Time: the Fourth Dimension 
Time is a measurement and cannot be travelled in, anymore than one can travel in an inch.  A dimension is a measurement used to describe an object or a point in space.  All dimensions are arbitrary notions. A line is measured in one dimension because only one coordinate is needed to specify a point on it or to determine its length (which is a series of points). A surface such as a plane or surface is measured with two dimensions because two coordinates are needed to specify a point on it or determine its area. A  cube, a cylinder or a sphere is tri-dimensional because three coordinates are needed to locate a point within this spaces, or to determine its volume.
     An object in motion is measured with four dimensions because four coordinates are needed to locate it space/time (reality).
     There is a common misconception people are confused by the term "fourth dimension" because science fiction has led them to believe that time is something that actually exists as a location.  This is incorrect, because there is no evidence that time actually exists outside of the confines of the human mind. When we measure time we are actually measuring motion, such as the movement of the hands of a clock.
     The fourth dimension is used to describe the motion and rate of motion of an object. All dimensions are notions in the mind of man. Or as Dr. Albert Einstein once said , “us physicists believe the separation between past, present, and future is only an illusion, although a convincing one. one”.


 Marcus Aurelius wrote, “Time is like a river made up of the events which happen, and a violent stream; for as soon as a thing has been seen, it is carried away, and another comes in its place, and this will be carried away too.”

We may imagine time as a flowing stream of water and reality is the flotsam and jetsam flowing within it.
A small object floating in a stream only affect other objects by coming in contact with them. To float upstream (go back in time) would require more energy than anything in the stream possesses. It would take less energy to float downstream (go into the future) but there is little evdience of this ever happening.

     A clock does not measure "time". Its movement represents movement of the Earth onits axis. 

    Einstein said,"Time is the fourth dimension."  When he said that he was not interpretting time (T) as a fourth dimension of space. Space is not 3D + T, instead, it is 4D. With clocks we measure numerical order of material change. With clocks we measure numerical order of material change. This numerical order is the only time that exists in a physical world. With this approach all immediate information transfers of quantum physics are explained in a more appropriate way. 4D space is a medium of quantum information transfers.

      Simply stated, the first three dimensions are used to specify an object’s location/movement in space (forward-backwards, left-right and up-down), while the fourth dimension locates its position in time. All four dimensions are used to specify completely the location or dynamism of an object in space. Collectively the four dimensions are inseparably interlinked and known as space-time.

      We are living in a three dimensional world, (possessing length, width and height), so we are unable to see the fourth dimension, as our physical world is constructed within these three physical dimensions only. We might feel or imagine time’s presence, but we can never actually detect it with our three-dimensional senses because it extends beyond our universe. We can only perceive time - the fourth dimension - as memories lodged at different intervals, with the result we perceive time moving in one direction - forward. A demonstration of four dimensional space-time’s inseparability is the fact that we cannot look into space without looking back in time - like we see the Moon as it was ~1.2 seconds ago and the Sun as it was ~8 minutes ago and so on