Time and space are the same thing, if you’re traveling in time it seems like you could travel in space at the same time.
Yeah but traveling in space takes time, so you can reason that traveling in time takes space.
Yes and that's how we ended up with American Football. In the original timeline, it never existed.
The goal posts and yard lines were all just decorative. People would come from miles away to sit and watch the field for 2 or 3 hours. Girls would do flips and shake pom-poms to encourage the grass to grow. Luckily the time traveler brought their egg ball with them and figured out something to do in these fields.
I think that's the joke. Media presents time travel as just inputting the date and off you go, but really you need to input time AND space because the two are interconnected.
Of course we could just imagine that all time machines somehow calculate the space itself just by knowing the current spacetime and the inputted time, but now we're giving writers too much benefit of doubt. In most cases time travel is used as plot device and very little thought is given to how it could work.
And an interesting sidenote. This also means that teleportation is a special case of time travel and if you've solved time travel you've probably also solved teleportation.
Media presents time travel as just inputting the date and off you go, but really you need to input time AND space because the two are interconnected.
Alternately since we're Earthlings, someone designing a time machine might think it's a good idea to automatically calculate the location using the Earth as a reference point because that's likely to be the most common use case and doing so would prevent you from dying to the void of space if you make a tiny math error. At which point you would just need to input the destination time if the target is the same location relative to Earth.
Or maybe the time travel happens by warping space in the first place (since you need to somehow overcome the speed of light problems anyway). Seems like a good job for a wormhole if someone wanted to write around the space/time/motion rules.
Wouldn't matter, because the problem isn't about space or motion, but about position. If you jump backwards in time but your position in the universe doesn't change then you are probably no longer on earth because the Earth moves about the sun, etc. To land somewhere meaningful, you'd have to calculate the target location relative to some reference point with a predictable location and as Earthlings we'd probably pick the Earth itself unless this is a time traveling spacecraft.
So you're saying that, if you're traveling in space it seems like you could travel in time at the same space.
If they were really the same thing, traveling into the past would be trivial. Greg Egan's Orthogonal series explores the consequences of space and time actually being the same thing. You can also the the difference in formulas related to proper time, where terms for space and time have opposite signs. Space and time have the same relationship to each other as real and imaginary numbers, in a fairly literal sense.
Couldn't this be solved even if they weren't linked by just flickering in and out of phase or whatever to keep gravitationally relative with the earth
A time machine would necessarily need to have some way of defining what reference frame one is stationary in space relative towards, because there is no universal frame that everything moves relative to. This suggests that a time machine ought to let you move through space as well as time
So to travel into the future and be in the "same place" relative to your planet you'd need to solve the n-body problem for at least your local system to a suitable length of time. A slight error might mean you appear inside the planet or in outer space.
Or maybe I don't understand this stuff. :-)
Mass bends spacetime so one could assert that a time machine could anchor itself to a sufficiently large mass, just like how things in orbit are still bound to the earth's mass.
You'd just send a drone back, to say 100 years ago, first and have it send you exact coordinates into the future.
Time paradox aside you'd probably have this data already, with all alternatives and can correctly time jump right away.
But by the time you have collected and evaluated all the drone data you and all the masses around you would already be in a totally different configuration, making the data useless.
But maybe a little jump to the time when you sent the drone out would be easier and then you could use the drone's data.
Since relativity tells us there is no universal reference frame, then it having its reference tied to earth is perfectly valid.
Also sidenote: my favourite idea about time travel is that time travel is entirely possible, but will never be invented, because the timeline where its not invented is the only stable timeline. Because any timeline where it IS invented gets changed as soon as you use it, meaning the timeline changes over and over again every time time travel is invented repeatedly either infinitely or until someone accidentally creates a timeline where its never invented, only then does the timeline stop changing and we can actually experience it. So because we exist and can experience time, we can deduce that we will never invent time travel.
There can be stable timelines with time travel - there's actually 3 states:
Perpetual instability, where the timeline changes each time the time machine is used but never reaches the same state twice
Perpetual cyclic stability, where people's actions in modifying the timeline lead to it eventually reaching the same state, eg. you go back in time to kill someone who becomes evil and oppresses you but the near death experience leads them capture you, so you can't time travel any more, and to blame your people and start oppressing them, leading to the same actions
Stability without time travel, which is the default state but incredibly hard to get once time travel is invented as with nobody to stop time travel being invented it would probably get invented again, however parts of a cyclically stable timeline could have nobody having access to time travel, but any actions by time travellers to stop time travel would likely lead to the second rather than third option
Yeah I think we don't have to worry about it for the same reason why you don't have to worry about getting thrown backwards when jumping in a moving train.
