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I'm developing a story where humans colonize a few planets. One planet, lets call it Planet A, has similar gravity to earth, air pressure, and solar radiation. You cannot however, walk on the surface of Planet A with out a space suit, and there is no life, nor most of the essential ingredients. Planet A is arbitrarily far away from earth, it could be in the same galaxy, or across the universe.

Planet A relies on Earth for resources. One day the means by which both communication and transport of those resources stops working (could be wormhole for example), to which the residence of Planet A, after a very long period of time, get the means to travel to earth working again, and travel to Earth.

Part of my story relies on the time between the communication blackout being different for the Planet A side of things, and the Earth side of things, with Planet A experiencing a significant time difference compared to how much time has passed on earth (factor of 2x to 10x longer on Planet A). Note however when Earth's solar system and Planet A's solar-system are connected their clocks are synced or approximately the same (ie time passes at similar rates on both sides). The process of synced time is handwaved, you do not have to explain why it happens.

Is there some sort of scientific explanation for how this could happen? I'm willing to handwave the method of transport between these two far off places, but I'd like to explain the time difference scientifically.

Note, this question is similar to Can time move faster on another world but I do not consider the following to be valid explanations:

  • Time travel, as in someone purposefully made a time machine to go back in time.
  • Extremely rare and unlikely occurrences that we've never actually experienced and don't have a real reason to expect they exist naturally (ie a planet moving at 10c and negative gravity...)
  • Planets and solar systems that were purposely manipulated to speed up time.

This question (and the answers) also don't appear to take the distance between planets into effect, and talk about two planets in general where mine requires earth to be slower planet, so you can't put earth in a massive gravity well or something unless that's plausibly already the case. Finally my question talks about a hand-waved method to connect the two places with "something", which could provide more ground to expand the possible answers since this "wormhole" can be softer science and aid in answers.

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    $\begingroup$ This question has some problems. You handwave how time is synced, but that is at the core of the question. Time ALREADY will pass at different rates for two planets not in the same reference frame. Relativity means they might pass slower or faster depending upon who is measuring. $\endgroup$ – SRM Dec 9 '19 at 17:02
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    $\begingroup$ What you're describing is timetravel. Saying "that's not a valid explanation" doesn't change that very much. $\endgroup$ – Starfish Prime Dec 9 '19 at 17:20
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    $\begingroup$ I am not sure how we can satisfy the science-based tag for this $\endgroup$ – Trevor Dec 9 '19 at 18:06
  • $\begingroup$ The way round you've put it (with planet A experiencing 2-10* more time than Earth) isn't going to work in any other way than Mathaddict's answer. If it were the other way round you could have planet A somewhat in the gravity-well of a black-hole (which the Earth isn't particularly). Could the planets be swapped around for the purposes of an answer? Barring white-holes which are a bit blue-sky in this context. $\endgroup$ – A new normal. Dec 9 '19 at 18:50
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    $\begingroup$ You've ruled out "time travel" but since transportation is hand-waved, would you consider a wormhole through time? $\endgroup$ – pants Dec 9 '19 at 19:07
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Your characters believed the connection to be a wormhole through space, but they have actually been using:

A wormhole through space AND time™

When the wormhole is lost entirely, your characters "repair" it by creating a brand new one. But since they are unaware of the time component, they don't take timeframe into account. Their wormhole connects the proper relative locations, but is "wrong" on the when component. They had no away of detecting the original time difference because the locations are so remote that there were no common events to observe from both ends.

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  • $\begingroup$ This answer offers a narrative. I welcome suggestions on how to be less plot based, or is this style is OK on this site? $\endgroup$ – pants Dec 9 '19 at 20:28
  • $\begingroup$ Great! this is the exact kind of answer I was thinking of when I made my comment to your suggestion $\endgroup$ – whn Dec 9 '19 at 20:28
  • $\begingroup$ Be warned: time paradox ahead. $\endgroup$ – pants Dec 9 '19 at 20:31
  • $\begingroup$ Yeah, but the question has a "science based" tag. There is no known way to produce a wormhole at all, never mind control it in this manner. $\endgroup$ – puppetsock Dec 10 '19 at 15:11
  • $\begingroup$ Sometimes the client asks for one thing but wants something else. $\endgroup$ – pants Jan 7 at 14:53
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You have added the "science based" tag. And that's a problem. There is no known way to make time pass faster on another planet.

