This is not common knowledge.
Time manipulation can produce many unexpected and strange effects.
Several of which have only been hypothesized by researchers in the field. Eyewitness accounts are rare, and are almost completely discredited. The problem with this esoteric study is that it requires a unique vantage point — one would need to be able to observe multiple points in time simultaneously, using a common frame of reference.
Which is impossible, of course.
However, theoretical time researchers have postulated the following scenario.
The Apple Tree Scenario.
Premise: Time travel exists. One can witness the full life span of an apple tree, from seed to sawmill. The researchers choose two points of reference, to limit the variables. The tree is 2 Years Old [a sapling] and the tree is 50 Years Old [full grown].
Experiment A: A researcher travels to the sapling and cuts an ‘X’ into the bark.
Result: An ‘X’ appears in the bark of the full grown tree.
Experiment B: The researcher applies a salve to the cut that accelerates natural healing and bark repair.
Result: The ‘X’ disappears from the bark of the full grown tree.
This scenario suggests that time seems to have a certain amount of elasticity. Cause rippling forward to effect – the observed node, or foci of attention alternating between multiple states dependent upon the actions taken in the past.
Of course this is a very basic thought experiment, which was not nearly exciting enough for these esoteric scientists. They began to hypothesize, what if the tree were a person? What would that person experience as they suddenly manifested a scar? Would memories of the assault appear in their mind, or could they simultaneously remember the previous continuity? And how would they feel when the scar disappeared? Can the human mind contain multiple concurrent events? Different versions of the same event all of which happened, and didn’t happen?
It gave the researchers a headache. So in a fit of self-mockery, the researchers dubbed the possible human effect, the Paradox Headache.