Rotational reference frames are out though! (Unless you want to deal with magic forces acting on your masses)
And since the earth rotates around itself and the sun, and the sun rotates around the center of the galaxy, you will always have to deal with a moving target.
Since I stay on earth now when I'm moving forward in time why wouldn't I stay on earth when I move backward through time?
Sure you can, but you need to adjust your position due to centrifugal forces all the time. A time machine would have to do that as well.
If a ball is flying in a straight line through space with a speed of 1m/s I can predict without much math where it will be at any point in time. In fact, if the reference frame is chosen such that the ball is stationary you don't need any math at all, because the ball doesn't move!
However, if you have a set of two balls orbiting each other you will always have to do math to calculate their position. I mean technically you could choose the reference frame that is rotating in sync with the balls. But still you need to do math to check that the centrifugal force, which is a real force coming from nowhere in this reference frame, exactly cancels out the gravitational pull between the two balls. Because rotating reference frames are not equivalent to each other!
I really don't get why the time machine would have to do any calculations at all. The time machine is in this reference frame. You seem to assume that by going back through time you'd be teleporting through time, which leaves the open question of where you'd appear. However, I'd much rather assume that you'd actually be "going" through time. You wouldn't cease to exist until you reappeared somewhere. Instead you'd be in the machine for some time until you'd get out of the machine again. That'd mean neither you nor the machine ever leave the reference frame.
You might have better luck and accuracy using our galaxy' s black hole for reference marker depending on how much time you intend to traverse
How much do you know about the "double slit" experiment and its subsequent variations? Because I think that's a rabbithole you'll enjoy. That first video is really just context; this next link is another video in that series, and this is the one that really pertains to the consequences of time travel: https://piped.video/watch?v=8ORLN_KwAgs
In most media time machines are also teleporters - many are explicitly so, with the destination space needing to be chosen at the same time as the destination time, but even when that's not shown they still make the time traveller suddenly vanish and then just suddenly reappear elsewhen.
One movie I've seen with a more "realistic" time machine is Primer. It's not at all a teleporter or portal. Very slight spoiler:
It sidesteps the whole issue that OP presents because the place where you exit the machine after traveling is just where the machine is when it's turned on to begin with. You can't time travel outside the machine, including to before it exists, and your path (in all four dimensions) is contiguous.
I prefer the H.G. Wells The Time Machine style of time travel , where you affect the flow of time instead of a discontinuous jump.
You're still attached to your current location, things just happen faster (in forwards or reverse). It also means that time travel takes time, which can be a handy plot tool.
Edit: grammatical swipe keyboard errors
Primer is one of my favourite movies ever. It was made on a budget of 3 peanuts and pocket lint, and it shows, but damn it's an interesting premise.
Still in my top 5. I think the acting is better than most science fiction blockbusters and every science fiction series.
Same with The End of Eternity - they can travel to different times at which the machine existed.
In fact, isn't it a bit similar with the only 'real' possibility of time travel - you create a wormhole and take one end on a relativistic journey to create a time difference between the ends, but the only possible travel is between the two ends that you have created.
Time machines have been invented dozens of times since the 1800s; there's s trail of them drifting through deep space.
I feel like the scientists smart enough to invent time machines would have thought of that
Well, since this was posted in Science Memes, I'll be so pedantic that science does not support the idea of travelling back in time.
It does support travelling forwards in time, at various speeds, but you'll constantly be aware of where you are (even if one method involves travelling really fast and therefore may still leave you in empty space).
I thought it was possible in relativity if only you could solve that pesky going faster than light problem. Only going to the speed of light is impossible. If you were to start out beyond the speed of light you should be traveling backwards in time. Mathematically that should be possible.
I have heard that notion before, but don't know how the maths is supposed to work.
I can tell you, though, that light would be going faster than light, if it could.
Here's a simple equation you probably know:
F = m * a
(F is force, m is mass, a is acceleration)
Well, if you rearrange it, you get this:
a = F / m
We currently believe photons to have no mass.
