Beside the length, width and depth, the three dimensions on space, another dimension exists. Time is that fourth dimension. Almost everything in the universe can be explained with the help of these four dimensions. When something with a mass placed in the time-space which consists with these four dimensions, it bends over to make the object steady. This curve property in the time-space is portrayed as the gravity. With the mass of the object, curvature of the time-space increase. When the curvature of time-space increase the gravitational field also increase. So with the mass of the object, gravitational field increase.
When the curvature of time-space increase, the running speed of time decrease. It means when the gravitational field increase, time become slower. I may give you an example to understand this phenomenon easily. Imagine a man wearing a wrist watch standing under a clock tower. Apparently, the ticking time of two clocks should be the same. But remember, gravitational field near the earth's surface is more powerful than the gravitational field up in the tower. So if you observe carefully the wrist watch which man is wearing ticks slower than the clock up in the tower.
Gravitational fields for time travelling
The above phenomenon gives us a hint about time travelling. If we can generate a gravitational field with enough power, we can slow down the time. This will slow down both physical clock and the biological clock. So every living and non-living thing inside that gravitational field will experience the time loss. But things out of that gravitational field will experience the ordinary time. So comparatively, time of things inside the gravitational field would be slower than the time outside the field. When we disengage the above gravitational field, things which were inside the field would be younger than the things which were outside the field.
Thatmeans the external world of the field has moved to the future while the internal of the field remained almost constantly. So the things which were inside the field have experienced a time travel to the future. But time travel to the past is impossible according to this phenomenon. At least, this deep link between time and gravitation will offer us a chance of travelling to the future.
