I was surprised when I read the OG time machine story by Jules Verne and this was a main plot point, and only later stories hand-waived it. You’d think it was something from later analysis of the idea. Almost like that Verne dude was clever.
Clark Ashton Smith wrote a similar short story where the inventor failed to take it into account. Upon realizing his mistake he decided to just wait for another planet to reach him, turning his time machine into a spaceship.
That’s actually a fascinating idea. All interstellar travel is based on the movements of the planets through space time. I bet it alternates between being technically faster and slower than FTL travel since you may have to wait for a time when your destination to pass into the planets past location.
Wow that’s a fun thought hole. Constraint certainly breeds creativity!
Classic sci-fi slaps hard
One way to resolve this is to have some kind of multiverse theory where you don’t travel back in time to your universe, but to a narrow slection of parallel universes that are also shifted slightly so that it spits you out in an analogous location to your initial departure.
that’s why you build it like a spaceship 🤷 ez
I hear police boxes and phones booths are popular as well.
Position isn’t absolute so if this happens this means you knowingly made the time machine memorize position relative to e.g… the sun rather than the earth.
Tine machine probably moved in its own inertial reference frame. That will actually get you lost in space because the inertial frame does not orbit around, which involves rotation(rotation is intrinsically non-inertial, i.e accelerating). Time machine’s frame will be moving in a straight line if its inertial
Or relative to the galactic center. That would put you even further off.
incorrect, that is not what this means. They could have forgotten about the position setting all together. Also why the suns position? it is also moving and non absolute, just like earths. Makes no difference in this meme
All of space is moving, you need to fix a reference point, there’s nothing to stop you making it earth
Earth frame isn’t inertial
They could have forgotten about the position setting all together.
You’re assuming that the time machine would just change the time and keep the position but there is no absolute reference frame, so the time machine should use some reference frame in which it keeps the position constant. It would then be common sense to have the time machine keep the position relative to the earth. Anything else would be pretty dumb, unless you want to use your time machine also for space travel to other planets.
why the suns position
That was just an example. It’s either the sun or the center of our galaxy, or some other reference point so if it wasn’t the earth then the sun is the next most logical option.
What you’re describing is a machine which moves both in time and space. A machine which only moves in time would result in this meme no matter how you twist it.
We can’t really say that for certain. The word “space” as we know it means nothing without the idea of relativity. Earth orbits the sun, the sun orbits the center of the Milky Way, which exists in a nest of clusters and super clusters … and then you get to the edge of the visible universe. My point is, if a universal frame of reference exists, we haven’t found it. “Absolutely stationary” isn’t something we can test for. Everything that we can observe appears to be moving around something, so can we even responsibly assume that there is a universal frame of reference? Or is it safer to assume that relativity all that there is (i.e. space-time has no boundaries)?
please explain to me how do you think being stationary in space works?
There are two ways of looking at it.
- The time machine is using itself as a point of reference to comply with general relativity. The only way to time travel is to move forward in time. The way to move through time would be to move a lot faster than the Earth, so that every minute for you inside the time machine would equal to many years for earthlings. And if you’re moving that fast you’ll fly away from Earth.
- The time machine somehow has a knowledge of the whole universe, this way a Newtonian model applies and an absolute point of reference exists. That allows unrestricted travel both forwards and backwards in time, but that also means that the Earth will inevitably move from under the machine to follow its path across the universe.
No matter how you twist it you’ll end up all alone in space. You need a machine which can move through both time and space at the same time.
You’ve got to entangle the same machine first over a massive macro quantum space-time superposition.
See, you get it.
I remember reading about this concept as a kid in a short story Neal Shusterman wrote called Same Time, Next Year. Blew my mind
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.
They are not, that would require changes in the strong force.
They wouldn’t; the expansion of space isn’t strong enough to change the distance between atoms; the force holding them together overcomes it.
I was under the impression that gravity was a constant force keeping the atoms closer together
More importantly it’s the electromagnetic force that keeps atoms together. Gravity only keeps planets and stars together and also solar systems and galaxies, but in ordinary objects it’s totally negligible.
“Weaker than Weak”.
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 scenario happens in the case where the rate of space expansion is increasing. It’s possible, but we haven’t seen any evidence of it yet, so far the rate appears constant, which means a heat death scenario.
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.
Should have watched Tom Scott
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?
That’s what einstein said. There is no fixed reference frame, but only relative ones. Every “inertial”(meaning, motion without any external force) frame of reference is equally valid as any other inertial frame movibg with respect to it.
But for sure we can tell earth’s orbit is not inertial since circular motion occur, which is due to external force of gravity.
