Why the most famous time travel paradox is no paradox

[Terxpahseyton]

I disagree. Look at disagreements between space travellers. They will disagree about many things, but causality isn't affected in any way, even though logically thinking through what they are reporting, you'd think that it would.

Space travelers also don't go back in time. But only - relative to each other - forward. Bygones are still bygones. Hence causality is still intact.

 

[Perfection]

I haven't seen Highlander...

I think the issue is coming up with a coherent story here:

For clarity sake Let's put together the following time travel scenario for discussion:

1979: No time travel occured
1980A: Perf hasn't gone back in time
1981A: Perf's parents meet
1986A: Perf born
2014A: Perf age 27 posts in time travel thread (right now)
2020A: Perf age 34 goes back to 1980
2021A: CFC collapses after mysterious disappearance of Perf

1979: No time travel occured
1980B: Perf age 34 appears
1981B: Perf age 35 prevents parents from meeting
1986B: NewPerf not born Perf age 40
2014B: Perf age 67 posts in alternative version of this thread
2020B: Perf age 74 does not go back in time
2021B: Perf age 75 chillin'

Which timeline is the real timeline? Which is non-existent?

 

[Terxpahseyton]

I haven't seen Highlander...

Neither have I

Which timeline is the real timeline? Which is non-existent?

At first the first timeline was real and the second non-existent.
Then things reversed.
At first the Highlander wore a yellow skirt. Than he wore a green one. And life goes on.

 

[Perfection]

When did things reverse?

 

[Terxpahseyton]

When you prevented your birth / changed anything in the past

I think the problem is that you seem to look for some kind of exterior point of orientation.

Be it some outer higher time (?) with which you can measure when what time-line existed or be it an absolute judgment of right or wrong time-line.

But I don't think such a thing exists. At least I have no reason to assume it does. That may be kinda uncomfortable to our POV, but I don't think it is in principle problematic?

 

[Perfection]

When you prevented your birth / changed anything in the past

And that was?

You posit a one true timeline, I'm questioning what the heck is it under my scenario...

I think the problem is that you seem to look for some kind of exterior point of orientation.

Be it some outer higher time (?) with which you can measure when what time-line existed or be it an absolute judgment of right or wrong time-line.

But I don't think such a thing exists. At least I have no reason to assume it does. That may be kinda uncomfortable to our POV, but I don't think it is in principle problematic?

I think it is quite problematic. It undermines the core notion of a unified reality in which we all inhabit. As I see it, both timelines need to be in some sense real and existent for a coherent view of everything that is going on.

 

[Terxpahseyton]

And that was?

You posit a one true timeline, I'm questioning what the heck is it under my scenario...

And I made it clear I think that both are and both are not, just at different instances of the timetravel-fueled "development" of the time-line

As I see it, both timelines need to be in some sense real and existent for a coherent view of everything that is going on.

I don't think my view is incoherent, it just can not be handled in the sense that it denies ultimate orientation.

It undermines the core notion of a unified reality in which we all inhabit.

But ask yourself - what is the alternative to my POV?
Magic time rubber-bands which tie you to your origin?
Many-worlds-theory?
Both seems ridiculously contrived.

But if it comforts you - I don't think it is actually possible to travel back in time.

 

[Perfection]

And I made it clear I think that both are and both are not, just at different instances of the timetravel-fueled "development" of the time-line

Both are and both are not is a contradiction that begs to be resolved.

I don't think my view is incoherent, it just can not be handled in the sense that it denies ultimate orientation.

Ultimately I believe you need a way of parsing views such that it works for all observers. It seems to me that throughout my journey through timelines A and B I am experiencing reality. It also seems to me that you'll live through timeline A (even past my disappearance), why should I deny that you are experiencing reality and will continue to do so even after I leave this timeline? Why should I think that I somehow nullified that experience we've shared together here once I've traveled back? Don't I still remember it? You're the one coming up with the screwed up rules not me.

But ask yourself - what is the alternative to my POV?
Magic time rubber-bands which tie you to your origin?
Many-worlds-theory?
Both seems ridiculously contrived.

and versions of history popping into and out of existence isn't ridiculously contrived? At least my view of alternate timelines is consistent.

And of course mine is somewhat contrived, time travel itself is contrived. If it exists and I can do such things as prevent my own birth reality is different then it appears to be.

 

[Terxpahseyton]

Both are and both are not is a contradiction that begs to be resolved.

Does the Highlander with a yellow skirt and the Highlander with a pink skirt both being real constitute a contradiction? Of course not. It simply means that the Highlander can change skirt colors.

You're the one coming up with the screwed up rules not me.

All I am doing is to look what happens when we can travel back in time. And IMO very consistently so.
What you are doing is making up rules so that the results are more to your liking. I can see now why people find a paradox if they insist on making up rules so that there is a paradox.

edit: To recapitulate:

- There is no reason to believe there are different parallel realities. So that is a no-go
- Time travel into the past means for all intends and purposes that things pop up out of nothing.
Everything else I have said follows from there.

