The first three dimensions, from a central point, can go in any of two directions. One way, or the opposite of that way. Humans have the ability to go forward or backward; left or right; up or down.
Time is different, though. It moves differently than the other dimensions. It can only go forward. You can't just turn around and go back in time like you can turn around and go back from a point on a line in any of our three perceived dimensions.
But is that true. Along with time comes the creation of new things. From this we can deduce that travelling the opposite of forward in time would yeild the removal of such things.
Memory would be one of these things. If we were to move forward in time, then decide to move back, all the memories we'd made would cease to exist.
How would you remember you were going back in time, then?
The jump would have to instantaneous; it doesn't make any sense otherwise. I mean, how long could it take you to go back in time? Exactly.
If at any point one were to travel through time, they wouldn't have a clue.
Travelling backwards would erase their memory, and travelling further back than the point at which they decided to travel back in time would be theoretically impossible on account of the fact that they would forget they were even travelling through time in the first place, unless the jump was instantaneous, which cannot be measured by time. Instantaneous is like the zero of time.
Travelling forward would create new memories. At any given point in your life, you are nowhere else but there. You remember things from further back in time. If you had just jumped from age 5 to 25, you would have 20 years of memory acquired instantaneously, and therefore would not be able to feel the jump through time. You can only feel time at all due to memories you have.
The only way one might "jump through time" noticably would be by way of another dimension: the infinite loop of space simultaneously occupied by an endless number of universes.
Time is an expansion of the universe, but only our universe. Other parallel universes have expanded further, or are still expanding to, the point at which the expansions of our universe currently occupy. The ability to make the universe expand faster or contract would not be perceivable. Only by travelling between the different dimensions would you be concious of your relocation to a different world.
A very different world it would be, too. With the variation of dimension would likely come the variation of reality. The world you enter would be different in at least one way to that which you left.
From this it can be concluded that changing your past would be impossible. You could never change the past; only the present of the universe you are currently located in. Also, you would almost undoubtedly be unable to return to the exact universe from which you departed.
~Hi.~
Back to further enlightenment.