Not exactly in those words:You said you're creating a new world
— noAxioms
I have never said this. — Luke
That says a parallel timeline [world] is needed, created since it doesn't otherwise exist. The 2nd sentence implies the 1990 new timeline branches off the 2024 'travel' event, which means no actual travel, just a universe creation event at 2024.there must be two (or more) parallel timelines in order for time travel to make sense. The timelines branch off into two or more timelines following the first time travel event. — Luke
OK, you acknowledge that the concept of a timeline implies the lack of presentism. There is no need for a 'progression of events'. Time travel under eternalism simply involves a worldline that is discontinuous, or doesn't follow a timelike path. So we ditch the presentism altogether, and that gives us a 1990 destination which we select as our target.my ontology of time involves a blend of presentism and eternalism (in short, that without presentism there is no 'progression of events', — Luke
Sounds like a copy to me. Old Bob is a continuation of the not-murdered original young Bob, not the Bob that gets murdered.There's no contradictions with it because killing the copy young-Bob isn't killing old-Bob's actual ancestor.
— noAxioms
You can call it a "copy" if you like. There are two parallel timelines, after all: one timeline in which Young Bob grows up to build a time machine and travel to 2024 and another in which Young Bob gets killed by Old Bob. — Luke
I don't have a single-timeline scenario. Heck, I don't have a scenario at all. Just trying to figure yours out. I've changed my guess significantly based on what you've said and based on some past comments that I read again. Is it better now?However, what supposedly happens to Old Bob in your single timeline scenario after he murders Young Bob?
Sort of like Marty (or his picture of his older siblings) beginning to fade as he slowly destroys any possibility of his parents hooking up. Hollywood loves this idea despite the paradox it creates.This would be the only realistic result — AmadeusD
there must be two (or more) parallel timelines in order for time travel to make sense. The timelines branch off into two or more timelines following the first time travel event.
— Luke
That says a parallel timeline [world] is needed, created since it doesn't otherwise exist. — noAxioms
The 2nd sentence implies the 1990 new timeline branches off the 2024 'travel' event, which means no actual travel, just a universe creation event at 2024. — noAxioms
How is this Bob in the new timeline the same Bob as the old timeline? — noAxioms
Sounds like a copy to me. Old Bob is a continuation of the not-murdered original young Bob, not the Bob that gets murdered. — noAxioms
I don't have a single-timeline scenario. Heck, I don't have a scenario at all. — noAxioms
Is it better now? — noAxioms
I've long since expressed that the branching solution resolves the grandfather paradox. — noAxioms
I don't recall seeing it at all. Or anyone who claims to have witnessed the Big Bang.Not sure if there was anyone witnessing the Big Bang
— Corvus
We did. It's not like it happened a finite distance away and the view of the bang has already passed us by. Of course the really early events are obscured by the opaque conditions back then. The window through which we look took a third of a million years or so to turn transparent. By that measure, nothing could 'see' the big bang since it was all obscured behind a blanket until then. — noAxioms
There is a difference, when you are just keep talking to yourself making the "If" statements to yourself, and when you actually make philosophical propositions in public claiming that it is true or at least valid and sound.Nothing ever gets proved. I can go to grandma's house if I have a car, and the weather is acceptable, and if I draw breath. But technically I cannot prove any of those.
Point is, requiring 'proof' is going to far. Evidence of X,Y Z is probably enough for plausible time travel. Right now, that evidence is very negative. — noAxioms
It sounds like we are talking about different time here. What is "proper time" and "interpretation of time"?I am not sure what the physical clock measures.
— Corvus
It measures proper time, which is very defined in both interpretations of time. It doesn't measure the advancement of the present, or the rate of the flow of time. That sort of time is more abstract, and there is no empirical way to detect it, let alone measure it. So maybe we're talking past each other when I reference the sort of time that clocks measure, vs you referencing the latter. — noAxioms
Sounds like a copy to me. — noAxioms
How is the 2nd clause different from the first? Both just seem to say that you can't travel to your own timeline, which is partly silly because I am doing it now. IOW, does forward time travel necessitate a branch in timelines?The time traveller was either never at the destination time and cannot return there without contradiction (having two conflicting histories on a single timeline), or else they were always there and therefore cannot "return" there. — Luke
Why this restriction? I go back to 1955 (standard destination). Hang around until 1970, and go back to 1960 this time, where "I" already am as a time traveler. What's wrong with that? Can he also make a 3rd branch off the original timeline? Can I, having just made the machine, branch a new line off some other timeline where I never existed in the first place, say some version of 1980 where my parents didn't survive WWII?Bob must travel to, and insert himself into, a past time at which he didn't always already exist as a time traveller.
or murder any of its past inhabitants. — Luke
does forward time travel necessitate a branch in timelines? — noAxioms
Can I, having just made the machine, branch a new line off some other timeline where I never existed in the first place, say some version of 1980 where my parents didn't survive WWII? — noAxioms
The time traveller was either never at the destination time and cannot return there without contradiction (having two conflicting histories on a single timeline), or else they were always there and therefore cannot "return" there.
— Luke
How is the 2nd clause different from the first? — noAxioms
Both just seem to say that you can't travel to your own timeline, which is partly silly because I am doing it now. — noAxioms
IOW, does forward time travel necessitate a branch in timelines? — noAxioms
Bob must travel to, and insert himself into, a past time at which he didn't always already exist as a time traveller.