You marked "Accepted" an answer by Mathadict about standard old relativistic time dilation. But this answer is wrong. If two planets are traveling relative to each other, then each sees the other as going more slowly. This is absolutely required by special relativity. Any other choice would mean that there was an absolute frame of reference, the fastest-time frame. And that would invalidate special relativity, which would wreck the whole sequence.

Try this. Let the two planets cross at t=0 for simplicity. One year later, Earth sends out a ship. Planet A sees that ship coming at the same speed they see Earth going. When the ship arrives they find 1 year of ship time passed, for a total of 2 years. But 10 years have passed on Planet A.

Earth POV

But now look at the same thing from the point of view of Planet A. After 1 year, they send a ship. And Earth sees it coming at the same speed we see Planet A going. And it gets here after 1 year of ship time. But on Earth, 10 years have passed.

Planet A POV

This symmetry is absolutely required by special relativity. You can't "win" using this. The path with the corner will always experience less time.

Now you could slow Earth. For example, you could put Earth in an orbit very close to a black hole. As you get closer to the event horizon, there is a time dilation effect. From the point of view of objects very far from the horizon, things near the horizon appear to age very slowly. Arbitrarily slowly, in fact.

Now it's pretty uncomfortable being at this location unless you have a black hole with very large mass. If you had a black hole with, for example, only a few 100 solar masses, the tides would utterly pull apart anything within even a few dozen times the event horizon radius. Tides would be ridiculous, millions of g's, before the time dilation became useful. However, if you had a black hole with many billions of solar masses, a galactic sized black hole, then you could get useful time dilation before the tides started to pull apart the protons in your atoms. That might possibly work.

So there is no way to speed up Planet A. But there is a way to slow down the Earth. It makes travelling between the two very expensive in terms of change of velocity. But then, you said that was powered by hand waving.

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  • $\begingroup$ Okay, so even though there would be time dilation effects it would be symmetric, so even if you bent space to get to planet A faster, handwaved and said now the effects due to time dilation aren't noticable, bent back, waited X years, and then bent it close again, it would be symmetric given no anomolies like a black hole. What about a black hole makes this not be symmetric then? $\endgroup$ – whn Dec 9 '19 at 21:56
  • $\begingroup$ Only one planet is near a black hole. It slows time only near itself. $\endgroup$ – puppetsock Dec 10 '19 at 15:07
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Just normal velocity Time Dilation would do it, this even solves the issue of why it doesn't happen when the planets are "connected"

If the earth is moving very fast in relation to the distant planet then time would move slower on earth than on the planet. But when they are close together, then they actually aren't moving very fast in relation to each other because the now shorter path between them.

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  • $\begingroup$ Um, what? "because the now shorter path between them" makes absolutely zero sense. $\endgroup$ – Starfish Prime Dec 9 '19 at 19:49
  • $\begingroup$ @whn wormholes link points in spacetime, not space. The endpoints of the wormholes are still moving fast compared to one another. $\endgroup$ – Starfish Prime Dec 9 '19 at 19:52
  • $\begingroup$ @whn perhaps you needed the magic tag instead of science-based and reality-check? $\endgroup$ – Starfish Prime Dec 9 '19 at 20:02
  • $\begingroup$ @whn That's not how the "science based" tag works. The text of this answer is not how special relativity time dilation works. If two objects are moving relative to each other then each sees the other moving more slowly. This has to be true, or there would be an absolute frame of reference, which would invalidated special relativity. $\endgroup$ – puppetsock Dec 9 '19 at 20:59
  • $\begingroup$ They said that the clock synchronization is handwaved, so having it return back to normal when the handwaving isn't happening should be fine. $\endgroup$ – Mathaddict Dec 12 '19 at 16:02

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