What happens when we drop an apple to the ground? It falls down, right? Why does it fall down, because of gravity. It’s the most common answer. Because it is the only answer. The General Theory of Relativity, I have seen a lot of people talk about it, even if they don’t know enough about it. It is the most popular theory that exists as of current time and that’s just because it helped to create a new world of physics, helped to improve the ongoing world of physics and used old physician tools and systems to prove it’s calculations. Einstein because of this became the most respected, important and brilliant scientist of all time, so I thought why not talk about it? The general theory of relativity opened the door to quantum physics, as Niels Bohr said. But Einstein never really embraced the quantum world it revealed. When you bring a magnet close to a piece of iron, it attracts the iron and it sticks to the magnet, and it just happens in empty space, right? The magnetic field of a magnet helps the magnet attract the piece of iron. Just like the magnetic field of a magnet, the Earth has a gravitational field, which keeps us all on the ground, without it we would be floating around just like in space because there is no gravity in space. The Earth gravitational field is limited to upon itself, which means it’s not so strong as a star’s or a black hole’s gravitational field. Well, you can’t have that much gravity in a planet, it’s too small for that. The Earth’s gravitational field decreases as you get away from it, just like that of a star’s or a magnet’s. So as we get more and more away from the Earth, the gravity demolishes. If you want to throw something into space as seen in cartoons, you have to throw it with so much force, that it should have that velocity to escape from the Earth’s gravitational force. To achieve that velocity, you have to be very fast, as that the speed of a rocket. The Earth’s gravitational force is what keeps the moon take orbits around us, it don’t orbit the sun because the sun is too far away and the subject (moon) is too small and also that the Earth’s gravitational force is way closer to it and is impacting it more. It’s like you have a small magnet, a piece of iron and a big magnet. Obviously, the big magnet would have more magnetic force now, so the small magnet being close to the piece of iron, and the big magnet being far from the piece of iron. Who wins? The small magnet, if you applied the logic of the Earth, the moon and the sun, you weren’t really correct. Any magnet can’t have that much force to pull a faraway object, even the strongest magnet in the world has to be close enough to the subject to attract it. Einstein said that bodies which are moving because of the force exerted on them by the gravitational field receive an acceleration. They accelerate because of the force exerted on them. One example of this which did not exist at the time Einstein wrote the theory is that dark matter has gravitational force which it exerts on existing matter in the universe. Some people may ask “Does dark energy have a gravitational force as it forces the universe to expand at a faster and faster rate?” Good question but no, it has a repulsive, anti-gravity force which reacts on the universe as a whole and stretches the very fabric of space-time. Therefore, we know that-: Acceleration=(Gravitational mass) by (Inertial mass) x (Intensity of the Gravitational field)
The mass obviously matters because if you are too big, you have too much mass, you would get less affected by the force. For example-: If a star is born close to a bigger star, the bigger star won't get affected by the gravitational force of the other star because its bigger than it. Why do planets orbit stars? I am sure your answer would be because of the gravitational force. But there is a bigger picture here than that. A star has so much mass that it literally bends the fabric of space-time and when it does bend the fabric of space-time, that forces the planets to revolve around it. Let me explain you in a practical way. Take a paper, hold it straight horizontally, imagine the lines on the paper to be the fabrics of space-time, now take a finger and place it on the paper with a bit of force. You notice that the paper is bent from wherever you put your finger, now if you take anything small like a bead, a very small one you and put it on the paper, a bit far away from where your finger is, you notice that that bead rolls down to the bent part of the paper where your finger is and that is exactly what happens to the other planets and a star, just that the planets don’t roll down fully. Because the planets roll down and they kind of get stuck in the gravitational force of the star, the star makes the planets orbit it, swing them around. An interesting thing is that wormholes were predicted by the general theory of relativity. They are also known as Einstein-Rosen bridges, because Rosen helped Einstein in the calculations. Wormholes are still hypothetical but the math still stays strong that they do exist. A wormhole bends the fabric of space time to reach faster from 1 place to another. It does not make you travel faster than the speed of light, a very common question. Interstellar explains wormholes in quiet a way. Scientists believe that wormholes are naturally occurring and do exist at the particle level and transmit tiny particles from 1 place to another. Mathematics predicts that wormholes are created when 2 bodies of great masses apply enough force on each other to create a tunnel connecting distant points. The General Theory of Relativity predicts that the universe is curved in a lot of individual parts. Geometry, especially Euclidean plays a great role in determining the shape of the universe. The curves in space-time as discussed earlier might be seen as ripples in a lake. Einstein said that the universe is spherical, but since the distribution of matter is not uniform i.e. it is not spread equally and there are some curves in individual parts of it, the universe would be quasi-spherical meaning it would be an irregular shape as a spherical. Well, the theory has made such big assumptions and opened the world to quantum mechanics, it is thus, with no doubt the most important theory in physics. It has proved so many things and it is a starter point for literally mostly everything we study today in higher and sometimes lower physics. It has also proved some previous assumptions made by scientists like Newton wrong. How can we end the blog without talking about Einstein’s most famous and important equation which bring a revolution in physics, E=mc². It is known as the Energy-mass equivalence equation where E is energy, M is mass, and c² is the speed of light. With no doubt, Einstein is the greatest and most influential scientist of all time along with his General Theory of Relativity being the greatest and most beautiful theory of all time and his energy-mass equivalence equation is the most beautiful equation in physics.
By,
Deeparsh Bhanot
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