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In a world where time travel is possible, but has not been invented yet, would travelers from the future come back to prove it exists?

Surely, they would bring that technology back in time to let the people of the past use it?

I have four theoretical explanations so far, can anyone explain them in more detail, or provide other possibilities?

  1. The people decided to ban backwards time travel to prevent mass panic in the past, or to prevent possible paradoxes.

  2. The people in the future went back in time to an alternate past. (Similar to the Many worlds interpretation but with time travel).

  3. The people come back in time to give the people in the past new technology, they then jump forward in time to see how humanity has progressed using this. The result is that the future they return to is different to the one they left.

  4. They cannot go back in time because it has already happened, and therefore they can only go forward in time.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Serban Tanasa Aug 11 '16 at 12:15
  • $\begingroup$ Comments are not for extended discussion. Use the chat chat.stackexchange.com/rooms/43800/… $\endgroup$ – Tim B Aug 18 '16 at 11:19
  • $\begingroup$ Time travel isn't possible in worlds; it's a feature of the Universe (where "Universe" is what we used to call the Multiverse). I know that sounds picky, but it's an important concept to keep in mind. $\endgroup$ – RonJohn May 4 '17 at 15:05

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You can only send energy, not solid matter. Eventually future people figure that out and build receiving devices, and two way time travel is possible from that point forward. They still split the timeline of course which every trial...

The static coming out of your radio and TV are the wails of trillions of doomed time travelers; all trying to get someones, anyone's attention.

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I quite liked how the 2006 film Deja Vu, staring Val Kilmer and Denzel Washington, handled "Time Travel" of sorts. I don't think it's a spoiler at all to say they could strictly view as an observer - although from essentially any conceivable angle, and for a very limited time into the recent past. Watch the movie, some aspect of this concept might prove interesting for you to adapt to your needs!

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Somehow, no one brought up a simple fact that it would cost more energy to jump further in time or space. Just because you can jump 2 feet on a pogo stick, doesn't mean you could cross a city on it. Similarly, lets say that time travel is invented circa 2300 and there are ways to deal with the usual paradoxes forecast in SF stories.

Going against the normal flow of time probably needs a huge amount of energy even for short hops. Moving back around a week or two might be close to the monthly energy output of entire world circa 2010, and jumping back a couple of months would be close to monthly output of the world in 2300 (which presumably has overall increased, but also humans are far more efficient with it).

In such a case, world government (UN or descendants) may collectively save up enough power to jump back a month and prevent/prepare for previously unforeseen emergencies. That would be a great use of time travel to help in the era that it exists, and get great acceptance from the public. But, even allowing a jump of a couple of years would be prohibitively expensive and hence infeasible - not to mention the completely insane idea of a 200 year time leap. And this is excluding any necessary budgeting for follow up interventions to solve time paradoxes and unwanted ripple effects of the journey.

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  • $\begingroup$ I think Angel's answer from yesterday already covered this. $\endgroup$ – sumelic Aug 13 '16 at 2:05
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In a world where time travel is possible, but has not been invented yet, would travelers from the future come back to prove it exists?

In theory, yes.

Here is the basis of that answer: According to certain texts, this has actually happened. People have seen the future, and even interacted with beings that have done things in the future. Then, these time travelers have gone back in time and reported it to people. The result is that their observations have been recorded in the ancient texts that report such things.

Another result is most of a world remaining unconvinced.

Surely, they would bring that technology back in time to let the people of the past use it?

Not quite so surely.

You're assuming that the people who are doing the traveling have control over the ability to initiate the travels, and they can effectively teach others, and that others will trust the messengers enough to follow the available instructions.

Another possibility is that the combination (of all of these things) is not entirely true.

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As others have said the distance the Earth has rotated, traveled around the sun and the solar system traveled around the universe would seemingly make it impossible not to end up in the deep void of space.

However.....

How about only being able to go back to certain points in time? Since the Earth would need to be in the exact same position (or nearby if you are in some sort of spaceship) you only have a window of x amount of time which you can travel back to. Assume that the Earth is in the exact same position every 2,500 years (I made that number up, I'm sure it is wrong). You would be able to travel back in increments of 2,500 years +- any amount of time in which it is feasible to get back to Earth on your ship.

We wouldn't know about it because we weren't in that window when someone was traveling (it was banned or forgotten or people decided not to use it to come to us or whatever.) Basically time travel isn't as easy as go to wherever and whenever you want.

(How do you think the pyramids were built? Clearly people came from the future with their technology and built it.)

