Not only is the earth never in the same spot, the solar system it's never in the same spot either. Even our galaxy is moving.
so would it be accurate to say that if one were to take a frame of reference on a large scale, say, the absolute centre of the universe (I know, but bear with me on this one), it's also fairly impossible to travel back in space as well as time, seeing as by the time it takes you to take a step back to your original position, the earth has already moved enough that you are no longer there relative to your reference?
I'm not sure "an absolute reference frame" exists. But, in your scenario they'd have to lead the shot so to speak. And jump in behind where they want to be.
And also any future position may be dependent on many variables that might be different each jump. If you were to go back in the past, the future location may be off greatly; just by going back may have altered the future location, insert multiverse theory etc
Well, I'm glad we got to the bottom of what's unrealistic about traveling back in time...
Time and space are pretty much linked so if you travel in time you can travel in spacetime :)
Yeah, but to my knowledge, you can only go forwards in time.
What you can do, is go forwards at a slower speed. So, if you sat yourself in a spaceship and accelerated to e.g. 10% of the speed of light, you might get out after what you perceive as a few years and find yourself in the year 2200 (I did not do the math), but you cannot go back from there.
Causal chains always have to follow causality. They can just do so less quickly, because, as far as my current understanding goes, the speed of light is actually the speed of causality.
(Sorry to bonk you with so much physics. I know that initial statement could have also come from someone who's never heard of the theory of relativity...)
You just need to reverse entropy haha
The thing is, a time traveling device would be like the one on Futurama. It just makes time flow at different rates. What people generally think of is a time teleport. And due to the nature of spacetime, a time teleport is indistinguishable from a space teleport. So any teleport should require precise spacetime coordinates, and n9t jist either space or time coordinates.
The bitch is figuring out a the spatial point of reference.
I don’t remember the name of the novel, so somebody help me with this. The concept is basically that scientists invent time travel, but use it as a teleportation device instead. Set the machine by a few seconds, you teleport the distance covered by the Earth during that time. They even use the technique to plan for an assasination of Kim Jong Un. Loved that one. Some innovative sequences using the ‘time machine’.
Edit: Found it. It's actually two books (original and sequel).
Split Second - https://www.goodreads.com/book/show/26216031-split-second
and
Time Frame - https://www.goodreads.com/book/show/37946554-time-frame
The first book takes its time revealing the 'time travel', but the second book dives head first into using the technology proficiently.
Accidentally read the second book thinking it was a stand alone. The story still held up so i made it half the book before i realized my mistake
It’s actually marketed as a standalone sequel, so you weren’t too far off. Plus I think the first one was more of an action thriller than about this invention. I actually don’t remember much from the first one. Most of what I remember is from the second one.
I hope there is an audiobook of these, sounds right up my alley
Same spot relative to what? What object do time machines use as a reference for their coordinates? It would make sense to be Earth, so it would be in the same spot all the time.
Weeeeell, not exactly.
It is true that things are all relative to each other. But think about it this was, if you fly out in a Starship in one direction for a light year, then turn around exactly 180 degrees and fly back, you wouldn't arrive back at earth, right? Mainly because things are accelerating due to gravity. And acceleration breaks symmetry.
It would of course depend on how time travel works, but since time and space are linked, it wouldn't be unreasonable to assume that you follow the same trajectory in space as you move through time. But that would be a straight line in the space+time dimensions still. Think of the paths in Minkowski diagrams.
Earth is a good one if you're only interested in time traveling on your home planet that happens to be Earth. But for a more universal perspective, I suppose the CMBR is the least arbitrary frame among all arbitrary frames
Well, I am traveling forward in time in home made Time Machine with the speed of one second per second. I do not see any problem you are describing. Now I just need to add the reverse, but I do not expect any issues of this kind either.
Oh like you can hit reverse.esrever tih nac uoy ekil hO
In this case, it makes sense to time travel from space and land on a planet upon arrival. Maybe all UFOs are just time travellers after all?🤔
This is why I think time travel will require both an entry and an exit portal, though it’d be through the same device. You’d walk in the portal at one point in time and space, then walk out of the exact same portal at another point in time and space. You’d only be able to travel between points where that time device exists in time and space, you’re using the same portal to travel to a different time in its existence. So no traveling back to the time of dinosaurs or the beginning of time or going to any point past when the portal no longer exists anymore. It’d solve the problem of having to deal with galaxies/stars/planets moving through space and would help mitigate some paradoxes, though not all and maybe even create others.
Calculations of the movement of celestial bodies is pretty accurate though. Figuring out where the earth was in the past is the simple part of time travel. Additionally you could just combine a time machine with a space ship and return to space nearby where the planet would be and then have a lander module or something just in case.
I thought about something like this when I was a little kid watching Back To The Future 2: "what if the ground had sunken somewhat since that mall was put there and the DeLorean emerged underground?" 
Weak premise considering the principles of relativity, and how our current understanding of time travel is basically rooted in SPACE-time.
Nor the solar system, nor the galaxy, nor the universe
I always assumed that teleportation would need to also be present for time travel. Clearly, just an assumption.
But would they be skeletons?
If they were orbiting a star for long enough, maybe. (Long enough = thousand or millions of years) Maybe a skeleton in a small cloud ?
At least this way you get to see space as you die, my worst-case scenario would be time travelling and arriving inside a concrete dam
Semi-relevant Tom Scott (actually about teleportation, but covers many of the same problems)
Teleportation is time-traveling as it allows you to be somewhere faster, change my mind
Nice one 👌
It's amazing how plausible this is
*any time
Since the universe is expanding.
Well you can always orient yourself relative to the aether /s
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