— Luke
Why this restriction? I go back to 1955 (standard destination). Hang around until 1970, and go back to 1960 this time, where "I" already am as a time traveler. What's wrong with that? Can he also make a 3rd branch off the original timeline? — noAxioms
Can I, having just made the machine, branch a new line off some other timeline where I never existed in the first place, say some version of 1980 where my parents didn't survive WWII? — noAxioms
Meanwhile, why do you want to kill anybody? — noAxioms
The young-Luke you find back there is not you since 'you' is presumably on the original timeline. You've no reason to kill this other person or for that matter, anybody. If you kill yourself, have you killed Luke, or did a copy kill himself? — noAxioms
If you kill yourself, have you killed Luke, or did a copy kill himself? — noAxioms
I think you need to consider the question I asked about the Studebaker in my first post in this thread (about post 57). Is that time travel? If not, why not? What is your machine doing that my example with the Studebaker did not? — noAxioms
I read almost all of the SEP article. Thanks for the link. Didn't know it had a page on the subject.I wouldn't call that time travel in the relevant sense. The SEP article attempts to draw the relevant distinction: https://plato.stanford.edu/entries/time-travel/#WhaTimTra — Luke
Him already being there was the point: To alter what he (younger self) would have otherwise done. I see no reason why the younger self cannot have already time travelled before. Another mistake could be made, 'necessitating' a second correction. I put it in quotes because the mistake cannot be corrected on the more original (more real?) timeline.My point was that it is senseless for Bob to travel to the past if he is already there — Luke
Poor assumption. If I'm to 'kill grandfather', I'd have to go back at least a century. Maybe I want to witness the asteroid taking out the dinosaurs. You can't put in a rule that says you can only travel a short ways to some past with you in it somewhere.I don't think so. I'm assuming that Bob returns to the same past that he lived through when he was younger — Luke
Any travel to the distant past will destroy the history you know. Everyone talks about critical events that make a change, but just appearing and stepping on a bug is enough. That said, killing grandpa isn't necessarily paradoxical. Maybe you're not actually related to him, but rather the mailman. I know my grandfather was a cheater. Why can't grandma be?I don't; that's the scenario of the Grandfather paradox. — Luke
Well, besides the fact that it isn't possible in the first place, there are valid scenarios discussed in SEP that allow travel to the original timeline. CTCs are one example.Call it a copy if you will but this is the only way that time travel is possible. — Luke
I don't make that assumption. I try to work it out.I assume that it is the Bob (or Luke) from the original timeline — Luke
I'm not recreating a time. I'm just moving a Studebaker forward in time by a century. That's pretty much exactly what you're describing, except in the forward direction. So tell me why that's not what I did. How do you back the assertion that the car didn't travel through time, but Bob (also going forward say) did. Was it the lack of a fancy time machine looking device with blinking lights and stuff? There's plenty of fictions where the machine isn't necessary.As I replied earlier, I wouldn't call this recreation of another time in the present time to be time travel. — Luke
Apparently what I am doing right now does count as time travel, so long as I move. — noAxioms
My point was that it is senseless for Bob to travel to the past if he is already there
— Luke
Him already being there was the point: To alter what he (younger self) would have otherwise done. — noAxioms
I see no reason why the younger self cannot have already time travelled before. — noAxioms
Another mistake could be made, 'necessitating' a second correction. I put it in quotes because the mistake cannot be corrected on the more original (more real?) timeline. — noAxioms
I don't think so. I'm assuming that Bob returns to the same past that he lived through when he was younger
— Luke
Poor assumption. If I'm to 'kill grandfather', I'd have to go back at least a century. Maybe I want to witness the asteroid taking out the dinosaurs. You can't put in a rule that says you can only travel a short ways to some past with you in it somewhere. — noAxioms
You also contradict yourself. You say on one hand that it is senseless to go to a time when you exist, and on the other hand you're presuming Bob does this 'senseless' thing. — noAxioms
Any travel to the distant past will destroy the history you know. Everyone talks about critical events that make a change, but just appearing and stepping on a bug is enough. That said, killing grandpa isn't necessarily paradoxical. Maybe you're not actually related to him, but rather the mailman. I know my grandfather was a cheater. Why can't grandma be? — noAxioms
Well, besides the fact that it isn't possible in the first place, there are valid scenarios discussed in SEP that allow travel to the original timeline. CTCs are one example. — noAxioms
I assume that it is the Bob (or Luke) from the original timeline
— Luke
I don't make that assumption. I try to work it out. — noAxioms
As I replied earlier, I wouldn't call this recreation of another time in the present time to be time travel.
— Luke
I'm not recreating a time. I'm just moving a Studebaker forward in time by a century. That's pretty much exactly what you're describing, except in the forward direction. So tell me why that's not what I did. How do you back the assertion that the car didn't travel through time, but Bob (also going forward say) did. Was it the lack of a fancy time machine looking device with blinking lights and stuff? — noAxioms
Recreating a piece of some past state. Indeed, this isn't time travel being described.
I can build a new 1928 Studebaker, even giving it the same serial number as one made in that year. Has that car time traveled or is it just a new thing? I satisfied the conditions of the OP by doing so. Is it even a Studebaker if I built it instead of the defunct company? — noAxioms
The SEP does consider travel to a parallel timeline (Meiland, 1974 or Deutsch and Lockwood, 1994) to be time travel despite the lack of rigorous simultaneity convention between separate timelines. Your idea seems to illustrate the same issue. What was this alternate timeline doing before Bob traveled to it? Was it different in any way? Did it have a 'present' 2024 that was altered by Bob's appearance in what was considered to be 1990 at the time?This could be achieved by something like 'waiting', which the SEP article categorises as not time travel. — Luke
You seem to regard them as copies yourself, as evidenced by several comments (my bold):However, you have suggested that the inhabitants of the second timeline are merely "copies". — Luke
So by this wording, the young Bob that gets killed is not Bob. He is not already there, but is rather killing a copy, somebody else, having left the young Bob that is actually himself back in the original timeline unkilled.There is no point or possibility of travelling to a destination if you are already there.
If the two of them were the same person, this would be a direct contradiction. But you seem to regard them as not the same person. So if (actual) Bob goes to some parallel world in 1990, and waits several years for the perfect opportunity to take out the young-Bob copy1 that is there. The moment comes, and he fires his gun only to find it wasn't loaded. Opportunity lost, and there won't be another one. But he has a time machine, so he goes back a day and loads the gun that yesterday-Bob (also a copy) can use to complete his task (of killing young-Bob copy2, leaving young-Bob copy1 un-shot back in the first alternate timeline).The younger self does not time travel; the older self does.
All the examples of 'is time travel' at the top of the SEP article are single-timeline examples. I'm not saying that traveling 'sideways' to a different line is or is not time travel, but I'm saying that those examples cannot all be senseless. Yes, they all have potential paradoxical consequences, all discussed in the article.I'm saying time travel is senseless on a single timeline — Luke
My reason for asking was to figure out justification of that assertion. I'm not saying it's wrong, just an arbitrary designation. Most designations of identity have pragmatic reasoning and are thus not arbitrary. This doesn't, so the question needs asking, and the answer needs justification.My answer was that it is Old Bob from the original timeline who time travels and kills his younger self (on the new timeline). — Luke
What was this alternate timeline doing before Bob traveled to it? — noAxioms
Did it have a 'present' 2024 that was altered by Bob's appearance in what was considered to be 1990 at the time? — noAxioms
You seem to regard them as copies yourself, as evidenced by several comments (my bold): — noAxioms
There is no point or possibility of travelling to a destination if you are already there.
— Luke
So by this wording, the young Bob that gets killed is not Bob. He is not already there, but is rather killing a copy, somebody else, having left the young Bob that is actually himself back in the original timeline unkilled. — noAxioms
The younger self does not time travel; the older self does.
