Time; The fourth Dimension

We are familiar with the three spatial dimensions, we deal with them in our daily lives. x-axis, y-axis and z-axis. We say that we can locate any thing using these three coordinates.
Let's take an example, Imagine that you want to meet one of your friends. Considering your current location to be the origin, you need to have three coordinates, you need to know the street number,  it would serve as y-coordinate, his house number or the number of building in that street which would serve as x- coordinate and the floor, which would serve as the z-coordinate.
But it's possible that by the time you'll reach there, your friend will be gone. He'll not be their and you won't be able to meet him, in spite of the fact that you knew his three coordinates. why is that so? the reason behind this is that you missed the fourth dimension, Time.
You needed the point on the axis of time in addition to the three coordinates of spatial axis in order to catch him. That's how time serves as the fourth dimension. Some of you might be thinking that this is only true for the bodies who are able to move on their own, yes it is true. But you must broaden your vision and think on a larger scale, because  frame of reference plays its part for the bodies which appear to be stationary to us. What I mean is, for a person on earth, a certain building will be stationary. But for someone in space, it will be moving, that's because of the fact that earth is continuously in motion, it rotates around its axis, it rotates around the sun. Plus, the earth is also moving forward in the space. And so is everything in our solar system, that's why the relative distances b/w planets &  b/w the sun and planets remains the same. In this way, nothing in the universe ever experiences the same space and time.
As all the three spatial axis are perpendicular to each other, the axis of time is also perpendicular to all of them. As it is perpendicular to all the spatial axes, we can collectively call these three axes as the space axis, and we can draw it against the axis of time like this:

When a body is at rest, it covers no distance in space which means its is covering all the distance in time. But when it starts moving, it starts to cover some distance in space, which effects its passage through time and consequently, it covers less distance in time. We do not experience these effects in our daily lives because the velocities are nearly equal to zero as compared to the speed of light which is 299,792,458 m/s. At which, all of  distance covered by the body is  in space which means it covers no distance in time. i.e. when we continue to increase the speed, the time slows down. This is called time dilation, mentioned by Einstein. And according to Einstein's theory of relativity, if  somehow we are able to travel faster than the speed of light c, our space-time vector will enter the second quadrant, which means we'll start to travel backwards in time.
Thus, Einstein declared that space and time are not independent entities, they are very much dependent on each other, motion through one effects the motion through other. He combined these two different things into one something, which he called as 'space-time'.
This theory has been tested through different experiments; one experiment was carried out using atomic clocks, in which one clock showed a slight difference when it was placed in a flying airplane for some period of time. It measured less time as compared to the atomic clock which was placed on the earth.
But the question is that what exactly time is. Is it just a dimension, is it a human invention? What is it? Actually, no one knows the right answer. We make time, we save time, we waste time, and we can tell what time it is, but have you ever thought that what is time?
In my opinion, time is the property of universe, it is the memory of universe, and everything which has happened, everything which is happening right now and everything which is yet to happen  is stored in the memory of universe called time. One thing is for sure, we can travel through time like we travel though the other dimensions. In a sense we are already time travelling at a rate of 60 seconds per minute. Throughout our lives, We've been saying that time passes, or time flows, but in reality we pass through time.  As a matter of fact, time is purely subjective, everything passes through the time according to its velocity. Plus, time also slows down around giant bodies and structures, due to the gravity. For someone sitting near the pyramids, time will pass slowly for him as compared to a person who isn't. Although, the factor will be so much smaller that he, or anyone else would not be able to experience that and it sounds strange too, but that's how it works.
We'll go through the possible methods of Time travel and the problems associated with them in the near future. That's all for now.