Something that bugs me about time travel.

[FPLOON]

Well... Who says that that version of future (2016) me was actually me (in the year 2016) from this "parallel universe"?

*mic drop*

(Besides, if there's one thing we learned as a society is that you can't stop the future from happening, especially when a future person travels back in time to warn that present time about it...)

 

[krazykidd]

I don't worry about it, if time travel we're ever going to be invented, we would already know about it.

What you should really worry about is how deja vu is really your brain perceiving a timeloop and how to expand and use said ability.

Not necessarily. I mean i think it would definately be possibe to travel back in time without the ability to interact with anything.

However i do think it's more likely we be able to " see" into the pass, kind of like through a looking glass , seeing past events in real time.

OT:

As usual with time travel, this all depends on whether there are multiple universes or just the one.

If multiple universes, then you don't have to give yourself the sandwich, because there's a universe where you never got the sandwich.

Else, if there's just the one universe, then you giving yourself the sandwich is a forgone conclusion and any attempt to avoid that fate will only cause it to happen.

This is what i actually came back to say.

 

[Sean Hollyman]

I think the alternate timeline theory is the one I like the most. Kind of like how Trunks going back and saving Goku from heart disease in DBZ.

 

[Dajmin]

I don't subscribe to any of these theories definitively.

Multiple universes is the easiest one to explain. You create an alternative where you didn't get your sandwich. Yawn, boring. Too easy. I don't think that's how it'd work if that was the case, although we'd never know because we'd conveniently always be in the "other" universe.

In my head, your universe simply evolves to adapt to the change. So in this case your future self no longer remembers going back in time and remembers instead feeling hungry. It's not such a significant change that the universe overall is all that different. Unless you died from hunger, meaning that your future self would cease to exist. Because you died. Simple.

Time travel is a messy one though. There's too many theories and the concept of changing the entire future is unimaginable. I just spent 10 minutes writing a version of this post that contradicted itself, so I'm ending here. Maybe a future version of myself can come back and get it right

 

[OrokuSaki]

I think the alternate timeline theory is the one I like the most. Kind of like how Trunks going back and saving Goku from heart disease in DBZ.

Except that the DBZ/Trunks theory of time travel doesn't make sense. Trunks would never be able to go home. If he changed the past then his future wouldn't exist anymore and he would travel forward in time and be met by an alternate version of himself (Probably the one from Dragonball GT).

 

[hermes]

Each decision creates alternate timelines. Even when you decide not to give yourself a sandwich in the past, a "parallel you" would decide to give yourself that sandwich, and that is the future self you met... That is only one of the theories.

 

[azurine]

My theory is that the universe would tear itself apart if there was an inconsistency in the space-time-continuum.

That, or fear of the unknown (the unknown being what happens when there's an inconsistency) drives whoever's causing it to correct the problem.

Last theory: It's all part of the multi-verse, in which case everything's consequence free.

 

[Godhead]

You should go back in time to give your past self that sandwich, but have it be a different sandwich from the one that you got from your future self that is now your present self.

Spoiler: It never ends

 

[The Event]

Can we all add our own paradoxes in here?

I get home one day to find a large envelope has been pushed through my letterbox. Inside the envelope are a full set of instructions for how to build a time machine.

I build the machine and follow the final instructions that say,
Write down all of these instructions, travel back to that date and deliver them to your own home.

Where did the knowledge of how to build a time machine come from?

 

[SirDerpy]

I personally subscribe to the belief of Fate with regards to this. Everything has been written like a perfectly executed novel, and things will follow this timeline down to the letter. Since it's already been written, there are no contradictions or paradoxes. If you invent a time machine, well, that's in Chapter 194235, page 24, third paragraph. If you decide to go back in time to kill your parents, it's already happened. Before you were born, in Chapter 194201, it was written that a man made an attempt on your parents' lives. He failed, because he was hit by a car and died. Now, you go back in time to kill your parents, you will get hit by a car and die. Because that's what happened, so that's what will happen. No contradictions are possible because they didn't happen.

Simple as that.

 

[fenrizz]

How do we even know if the universe cares?

I'm inclined to believe that the universe simply does not care and your life continues as normal wether you go back with the sandwich or not.

 

[V4Viewtiful]

That sounds like a time Paradox.

See if the purpose of giving you the sandwich in the past was so you wouldn't have to in the future than as sn as the sandwich was give that reality your future self came from would cease to exist there by closing the loop.

Now if the time space continuum depended on going back in time to going back to give that sandwich it will either create 2 separate realities or both continue one with the sandwich and one with your future self absent for a while.

This is the Loop in which you could end everything, the sandwich can cause a paradox destroying the universe if the loop isn't continued. so by not going back in time when your future self did at the exact same time Time will either fix itself by adjusting the universe (memories, events ect.) or destroy itself and start over to the point time was altered. Unlikely if time resets the person who altered reality won't remember a thing but could have a feeling of Deja Vu.
I say this because if time travel is possible what ever particles or energy source used could affect your body in many ways, yor memory may even adjust when time is altered actively.

