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Time is very essential part of our life. We all know that time waits for none and it always moves forward. The direction of time is always towards the future from the present, not from present to past. But this is just the basic understanding.

Time existed even before the invention of clocks and watches. While clocks and watches are just a measuring device of time.

## What exactly is time? Why is it so important?

Physics is the only subject which gives us a detailed view of time. So, let’s understand about time.

### History of Time

The history of time is huge. But we came to know about it and its properties only after studying the fastest thing in the universe i.e Light.

Light and its particles along with its speed forced us to consider the time factor and include it in a bigger picture.

*But why did studying time became so important?*

In the mid 19th century, James Maxwell proved that light is an electromagnetic wave and it travels at a constant speed in a vacuum (like space) for everyone. This led to a rise in many questions which later proved by other scientists.

## The concept of Classical Relativity

Einstein discovered the **Classical Relativity** which says that no object in the universe is in absolute rest or motion. Every object move relative to each other.

For example, Suppose two boys are throwing a ball to each other in a moving truck. The velocity of the truck is 60 mph. While the velocity of the ball is 5 mph.

For both the boys, the speed of the ball is 5mph.

But what if someone watching from outside the truck? Will it be the same speed for him also?

Of course not he would observe the ball is moving at a speed of 65 mph. Both the speed of the ball and the truck will come into consideration.

i.e 60(velocity of truck) + 5(velocity of ball) = 65 mph.

Now*, Do you think the person outside the truck is at absolute rest?* No, the boy is also constantly moving since our earth is constantly moving. Sun, Moon or the entire galaxy is constantly moving. Then how can the person be at rest?

Nothing in this universe is at an absolute state of rest. Everything is constantly moving in relative to each other. This is the *classical relativity*.

As we’ve noticed in the above example, the speed of the bus also comes into consideration while counting the speed of the ball.

*Does this same principle apply to each and everything in the universe?*

*Is speed for everything in this universe is related to each other?*

*Is there anything in this universe which has a constant speed irrespective of its source?*

**James Maxwell** gave a very good contribution to this topic. According to him, light is just an electromagnetic wave traveling through an empty space whose speed will be constant for all observers.

It doesn’t matter whether that beam of light is coming out from a fast moving vehicle or a stationary vehicle. This shows that light is universally constant.

## The problem of 19th Century

According to classical relativity, Light travels at a speed of **186,000 miles/sec**. But one question arises, *Light travels with relative to what?*

This was one of the biggest problem in the 19th century.

Einstein knew about this and he accepted it. He accepted that the speed of light is constant for all observers. Also light travels at a fixed speed of 186,000 miles/sec. He then started his research on this topic.

In *1905*, Einstein placed a hypothesis, which later became one of his most famous theory. The theory was “** Theory of Special Relativity**” where he discussed light in detail.

This theory solved many problems. But what was so special about this theory?

Einstein proposed that in order for the speed of light to be constant at 186,000 miles/sec, one element has to slow down. And the element was **Time**.

If an object is in motion and travels at the speed of light, then for that object time has to slow down to maintain the constant and consistent speed of light.

Since time slows down, so now the speed of the object will be constant with respect to the speed of light which is 186,000 miles/sec. This phenomenon is called **Time Dilation**.

This sounds a bit awkward, as we don’t experience these things in our day-to-day life. But this is the reality which Einstein proved in his theory.

Einstein believed that *time* and *space* are the same elements. According to him, space and time are related to each other.

The faster you move in space dimension, the slower will be your time dimension. And if you travel closer to the speed of light, your clocks tick will be slower. Catching the light speed will completely stop time.

The particles of light i.e *photons are massless*. So, it is hard to catch the speed of light which is nearly impossible.

According to this theory, if we can exceed the speed of light, we will be able to go backward in time i.e into past. However, this is only a theory. It may or may not be true.

## Conclusion

- We understood
*what exactly time is*, and how it works. *Space*and*Time*are intertwined into a common fabric of the Universe which is called as**Spacetime.***Time is relative*and depends on the speed at which an object is moving.- An object moving at a closing speed of light will have their clocks tick slower, because of
*Time Dilation.*While reaching light speeds passage of time will stop altogether.

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