Time Travel Theories
Traveling through time is currently only possible in science fiction. Unfortunately, time travel is not represented clearly or consistently, therefore time travel is very confusing to the average person. However, I am here to help clarify time travel a bit. Basically, there are two theories to time travel.
First, consider the most basic timeline as a straight path with no time traveling, such as this example.
The first concept of time travel is that there is only a single possible timeline. In this timeline, all time travel to the past has already occurred, including time travel or time jumps starting from the future. Here is a visual illustration of this first theory.
This simple single timeline theory is actually very complicated, because this theory allows for time paradoxes. For instance, the most famous example of a time paradox is for a time traveler to go back in time and somehow prevent their existence from happening, such as killing their own parent before their parent has any children. As a result, the time traveler would not have been born, and thus the time traveler could not have prevented their existence from occurring. If this happens, then time has run into cause and effect loop that never resolves itself. This loop is often called a time paradox. In my opinion, either paradoxes must be resolvable or traveling back through time is impossible under this simple single timeline theory.
On the other hand, there is a split timeline theory that can handle time paradoxes. In this theory, whenever a time traveler travels backwards through time, a new timeline is immediately created. Here is an illustration of this second theory.
Under this new theory, each timeline will never intersect. Going back to the example where the time traveler went back in time to kill one of their ancestors, Timeline #1 would be the timeline when the time traveler was born and traveled back through time. Timeline #2 would be the timeline when the time traveler was not born and thus did not travel through time. As a result, there is no paradox.
It is assumed that the first timeline, Timeline #1, would continue to exist after the initial time travel starts. At least until the very end of time or the end of the universe.. or both.
It is also assumed that it would be impossible to jump from one timeline to another. For instance, if a time traveler jumped back in time to a point before the two timelines split, then a new third timeline would be created and time travel into the future would be on this third timeline instead of either the first or second timelines. As a result, this time traveling theory could yield an infinity number of timelines while never having any time paradoxes.
Therefore, anyone traveling back in time would not be able to return to their original time in their original timeline. So the only possible "safe" time traveling would be into the future, and then traveling back in time to the original point in time when the person originally left to travel into the future. Even if new timelines are created in this scenario, the first new timeline should be nearly identical to the original timeline, so the time traveler would not perceive any changes.
Of course all of these examples are just thought experiments, since time travel is currently not possible. However if it will be possible to travel back through time from the future, then all time travel to our past would have resulted with the creation of other timelines. Thus, this timeline would be oblivious to all future time travel into our past, since they only occured in the past of other timelines.
There could be only two ways that we could observe time travelers in our past or present. First, we are on a timeline created after time travel completed, however those time travellers would not be from our future. These time travelers would be from the future of a different timeline. Second, time travel from the past to the present (i.e. traveling forward through time) could also be observable, assuming no new splits in our timeline were caused by time travel into our past.
Or else, time travel is not possible and will never be possible.
by Phil for Humanity