That's how I see things anyway.

 

[2xDouble]

There is a relevant idea floating around physics and science-fiction... I forget the name of the theory, so I shall refer to as the "Timelord Fixed-point theory". Basically, one theory about timetravel paradoxes and resolutions states that time becomes immutable once certain events are fixed in place. eg: You will give yourself a sandwich because you gave yourself a sandwich. It may be under different circumstances than you were expecting, for example: you go on a different day, but tell yourself that you left on the "correct" day to cover your laziness, or it wasn't actually you, just someone who looks like you (a robotic clone of yourself from the distant future?) makes the trip instead of "real" you, but tells you the same information you were told to disguise your/its true nature... regardless, because the time-travel event has already occurred, something will happen to cause the event to occur again, and the paradox will resolve itself.

Of course, the parallel dimension theory (often referred to as the "Back to the Future theory") also works perfectly fine in this scenario.

 

[Piorn]

Time-Travel works with Narrativium.
It follows the rules it needs to establish a narrative, and any attempt to follow and or disrupt that narrative becomes part of the narrative itself.
If it doesn't, then there is no story, nobody knows about what happened and for all intents and purposes it doesn't exist, and we don't talk about it.

And since ex falso quodlibet (falso being "timetravel exists") , it's not about what's "real" or "true", it's about enjoying the ride.

 

[Zack Alklazaris]

I'll try and explain it using a scenario.

So there you are, sitting on a bench and you're pretty hungry. Suddenly your future self from 2016 pops in and gives you a sandwich. Then he leaves.

So you live your life normally until 2016, and you realize this is the day that you're supposed to go back and give yourself the sandwich.


What would happen if you choose not to?

It's already happened in your past, but how can it happen if you don't go back and do it?

One of two things would happen. It depends if you're on the side of linear time or nonlinear time.

In a linear time you would suddenly no longer have the sandwich, never of eaten it, perhaps not even remember it. A good example would be, You went back in time to preserve and reconnect your left hand that you lost in a circular saw 2 years ago. You fix your past self and warn him to warn his own past self, but then he forgets 2 years later. The hand should instantaneously be gone. This might occur after the 2 years or it might take till you die thus making it impossible to save you hand in the past.

In nonlinear time you'd travel into the past and altered history. However the present that you left has already written all of that history so it will remain unchange. After you give yourself the sandwich and return, you'll return to an alternate timeline that has you eating that sandwich 2 years ago. There would also be two of you. You, the time traveler, and you the one you visited in the past, now grown 2 years to your present.
The you who traveled back in the first place has in no way consumed this sandwich as that part of history was already written when he left. However, the you in the past that has grown 2 years did consume it. Now if the past you forgets to go back into the past and give yourself a sandwich nothing should happen. That history in this new timeline has you eating the sandwich. So you don't have to go back, you'll only run into the original you giving yourself a sandwich.

It can be a little confusing, my best analogy would be writing a story with a pen, then wanting to change something. You save your original story and continue to write it without the new changes. You take out new paper and copy everything, word from word, until your first new change. Then start writing in your changes on the new paper adjusting anything that might be affected by those changes as you write. So if you were to finish your story you'd have two stories that have alternate events. Once it is written, it can not be erased, you have to start fresh.

 

[McKitten]

Timetravel is kinda like faster-than-light travel in that it simply doesn't work with fundamental laws of the world we live in, so you'll have to pick something that gets thrown out.

In case of time travel you have two choices,

The first is you throw out any notion of free will or even randomness. The universe is wholly pre-determined, everything that happened and will happen is set in stone and nothing can change. If you receive a sandwich from your future self that is because that was predetermined to happen, and in the future you will travel back to hand it over because that is as well. Paradoxes simply do not happen and you do not have any say in the matter because you cannot make any choice to change what will happen (or make any choice at all for that matter).

The second option is to throw out causality. There is no more causality because time travel destroys any notion of a linear direction of time. This is not really easy to imagine because our brains are simply not structured to deal with such notions (in fact our brains have evolved in a way that we even tend assign causal relationships where there are none) but theoretically it is possible.

So, to borrow from the FTL saying: Free Will, Causality, Time Travel, pick any two.

The often used (in SciFi) idea of parallel universes is really a cop out because explaining paradoxes away like that means you're not actually doing time travel any more. If travelling into the past cannot affect your present, you're not actually travelling to the past, you're travelling to a past-themed amusement park, complete with a clone of your younger self. Of course, in many "time-travel" stories a past-themed theme park is what the author actually was looking for, not a story about actual time travel.

 

[Insideout Ink Demon]

always bugs me that the earth orbits the sun at silly MPH. so as soon as you time travel, you'd just end up in space, so little sci-fi addresses this

 

[McKitten]

There is no absolute coordinate system, there is no more reason for you to end up in space than there is for you to not end up in space.