Philosophy Lexicon of Arguments

Time travel: A time travel is the traveling of one or more subjects from their respective present into a time which, from the point of view of these subjects, lies in the past or in the future. It is usually assumed that the traveler maintains their age and biological condition. Therefore, in the case of time travels, a hierarchy of several times is to be assumed, namely the proper time of the travelers which determines their biological age, the duration of the procedure of the travel and the historical time of the "destination". Logical problems associated with time travel are inter alia contradictions related to the fact that events of the past could be influenced after they occurred. See also time, time reversal, symmetry, time arrow, grandfather paradox.

Annotation: The above characterizations of concepts are neither definitions nor exhausting presentations of problems related to them. Instead, they are intended to give a short introduction to the contributions below. – Lexicon of Arguments.

Author Item Excerpt Meta data

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V 67
Time Travel/Lewis: thesis: it is possible. - The paradoxes are merely curiosities. - They involve a discrepancy between time and time - problem: how can the same event (departure and arrival) be separated by two time distances with different length. - Wrong: to postulate several time dimensions. - For the time traveler would not be able to find his comrades on a surface.
V 69
Solution: separation of external time and personal time of the traveler, as measured by his clock - no matter what happens to the clock - we do not want to define time operationally, but functionally. - I.e. the clock is infallible by definition.
V 70
Functional role in the event pattern of time traveler. - E.g. his hair is growing, but that is not time, but only the same role as in normal life. - It is the personal time of the traveler - this is sufficient to transfer the temporal vocabulary.
V 71
Time travel: the life of the traveler is like a railway track: e.g. a place 2 miles east might as well be a place 9 miles west. - E.g. loop: the track crosses an earlier section of itself once - external time: unique encounter - personal time: repeated - Event: separated in the personal time, united in the external time. - Time Traveler: is not there twice in full person, but in two full states. - (> Person state) - Problem: What unites these states. - (Unlike normal people, no problem). - Different problem: if the time travel is instantaneous, there is a break in the time line. - Then there are two people and none of them is the Time Traveler.
V 73
Time travel/Causality: 1) the time travel requires personal identity and thus causal continuity. - Thus reverse direction. - The direction of counterfactual dependence and causation is controlled by the direction of other asymmetries of time, so reverse causality and thus causal loops cannot be excluded. - That does not mean that the loop as a whole is the cause or can be explained. - Problem: information transfer - e.g. if the information must be transmitted first to build the time machine, there is no solution. - The person and person states of the time travel have to be defined simultaneously. - Otherwise, they will be assumed to be mutually circular.
V 74f
For the journey we only need three-dimensional space without time as a fourth dimension.
V 75f
Time travel/Grandfather paradox: the past cannot be changed, because moments cannot be split into temporal parts which could be reversed - murder of Grandfather is either contained timelessly in the past or it is timelessly not contained. - Wrong: Original and new past: instead: one and the same localized twice (like railroad crossing in eight-shaped railway track). - So killing during Time travel is a contradiction: both killing and not killing - but past no particular character. - Also present and future unchangeable, because their moments have no temporal parts. - ((s) developments may probably be influenced.) - Can is ambiguous: a monkey cannot speak Finnish, because of its anatomy, I can’t speak it, but I have not learned it. - Narrower and broader set of facts - Murder of grandfather possible because of narrow set: everything you need for murder - but no more set: father-son relation, the end of life of the grandfather, etc. - Branched time: (branching after the murder of the grandfather) no solution, because the past is not changed. - It is consistent that the grandfather is alive and dead, but in different branches, but there are not two events.

Explanation of symbols: Roman numerals indicate the source, arabic numerals indicate the page number. The corresponding books are indicated on the right hand side. ((s)…): Comment by the sender of the contribution.

D. Lewis
Die Identität von Körper und Geist Frankfurt 1989

D. Lewis
Konventionen Berlin 1975

D. Lewis
Philosophical Papers Bd I New York Oxford 1983

D. Lewis
Philosophical Papers Bd II New York Oxford 1986

LwCl I
Cl. I. Lewis
Mind and the World Order: Outline of a Theory of Knowledge (Dover Books on Western Philosophy) 1991

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Ed. Martin Schulz, access date 2017-07-25