Alastair Reynolds' novel Pushing Ice (2006)[1] covers exactly this topic: a bunch of humans are trapped on an alien spaceship accelerating indefinitely, and all the involved relativistic effects are covered in the book. While it's not Reynolds best book, it's definitely worth reading just for the clarity and accuracy of the description of the relativistic effects (Reynolds is a former ESA astrophysicist).
Tau Zero by Poul Anderson is another one on the same line; a Bussard ramjet damaged such that it couldn't turn around. Because the Bussard ramjet provides both propulsion and radiation/particle shielding, they can't turn it off, so just get faster and faster...
There’s a short story in the Expanse Universe where Solomon Epstein is killed by his experimental propulsion system when it accelerates so fast that he can’t reach the controls to turn it off and then blacks out.
The drive is named posthumously after him based on the design notes found on his computer by his widow.
In The Forever War by Joe Haldeman, soldiers are sent out on relativistic journeys to fight a war with aliens. Each time they come back, Earth culture has changed, and eventually it becomes unrecognizable to the soldiers, and Earthlings forget or stop caring about the war.
It was an allegory for the U.S. involvement in the war in Vietnam, in which Haldeman fought.
The ‘specific impulse’ of a rocket engine is one measure of its ability to convert the energy in its fuel into forward thrust. Its unit is ‘seconds’, and its measure could be interpreted as ‘how long could one pound of fuel produce one pound of thrust’.
If your rocket starts off 2/3rds fuel by mass, this will result in an average acceleration of 1g as the mass of the fuel is consumed.
The most efficient chemical rockets we have today have a specific impulse in the ~470 second range. The highest specific impulse thrusters of any sort that we have in wide use today are ‘ion thrusters’, which have specific impulses in the 50,000 second range (but can’t generate much thrust at all).
So 10-12 hours at 1g is about as much as we can do with existing hardware.
Interesting to note that when you are travelling close to c, even intergalactic vacuum requires a lot of mass ahead of you so the ship is not vaporised.
Remember that when you are travelling to that galaxy 18 billion light years away, you’ll hit every photon it sent our way over 18 billion years in just about 45 years.
Relativistic speeds are a plot point in Andy Weir's recent book "The Hail Mary Project". You might know him from the Martian a few years ago.
Scott Manly did a Youtube episode on all sorts of weird propulsion mechanisms that people have come up with over the years a few months ago: https://www.youtube.com/watch?v=QEZv_OXA_NI. There are some interesting concepts in there. Including the anti matter based concept discussed in the article. Particularly fusion looks like it might get us some interesting amounts of delta v.
> "In fact, so long as you kept adhering to this plan, you could choose any destination at all that’s presently within 18 billion light-years of us, and reach it after merely 45 years, max, had passed. That ~18 billion light-year figure is the limit of the reachable Universe, set by the expansion of the Universe and the effects of dark energy. Everything beyond that point is currently unreachable with our present understanding of physics"
There is a misconception that expanding space prevents us from ever reaching a destination. It's counter-intuitive (https://en.wikipedia.org/wiki/Ant_on_a_rubber_rope) but falls out of the math. If space expands at a constant rate, you could eventually reach any destination at any velocity.
But if the expansion of space is accelerating (which we believe currently), this is not true. There really would be destinations that are unreachable.
You would continue to travel further from your origin, but also witness your destination accelerate away.
Well, an accelerating mass emits gravitational waves; and your spaceship is asymptotically infinite-mass; so at some point you destroy the universe. (Or at least the parts that are causally connected to you -- I guess cosmic expansion would save parts of it?)
The way I understand it is that it's not impossible to cover the distance, but that by the time you do, the distance between your starting point and your destination will have (at least) doubled due to the expansion of space.
So you're still as far away from your destination as in the beginning (or even further), but now you're the same distance from your starting position as well and are effectively stranded.
Fantastic sci-fi novel with continuing modern relevance. Often interpreted as metaphor for the author's experience in the Vietnam War, and his return to American society after what felt like a period of otherworldy time-dilation.
The graphic novel version is great too, if you can find a copy:
The time dilation aspect in space travel is the most neglected in popular sci-fi. In many of these, there are intricate installations of some sort cryogenic sleep devices because the script authors assume that it takes you 150 years of travel at light speed to get to a place that is 150 light years away.
For a hard science fictional version of this, check out Poul Anderson’s “Tau Zero”, from 1970, according to Wikipedia. I read it a few years after that, and it’s stuck with me since. A ship with a Bussard ramjet runs into troubles and has to keep accelerating, into the far future.
A 1982 sci-fi novel, where a interstellar spaceship reaches the destination star, after travelling a very long, but unknown time (part of the plot).
I do not want to spoiler too much, but it was written by a academic physics/philosopher and his wife a mathematician. Deep shit.
Should be standard read in schools.