— Luke
If the two of them were the same person, this would be a direct contradiction. But you seem to regard them as not the same person. — noAxioms
So if (actual) Bob goes to some parallel world in 1990, and waits several years for the perfect opportunity to take out the young-Bob copy1 that is there. The moment comes, and he fires his gun only to find it wasn't loaded. Opportunity lost, and there won't be another one. But he has a time machine, so he goes back a day and loads the gun that yesterday-Bob (also a copy) can use to complete his task (of killing young-Bob copy2, leaving young-Bob copy1 un-shot back in the first alternate timeline). — noAxioms
All the examples of 'is time travel' at the top of the SEP article are single-timeline examples. I'm not saying that traveling 'sideways' to a different line is or is not time travel, but I'm saying that those examples cannot all be senseless. Yes, they all have potential paradoxical consequences, all discussed in the article. — noAxioms
My answer was that it is Old Bob from the original timeline who time travels and kills his younger self (on the new timeline). — Luke
My reason for asking was to figure out justification of that assertion. I'm not saying it's wrong, just an arbitrary designation. Most designations of identity have pragmatic reasoning and are thus not arbitrary. This doesn't, so the question needs asking, and the answer needs justification. — noAxioms
You wanted to explore the implications. I'm trying to do that. — noAxioms
That part is just you saying it. It could be just as easily said that everybody (including old Bob) in the copy timeline is a copy. The machine could split Bob just like it splits everything else. The story doesn't go like that, but the story could go like that. It would still be time travel of a sort, especially from the PoV of the Bob on the created timeline.It's not a copy of Old Bob, since he time travels from the original timeline to the new timeline. — Luke
I take it you're not a historian. Those guys would love a machine that lets them go back, even in a way that cannot alter anything, just watch.What's the point (or possibility) of time travelling to the past if it is to leave the past completely unchanged?
I think we're doing considerable damage to causality if any of this were plausible. OK, the Einstein time travel doesn't violate causality, but I personally don't think that one counts even if it meets the SEP definition.This is the only way to avoid contradictions, paradox and violations of causality.
The SEP article gives several examples of a single timeline without paradox, Some of the best are the loop ones, including a case where you don't even need to invent/build the machine. You just give it to your younger self when you're done with it.Right, but I'm attempting to point out why I think single-timeline examples of time travel are senseless, and why I believe that a second timeline is necessary to avoid contradiction or paradox.
You don't seem to understand my point, which is that there is not obvious convention as to if the old-Bob in the copy timeline is the same old-Bob from the original timeline. The usual conventions for saying this person is the same person that looked like him yesterday. "I bought a can of beans yesterday": True? By convention, yes, the person who bought the can of beans is the same person that submitted this post. We know that because we know the convention. There is no convention for crossing timelines. To me it looks like old-Bob commits suicide, but builds a copy of himself (and the machine) in a timeline with a copy of everything else. The convention could just as easily say that.Most designations of identity have pragmatic reasoning and are thus not arbitrary. This doesn't, so the question needs asking, and the answer needs justification.
— noAxioms
I am arguing that Old Bob cannot have been in the past originally, because Young Bob had not yet grown up to build a time machine or to time travel. — Luke
It's not a copy of Old Bob, since he time travels from the original timeline to the new timeline. — Luke
That part is just you saying it. It could be just as easily said that everybody (including old Bob) in the copy timeline is a copy. The machine could split Bob just like it splits everything else. The story doesn't go like that, but the story could go like that. It would still be time travel of a sort, especially from the PoV of the Bob on the created timeline. — noAxioms
What's the point (or possibility) of time travelling to the past if it is to leave the past completely unchanged?
I take it you're not a historian. Those guys would love a machine that lets them go back, even in a way that cannot alter anything, just watch. — noAxioms
I think we're doing considerable damage to causality if any of this were plausible. OK, the Einstein time travel doesn't violate causality, but I personally don't think that one counts even if it meets the SEP definition. — noAxioms
The SEP article gives several examples of a single timeline without paradox, Some of the best are the loop ones, including a case where you don't even need to invent/build the machine. You just give it to your younger self when you're done with it. — noAxioms
...imagine a time traveller who steals a time machine from the local museum in order to make his time trip and then donates the time machine to the same museum at the end of the trip (i.e. in the past). In this case the machine itself is never built by anyone—it simply exists.
...imagine a time traveller who explains the theory behind time travel to her younger self: theory that she herself knows only because it was explained to her in her youth by her time travelling older self.
Imagine a time traveller who visits his younger self. When he encounters his younger self, he suddenly has a vivid memory of being punched on the nose by a strange visitor. He realises that this is that very encounter—and resignedly proceeds to punch his younger self. Why did he do it? Because he knew that it would happen and so felt that he had to do it—but he only knew it would happen because he in fact did it.
There is a sort of paradox with that scenario which is how the machine experiences no entropy: It stays perfectly new at all times, which isn't plausible for something that is thousands of years old. — noAxioms
I am arguing that Old Bob cannot have been in the past originally, because Young Bob had not yet grown up to build a time machine or to time travel.
— Luke
You don't seem to understand my point, which is that there is not obvious convention as to if the old-Bob in the copy timeline is the same old-Bob from the original timeline. The usual conventions for saying this person is the same person that looked like him yesterday. "I bought a can of beans yesterday": True? By convention, yes, the person who bought the can of beans is the same person that submitted this post. We know that because we know the convention. There is no convention for crossing timelines. To me it looks like old-Bob commits suicide, but builds a copy of himself (and the machine) in a timeline with a copy of everything else. The convention could just as easily say that. — noAxioms
By your rules, a person can only be in the presence of but one actual time traveler, even if other people on the timeline also remember time traveling.he should not be surprised by his sudden appearance at an earlier time, unlike everyone else on the new timeline (who we would assume have never encountered a time traveller before). — Luke
That would be a different convention. The new timeline is a rewrote-history according to traveled-Bob, and the old timeline becomes the copy from which he originated.Also, instead of considering the new timeline as a copy, you could consider it as a re-writing of history, but one which does not eliminate the original timeline.
There are stories/scenarios in which nothing is altered. It's more like watching the past on TV since nothing there can detect you.if they were to travel to the past then that would be altering something about the past
The twin goes out and comes back, and the two twins are no longer the same age. Not sure what you've been reading, but the proper time going out and back is less than the proper time of a direct path between the two events where the depart and meet up again. None of this requires anything communicating or having knowledge of what the other is doing.Incidentally, based on my very amateur understanding, I had thought that once the Einsteinian "time traveller" had returned to Earth, the same amount of time must have elapsed on Earth as it has for the traveller, given the time dilation effects of turning their ship around in order to return. When I read about the twin paradox long ago, I figured that although one twin can be in the future of the other, there is no way to transmit information to the Earthbound twin which could give them advanced knowledge about the future and that they must both return to the same proper time when they meet again. However, I admit that I don't fully understand these things and I'm probably way off. Besides, those sorts of time travel scenarios involving that type of "time travel" are not what I had in mind here.
