In the previous post, we discussed the special theory of relativity. If you didn’t read it yet, then please go through it by clicking here before going through this post, otherwise, you will not be able to understand it. In this post, we will discuss the modified theory of his previous theory i.e General Theory of Relativity. So let’s get started.
General Theory of Relativity
In 1905, physicist Albert Einstein determined that the laws of physics are the same for all non-accelerating observers and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time.
But Albert Einstein didn’t satisfy yet and tried to include acceleration in the theory, after spending almost ten years he published his theory of general relativity in 1915. In this theory, he explained that massive objects ( i.e. planets, satellites etc.) cause a distortion in space-time, which is felt as gravity.
In our practical world, Newton’s Law of Universal Gravitation applies almost to all physical bodies which possess mass and we can determine and calculate the behavior of different physical quantities (i.e. velocity, acceleration etc.). The bending of light was never actually predicted by Newton but, in combination with the idea from special relativity that all forms of energy (including light) have an effective mass, then it seems logical that, as light passes a massive body like the Sun, it too will feel the pull of gravity and be bent slightly from its actual path.
Curiously, however, Einstein’s theory predicts that the path of light will be bent by twice as much as does Newton’s theory, due to a kind of positive feedback. The English astronomer Arthur Eddington confirmed Einstein’s predictions of the deflection of light from other stars by the Sun’s gravity using measurements taken in West Africa during an eclipse of the Sun in 1919, after which the General Theory of Relativity was generally accepted in the scientific community.
The theory has been proven remarkably accurate and robust in many different tests over the last century.
Terms derived from this theory
There are many terms and concepts originated from this theory. Let’s discuss on some concepts and get some overview as well.
By the general theory of relativity a term comes out from it and it is called gravitational waves. It was said that by the collision of two or more massive space body such as black holes, gravitational waves formed in the form of ripples just like if a stone is thrown into the water, But by then it had no proof.
As I already told that the event of the collision of two black holes is very violent and are thought to be able to create ripples in space-time known as gravitational waves. But In 2016 an organization called Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that it found evidence of these tell-tales.
As time passes, the organization anticipates that more gravitational waves will be detected by LIGO and other upcoming instruments, such as the one planned by India.
Black holes are incredibly massive bodies but cover only a small region. Because of the relationship between mass and gravity, apparently, their density is very high (can’t even imagine). This means they have an extremely powerful gravitational force. Virtually nothing can escape from them even light.
Theoretically, any universal body can become a black hole. Are you kidding………? No, I’m not. If you able to contract any physical body which possesses mass into Schwarzschild radius then that body will turn into a black hole.
Let me take an example, If you somehow managed to contract the earth’s size into a ball of 1 cm radius size, then our earth will turn into a black hole. Interesting………? Isn’t it……….
Black holes have two major parts:
- Event horizon: The event horizon of a black hole is the boundary around the mouth of the black hole where anything loses its ability to escape. Once a particle crosses the event horizon, it cannot leave. Gravity is constant across the event horizon.
- Singularity: The inner region of a black hole, where its mass lies, is known as its singularity, the single point in space-time where the mass of the black hole is concentrated.
Time travel has always been one of the most curious concepts in the world of science and always will. Even you must have watched some movies about this concept. If you haven’t watched any movie yet on it, then please go and watch it. Star Trek-Beyond, Interstellar are some great movies. Interstellar is my personal favorite and I assure you that this movie is not just a movie but something even more. You will feel thrilled and excited for sure after watching it.
Einstein’s theory of special relativity says that time slows down or speeds up depending on how fast you move relative to something else. Approaching the speed of light, a person inside a spaceship would age much slower than his twin at home. Also, under Einstein’s theory of general relativity, gravity can bend time.
Lets picture a four-dimensional fabric called space-time. When anything that has mass places on that piece of fabric, it causes a bending of space-time. The bending of space-time causes objects to move on a curved path and that curvature of space is what we know as gravity.
Both the general and special relativity theories have been proven with GPS satellite technology that has very accurate timepieces on board. The effects of gravity, as well as the satellites’ increased speed above the Earth relative to observers on the ground, make the unadjusted clocks gain 38 microseconds a day.
In a sense, this effect called time dilation, means astronauts are time travelers, as they return to Earth, they would be slightly younger than their identical twins that remain on the planet.
Quantum field theory in curved spacetime
General relativity is only one of the pillars of modern physics. The other is quantum mechanics, which describes what happens at the atomic and subatomic scale. Its modern incarnation, quantum field theory, has been spectacularly successful at describing and predicting the behavior of fundamental particles and forces.
The main challenge now is to combine the two ideas into one overarching theory, to be known as quantum gravity. Such a theory would be crucial for explaining the first moments of the big bang, when the universe was dense, hot and small, or what happens near the singularity at the cores of black holes, where the effects of quantum physics may compete with those of general relativity.
Although there is as yet no final theory of quantum gravity, there are several candidate theories being actively explored.
These are some key terms and principles derived from this theory. We will discuss these and some other terms briefly in the upcoming posts. If you have any suggestions and queries related to the post, let me know in the comment section below. Please do share this post to your circle to explore the knowledge you must know.