If light has no mass, why is it affected by gravity? General Relativity Theory

what is gravity two famous scientists did research on how gravity Works Newton was the foremost of them what Newton is explaining about gravity is that all things in the universe have mass there will always be an attraction between two objects or every Mass attracts every other Mass the gravitational force of an object also varies according to its mass that is an object with a greater mass pulls a lighter object to its side the greater the distance between two masses the less their gravitational force decreases force is inversely proportional to the distance to the power of two this means that if the distance increases by two times the force will decrease by four times if the distance increases by three times the force decreases by nine times this is what Newton explained about gravity everything happens just as Newton said the Earth orbits the Sun the moon orbits the earth and the universe itself Works according to Newton's gravity if the Sun's gravity is so strong why didn't the Earth smash into it distance and angular momentum are relevant factors in this context well everything's all right this was accepted by everyone who was there then because it fits perfectly according to physics But Here Comes the biggest confusion the distance between the Sun and the Earth is about 150 million kilometers will there be a force for such a distance for example if I kick a ball there is contact between me and the ball so there is physical contact that makes the ball move but what lies between the Sun and the Earth is the greatest distance that being the case scientists are gradually confused about what the kind of force that causes binding between such objects and this is where Einstein joins according to him gravity is not a force but it doesn't make sense why does it happen if there is no gravity what's making it happen then which mysterious thing causes it but his explanation for it though not understood by anyone at the time was understood a few years later and it was that discovery that elevated him to an important scientist in the world so what was his Discovery let's see how that works [Music] our universe looks like it is empty but in reality it is not empty empty spaces are not really empty the whole universe is like a fabric sheet that sheet combined with fourth dimension time becomes space time he says curvatures in space-time are responsible for gravity let's take a fabric mat for example and make a fat man sit in the middle of it and make a skinny man sit in the edge of the mat now we will see that the mat bends inside where the fat man is so the skinny man is automatically pulled towards the fat man the fat man does not exert any force and even if he doesn't touch him the skinny man is drawn towards him similarly gravity occurs for everything in the universe as the sun bends space-time the Earth is attracted towards it it is not a force as space bends it has an impact on the objects on the Curve the Mast tells space-time how to curve space-time tells the mass how to move now it's easy to explain how Einstein came to realize this he found out the truth through thought experiments then the mathematical equations were also confirmed he's sitting in his office one day when he sees a man cleaning the windows of a building close by he starts to think about what would happen if that person fell down while it may seem strange to us to hear this Einstein describes it as the happiest thought in my life let's look at the things that crossed his mind we will lock the man who was falling from the top of the building into an elevator a man who is falling will not feel any Force since he is inside the elevator and there is no reference point he can't realize if he falls down or floats the phenomenon of falling down as a free fall without any reference point is like floating in space that is according to physics there is no difference between a person who falls from the top of a building and floats in space both of them wouldn't feel any gravitational force so empty space weightlessness is equal to free fall on Earth let's move on to the next step now I'm floating in space inside the lift and there's a ball also floating with me a motor engine has been fit into the bottom of my lift and I started that engine and accelerated the lift upwards at a speed of 9.8 per second Square 9.8 is 1g the gravitational force for Earth now what happens when I accelerated the speed is that the ball floating with me will fall down on the lift floor and I will also be pushed towards the bottom of the lift I feel the same amount of gravity on Earth as I feel inside the lift that is accelerating at a speed of 9.8 meters per second Square in space whatever can be done with the help of gravity on Earth can also be done in this lift I don't feel any difference whether in space or on Earth so free fall on Earth is equal to free movement in space gravity on Earth is equal to 9.8 meters per second Square acceleration in space that is acceleration causes gravity now I'm in space inside a lift and I turn off that engine and the lift is made to float steadily in one place what will happen if I throw the ball in straight when I throw a ball it goes in a straight line what if I throw that ball at an exhilarating lift the ball will go down in a curved path and hit onto the floor so far everything is going well now I've switched from the ball to a light beam how will it go if I torch the light in the accelerating lift light is known to always go in a straight line at constant velocity if you throw a ball on the earth it will travel in a curved path and then fall to the ground if the ball is thrown from an acceleration lift in space it will also travel in a curved path does that mean light itself will be able to bend can light be bent even though it has no mass and always moves in a straight line Einstein says it will bend yes it is possible if there is something called space curvature as he claims how do we find it the lift that is accelerating at just 9.8 meters per second Square does not have enough opportunity to bend the light so now I change the acceleration speed from 9.8 to 98. according to Einstein's prediction the bend of light and acceleration at 98 meters per second square is very small that is it bends only the size of an electron this means that if we increase gravity or acceleration light can bend more and more well how do we prove this in those days it was impossible to build an engine that had such acceleration and implement it in fact not even a rocket was invented at the time but we have gravity the sun was the strongest gravity when it comes to our nearby things its gravity is 28 times stronger than Earth's because its mass is 330 000 times bigger if we calculate what will happen in that gravity the gravity will bend the light to 1.75 Arc seconds and Arc second is 360 degrees in a circle and if you take one degree of it it has 60 Minutes within it and 60 seconds per minute of these 1.75 Arc seconds is very small in 1915 Einstein published his theory with equations everyone was confused when they saw this Theory what is this what is he trying to say no one understood it at the time then four years later Arthur Eddington the greatest astronomer at the time from England set out with his team to experiment with this at that time they knew the exact location of some of the stars and if Einstein's theory was correct the star behind the sun should be visible somewhere else because the light should bend and be visible to our eyes they were waiting for a total solar eclipse because the sun's brightness makes it hard to see nearby Stars when the day of the solar eclipse came Arthur eddington's team started taking pictures to their surprise the star showed up in the photos in a place they hadn't expected gravity had bent light itself because space-time had been bent for example I go straight from one place to the North Pole as far as I'm concerned I'm going in a straight line but to an outside Observer I appear to be taking a curved path similarly light always traveled straight and because its path is curved it also bends so the shortest path of light can be a curved one now you may have a doubt if the space at the bottom of a mast object only bends the space Bend at the top of that object all the space-time curvatures we see in the video are shown in 2D visuals so that we can easily understand them its 3D form is hard to understand but that's exactly the case it was only after this space-time curvature was demonstrated that Einstein was celebrated as the greatest scientist this thought experiment is not a simple one it is the greatest thought in human history this simply explained not only gravity but also showed the world how the entire universe works this is called a general theory of relativity that's what space-time curvature is but how did this time come in it how does space-time explain time deletion the special relativity Theory provides an explanation and we'll see it in detail in the next video

Channel: Klonusk

Views: 1,684,401

Keywords: General relativity theory, Einstein’s gravity, General theory of relativity, Space Time curvature, What is gravity, How gravity works, What is general relativity, General relativity explained simply, Simplest explanation of general relativity theory, Einstein theory of relativity, what is space time curvature, Einstein, General theory of relativity explained, Space time explained

Id: KXhJDPu0G-E

Length: 9min 21sec (561 seconds)

Published: Tue Nov 08 2022