Edit:typo
Shouldn’t it be (at least theoretically) possible to find some sort of geometric center where - on average - the rest of the universe is expanding away from?
Turns out, no; every point is expanding away from every other point, so every point sees itself as the center of expansion.
That could sort of explain why it’s inherently impossible to determine the center - but that doesn’t rule out the existence of a geometric center of the universe, right?
Kiiiind of. I suppose we haven’t definitively ruled out a geometric centre, but it runs up against Occam’s Razor in a really big way. A centre of the universe would require some kind of boundary or edge to the universe, and the physical dynamics of how that would even work are very much non-trivial.
Generally the universe is thought to either loop back on itself like the surface of a globe, or extend infinitely in every direction.
For a geometric center you would need a boundary of the universe
No, for the same reason you can’t find a point a balloon is expanding from on its surface. Everything is expanding everywhere.
I’m not sure if I follow the balloon analogy. Sure, you can’t find the center on it’s surface. But somewhere within the balloon, there is a center. It might be virtually impossible to determine the center while actively inflating the balloon, but that doesn’t mean there isn’t any center? What makes the rest of the universe fundamentally different from an inflating balloon? I’m genuinely curious.
With the balloon analogy it’s not about the center of the volume, we ignore the volume and assume that the surface is a 2d universe. That’s what’s impossible to find the center of. I don’t really like that analogy though personally so I’m not going to discuss that one further.
Just think about it this way: the observable universe can only be so big (because when the expansion between two distant enough objects is faster than the speed of light/causality, they no longer have a means of interacting). We don’t observe any sort of obvious boundary to the universe within our visible portion that we might be able to assume a center based on. So it’s not that we know that there isn’t a center (afaik, someone correct me if I’m wrong), it’s that it’s likely impossible know that there is, let alone find it from our position in the universe. So, we might as well assume that it’s all relative.
Imagine you woke up on a raft in the middle of the ocean on an alien planet. It’s foggy, you can’t see stars, you can’t see any landmarks at all. There are other things floating in the water too though. There might be a geometric center to that ocean, but you can’t see it, and you have no other hint at where it is. For all you know, the entire planet is ocean and there’s is no center to find. This is sort of the situation we Earthling are in now, except that at least the the rafter can drift and perhaps eventually find and map out a coast. Because our space-time is expanding, our observable universe will never be bigger than it is now.
OK, so what we discovered was that if we look far into the universe, all stuff is moving away from us (we can measure that using the famous red shift). Additionally, the farther something is, the faster it is moving away from us.
Now the simplest explanation would be that the Earth just happens to be exactly in the middle of this expansion. However, it is much more reasonable to assume our location in the universe is not special in any way and that you’d see things moving away from you if you did these measurements anywhere else. If that is so, the universe is expanding, everywhere. There’s more space in the universe every second and there’s still the same amout of matter, hence it is becoming larger, emptier and colder.
The next step is to look back and think of how the universe looked in the past. Since it’s getting bigger and bigger, it must have been smaller before and if you go back in time enough you’ll find a tiny universe that still has the same total amount of matter in it, just densely packed into possibly just a single point. Hard to say what preceded that moment, but we can predict a universe which started as an incredibly energetic singularity which exploded out and has been growing ever since. We call that moment the Big Bang and if anything, that is the centre from which everything is expanding. Not found somewhere in space but in time.
Back to the balloon analogy, the centre would be the deflated little thing you start with. Maybe a better analogy would be the little clump of molten glass at the end of a glassblower’s pipe. He begins to blow, the big bang happens, expansion starts. Fast forward 13.7 billion years (which happens to be today) - the glass has expanded into a large spherical object and there’s some tiny people living on it.
They only live on the surface of the glass and the sphere is so huge (or they are so tiny) that they can’t even tell that their world is spherical. They measure distances to some other specs littered across the glass and find that they are all moving away from them, faster the farther they are. Their universe is expanding, but where is the centre of expansion? They cannot point to it, because they only live in two dimensions, fully defined by the sufrace of the sphere. But if they could point in a direction perpendicular to all the spacial dimensions they know, they could point to the point where the sphere started, long in their past.
So the right question is not form “where” the universe expands but “whence”. The Big Bang. The very start. Somewhere far in time, which is just another direction, perpendicular to up, left, forward.
I very much appreciate the effort to write your repsonse, and if you’re out of time or energy I completely understand.
So if I’m understanding you right, we’re 3-dimensional creatures living in a 4-dimensional universe, with the 4th dimension being… time? And time behaves completely different from the other 3 dimensions, which is why we can’t just disregard or freeze it when trying to determine a center?