 

[Perfection]

Does the Highlander with a yellow skirt and the Highlander with a pink skirt both being real constitute a contradiction? Of course not. It simply means that the Highlander can change skirt colors.

We resolve that by saying Highlander wore yellow on Monday and pink on Tuesday. We're talking about different locations in spacetime. Just like how I supply an A and a B to resolve contradictions. You have thus far been unable to supply means of doing such.

- There is no reason to believe there are different realities.

2014B 67 year old Perf remembers two versions of 2010 (2010A and 2010B). That's a reason. Why would you deny the reality of what he says?

 

[Terxpahseyton]

We resolve that by saying Highlander wore yellow on Monday and pink on Tuesday. We're talking about different locations in spacetime. Just like how I supply an A and a B to resolve contradictions. You have thus far been unable to supply means of doing such.

Because we - so it seems - just can not have them in this case. You may not like it, but that isn't really a convincing argument in itself. And you don't seem to have more to go on.

2014B 67 year old Perf remembers two versions of 2010 (2010A and 2010B). That's a reason. Why would you deny the reality of what he says?

Okay it is "a" reason. But not a very good one.
When there is a clash of what Perf got in his head and what makes for a more simple, less presumptuous and more logical explanation - which is that what Perf did did not magically create another whole reality - the simple explanation wins. Which is that what Perf remembers is gone. I think this is a pretty orthodox way of rationally trying to assess the world.

 

[Samson]

It seems to me that there is no observable difference between the "many worlds" explanation and the "many timelines" explanation. There are differences, for example does there "exist" a version of reality where CFC collapses for lack of Perf, it would seem the many worlds explanation says yes, and the many timelines says no (because that timeline ceases to be when Perf leaves it) but since there is no way to tell from either version does it really matter?

 

[Gucumatz]

I see nothing wrong with what you are thinking

But spontaneous appearance creates all sorts of potential conundrums. You could go forward in time until tech reveals how to make life, then go back so far in time that you introduce life as you designed it without any paradox. After some point of travel, the amount of matter twisted in time would begin to collapse itself though

 

[Perfection]

Because we - so it seems - just can not have them in this case. You may not like it, but that isn't really a convincing argument in itself. And you don't seem to have more to go on.

Okay it is "a" reason. But not a very good one.
When there is a clash of what Perf got in his head and what makes for a more simple, less presumptuous and more logical explanation - which is that what Perf did did not magically create another whole reality - the simple explanation wins. Which is that what Perf remembers is gone. I think this is a pretty orthodox way of rationally trying to assess the world.

Your attempts at ridicule are feeble. You're saying that I can make the timeline/reality/whatever I currently inhabit not exist, how much of a further stretch is it for me to make a new one?

The other thing that needs some careful thought is your usage of "gone". What does it mean for a time to be gone? What differentiates "gone" time from "non-gone" time? It also could be the case that I didn't make the new timeline, merely traveled to it.

Lastly I think the biggest issue is you seem to deny that when Perf comes to 1980B, he comes from anywhere, but that's clearly not the case. To understand Perf and his story you need to know about this alternate timeline, that alternate timeline is something that you need to account for. It is not merely non-existence. Simplicity is valuable only if it accounts for the known facts.

 

[timtofly]

The paradox is not "can it be done", but "can you kill yourself and still live" It is a known fact even in time travel that if you never existed, you would cease to exist if you tampered with your existence. Yes you can tamper with it, but why would you?

Time travel does not over write the laws of physics and biology. When you time travel you do not go to a different time, world, or reality. There is only one real time. Traveling to alternate realities is not time travel. That would be alternate reality travel. If you kill yourself that is not a different reality. You either never existed, or you are stupid. You would never have existed to kill yourself the next time around. There was no first time around.

If you are into killing anything, it would have to be right before they died any way. Because doing it would change the past reality, but only variably. The more indiscriminate killing one does, the more the past timeline would change, and there would be a possibility that you would kill yourself and you would never have time traveled to begin with. Thus your time travel would never have happened, and you would not have changed the original timeline at all.

It would be highly doubtful to figure out, unless one can know every single complex relationship of the time line to figure out how to affect it without removing your existence from it. Then you would have to be pretty well capable of forcing people to change their choices to fix the timeline. When people say there are multiple timelines, that may be correct. But they would only exist if someone actually time traveled and changed the outcome of each person's choices that ever lived. It is only changing it at the time it happened that would create an alternate reality. The further back in time the change the more radical the reality. So much so that according to some there would be totally different species. But that would be impossible to do, because if one never existed, the time line would never have changed at all to produce the you that produced the alternate reality. Although if the timeline ever was changed, this conversation would never have happened. It seems that we are pretty safe in saying the timeline is pretty much intact.

 

[Old Hippy]

The paradox is not "can it be done", but "can you kill yourself and still live" It is a known fact even in time travel that if you never existed, you would cease to exist if you tampered with your existence. Yes you can tamper with it, but why would you?

time travel and killing yourself are explained very easily in the film 'loopers', it is all so straight forward...