Does not follow. That sort of reasoning is only valid if time travel is not possible. The whole point is that it was never built.The scenario wants us to imagine that this is a logically-sealed causal loop. However, the time machine must have been built by someone else in order for it to have been stolen and then donated to the museum.
The existence is caused by its own time travel to the past. Such is the nature of closed loops. Still, in my prior post I pointed out a hole in that story.It wasn't the time traveller that built it, so it cannot be the donation by the time traveller that causes the existence of the time machine.
That version works better since it mostly solves the problem I identified....imagine a time traveller who explains the theory behind time travel to her younger self: theory that she herself knows only because it was explained to her in her youth by her time travelling older self.
The closed-loop scenarios illustrate free will (or more precisely, the lack of it) better than any discussion about reality where there's no pragmatism to it.I don't buy the fact that the time traveller could not have done something else.
It takes say 10 years from donation to museum to getting stolen. It ages 10 years during that time after which it goes back 10 years and does it again, and again... Infinite age since it's stuck in a loop. Somebody has to do one excellent refurbishment effort somewhere during each 10 years.[The machine] stays perfectly new at all times, which isn't plausible for something that is thousands of years old.
— noAxioms
I don't follow why it must be thousands of years old.
It's a loop. It has no finite length, just a period, just like there's no end to walking east.I imagine the causal loop in these scenarios to be a much shorter period than thousands of years.
he should not be surprised by his sudden appearance at an earlier time, unlike everyone else on the new timeline (who we would assume have never encountered a time traveller before).
— Luke
By your rules, a person can only be in the presence of but one actual time traveler, even if other people on the timeline also remember time traveling. — noAxioms
Also, instead of considering the new timeline as a copy, you could consider it as a re-writing of history, but one which does not eliminate the original timeline.
— Luke
That would be a different convention. The new timeline is a rewrote-history according to traveled-Bob, and the old timeline becomes the copy from which he originated. — noAxioms
if they were to travel to the past then that would be altering something about the past
— Luke
There are stories/scenarios in which nothing is altered. It's more like watching the past on TV since nothing there can detect you. — noAxioms
The scenario wants us to imagine that this is a logically-sealed causal loop. However, the time machine must have been built by someone else in order for it to have been stolen and then donated to the museum.
— Luke
Does not follow. That sort of reasoning is only valid if time travel is not possible. The whole point is that it was never built. — noAxioms
It wasn't the time traveller that built it, so it cannot be the donation by the time traveller that causes the existence of the time machine.
— Luke
The existence is caused by its own time travel to the past. Such is the nature of closed loops. — noAxioms
Still, in my prior post I pointed out a hole in that story. — noAxioms
Infinite age since it's stuck in a loop. Somebody has to do one excellent refurbishment effort somewhere during each 10 years. — noAxioms
You're not reading my comment. I said that by your rules, a person can be in the presence of at most one actual time traveler. We could have a factory that made them like bags of cheetos, and everybody used them to get to appointments and catch the traffic light that just went yellow. If they were used like that, the planet would quickly have a population of zero in not just the original, but all the timelines. Despite that prediction, no person would ever be in the presence of more than one actual time traveler, which is the one and only person that created the specific timeline the person finds himself in (if he's still in it and hasn't left already).By your rules, a person can only be in the presence of but one actual time traveler, even if other people on the timeline also remember time traveling.
— noAxioms
I'm considering Bob to be the first ever time traveller.. — Luke
But the way you describe it, it isn't really the past, just a different timeline which maybe looks like 'the' past, but is actually just another line, 'a' past at best, one of many. There is only one 'the' past, and you didn't go there.if they were to travel to the past then that would be altering something about the past.
Except he can't leave (turn off the TV so to speak). OK, I agree that it stretches the definition too much. But if he's there at all, history is gone. If I go back 250 million years to see the early evolution of mammals, I'm sorry, but humans will never evolve from that timeline. Your very presence destroys that, although it doesn't prevent the asteroid that wipes out whatever is there instead of the dinosaurs.Well, I wouldn't call [a read-only verision] "travelling to the past", That is just somehow viewing the past at the present time of the viewers.
the time machine must have been built by someone else in order for it to have been stolen and then donated to the museum. — Luke
Does not follow. That sort of reasoning is only valid if time travel is not possible. The whole point is that it was never built. — noAxioms
Try to state the logic of your statement formally. What are the premises? How does your conclusion (that the closed-loop machine must have been built) follow? One of your premises is perhaps that all things need creating at some point, but that premise begs a universe with no closed time curves.You will need to explain why my objection does not follow.
I accept that premise, at least for purposes of this issue.If you don't have a time machine then you can't time travel
Why not? It works, does it not? This is worded as a conclusion, not an additional premise. I don't accept it since 1) it doesn't follow from the premise, and 2) it is easily falsified by counterexample.so you can't then obtain that time machine (or its technology) via time travel.
The one we discussed: the machine needing to exist for infinite time without showing any wear. Hence better to be handed the plans than to be handed the machine. The movie predestination works that way. It depicts a closed loop, without the infinite-age issue.Which hole are you referring to? Entropy?
It wouldn't be a loop if it had. Loops don't have a start.The loop could have started only 10 years ago.
You're not reading my comment. I said that by your rules, a person can be in the presence of at most one actual time traveler. We could have a factory that made them like bags of cheetos, and everybody used them to get to appointments and catch the traffic light that just went yellow. If they were used like that, the planet would quickly have a population of zero in not just the original, but all the timelines. Despite that prediction, no person would ever be in the presence of more than one actual time traveler, which is the one and only person that created the specific timeline the person finds himself in (if he's still in it and hasn't left already). — noAxioms
Actually, nobody would use the machines, due to the overwhelming evidence of it being nothing more than a self-annihilation machine. So good thing Bob is the only person that has one, and only Bob fails to exist in pretty much any of the timelines. — noAxioms
But the way you describe it, it isn't really the past, just a different timeline which maybe looks like 'the' past, but is actually just another line, 'a' past at best, one of many. There is only one 'the' past, and you didn't go there. — noAxioms
But if he's there at all, history is gone. If I go back 250 million years to see the early evolution of mammals, I'm sorry, but humans will never evolve from that timeline. Your very presence destroys that... — noAxioms
Loops don't have a start. — noAxioms
Try to state the logic of your statement formally. What are the premises? How does your conclusion (that the closed-loop machine must have been built) follow? One of your premises is perhaps that all things need creating at some point, but that premise begs a universe with no closed time curves. — noAxioms
Right. Neglected that bit.Unless more than one person used the same time machine to time travel together. — Luke
well, if everybody had one and knew it worked, I suppose they'd all use it and exit any particular timeline. It's sort of like heaven: The sales pitch is great, but if it's such a better place, why does nobody voluntarily hit the button and go there? It's because from the perspective of the original timeline, it just looks like you vanish, never to be seen again. There is zero evidence that it is safe, let alone works.I don't understand why the planet would quickly have a population of zero in all timelines though.
