute" Gives me chills....
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for those who cannot figure out things easily, this channel is an ultimate piece of gem. thank u very very much for all these illustrations, explanations, etc ... for everything.
