the question has been postulated, "Is time travel into the past theoretically possible?"
We must first clearly define what we mean by time. One definition is the one used in the Motion in a Matrix Model which is something like this, "Time is a measure of sequence referenced to some reproducible sequence of motions in three dimensional space." That is, time is a measure of sequence. Past time consists of all of the sequential actions which have led to a particular instant. The past is a completed set of sequential actions. A set, which traced backwards, expands by some huge geometric factor, instant by instant. For a person to actually travel back in time to some predetermined instant in some particular sequence would necessitate a retrograde reconstruction of that entire "fabric of the past" and at the same time be a part of it which was not interfering. Additionally, since the "time traveller" would be travelling through a sequence, they would be constructing a retrograde replica of a certain past into their own "future." Going both ways at the same time is what would have to be happening.
Another way of looking at it is to say, " The past is a fixed set of results of "random" actions, the future is an "open" set of random actions. To do a controlled activity in either arena without changing the situation by those actions would not be possible." Time travel for a physical being is an impossibility.
Having ruled out travel to the past as a physical being, we have to consider time travel as a possible observer. This we do every day when we study light from the stars. Going farther into abstruse theory, we might suggest that were it possible to determine the extent of the matrix in which we exist, to the point of being able to determine a central point, it might be possible to determine the sequence of actions which was necessary for a certain particle to reach a certain point in absolute space and by means of a computer simulation do a retrograde simulation. This is what is done in trying to find a birth for the universe.