And Bob is missing from every timeline except one. Of course on the other timelines, there may be many people that attest to having traveled, and the evidence is there that it works. Those timelines would empty out faster than the original, if only from people going back to times when there were still people to meet.Bob would continue to exist on any timeline he travelled to (at least, until he dies).
With a time machine of course. That sort of logic only holds water because there are no time machines possible.But how could I already be there before I time travel?
Evolution is a chaotic function. The popular term for it is 'butterfly effect'. The killer asteroid is not chaotic, so you don't alter that, but evolution is a random process, and you've totally altered that. People are not an inevitable result of the state of 250 million years ago. It's an inexpressibly low chance even without the traveler mucking things up. OK, that last statement presumes a lack of hard determinism. Our discussion has a lot of quantum interpretation implications as well as implications for interpretation of time. The SEP article didn't mention the former.If I go back 250 million years to see the early evolution of mammals, I'm sorry, but humans will never evolve from that timeline.
How?
No. The whole point of them is that they are uncaused. They'd not be a loop if they were caused. That it doesn't fit in with your notion of singular causality is irrelevant since all those rules must be discarded with reverse causality.Maybe it all boils down to this. I'm arguing that causal loops require a start; that there must be an initial time travel event which causes the loop in the first place
I added bold labels. Let me know if I did it wrong.My premises would be that:
P1 - one cannot time travel without a time machine
P2 - time machines need creating at some point
P3 - there must be an initial time travel event following the creation of the time machine, when the time machine is first used to time travel
P4 - the initial time travel event cannot cause itself (e.g. by a prior time travel event using the newly- invented time machine).
I don't understand why the planet would quickly have a population of zero in all timelines though.
— Luke
well, if everybody had one and knew it worked, I suppose they'd all use it and exit any particular timeline. It's sort of like heaven: The sales pitch is great, but if it's such a better place, why does nobody voluntarily hit the button and go there? It's because from the perspective of the original timeline, it just looks like you vanish, never to be seen again. There is zero evidence that it is safe, let alone works. — noAxioms
Bob would continue to exist on any timeline he travelled to (at least, until he dies).
— Luke
And Bob is missing from every timeline except one. Of course on the other timelines, there may be many people that attest to having traveled, and the evidence is there that it works. Those timelines would empty out faster than the original, if only from people going back to times when there were still people to meet.
Nobody on these worlds knows who the actual time traveler is (the one that created this world), not even Bob. — noAxioms
But how could I already be there before I time travel?
With a time machine of course. — noAxioms
That sort of logic only holds water because there are no time machines possible. — noAxioms
They'd not be a loop if they were caused. That it doesn't fit in with your notion of singular causality is irrelevant since all those rules must be discarded with reverse causality. — noAxioms
P1: I said I would accept this for this purpose, but there is no such requirement. If time travel was possible, somebody might be able to do it just by willing it. If a machine can do it, why can't a creature evolve a way to do it. The premise is something like saying you cannot get to grandma's house without a car. Well, that's false since evolution has given us a means of machineless locomotion. — noAxioms
P2 is unacceptable. It's like trying to prove God by asserting that the universe needs creating at some point (which is itself a self-refuting argument). An un-created time machine does not violate any rules in a universe where time travel is possible. — noAxioms
An un-created time machine does not violate any rules in a universe where time travel is possible. — noAxioms
P3 seems false. I might make a time machine but never use it. We presume you mean the machine in the loop, so yes, it just happens to get used (the 'first time' say) in the story you are creating. I put 'first time' in scare quotes because there can't be a first time in a loop: — noAxioms
P4 is OK, but seemingly irrelevant since your story involves only a single time travel event, no loop at all. — noAxioms
Agree that if the people (especially those on the original timeline) fear the readily available devices, they wouldn't get used and the population remains.so it does not follow that every timeline would quickly have a population of zero. — Luke
If you time travel to the past, by definition you end up somewhere 'before' the event where you initiated the travel. I kind of lost track of the context. Are we talking about the loop here?What I meant was: how could I already be in the past before I have ever time travelled?
I don't see how that follows with the loop scenario. There would be no 'first time' to a loop. As I said, there can be no odometer on the machine counting jumps. That would be a contradiction.I could already be in the past (on a single timeline) if I had time travelled before but, given causality, there must have been a first time that I ever used the time machine to time travel.
I don't understand this. If the jump is from 2024 to 1990, then 1990 is 'the past' destination, and you are not in a past that is prior to that except perhaps as a young person, the one that you teach.How could I already be in the past prior to that?
We're presuming they're possible, hence the logic you give being fallacious. Things that are impossible in this universe are not impossible in this alternate universe where time travel makes for different causal rules. A loop is valid under the new rules. It doesn't violate anything except the rules of this universe.That sort of logic only holds water because there are no time machines possible.
— noAxioms
Why are no time machines possible? That's not something I've said.
You need to discard the causality rules of this universe, yes. The rules are different in the universe we're discussing. With the loop scenario, there is no 'first ever' to it. You can't count them. The loop is just there, and is self-consistent.We can just discard causality and assume that time machines don't need to have had a first ever use, and we can conveniently disregard whatever history led up to that first ever use?
Not if it is part of a loop. The whole 'must be a first time for everything' is only a rule in a universe like ours, intuitive to us, but not true in the sort of scenario we're discussing. Yet again, a simple counterexample falsifies your assertion. So maybe this time traveling creature never evolved, but just is. Again, there are movies depicting pretty much this.but if a creature evolved a way to do it, then there must have been a first time that they ever time travelled.
I will not. We're discussing the possibility of closed loops, and loops falsify P2.If you accept that one cannot travel without a time machine (P1) - at least, for the sake of argument - then it follows that a time machine (or the means for time travel) must be created or have evolved or somehow brought into existence in some manner.
I don't find that evident at all. It violates Einstein's theories for starters, which suggests that time is part of the universe, and not something in which the universe is contained and in need of being created.it's merely assuming the universe must have been brought into existence (which is quite self-evident).