It’s a bit more complicated than that. One of the consequences of theory of relativity was the realisation that time and space cannot be separated and it only make sense to speak of “spacetime”, a four-dimensional continuum rather than just three as we thought until that point. As far as I understand it, time is not really different from the other dimensions, it just seems that way to us.
I heard an explanation that has to do with entropy - the total amount of entropy is always increasing (I’m not going to even try to explain this since I only barely understand that myself) and the act of encoding information (whether we’re talking a brain forming a new memory, a computer storing some data, or me writing this comment) is a process that always increases entropy, therefore any kind of memories can only be of things in the past rather than the future, and so every moment of our lives feels like “now”, the boundary between the written and the unwritten. I don’t think we’re actually moving in time. It’s just an illusion.
That said, while my earlier explanation is simplified and probably contains a ton of inaccuracies, I’m fairly confident it’s accurate in broad strokes. This comment though, I’m not nearly as confident this is the current scientific consensus. Just what makes sense to me, so take it with a grain of salt.
If you’re interested in stuff like this, I cannot recommend The Elegant Universe by Brian Greene enough. Unlike me he’s someone who actually knows exactly what he’s talking about and he explains everything much better than I ever could.
It’s not, because the space itself is expanding
There is not central point in the universe, and no way to calculate a position. Everything is relatove
Here, that might be interesting to you.
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
There actually isn’t a center of the big bang, every point is expanding away equally.
Isn’t everywhere kinda the center?
Effectively, yes
I think you’ll run into the three body problem.
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).
Nah, this thing with the planet moving under you is stupid because it assumes a fixed reference frame which is not a thing in our universe. Any movement is always relative to something. You can’t just “stay in place”. Having the Earth move from under you is very arbitrary.
Even if you assume any frame is valid, you have to pick inertial frames. So even if you travel few days, you will be off from earths orbit into space since earth is in circular motion which is acceletared
Yeah, these jokes always assume a jump back in time, not some sort of rewinding for just the traveler.
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.
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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.
I cant watch that movie without thinking of all the unintended consequences. Pilots on planes snapped out, plane goes down, when pilot is snapped back, where plane use to be, but is now free falling.
Maybe they just end up in the plane where it is now. You’re overthinking it. It’s not a monkey’s paw and they weren’t using it with intent to harm.
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?
It wasn’t matter that “banged”, it was space-time itself. We observe space expanding, and when we extrapolated backwards eventually we found the point when space-time (not necessarily the stuff inside it) was just a single point, and we called that point “the big bang”. That’s just what the current math says of course, but because of the rate of expansion and the speed of light, we can only observe so much of the universe, past and present. Even when we observe far out and way back to soon after the big bang, we don’t see it all, our scope is limited even within space-time. And from what we can observe, nothing indicates a center. For all we know, there isn’t one, just like you can’t paint a dot on the surface of a ball and call it the center of the surface, every point on the ball’s surface has equal claim to that. In that situation relativity is all that there is. Unless there’s a massive breakthrough, it’s looking like the laws of physics won’t permit us to know if a center exists, let alone find it.
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.
would not the fact that blue shifted galaxies being rare, mean that in general all galaxies are red shifted from the perspective of all galaxies, thus they are expanding away from a point on a similar vector, and thus have a central point?
And a balloon does have a vector of direction: the mouth piece
would not the fact that blue shifted galaxies being rare, mean that in general all galaxies are red shifted from the perspective of all galaxies, thus they are expanding away from a point on a similar vector, and thus have a central point?
No, it means the opposite. They are expanding away from all points, because space itself is expanding. In fact, stars are able to move away from each other faster than the speed of light, which is only possible because space is expanding. Again, like the surface of a balloon, we can imagine that the further away two points are from each other, the faster they’ll move away from each other as the balloon expands, so even if there’s a certain maximum speed that you can move along the surface of the balloon, if two points are far enough away from each other the rate that distance is created between them can exceed that speed.
If there was a single, specific point in space where all the stuff came from, then we wouldn’t observe the same thing in every direction. Sure, we might see stuff ahead of us redshifted because it’s moving faster and stuff behind us redshifted because we’re moving faster, but we should also expect to see stuff to the sides moving alongside us at similar speeds that would not be redshifted. The fact that there’s consistent red shifting in every direction, getting more pronounced the greater the distance, leads us to the conclusion that space is expanding.
And a balloon does have a vector of direction: the mouth piece
It’s an analogy, don’t take it too literally.
No central point there
