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Years ago, people thought the Sun revolved around the Earth. Galileo first and then Copernicus found out that the event was just the opposite. Earth, along with other planets, revolves around the Sun. Have you ever wondered why people thought so? Have you not wondered the same when you were a kid? The challenge against this simplified thought is Einstein’s first step in the **theory of relativity. **This is an elementary yet decisive theory that is one of the foundational concepts of the Earth. Let us know the basics of the idea of relativity. Then, we will delve deeper into it with explicit examples that everyone can understand.

## What is the Theory of Relativity?

The theory of relativity by Albert Einstein states that space and time are relative, and all motions must be close to a frame of reference. According to this notion, the laws of physics are the same everywhere.

Two fundamental concepts of Einstein’s theory of relativity are:

- There is no absolute reference frame for motion or time. One can measure velocity if the object or momentum is only about other things.
- The speed of light is irrespective of who measures it or how fast the person is moving and who counts it.

Two theories are connected to relativity theory: Special Relativity Theory and General Relativity Theory.

Let us have a break here before delving deeper into these two theories. Some easy examples can ease your confusion about the theory of relativity.

## Easy Examples of the Theory of Relativity

- Suppose you and your friend (Binita) sit inside your school bus with other children.
- Now, your other friend, Nehal, is watching you outside the bus.
- The bus started moving, and Nehal said, “Binita is moving.
- But, Binita is sitting beside you, and you can see that she is not moving.

Both of you are right. Do you know how? Focus again…

- As Nehal stands outside the bus, the bus moves according to her concerning the buildings and the trees outside.
- As Binita sits inside the bus, she is also moving with the bus.
- You are sitting on the bus with Binita and your classmates. According to you, Binita is not moving because she sits like you and the other students.

You and Nehal are right here because you exist in two states. We will understand the theory in a more simplified way. Before that, we will know what a particular relative theory is.

## What is Special Relative Theory?

In 1905, the theory of special relativity was first introduced by Einstein. This theorem deals with the structure of space-time. Einstein explained the idea based on two postulates –

- The laws of physics are the same for all, irrespective of the observer’s velocity
- The speed of light is always constant regardless of the motion of the light source or the motion of the observer

Thus, the concept of time travel came from Albert Einstein’s theory of relativity. He also added that the time tics decrease with the increase of the person’s velocity. But, this phenomenon is hard to notice as the decrease in time is relatively very low compared to the rise in time. You can make time stand still by increasing the velocity of light, known as time dilation. Other surprising consequences of this theory are:

### Length Shrinking

Objects appear shorter in the direction they are moving concerning the observer.

### Relativity of Simultaneity

Two actions, simultaneous for one person, may not be simultaneous for another person in relative motion.

### Mass

Scientists have observed over the years that the object’s mass increases with the velocity but never knew how to calculate it. This theory offered the solution to their problem that explains that the increased relativistic weight of the object is equal to the kinetic energy divided by the square of the speed of light. Thus, the study of relativity led to the invention of a grand theory, E=mc², where E is energy, m is mass, and c defines the velocity of light.

## General Theory of Relativity

Around 1907-15, Einstein developed the **general theory of relativity**. States that being at rest in the gravitational field and accelerating are physically identical. An observer sees the ball fall similarly on the rocket and Earth. Rocket’s acceleration equals 9.8 m/s2, which makes it possible. Newton’s special relativity and gravitational theory are related to this theory. Some consequences of special relativity are:

### Gravitational Time Dilation

- The passage of time is highly influenced by gravity. You may have heard that astronauts age slower than us because clocks run slower in the deeper gravitational wells than in general gravitational levels.
- As the universe keeps expanding, the parts of it are moving away from Earth faster than the speed of light.
- Light rays bend in the gravitational field.

## Some Regular Phenomenon’s Connected to the Theory of Relativity

Your school does not teach physics to bore you. If you focus a little, you will see how everything abides by the physics’ rules. Our daily life events are deeply intertwined with the laws of physics. Let us find some of them:

- GPS: Sometimes GPS might take your route to the rivers, but, trust me, they also abide by the physics rule. GPS wants to know your “current location” whenever you plan to find a path. It is because satellites that are the backbones of the GPS whoosh around the Earth at a pretty healthy speed. Though 10,000 kilometres/hour seems fast for you, this is nothing compared to the speed of light. Satellites get older by 4 microseconds every day because they experience time dilation. After a day, your location can be up to 8 kilometres away from your actual site. As the satellites are programmed to consider these effects, these discrepancies do not happen.

- Have you ever wondered why gold appears to us as yellowish? The theory of relativity contributes to this as well. The electrons in gold are 79 in number and zoom around an atom of gold, and the same number of protons move in the nucleus. They move at roughly half the speed of light, so they are not dragged into the nucleus. This creates a relativistic effect as the electrons are moving so fast. The shells are squeezed together because of relativity, and it starts to absorb blue light with a minor frequency. Now, our eyes catch only the red light because the blue is absorbed. Hence, gold reflects a glamorous, yellow sheen.

The deeper you go, the more you realise that this Earth is about the theory of relativity. Einstein paved a long path for scientists to come in the future. If they work on the theory more, the mystery of this universe will soon be revealed.

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