I would like to propose the following situation: (1) time travel to the past is possible, (2) there is only one version of the past, one timeline and (3) the past (or the future) cannot be changed. If so, then paradoxes must emerge (the grandfather paradox, for example). If this situation comes to be true my question is: Shouldn't a "logical constraint" arise to prevent the emergence of paradoxes in time? Maybe some kind of force field unknown to current science? This could explain why there are no tourists from the future appearing publicly. They simply can't because a logical (non) physical barrier prevents them. (However, they may be disguised among us in the present society.)
I will try another approach. There are four premises and one conclusion:
(1) time travel to the past is possible,
(2) there is only one version of the past, one timeline,
(3) the past (or the future) cannot be changed and
(4) there can be paradoxes (the grandfather paradox, for example)
Conclusion: Logic recommends that a kind of resistance or barrier should arise in order to avoid any paradox.
My question is: Does the conclusion make sense?
Side note (trying to clarify):
If we take into account premises 2 and 3 and imagine a time travel to the past, we have to admit that a situation like that of the grandfather's paradox would not be possible. For reason tells us that what has already happened cannot be changed, and since there is only one version of the past, a single timeline, it is not possible for the traveler to divert to another. Therefore the past must be considered fixed, unalterable. But even if the traveler tries to kill his grandfather, logic recommends that some kind of barrier should prevent the action of the traveler, being the past fixed. Whenever the traveler tries something against his grandfather that means changing history, a resistance must arise in order to prevent his actions. It's as if someone bumped into a wall. Only events and actions that do not imply changes in history would be possible. In other words, the traveler may be part of history but cannot change it. This would be a logical constraint in the structure of space-time that could not be broken.
I believe this text is an interesting complement: Heather Dyke (2005). The metaphysics and epistemology of time travel. Think, 3, pp 4352