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    $\begingroup$ Hi, welcome to worldbuilders! :) I do have a question about this - you've said "the Earth would need to be in the exact same position". The question is, same position relative to what? If it's the same position relative to the Sun, then there seems to be no reason for this to be the case as the Sun is also moving relative to the centre of the galaxy (and pretty much everything really). The Sun's orbit only intersects itself once every ~225-250 million years, ignoring the fact that the galaxy itself is probably moving relative to the galaxy cluster... $\endgroup$ – Mithrandir24601 Aug 10 '16 at 19:07
  • $\begingroup$ @Mithrandir24601 Relative to everything. This is obviously assuming that the universe is not infinite and at some point Earth will end up at exactly the same location that it was in, in space, in the past. (Basically at some point there isn't something bigger that is orbiting as well). I made up the number 2,500 off the top of my head. If you could only travel in increments of 250 million years that would explain even more why we have not been visited. It may be that its only possible to travel in increments of billions of years and by then humans may have died off. $\endgroup$ – yitzih Aug 10 '16 at 19:44
  • $\begingroup$ An advanced enough society which can travel in time will certainly have zero problems with either a) calculating where the earth was XXX years ago and adjusting accordingly or b) implementing the time travel in such a way that it uses earth as a fixed frame of reference. As many others, this answer does not address the question "if t.t. is possible, for what reasons would people not go back" but instead simply says "t.t. is not possible". $\endgroup$ – AnoE Aug 12 '16 at 14:40
  • $\begingroup$ @AnoE I'm not suggesting time travel is impossible. Rather I'm suggesting it would be impossible to travel across such a distance of space in no time at all. Essentially you could only travel through time to a time when Earth was in its same position which could only be possible every x amount of years. You can't necessarily travel through time (at least backwards or faster forward than we do automatically) and space at the same time which could mean that no matter what frame of reference is used this could be true. $\endgroup$ – yitzih Aug 12 '16 at 15:11
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    $\begingroup$ I understand what you want to say, but it does not make sense to talk about "the earth going back to same position". In relation to what? The sun? The center of the galaxy? The center of our galaxy cluster? Center of the universe? If you have to pick a frame of reference, you'd pick earth itself (including its rotation around itself of course), which would be physically completely equal to picking any other frame (like the sun). All in the context of time travel being possible, as posted by the question, of course. $\endgroup$ – AnoE Aug 12 '16 at 15:25
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....or provide other possibilities?

5 : Timetraveller's come visit all the time but we don't notice them because they're very good at staying un-noticed and the time-police make sure of it.

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As a programmer I am fully qualified to say that time travel is utterly worthless if you change ANYTHING. Why? Because it creates an infinite loop.

Explanation:

If I want to stop Hitler from committing the Holocaust, I'm going to time travel back and kill him. So, I go back I kill Hitler and stop the Holocaust. Boy, that was easy. Now, IF I didn't cause a parallel dimension, or alternate reality, and assuming I actually changed the timeline I came from, let's follow history, from the death of Hitler.

Hitler dies young, no Holocaust. No history books talking about the Holocaust. I am born, I grow up never knowing about the Holocaust. I invent my time machine, I do something else that isn't killing Hitler, because I never knew about him. Hitler is now not killed in his youth. He grows up and commits the Holocaust.

Rinse & Repeat.

There is some flexibility depending on how time actually works. The way I tend to think about it, time have already happened, so future you stops existing once Hitler is killed (aka the first big change that changes your course to create the time machine and go back). Therefore, the you that wants Hitler dead stops existing entirely, because he "never existed" anymore, only the other you exists, but then he stops existing once he doesn't kill hitler. Aka, the universe just keeps ground hog daying around the time of Hitler's "Death", and the time you would have gone back to kill him in the timeline where is still alive.

However, if your time is always linear, or if your time machine somehow stops you from being affected by the change, you could go forward in time (after killing Hitler), and convince yourself that you have to kill a young Hitler in the past once you invent the time machine. This may be difficult to do depending on how much you have a problem with killing people just because a lunatic who looks like an older you tells you to. If you can convince yourself to go back in time without the Holocaust existing and killing Hitler, you can keep there from being an infinite loop.

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Personally, I find most of the existing time travel theories to be garbage.

I don't think there can be a paradox. The simple reason is that time is relative. Let's say you have a personal time travelling device. You turn it on and are transported back to before you were born. For whatever reason you take an action that results in the death of your parents.

Current theories would say that one of two things will happen. Either you have just created a new universe (I think this is cheating) or you cause a paradox and everything either blows up or resets (I think this is lazy thinking).

My theory is that nothing happens to you. You, and whatever you have with you, still exists because your specific time reference hasn't changed. You'll still have your memories - after all those are just electrical impulses in your brain. You'll still be alive. However, the future will be at least somewhat different when you jump back.

So, to answer the questions:

  1. Bans are a waste of time unless you can actually enforce it. The only possible way to enforce this is if there is a unique energy signature given off by the device that can be tracked by satellite. Further it would have to be detectable in such a way as to give any enforcement people plenty of time to get there and stop it.

  2. Obviously I don't think this is a possibility.

  3. Possible, likely even.

  4. This item doesn't make sense. If the past is locked then by definition the future would be too.

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When time travel becomes possible, exploring other times and cultures is as popular to them as cell phones and the internet are to us now. Even though there's such a grand choice of times and places to choose to visit, some have undoubtedly chosen ours.

Why haven't they told us all about it?

We've changed quite a bit physically, and none who have gone back far enough long enough to learn now's human forms has taken this knowledge back to them... for very plot-specific reasons.

To be here, they are in the physical forms they know how to create here, and none of these forms very many people of today can or choose to communicate well enough with yet.

Plus, we are to them, sort of like Australopithecus is to us... If we went back in time to visit Lucy, would we try to explain the internet to her, or more likely just expose ourselves to her until she trusts who we are and possibly teach her our most basic communication styles instead?

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a) You travel to the past.

b) This changes the future. Regardless of how careful you are. Even displaced air molecules count.

c) Because of this your journey to the past is also changed, at least slightly.

d) a>c sets up a feedback effect. You keep changing the past, which changes the future, which changes the past etc.

e) This feedback loop potentially repeats forever. The only reason this feedback effect would ever stop is if a self-consistent timeline emerges.

f) Therefor, to a outside observer without some godlike hyper-time observational powers the only time travel allowed is ones that result in the time travelers trip not being changed in any way at all by their own actions. Publicly introducing time travel would almost certainly do that - it would be a well known historic event. Therefor it cant be done. If time travel is possible at all, the trip must be observational only. Or, at least, no changes serious enough to effect the time traveler.

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protected by Community Aug 10 '16 at 20:41

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