Pop science view maybe. OK, if one confines one's definition of 'the universe' to just what evolved from the big bang, then a good deal of them would suggest a larger structure from which that bang was initiated. But there is no before/after without the sort of time that boiled out of the bang, so calling it 'before' is misleading.Hopefuly we can agree to the standard scientific view that the universe's existence began with the big bang,
Sorry to be so buggy, but I don't buy that either. The phrase once again implies a universe contained by time, and not the other way around. Yes, there are those that suggest something like that, in denial of Einstein's postulates.but even if we might assume that the universe has always existed
Your wording suggests that the machine exists at all times, which isn't the case. It exists in the loop in the museum case. It doesn't exist at other times.To say that time machines have always existed is more like saying that waffle irons have always existed.
Same counterexample falsifies this.An un-created time machine does not violate any rules in a universe where time travel is possible.
— noAxioms
Sure, but it would imply no time travel.
The kind of causality rules you're thinking of don't exist in a universe with time travel. A first time for a loop would contradict its existence, which is travel from the other end of the loop and not somewhere else.Why can't there be a first time in a loop? Loops are immune to causality?
Not following. There a possibility of a loop that doesn't involve time travel? Example please.P4 [the initial time travel event cannot cause itself (e.g. by a prior time travel event using the newly- invented time machine).] is not irrelevant. I'm saying that if a loop involves time travel (as the examples in the SEP article do), then we can consider the first ever time travel event in that loop and what preceded it. Unless you are arguing that there is no causality in a loop or that time travel loops and time machines in loops have always existed? Why should causal loops be immune from causality; from having been caused? It seems like a bit of magic.
What I meant was: how could I already be in the past before I have ever time travelled?
— Luke
If you time travel to the past, by definition you end up somewhere 'before' the event where you initiated the travel. — noAxioms
There would be no 'first time' to a loop. As I said, there can be no odometer on the machine counting jumps. That would be a contradiction. — noAxioms
That would be a contradiction. — noAxioms
I could already be in the past (on a single timeline) if I had time travelled before but, given causality, there must have been a first time that I ever used the time machine to time travel. How could I already be in the past prior to that?
— Luke
I don't understand this. If the jump is from 2024 to 1990, then 1990 is 'the past' destination, and you are not in a past that is prior to that except perhaps as a young person, the one that you teach. — noAxioms
Things that are impossible in this universe are not impossible in this alternate universe where time travel makes for different causal rules. — noAxioms
The rules are different in the universe we're discussing. With the loop scenario, there is no 'first ever' to it. You can't count them. The loop is just there, and is self-consistent. — noAxioms
Not if it is part of a loop. The whole 'must be a first time for everything' is only a rule in a universe like ours, intuitive to us, but not true in the sort of scenario we're discussing. — noAxioms
So maybe this time traveling creature never evolved, but just is. Again, there are movies depicting pretty much this. — noAxioms
I will not. We're discussing the possibility of closed loops, and loops falsify P2. — noAxioms
To say that time machines have always existed is more like saying that waffle irons have always existed.
— Luke
Your wording suggests that the machine exists at all times, which isn't the case. It exists in the loop in the museum case. It doesn't exist at other times. — noAxioms
An un-created time machine does not violate any rules in a universe where time travel is possible.
— noAxioms
Sure, but it would imply no time travel.
— Luke
Same counterexample falsifies this.
Imagine you're holding one of those party poppers that you pull and it explodes a bit of confetti around. You're about to do it and a box appears in front of you from which a some guy jumps out and explodes his own party popper as he says "three!". Then he grabs yours (unpopped), and apologizes, says the box is a time machine that goes back 8 seconds, the says "One, two, ..." and the box disappears, leaving you simply befuddled. That's what an 8 second loop looks like. — noAxioms
The kind of causality rules you're thinking of don't exist in a universe with time travel. A first time for a loop would contradict its existence, which is travel from the other end of the loop and not somewhere else. — noAxioms
Not following. There a possibility of a loop that doesn't involve time travel? Example please. — noAxioms
OK, Bob makes the machine and uses it to go from 2024 to a new timeline starting at 1990. Any point on the original timeline before Bob vanishes from it is the time before the first travel event. There is no time on the new timeline before the first travel since it starts there, kind of per last-Tuesdayism.I was talking about the time before the first time travel event; before you've ever time travelled. You're talking about what happens if (or after) you time travel, so you're not talking about the time before you've ever time travelled. — Luke
There can't be one on the machine that jumps in the loop. Bob's machine can have an odometer, no problem.Why can there be no odometer on the time machine counting jumps?
Just repeating the same question doesn't make it clear. Are we talking about Bob and the copy-timeline scenario? If so, you need to specify which timeline you're referencing when talking about one thing being prior to another.Sorry to be unclear again. What I meant was: how could I be in the past as a time traveller prior to the first use of the time machine.
That's what you are apparently trying to figure out. I don't know either, so I'm also exploring. What I don't do is presume the usual rules, such as that a place that almost looks like the state of things in 1990 is prior to the state of things in 2024. I also don't presume that the cause of a thing is necessarily prior to the thing. That's a pretty obvious one to throw out.What are these different causal rules?
Agree. We're trying to keep that. The loop is causally closed, so I don't see it as a contradiction. The cause of the 8-second guy is his own travel event 8 seconds later.There are still causes and effects, it seems.
There is no first time for the loop, or if there is, it's the only time. There is after all but the one jump, per the external timeline, presuming its a simple loop. Only the machine's timeline has multiple jumps, plus its contents if those contents go from arrival all the way back into the machine at departure.The older self can teach the younger self about time travel technology and the younger self can then use that knowledge in order to time travel from the future to the past. Or, the younger self can steal a time machine from the museum and then later use that time machine in order to donate the time machine back to the museum. The only different causal rule appears to be that there can be no first time travel event or that we are not allowed to talk about the first time travel event, for some unspecified reason.
The ones not OK lead to contradictions. The looping machine having its own 'first time' leads to a contradiction. It would effectively be an odometer going from 0 to 1, and we showed how that is a contradiction.So some causal rules are okay, but not others?
It came into existence by traveling from 'the future'. You can ask and that's the answer. That universe allows that sort of causality.We may never ask/explain how a time machine came into existence in the universe
By being donated of course.but it's okay to ask/explain how a time machine came into existence in a museum?
You're trying to find a logical inconsistency, and I don't see one. Before the loop, the machine simply doesn't exist, nor does it after. The 8-second machine exists but for 8 seconds. Not time to study and figure out how its done, something the museum guys might decide to attempt.It's logically self-consistent as long as we never consider a loop as having a first time travel event or what preceded it, it seems.
The same way that the lack of the most eastern point isn't a logical inconsistency? It's only inconsistent if you presume there must be a first time (on the machine's timeline), so that's apparently a wrong thing to presume. There's a first time on the world's timeline. Isn't that enough? This presumes that the external world is itself not a loop. There are hypotheses that suggest otherwise, a sort of cyclic model of the universe.But how is it logically self-consistent that there was never a first time travel event?
