Today we are going to talk about a very interesting phenomenon, which has come into existence with the Einstein's special theory of relativity. We are not talking about any other things, we are only talking about THE TIME DILATION.
In the special theory of relativity Albert Einstein shows that time is a relative quantity. According to the Einstein the flow of time is same as the flow of river, we know that sometimes river flow fast and sometimes this river flows slower. Exactly same as river, time also flow sometimes fast and sometimes slow.
But when does time flow slower and faster? This is the question. In the form of answer, it's one explaination is in the special theory of relativity, and one explaination is in the general theory of relativity.
According to the Special theory of relativity (STR), slowance and fastance of time only depends on the speed of the object.
T = D/S
If speed is very large then time becomes very slow or you can say very small. And if speed is very small then time becomes fast or you can say it becomes large. The magnitude of dilated time, is given as follows:
t =t0/√[1 (v^2/c^2)]
Where t is dilated time , t0 is rest time , v is travelling velocity , c is speed of light.
Let's understand this statement by a thought Imagination.
Imagine for a two clock , one of them is in the rocket and one is on the earth at rest. This rocket is very powerful and can fly with the speed of light. If rocket starts flying with the speed of light then due to having maximum constant speed (Speed of light) ,
then time in the rocket will be nearly stopped. When the rocket stop to his destination then the people in the rocket feel that time doesn't change so far for him. But the clock which is on the earth , time change to this for a large extent , because this clock is at rest.
But, what is time dilatation?
We will talk about it after giving the second explaination on the basis general theory of relativity.
According to this theory... Slowance and fastance of time depends on the mass of the object or we can say to, its gravitational potential.
Take a two clock put one clock on the earth and put another clock on the very massive objects that is the BLACK HOLE. Then it is noticed that the clock which is nearer or in the black hole or on any massive objects , time passes slowly for that clock . But that clock which is on the earth , time passes fastly for that.
But why does time passes slowly near a supermassive objects ie. The black hole.
Let's find out the answer of this question...
According to the general theory of relativity , we know that, large masses objects create large distortion in the space time. This large distortion gives the large space time slope, and this large slope gives a very high acceleration due to free falling, or simply says the acceleration due to gravity.
And sometime this acceleration is about to speed is light, depending on the massiveness of the black hole. this is the reason of why light can't be escaped from any black hole.? but if when a object enter in the slope of a black hole then he starts moving around it (revolution) with the approx the speed of light , along the accretion disk.

Motion of object around the black hole Image courtesy : Nat. Geo. Ch. 
If it is moving around the black hole with the approx of speed of light , then we know that time becomes slow for that object, we have seen this in special theory of relativity.
Now it's time to give a definition to the term time dilation.
Time dilation is nothing , but it is only the measurement of difference of the elapsed time between the two clocks , either the two clocks are in the relative motion to each other or the two clocks located near the two different object masses. ( In which first object is very massive and second object is less massive than first). We have discussed this definition above in full length.
Time dilation gives birth the new concept that is TIME TRAVEL. We will talk about it in coming articles.
Very nice
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