The problem of causality (time travel)
Posted 2/3/18 , edited 2/4/18
I was watching stuff like back to the future recently and the butterfly effect and gods forbid I got to thinking about causal problems involving travelling backward through time..

To begin, for all intents and purposes this is a thread about problems with travelling back through time, not forward.

So, as I recall, if you could go back in time to, I dunno, say, kill yourself or some such hypothetical (don't ask me why but if yourself did that for the sake of whatever reason we don't need to know.)

You can say you can't and why you think that is the case. You can say you can but who knows what would be the result. So it goes, you go back, do it, but, you have destroyed your future self, making it impossible for you to go back to destroy yourself, and now, does all of existence unravel as a result? Or rather some "invisible barrier" prevents this or, more likely I think, you now don't have a reason to go?

Note: Even if it isn't to per se "kill yourself or napoleon" , the possibility of changing something might negate your reason for going in the first place.

Black holes, they exist, parallel universes may exist, so here we go, you've went and done something selfish, went centuries back to reshape history on a grand scale. What happens next, do you stick a post-it note on your refigerator, must still go back to do that later or the universe might make a decision and wipe you out.

Let us assume you took a gamble and caused some ripples. How do you see this going? What did you do, did you succeed, or did you (OMGOSH!) Erase(TM) yourself and or all of us. But rule is, you did it. WTF HAPPENED?

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Posted 2/3/18 , edited 2/4/18
The short version:
If changing the past with any noticeable results was possible nobody would ever do it because they'd have no reason to.
If your changes had catastrophic effects and you knew you'd just go back and prevent yourself from going to the past. So again, in essence no timetravel happening.

The longer version:
Depends on what theoretical model you base this on.

I) There's only the one timeline/universe:
Nothing* happened.
Suppose there was something I wanted to change in the past. Further suppose that I somehow went back and changed it.
In changing the past I also change my future to one where I don't travel back in time because I have no reason to, since things already happened the way I wanted anyway.

*the timeline changed. But since nobody would have any recollection of the original timeline nobody would know or notice.
In the variation where I as the timetraveler still had my recollection of the original timeline (and by extension none of what "actually" happened between the point I changed history and travelled back to the present) I would be considered quite delusional.

II) There are multiple timelines/universes:
a) You can only travel to the past and future of timelines other than your own:
If you travelled back to the present after making your changes nothing you would notice would be different, your timeline remains unchanged. The timeline you did change would presumably reconfigure to a state where your changes happened all along.

If you decide to stick around after making your changes you'd see a potentially different history to the one you know unfold from there but depending on how far you went back you probably wouldn't live to see what the "present" shaped by your changes looks like.

b) You can travel along your own timeline:
See I)

c) Timetravel is only sending your current consciousness into a past or future version of yourself, memories and all:
That's pretty much the plot to Steins;Gate with or without the part where the universe insists on certain things to happen.
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Posted 2/4/18 , edited 2/4/18
I always thought there would be no way to send your physical future self back in time, you would basically be your past self.

So you could only go back as far as your age, because I would think just you being in a certain time you never existed in would completely rearrange the entire structure of time itself, when you could only potentially take the consciousness you have now, but only be able to change the world around you for yourself, which may or may not have an inherent effect on the rest of the world during that time.

I think that would be more logical, since the people you already know that haven't met you yet would either meet you the same way, or you would meet them in a different way if you choose to change something in the past. I mean any little change could potentially save you time, or completely alter your own timeline.

I mean if you went back in time to kill yourself, that would mean hitting the reset button up until that point. So life would go on, but anything you did after that point in time would ultimately never exist, only the memory of when you decided to kill yourself, making the past stay relevant to your life and the people around you, but the future would really not change that much unless you actually effected the world on a larger scale. I mean it wouldn't have a ripple effect if you actually never had a ripple effect on the world in the first place.

So basically you have to be important to actually really screw with time, since people see you as a direct result of causality, leaving the world susceptible to the potential alterations if you do in fact create an issue both big or small.
Posted 2/4/18 , edited 2/5/18
You'd have to try to be like water (lol)
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Posted 2/10/18 , edited 2/10/18
Closed because OP nuked.
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