If space is always expanding, I’d really like to know if a time traveler would experience issues existing in a universe where the space between atoms is different from the one they left.
this post was submitted on 13 Mar 2025
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I was under the impression that gravity was a constant force keeping the atoms closer together
Space itself is constantly expanding. Theories of the Big Rip predict the space between atomic particles could become vast enough to rip them apart.
The big rip concept comes into play when the expansion rate starts to become faster than the forces holding molecules and atoms together. As far as current cosmic expansion goes, it only applies to space between galaxies. The current expansion rate is so weak it's not enough to overcome forces that hold galaxies together.
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I know we're in a meme community but this did get me thinking... Not only is the Earth spinning but it's also in an orbit around the Sun which is also orbiting around the center of the Milky Way which is moving through space relative to other galaxies and so on.
Do we have enough information to calculate a position in space in the future for Earth without a fixed reference other than current point?
There is not central point in the universe, and no way to calculate a position. Everything is relatove
This is why Doctor Who has a time and space machine. Also because the BBC didn’t have the effects budget to show him flying around.
We also get a few glances of the coordinate system that the time machines use in doctor who. It appears to have enough digits for a date/time as well as an X/Y/Z grid coordinate.
I don't think we have a relative fixed point to go off unless you choose the centre of the big bang. It's all relative to other things around us which are also moving lol
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I think you'll run into the three body problem.
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This blew my mind. All those movies!
So, Back to the Future's a bunch of bullshit?!
It's possible to assume that the professor did the math.
But yeah any time machine would also basically have to have space travel built in to compensate.
They knew that when they wrote Dr Who (IE the time travel machine is called a TARDIS (Time and Relative Dimension in Space).
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There's a ton of issues with time travel. That could be one, but most fictional time-travel devices can be said to accommodate for the difference in distance. It would just be boring to explain on-screen.
floating astronaut with pistol always has been
That's why doctor who works, its very clear about the fact that TARDIS travels in spacetime, it can do only time, only space or both space and time and they can get away with time traveling and still staying on earth
It could be explained as a time and space machine but just saying time machine is easier.
That's how ive always thought of these things in my head.
but imagine if you could set it to the same time but different distance, it would allow you to teleport, that might be too strong.
Sounds like a good tech concept for a story
It should be illegal to remind people (me, particularly) about Steins;Gate while they're at work
I can't be fucking crying on the clock, dawg
It's just another problem with the mechanics of the snap at the end of Avengers: Endgame
Magic exists in that universe though and they're using some of the most powerful objects in the universe. So like if it's granting a wish, you just wish that everyone comes back to earth or whatever. It's not even really a suspension of disbelief. It feels more silly to think that genius scientists using wish granting artifacts wouldn't remember to account for the movement of the earth through space.
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Wow, I never thought about that.
It's even cooler if you remember we send something to the moon even with all this variables and no calculators humans were able to know where the moon would be
Of course the moon is relatively close but still
Math is hard.
Oooohh. Thanks for the tip, just added that into my time travelling port o pottie's destination algorithms. Gotta respect the earth be moving and shit.
Also, the earth will never be in the same place twice. So it's not even like you can only jump increments of a solar year.
And its not like there even is a same place. Position is relative, but to what in this case? Doesn't even make sense
well it's likely the big bang has a central point, no?
Imagine the universe as the surface of a balloon. The Big Bang Theory stipulates that at one point, the balloon was extremely small, like a single point. But now that the balloon is bigger, you can't find a particular spot on the balloon where that point was, because everywhere was that point. No matter where you are in the universe, if you turned back time and shrunk the balloon back down, you would be at the point of the Big Bang. Nowhere is closer or farther away from it.
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No central point there
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Also ghosts likely wouldn't be affected by a gravitational pull, so the concept doesn't make sense and there'd just be a trail of ghosts in space.
Can't they just float and follow the Earth? Or would it be too fast? What's the terminal velocity of a ghost?
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Glad I’m not the only one confused. Who’s talmbout ghosts
I also think about this a lot.
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See, that's a problem they always skip in time-travel movies.
At least in Doctor Who, the T.A.R.D.I.S. can't teleport through space as well as through time, solving that problem. But most time machines don't
Heyy this property features in the accidental time machine by Joe Haldeman
Same place relative to what?
It's space-time, not space and time. Moving backwards in one moves you backwards in the other.
I always wondered about this