Insert that into the equation and you get a division by zero, but our closest approximation means acceleration is infinite, as soon as any non-zero force is applied.
Infinite acceleration results in immediate infinite velocity. It makes no sense for light to only accelerate until 300,000 km/s and then take its foot off the gas pedal.
This is why it's instead believed that there is a speed limit to causality itself.
The speed of light (as well as of gravitational waves and other massless things) just happens to be the same value, because they're going as fast as is possible.
Here's a video about the speed of causality: https://www.pbs.org/video/pbs-space-time-speed-light-not-about-light/
if you believe in the notion that the universe is cyclic then you can mimic time traveling backwards by traveling forwards, past the end of the universe, and stopping at just the right time in the new universe.
e.g., to get to 1700 you’d go (present time) -> (death of the universe) -> (1700 in next universe)
But what if the absence of the atoms of your body affects how the universe collapses and in turn expands?
If you've already done six impossible things today, why not stop for breakfast at Milliways?
If the universe is cyclic, then the version of you from the previous one is also jumping to a time before when you left. It works if the board gets reset to the exact same position and true randomness doesn't exist. We're talking down to the electron scatter of radioactive decay.
If the universe is cyclic, then that would define it as a closed loop without any energy being removed or added. The very first instance of yourself traveling through time would break the loop by removing themselves from their iteration of the universe and reinsert into a future iteration. During those two points, the universe would now function with a deficit. This deficit could affect how it cycles to subsequent iterations.
What if that discrepancy in energy affects when the universe starts to contract or it's speed to the big crunch/bang and subsequently the time to, and speed of expansion. Maybe it could even prevent the big crunch from reaching critical mass, where it would normally trigger a big bang, and stop the cycle altogether.
I mean, personally, I actually don't believe that the Big Bang created everything out of thin air vacuum, because much like travelling backwards in time, that would break causality.
It makes much more sense for everything to just have always existed and the Big Bang is merely a very visible event + expansion afterwards.
I'm open to the notion that expansion and contraction happen in some sort of cycle, because well, many things do.
But for it to be cyclical to the point where it repeats precisely the same? Why?
Can't we just let the universe flobber on its merry way without assigning some higher meaning to everything it does?
What if I think of it as a pancake?
Actually it was my work in the field of pancake time that brought about widespread internet ridicule
Pizza is a better example. Particularly a NYC style.
The thing about time/space travel is that you can only really travel within your cosmic neighborhood, or "slice". You can move linearly across the surface, but if you want to actual travel through time, you have to fold the slice.
Now, if you want to expand beyond your cosmic neighborhood, then you really gotta think more like a calzone.
I like the idea that time machines are like phones in that you need a receiver to pick up the signal. A consequence is that you can only travel back to the time that the machine was turned on.
Imagine building the first receiver, and immediately have 20 people spawn within the same space
More like 2 million inconsiderate time tourists comming to gawk at the first reciver..
You may enjoy Ted Chiang's The Merchant and the Alchemist's Gate, the short story.
The whole book is great if you like thought-provoking sci-fi premises I guess: https://www.goodreads.com/en/book/show/41160292
Wow, I did not expect to find a fellow Ted Chiang enjoyer. The Merchant and the Alchemist's Gate is one of my favorite.
This meme format having a redemption arc is my favorite. It wasn’t super sexist, but it was just unnecessarily sexist.
Time machines don't exist and (as far as we know) cannot exist. Therefore, we can say they work however we want. If you can travel back in time, surely you can do that while remaining close to an arbitrary point of reference.
Hence how the artist was able to choose that the time machine in this context rewinds time while conserving the universal position(?)... Relative to the center of the universe(??)... assuming eucledian space(???)
That's probably the guy that offered people a few dollars and a chair to watch all of earth's history.
https://astronomy.stackexchange.com/questions/33514/how-fast-are-we-moving-relative-to-the-cmb#33515
Earth moves with somewhere between 230-500km/s, long term average should be 370 km/s
https://en.m.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System
https://en.m.wikipedia.org/wiki/History_of_Earth
The solar system and earth formed 4.6 billion years ago.
https://numbat.dev/?q=370+km%2Fs+*+4.6+billion+years+-%3E+ly%E2%8F%8E
That means the solar system travelled 3.45-7.67 million light-years (5.67 for the average speed) since then.
