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There have been many time travelling questions here, but I am not sure if this one specifically has been asked. Is it really possible to travel back in time and is it theoretically possible? This question states that one possibility is that:

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

Is this really true? On the other hand, Wikipedia states this:

Time travel to the past is theoretically possible in certain general relativity spacetime geometries that permit traveling faster than the speed of light, such as cosmic strings, traversable wormholes, and Alcubierre drives.

NASA also states this:

We can't use a time machine to travel hundreds of years into the past or future. That kind of time travel only happens in books and movies. But the math of time travel does affect the things we use every day. For example, we use GPS satellites to help us figure out how to get to new places.

Could anyone provide a detailed answer concerning which is actually correct?

Story:

I am writing a story on where a person travels back in time to prove its possible to the people in the past before getting found and arrested by the future people for "time travelling". But I want to keep the story "factual" and "as real as possible". I'm sure it is somewhat "possible", but I want to make sure the person in my story uses the right method to time travel in the first place, and that time travel is actually possible as well.

Context:

  • Year 6814 (not sure if it really matters, just a year that is technologically advanced enough to time travel).
  • Future world is technologically advanced enough to time travel to the past version of the same world.
  • The past version of Earth is the year 2050, where the technology is better than current standards, but not powerful enough for time travel obviously.
  • The future is a complete "utopia" setting, the people there have all the food, water, luxury, and technology they could ever want. There might be a few stranded groups of people who do not really want to live there for which I will not provide any reasons due to the context of this question.
  • There is a law in the future to not time travel back in time, if it is even possible for us people in 2022.
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    $\begingroup$ What is your world building problem? This sounds like a theoretical physics question $\endgroup$
    – L.Dutch ♦
    Jun 10, 2022 at 2:20
  • $\begingroup$ My question is exactly the same as this (why haven't people come back to tell us about space travel), but seeing my context is slightly different, I didn't add it yet @L.Dutch. Or should this question be deleted due to similarity to other question or should be asked on physics SE? $\endgroup$
    – DialFrost
    Jun 10, 2022 at 2:25
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    $\begingroup$ "Time travel to the past is theoretically..." - problem there, it's not a theory per-se. It's an hypothetical postulate. The theory can't exist until the phenomenon has been observed. Wikipedia is just plain not scientific in its language on this point. To say which if either is correct would entail knowing more than we do about the way the universe works. We have not done it yet. Tell you what, I'll travel to the distant future and find out...... OK I'm back, and I'm keeping the secret to myself. $\endgroup$
    – Escaped dental patient.
    Jun 10, 2022 at 2:30
  • $\begingroup$ @JiminyCricket. Shouldn't it possible to prove it "theoretically"? Or in this case tampering with time is really hard to "solve". And when you said "problem there", is my question on-topic? I was inclined to delete my question when L.Dutch commented $\endgroup$
    – DialFrost
    Jun 10, 2022 at 2:33
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    $\begingroup$ Here's not the place to get into philosophy, but we simply don't know what's possible in this regard. We have hypotheses, many - but none of them is "correct". We simply don't know what the facts are in this regard. We'd need more criteria about the setting to decide which might "fit best" for you. Could you add some details about the setting/tech-level etc.. $\endgroup$
    – Escaped dental patient.
    Jun 10, 2022 at 2:52

2 Answers 2

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Not Really

Technically, you can travel back in time. I don’t know how you would manage it or the science behind it, but for arguments sake you go back in time. If you try to change something, one of two things will happen. 1) You won’t be able to. 2) You’ll find out that was already in the timeline.

Essentially, if you find yourself in the past, just chill because the space-time continuum shouldn’t let you mess anything up.

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    $\begingroup$ Please do not answer questions that so obviously fail the rules of the Stack. To quote the Help Center, "Answer well-asked questions: Not all questions can or should be answered here. Save yourself some frustration and avoid trying to answer questions which are unclear or lacking specific details that can uniquely identify the problem [or] are not about worldbuilding as defined in the help center." $\endgroup$
    – JBH
    Jun 10, 2022 at 9:05
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There is a deep problem with "time travel". That is: how to know where to go back to. Nearly every story that uses time travel acts as if the earth is standing still. But that is not the case. The earth is spinning, wobbling around the earth-moon center of gravity, orbiting the sun which is orbiting the galactic center which is moving in the galaxy cluster. The universe is expanding. And there is likely to be more that we don't know.

The probability is that anyone who travels back in time will wind up in space vacuum rather than on the surface of the planet. That would be a better result than suddenly appearing 100 km deep underground.

Measuring where someone is standing on the surface of this planet compared to the center of the galactic cluster requires a tremendous precision and I doubt that any technology could reliably achieve that.

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