As the term indicates, time, here is being ‘dilated‘ or the interval gets elongates through time. This whole thing is related to observations and relative motion.
When a process takes place and if we are seeing them, then we can say there are two categories here, which is depended on the relative motion: The observer and what is being observed.
When the relative velocity increases, the observer feels that, the time of what is being observed, flows slowly. As the speed nears the light speed, the observer feels that, the time of what being observed is not at all flowing.
We use the word frame to represent the system under consideration. Asking, ‘what is the boundary of this frame’ is a good question, but that too depends on the observer and what is being observed.
Let’s try some examples to know what a frame is
I am flying a kite. Here, I am the observer, who is flying the kite and my kite is what being observed. We say this both on the basis of ground, which is the earth, which is at rest. But is it really at rest? Our Earth isn’t revolving around sun? Then how can we say that earth is at rest? That’s where the frame plays its role. When we consider our self and the kite, our frame is limited inside the earth. We don’t have to bother outside it. I can’t precisely say that ‘the atmosphere is the boundary, or the sea is the boundary like such, because they are arising from our predominant thoughts.
Now, i am sitting on a chair, let it be on my room. Well, i am at rest; looking at the number of bars of my window. But am i actually at rest? No, it isn’t. Here too, the earth is revolving. But well, i consider my self and my chair at rest, with respect to the earth.
The frame, which is at rest, inside earth.
Now, i am going in my car, straight in a highway. Of course, you are too coming along with me. But, in your car, in my direction.
Consider we both have same speed. What do you feel? we can talk to each other, we can hold our hands each other.
But, what if, there had a slightest change in the speed of any of us? We would have to shout to hear each other, we can’t hold our hand any more. Because, we were relatively at rest, when we had same speed, but not when we had different; even slightest difference will cause the problem. This tells us, that for this entire car-example, we don’t have to bother anything else, just the relative speed among us.
(Confusingly, the earth, which is always at rest, for every experiment in earth creates some problem for the beginners)
Now, we became rich, consider we had Rockets for leisure time :P.
We do the same car-experiment in rocket: a Rocket experiment.
First we together go in same direction, with same speed. Let’s make the speed a 100 kmph, for our easiness. We now change the speed slightly, by a 0.1 kmph.
What will happen? We will find the same result, we found in the car.
We don’t have to bother the resting earth now, as we are in the space; Here we consider the two of us, namely: our relative speeds.
Here we, each other are the boundaries of our frames.
Now, change the speed of rocket.
Make it nearly the speed of light. If both of the rockets are going together, nothing happens. We don’t feel anything.
Consider, my rocket had some engine problems. So, i landed in the nearest planet. But you didn’t wait for me, went along with your rocket. I switched on the robots in my rocket, they started repairing my rocket. While, i looked at my watch.
Its running as usual.
Now ,if i had the opportunity to see your watch (which i really can’t, but imagine if i can) then i will see your, second hand is moving slowly.
This happens only for me, when i am at my own frame, observing you, who is now travelling with relative speed of light, in your own frame. This is what i feel.
What about you? What does you, feels, if you was looking at my watch? you doesn’t feel anything. As usual. But if…you just looked back (think You can see my watch too :P),you will see my watch running faster.
Here, you are in your own frame, with your rocket going with relativistic speed. But what about me? I am moving with a small velocity, the velocity of my planet. Still, I am at rest for me, not moving at all.
Here, when your velocity is very very high, the frames in which observer and what being observed would be in different frames, which have their own velocity. Whenever we looks at a different frame from our frame, we feels that their time is slow(only when that frame is at least having a slightest higher velocity than us).
We doesn’t feel this, if that frame is in rest with us or having same velocity with us.
Here, I repeats the word ‘feel’ every time. Because, it’s just a feeling for us, unless we understand the ‘adaptation’ our body and observing capability have made into us.
We can see that the time gets different speeds, because of the reason that, there isn’t actually any perfect or universal time. What feel to be real is the time which is along with us. Whoever travelling faster than us may have a slower time and whoever having a slower speed may have a speedy flow of time. This all are relative. This all are feelings.
Please don’t compare this feeling, with emotional ones, which we generally uses.
Here no one has changed anything. Whenever we feel that, another frame’s speed is more, and their time is flowing slowly, we only feel that they are evolving slowly. But to them, it’s a normal one.
It’s just like the saying “it might be easier for you, but not for me” or “it might be easier for me, but not for you”. Here, the saying depends on the person who says it and to who he or she refers to.
Both statements are correct for the one who says it, but at the same time incorrect for the other ones.
When you start to think from the other person’s side, you feel “oh! That’s too correct, then how can I be wrong”? This arise from the thought that, ‘if I am true, he is wrong’ or ‘if he is true. I am wrong’.
Well, I have used the verbal phrases to convey my idea, but never think; you can equate these verbals to the physical meaning, and don’t interpret the symmetric poetry of phrases to be relativistic.
Kindly Note that,the frames I told above,when obeying the Newton’s laws of motion,we call them as Inertial Frame. If you really understood what this frame is,kindly continue to read the basics of General Relativity
Complete Article at LetsPhysics