The infinite-age universe hypothesis similarly suggests the impossibility of tracing back to a first event. A loop without a beginning is not in contradiction with anything.Does time or causality work differently in these scenarios such that it would be impossible to trace back to the first time travel event?
It's true in our universe because I cannot think of a scenario where at some earlier time there is not a mug, and at a later time there is a mug, and that there it a beginning to the mug's timeline. The timeline of the mug and that of the rest of the universe is completely parallel, so there must be a 'first moment' for it. In this alternate universe, the mug timeline might not be parallel. It still has a first (and only) time in the universe timeline, but not on its own timeline, which isn't parallel to the one 'outside'.Not if it is part of a loop. The whole 'must be a first time for everything' is only a rule in a universe like ours, intuitive to us, but not true in the sort of scenario we're discussing.
— noAxioms
How is it "not true"? It doesn't seem to me that it's not true; it seems that you just want me to ignore it.
If a machine that loops and is never created can exist in some consistent way, then so can a creature than has no evolutionary ancestory. It just appears from some retrocausal event, and its existence somehow eventually plays a role in that eventual retrocausal event.We're dispensing with evolution, too?
OK. The 8 second machine is created in front of me at some point, and un-created 8 seconds later when it vanishes. Works for me.I suppose I could alter P2 to say that time machines involved in human time travel need to be created at some point.
Dangerous to use the word 'first' when the temporal ordering of things is not objective. I think that's where a lot of the trouble comes from.Or, better still, P2 could say that there must be a first human time travel event associated with the human use of a time machine or time travel device/technology (assuming that any such events occur).
Nope. It came into existence when it first appears, not 'uncaused'. It doesn't exist at any time before that, so that is it coming into existence. It gets donated to the museum some time later and yet later is stolen and vanishes from existence forever after as it causes the earlier event.You are effectively telling me to ignore how the time machine came into existence originally.
I just made them up as another example which isn't directly self contradictory.now you're invoking fanciful beings that can time travel without any time machines and other magical shenanigans in order to try and save the "self-consistent" logic of causal loops.
No, you are the spectator who has somebody use your popper and then take it from you. The person in the box is, well ... something else. It is along those lines that you should tear this apart. A human makes a great odometer, and you can't have an odometer, so the guy is perhaps not human?Am I supposed to be the guy in the box/time machine, because this doesn't sound like a causal loop
Yes to the first. No, it's never you. You're left behind being befuddled, remember? You never see him again. It very much is a loop, and a very tight one.it's just a guy using a time machine to go back in time every 8 seconds to do the same thing repeatedly. It's unlike the other causal loop scenarios because it's not clear that I ever become the guy in the box/time machine. Or was that part left unsaid?
Un-create means to cease existing. From the perspective of the linear timeline, Any traveler uncreates his machine and himself. It's just gone leaving not even disassembled parts. Of course on the machine's timeline, it just has an external environment change and isn't an act of creation or uncreation at all.I thought by "un-created" you meant that the time machine was not created or did not exist. Did you mean "uncaused"?
For the most part I agree. But single-timeline travel isn't necessarily contradictory so long as one does not make choices known to be different than those made before. It does require a sort of lack of free will as it is often defined.Right, that's why I've been arguing that time travel only makes sense on multiple timelines
Any loop in time is contrary to the sort of linear ordering of all events that we find intuitive. No, it doesn't have to be labeled 'time travel'. A cyclic universe is a nice loop that isn't considered time travel because there is no linear timeline laid alongside the loop.I was just trying to restrict it only to causal loops that do involve time travel, in case you were about to bring up any causal loops that don't.
OK, Bob makes the machine and uses it to go from 2024 to a new timeline starting at 1990. Any point on the original timeline before Bob vanishes from it is the time before the first travel event. There is no time on the new timeline before the first travel since it starts there, kind of per last-Tuesdayism.
I lost track of the question about this 'time before'. Are we talking about say 2023 on the original timeline or am I still getting it wrong? — noAxioms
...it would be logically impossible to travel to 'the past' (i.e. on a single timeline) unless I was somehow already there before I time travelled. But how could I already be there before I time travel? — Luke
There can't be one on the machine that jumps in the loop. Bob's machine can have an odometer, no problem.
The contradiction: Suppose, just before the jump, the odometer reads x. It arrives at its destination (8 seconds in the past in my popper example) and immediately increments the thing to x+1. This contradicts it leaving 8 seconds later with a reading of x. — noAxioms
That's what you are apparently trying to figure out. I don't know either, so I'm also exploring. What I don't do is presume the usual rules, such as that a place that almost looks like the state of things in 1990 is prior to the state of things in 2024. I also don't presume that the cause of a thing is necessarily prior to the thing. That's a pretty obvious one to throw out. — noAxioms
I think the rule you find hard to discard is that all seemingly artificial things must somehow be invented and assembled at some point, and the examples we show are consistent without all those steps. Sure, the machine is built in the teaching loop, but the technology knowledge (the inventing) is the loop, information that is never gleaned, but is merely passed on. — noAxioms
I suppose I could alter P2 to say that time machines involved in human time travel need to be created at some point.
— Luke
OK. The 8 second machine is created in front of me at some point, and un-created 8 seconds later when it vanishes. Works for me. — noAxioms
Dangerous to use the word 'first' when the temporal ordering of things is not objective. I think that's where a lot of the trouble comes from. — noAxioms
Nope. It came into existence when it first appears... — noAxioms
But single-timeline travel isn't necessarily contradictory so long as one does not make choices known to be different than those made before. — noAxioms
Given physics where there is a timeline that is the original one, that line cannot have a time traveler in it at all. All the copy lines have but the traveler(s) that created that line (assuming the machine had one or more passengers). So in those lines, any traveler was already there at its start.As I said earlier:
...it would be logically impossible to travel to 'the past' (i.e. on a single timeline) unless I was somehow already there before I time travelled. But how could I already be there before I time travel?
— Luke
Yes, we are talking about the original timeline. — Luke
Because it reads x when it appears 8 seconds before that. You know that. It's on the outside and you read it. You can't read it being x, x+1, and all the other numbers. The number has to match at both ends, or it didn't come from that 8-seconds hence jump. It wouldn't be a loop, just a stopover, and a different party popper than the one he took from you.Why does it need to revert to a reading of x again 8 seconds later?