Spoiler :

Link to video.

 

[NetGear]

Problem with time travel is that when you time travel your muscle used to be cow. Your blood somevodys piss recycled. So unless your matter can go back in time without being recontituted into all the crap that used to belong in the past, you won't exist anyway. And if you somehow exist in thus timeframe despite all this, killing your mother isn't the worst offense to time paradox you have to worry about.

 

[Hojsimpson]

The time-paradox paradox (double paradox) is that if you kill your parents or stop you from being born, the person who stops you from borning (you) dissappear, so nobody is there for stoping your born.

Years ago I thought that if time travels were possible there must be one parallel universe per every unit time (time is finite), so if this universe aren't connected you can do what you please.

About the twin paradox, what if they were talkin with radio? (ignoring the speed of the radio)
Let's pretend for 1 twin 1 second is like 10 seconds. So if they were talkin with radio, a word that were said in 1 second for him would be said in 10 seconds.
Any thoughts?

 

[Terxpahseyton]

It seems to me that there is no observable difference between the "many worlds" explanation and the "many timelines" explanation. There are differences, for example does there "exist" a version of reality where CFC collapses for lack of Perf, it would seem the many worlds explanation says yes, and the many timelines says no (because that timeline ceases to be when Perf leaves it) but since there is no way to tell from either version does it really matter?

It can be discussed, this is a place of discussion, so yes it matters
Besides, many-worlds could also mean that one could - somehow (hey, we can already travel back in time) - return to ones own world. Or go to another world without time-travel involved at all (which would prove that many-world-theory is correct). Moreover, if many-worlds is incorrect, people may be very uncomfortable with the risk of non-existence and may want to ban time travel altogether. Religious may be afraid that their souls are gone or something.

But spontaneous appearance creates all sorts of potential conundrums. You could go forward in time until tech reveals how to make life, then go back so far in time that you introduce life as you designed it without any paradox.

See to me such "solutons" to time travel issues which postulate that one was "meant" to travel back in time - those are the ones that make no sense to me and which constitute a paradox.
For instance: Before I could time travel and create life - life had to already exist! That makes no sense whatsoever to me.

After some point of travel, the amount of matter twisted in time would begin to collapse itself though

Sorry but that made me laugh. And I have no idea what you just said

You're saying that I can make the timeline/reality/whatever I currently inhabit not exist, how much of a further stretch is it for me to make a new one?

Making the current one not exist is not a stretch. Time travel into the past is a stretch. Changing the future is not. Right now you change the future by whatever decision you are making. It is absolutely no stretch that you will do the same at whatever point of time you are.

The other thing that needs some careful thought is your usage of "gone". What does it mean for a time to be gone? What differentiates "gone" time from "non-gone" time?

That seems to only bring us back to the issue that we have no way to separate the two other than by saying "one/many was/were once, one is now". But as said I don't find this inherently problematic but only in so far problematic in that it would be cooler if we had some quantifiable way to separate the two.

It also could be the case that I didn't make the new timeline, merely traveled to it.

It could also be the case that I am Madonna.

Lastly I think the biggest issue is you seem to deny that when Perf comes to 1980B, he comes from anywhere, but that's clearly not the case. To understand Perf and his story you need to know about this alternate timeline, that alternate timeline is something that you need to account for. It is not merely non-existence. Simplicity is valuable only if it accounts for the known facts.

Physically Perf does pop out of nothing. As said this is what time travel necessarily is. For the moment of time Perf appears it hence makes no difference weather real Perf traveled back in time or a truly fake Perf with fake memories just truly popped up out of nothing.

It is a known fact even in time travel that if you never existed, you would cease to exist if you tampered with your existence.

Known tropes = known facts?

Problem with time travel is that when you time travel your muscle used to be cow. Your blood somevodys piss recycled. So unless your matter can go back in time without being recontituted into all the crap that used to belong in the past, you won't exist anyway.

Since it is called time travel and not time reversal or something that seems to be the assumption.

And if you somehow exist in thus timeframe despite all this, killing your mother isn't the worst offense to time paradox you have to worry about.

What paradox do you mean? That you can change the past to begin with? We can time travel into the past, that is also the assumption. Get over it
But you make a good point. The mere fact that we can time travel already establishes that we can change the past. And from that follows that we can change the future.
From that follows that we can destroy past and future as they were previously. Unless baseless assumptions like many worlds or nonsensical assumptions like absolute realities where it is all destined to happen come into play.
And since future is tied to the past, but not the other way around - duh - it doesn't matter weather I prevent my birth. I already changed the past on account of traveling back in time. I am already part of the past.

The time-paradox paradox (double paradox) is that if you kill your parents or stop you from being born, the person who stops you from borning (you) dissappear, so nobody is there for stoping your born.

Thanks Einstein for rescuing the thread.

 

[brennan]

Why does everyone have such a problem with time travel being impossible?