That plural form (millions of light years) is borderline, but actually not incorrect.
I honestly think this would not happen because you would be time-travelling in the Earth's frame of reference
Yeah, or if the time machine is genuinely a teleporter, then the invetor should at least know how to correct for drift.
I mean, it's the space-time continuum, it's connected! As the documentary Stargate SG-1 shows, we're well acquainted with spatial and chronological drift over interstellar distances.
There is no space reference in time traveling only a time reference, the time traveler don't change his start point, but the Earth and the whole solarsystem do. If you travel 6 month to the future, you are still in the point where you started, but the Earth will be on the other site of the Sun. A time machine must be a spaceship, otherwise you won't survive. That is the error of almost all movies about time travel since H.G.Wells.
This is a huge assumption. Why is it necessary that time would not have a space reference? I'd actually say that based on relativistic physics there probably is a space reference because the dimensions are linked. I think it's possible that the momentum of the current movement could remain constant and thus stick the time traveling device to the earth. Coming to a complete referential stop in space would require beyond immense energy and be inefficient if one only wants to travel in time
If you travel 6 month to the future, you are still in the point where you started, but the Earth will be on the other site of the Sun.
Why would you remain spatially locked to the sun? The solar system is moving around the milky way. The Milky way is traveling at around 370 miles per second if we use the universe as a frame of reference. A point is both a place and a moment. Everything is moving relative to everything else. Time travel is also space travel.
Kinda depends, doesn't it? A travel that let's you see glimpses of reality/earth implies you're making smaller skips that may keep you somewhat held in place. Being able to establish a vector through time may also imply control of vectors in space.
Also, six months would likely take us farther than the other side of the sun. If we're completely de-referenced we might be able to find a universal reference frame or some wild shit.
Being human sucks.
This. It would have to be set as relative to something, why you would define that as any object not Earth or on Earth is a mystery to me
Ooh, new science fiction idea. We built a time machine and can only use it to reach other star systems. But just those that have been or will be at the same "spot" as earth.
With the reference point being a black hole at the center of the milky way from which it derives all it's power, love it: get a draft to my desk before July 19th and we'll talk potential remuneration.
I think gravity is the solution to this problem. The time machine just has to be able to lock on to the earths gravitational force from across time
Earth rotates at about 460m/s around it's own axis.
and I'm sure scientists have access to a more precise number than that.
we dont have to detect what we can calculate
We have a machine that can track planets through time and space and you only want it to work on Earth?!?
It would only work on earth because we've only given the time/space machine information about the rotation of the earth.
But my question is more about science theory than fiction. Does observing gravity give any information about how fast that mass is rotating?
"It would only work on earth because we’ve only given the time/space machine information about the rotation of the earth."
So you're the one that only wants it to work on earth then.
And no. "Observing" Gravity does not give any information of how fast an object is spinning around it's own axis.
So you're the one that only wants it to work on earth then.
No. Are you suggesting we supply this machine with the rotational velocity of all planets in the known universe? Or some other solution?
How could we jump to a planet on the other side of the galaxy?
Well, since no one bothered to create a savepoint, we can't travel back in time anyway.
I'd like to believe that mass (and then by extension the Earth) "defines" the spacetime around it as much as it distorts spacetime near it. I suspect this may even be the underlying cause for the observation of speed of light being constant in the presence of earth/solar/galactic movement.
It'd be really interesting if time moves at different speeds in different bits of the galaxy, find out that none of the other solar systems have life because closer to the galactic center of someone dropped a teapot when the first life evolved on earth it still wouldn't have hit the floor.
Of course there's a lot of reasons this isn't the case but I dismiss them by saying they're all just an effect of distortion due to time variance.
Maybe we'll get s message from voyager saying 'arrived at a star 224 light years away, it was super quick because there's no time in the middle so you just skip that bit'
Similar to a solar system's habitable zone there exists (or is suspected to exist) a galactic habitable zone. I think because of cosmic rays and radiation. So I guess most habitable planets would have more or less the same time dilation.
When I was a kid I thought that spacetime was created by mass. I thought that if you were to ever find the end of the universe you wouldn't be able to travel beyond because you would just create new spacetime everywhere you went.
And I thought that was scientific consensus. No idea where I got it from, though.
My view has always been that space is "round", that there is no end of the universe because it just loops back around. Apparently this is all still unknown.