OK. That's not something we discussed yet. How does it empirically differ from the branch thing? The old 'history' goes away, so there's nobody to witness the population of the world going down. There are a whole mess of uncaused events going on, but besides the classical impossibility of that, no other contradictions. You have people who don't have valid identification. Maybe no other people at all. So the empirical experience of those you don't take with you is irrelevant, and the empirical experience of the traveler is identical to the experience of the guy in the branching model. So this sounds like a different interpretation of the exact same experience.On reflection, I want to reject my suggestion that there is more than one timeline. You've helped me to see that this is not really what I had in mind. What I have in mind is that there is only a single timeline but that the effects of the first time travel event overwrite the past of the original timeline (starting from the destination time of the time travel event, e.g. 1990).
OK, back before the earliest time, before the destination of any retro-time traveler.This might create a causal loop or it might not. However, the main idea I've been trying to convey all along is that there must be an original version of "the past" prior to the first ever time travel event
Suppose I travel to 1990. How is what you call the original line (the one I remember with cellphones and all) is 'the past'? It's not before 1990, and for that matter, it's not after either. It just isn't at all.and is necessarily different to the version of "the past" that exists post-time travel.
But all your scenarios describe exactly that, including pretty much every fictional story that I can think of. Time travel, as envisioned, necessitates technology or at least some object/person appearing uncaused from nothing, or worse, replacing what was otherwise at that spot. Remember terminator? This sphere of space replaces what was there with some air and a naked person. Nobody says what happens to the stuff that unfortunately happened to be where that ball appears, which by chance might possibly be half of another naked person.This helps to retain "normal" causality, thus removing the need for the magical appearance of time machines or technology "out of nowhere", existing uncaused
Well, the paradoxes are gone at least. Nobody can demonstrate the typical definition of free will.And it retains free will.
They'd not be loops at all then. The 8-second guy would simply die in moments the same way the half-of-naked person did. It's a hazard of living in such a world is that your life expectancy outside the machine is moments at a time, and no better inside the machine since no time passes in there (unless you assert otherwise I guess).In fact, causal loops can be avoided
It's not created for the time traveler any more than the time traveler is created or has an age.OK. The 8 second machine is created in front of me at some point, and un-created 8 seconds later when it vanishes. Works for me.
— noAxioms
That doesn't explain how the time machine was created for the time traveller.
8 second guy has a first and only appearance, yes. From his looping timeline, there is no first anything. It's a circular timeline.It has a first appearance?
What you describe above is a single preferred timeline scenario, with all the non-preferred timelines being nonexistent. I am not sure if there are 'different choices' involved since there is but the one timeline, and thus one choice being made at any point in time. Sure, you remember making different choices, but those are memories of nonexistent times.But is single-timeline travel necessarily contradictory, even if one does make different choices post-time travel?
As I said earlier:
...it would be logically impossible to travel to 'the past' (i.e. on a single timeline) unless I was somehow already there before I time travelled. But how could I already be there before I time travel?
— Luke
Yes, we are talking about the original timeline. — Luke
Given physics where there is a timeline that is the original one, that line cannot have a time traveler in it at all. All the copy lines have but the traveler(s) that created that line (assuming the machine had one or more passengers). So in those lines, any traveler was already there at its start. — noAxioms
Given the physics of a single timeline, various machines might travel here and there, but there would be presumably some earliest one (to see dinosaurs say). In such a situation, there is no traveler before that earliest Cretaceous period. — noAxioms
There are valid scenarios with such a single timeline, but the traveler (if it is human) is part of 'the past' then and lacks the free will to do otherwise. I agree this runs into serious problems if he knows what he does (say a minute ago) and goes back explicitly to do a different thing. No amount of determinism is going to prevent that. Determinism is not a thing with a will different than yours. Nobody seems to realize that. — noAxioms
Why does it need to revert to a reading of x again 8 seconds later?
— Luke
Because it reads x when it appears 8 seconds before that. You know that. It's on the outside and you read it. You can't read it being x, x+1, and all the other numbers. The number has to match at both ends, or it didn't come from that 8-seconds hence jump. It wouldn't be a loop, just a stopover, and a different party popper than the one he took from you. — noAxioms
OK. That's not something we discussed yet. How does it empirically differ from the branch thing? The old 'history' goes away, so there's nobody to witness the population of the world going down. There are a whole mess of uncaused events going on, but besides the classical impossibility of that, no other contradictions. You have people who don't have valid identification. Maybe no other people at all. So the empirical experience of those you don't take with you is irrelevant, and the empirical experience of the traveler is identical to the experience of the guy in the branching model. So this sounds like a different interpretation of the exact same experience. — noAxioms
This might create a causal loop or it might not. However, the main idea I've been trying to convey all along is that there must be an original version of "the past" prior to the first ever time travel event
— Luke
OK, back before the earliest time, before the destination of any retro-time traveler.
Or do you mean 'first' on the timeline of some traveler instead of on the one world timeline? — noAxioms
and is necessarily different to the version of "the past" that exists post-time travel.
— Luke
Suppose I travel to 1990. How is what you call the original line (the one I remember with cellphones and all) is 'the past'? It's not before 1990, and for that matter, it's not after either. It just isn't at all. — noAxioms
It all sounds like a re-growing-block model, except that disallows forward time travel since the destination specifed doesn't yet exist. I set sights for the year 3000 (like in Futurama), but while my machine is waiting for Y3000 to come around, somebody else uses a time machine to go back to 1985, thus obliterating me and the destination I targeted. same fate awaiting all those people paying for cryonic preservation. It requires a stability that just isn't there. — noAxioms
This helps to retain "normal" causality, thus removing the need for the magical appearance of time machines or technology "out of nowhere", existing uncaused
— Luke
But all your scenarios describe exactly that, including pretty much every fictional story that I can think of. — noAxioms
Nobody can demonstrate the typical definition of free will. — noAxioms
It's a hazard of living in such a world is that your life expectancy outside the machine is moments at a time — noAxioms
and no better inside the machine since no time passes in there (unless you assert otherwise I guess). — noAxioms
OK. The 8 second machine is created in front of me at some point, and un-created 8 seconds later when it vanishes. Works for me.
— noAxioms
That doesn't explain how the time machine was created for the time traveller.
— Luke
It's not created for the time traveler any more than the time traveler is created or has an age. — noAxioms
It has a first appearance?
— Luke
8 second guy has a first and only appearance, yes. From his looping timeline, there is no first anything. It's a circular timeline. — noAxioms
But is single-timeline travel necessarily contradictory, even if one does make different choices post-time travel?
— Luke
What you describe above is a single preferred timeline scenario, with all the non-preferred timelines being nonexistent. I am not sure if there are 'different choices' involved since there is but the one timeline, and thus one choice being made at any point in time. Sure, you remember making different choices, but those are memories of nonexistent times. — noAxioms
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