| 23019 | The interesting time travel is when personal and external time come apart [Lewis, by Baron/Miller] |
| Full Idea: Lewis says a journey only counts as interesting time travel if there is a disparity between personal time and external time. …It is also necessary that the person at the beginning of the journey is the same as the person at the end of the journey. | |
| From: report of David Lewis (The paradoxes of time travel [1976]) by Baron,S/Miller,K - Intro to the Philosophy of Time | |
| A reaction: Other cases would presumably be the whole of time accelerating or slowing, or going into reverse. |
| 23021 | Lewis said it might just be that travellers to the past can't kill their grandfathers [Lewis, by Baron/Miller] |
| Full Idea: Lewis denied that the grandfather paradox makes time travel impossible. Time travel does not entail that it is possible to kill your grandfather. Maybe the traveller fails in their attempt every time they try to do it. | |
| From: report of David Lewis (The paradoxes of time travel [1976]) by Baron,S/Miller,K - Intro to the Philosophy of Time 8.2 | |
| A reaction: The problem with this answer is that killing the grandfather is only an extreme case of making any change in the past which ripples forward into the present. Virtually all changes by the time traveller would be impossible (though not contradictory). |
| 22911 | At least eternal time gives time travellers a possible destination [Bardon] |
| Full Idea: If all past, present and future events timelessly coexist, then at least there is a potential destination for the time traveller. …The Presentist treats past and future events as nonexistent, so there is no place for the time traveller to go. | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 6 'Fictional') | |
| A reaction: Not a good reason to believe in the eternal block of time, of course. The growing block has a past which can be visited, but no future. |
| 22912 | Time travel is not a paradox if we include it in the eternal continuum of events [Bardon] |
| Full Idea: As long as we understand any time travel events to be timelessly included in the history of the world, and thus as part of the fixed continuum of events, time travel need not give rise to paradox. | |
| From: Adrian Bardon (Brief History of the Philosophy of Time [2013], 6 'Time travel') | |
| A reaction: This would presumably block going back and killing your own grandparent. |
| 23020 | If a time traveller kills his youthful grandfather, he both exists and fails to exist [Baron/Miller] |
| Full Idea: It is surely true that if a time traveller travels back in time and succeeds in shooting his youthful grandfather then the time traveller both exists and fails to exist. | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 8.2) | |
| A reaction: This is the best known paradox of time travel. It is a special dramatic case of making any change to the past. If the traveller kills his neighbour's grandfather, his neighbour should vanish. Moving a speck of dust could have enduring results. |
| 23022 | Presentism means there no existing past for a time traveller to visit [Baron/Miller] |
| Full Idea: A time traveller can only travel to a location if the location exists, But if Presentism is true then past locations do not exist, so time travel to the past is impossible. | |
| From: Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 8.3.1) | |
| A reaction: Might a time machine actually restore the past time which had ceased to exist? Then the problem is the information needed to achieve that. |