So, if you constantly accelerate for 45 years you will travel 18 billion light years to the edge of the observable universe. But, if you continue for another 45 years you won’t move beyond that point? Or do you move beyond that point but don’t reach anywhere, it’s all darkness? Or do you seem to stand still while the observable universe behind you expands past you to where you can no longer see it?
So in a way, this is time travel. If you wanted to see what the world looks like in five thousand years, you could get on a spaceship, accelerate way out to wherever and back, and voila! you've fast-forwarded five millennia.
A fascinating thought. The ship and crew would surely be long forgotten. You may be greeted as an alien visitor, until the people of that time recognize your relatively ancient technology from fragments of historical records. Too bad you speak a language nobody else even remembers.
Or perhaps you emerge as gods on a pillar of fire from the sky, witnessed by the primitive-again survivors of whatever has played out since you left.
I'm strangely tempted. If you offer me a ticket on such a ship, I might just come along.
Sure, with the comfortable acceleration of g during the first half of the journey and decelerating during the rest of it, I could arrive to, say, Andromeda galaxy in a few dozen years. The biggest question, though, for me is: OK, I’m here, now what? (Having a vivid imagination, as a child I once imagined myself standing on the Moon’s surface, looking at the distant Earth shining just above the horizon and the eerie landscape below. The first and the only thought I had at that moment was: “What the hell am I doing here?”)
The year is 1492. You're imagining standing on the shore of a vast continent, unexplored by your people. The only feeling/thought you have at that imagined moment is “What the hell am I doing here?”
That is perfectly reasonable! But I hope you can appreciate that the imagined feeling/thought is not shared by everyone.
The theoretical limit is "to the edge of the Hubble horizon, as long as you don't mind it being a one way trip."
As you approach 'c' time dilation shrinks time for you. Keep accelerating and eventually a million years outside your reference frame is mere days or hours inside the spacecraft. You could travel to the Andromeda galaxy or beyond as long as you were okay never returning to Earth or returning to a different geological epoch than the one you left. Go far enough and the sun might be in its red giant phase when you get back. You may have aged a few years or decades.
This of course requires stupid amounts of energy and theoretical near maximum specific impulse, what I once heard called a "physicists' nightmare propulsion system." Something like a "photon rocket" or a relativistic velocity ion drive (propellant exit velocity near 'c') plus a very efficient fusion or antimatter reactor might be able to get you there. It was called a physicists' nightmare because if containment fails you become a flash of gamma rays in less than a nanosecond.
One of my favorite wild speculations is that hypervelocity massive particles like the "OMG particle" are the jet wash from someone's engine.
> If it weren’t for Einstein’s relativity, you might think that, with each second that passes by, you’d simply increase your speed by another 9.8 m/s. If you started off at rest, it would only take you a little less than a year — about 354 days — to reach the speed of light: 299,792,458 m/s. Of course, that’s a physical impossibility, as no massive object can ever reach, much less exceed, the speed of light.
> The way this would play out, in practice, is that your speed would increase by 9.8 m/s with each second that goes by, at least, initially.
From the point of view of an external observer, this seems clear enough: the ship's acceleration would reduce, at first gradually, then ever more sharply as its velocity approached c.
But what about from the point of view of the ship's crew? Would they also measure a drop in acceleration -- e.g., would they weigh less?
Or would it be that they would measure the same acceleration, but the final picosecond (according to their clock), which would without relativity push their velocity to and past c, instead stretches out infinitely, thanks to ever-increasing time dilatation?
The implications of time dilation when moving near c are also explored in the Three Body Problem trilogy, and pushed to the extreme as well. It’s quite a mindfuck if you still have ties to the place you’re leaving, but interesting if you don’t.
There’s all the interesting idea of just accelerating forever, till the end of the universe (which comes faster than you think if you’re going that fast).
We're really spoiled by modern rapid global travel. In the 1930s half of my maternal grandmother's family emigrated to New Zealand. I've only ever met two of those relatives once in the 1990s, but before jet travel such contact was impractical for most people. That's why whole family groups, or even communities would move together.
And all at 1g... I wonder what forces the human body is capable of adapting to over a long period.
What happens if say we double the thrust, presumably halving the timescales and doubling the experienced "gravity"... would a human body be able to adapt and get stronger? or would we experience adverse side effects? (not necessarily mutually exclusive). It could even be a way to acclimatise to a different planet's mass before arriving.
[EDIT]
Looks like 2g is reasonable. The limit is higher but it sounds a bit ridiculous, astronauts would all have to compete in the strongman competitions for 4g. Any higher and we wouldn't be able to walk without breaking our bones.
I never knew you could get that far in that amount of time (experienced by passengers) with just 1g of force so it’s thoroughly interesting and in some sense everything is quite close: as long as you are
OK with a one way ticket.
It's important to note though that this kind of ship is still impossible as far as I remember - even with matter/antimatter reactions (which theoretically gives you E = mc^2 energy, the maximum possible per kg), you can't get enough energy to accelerate to the mass of the fuel to 1g, nevermind the rest of the ship, for the duration required for interstellar travel.
One of Heinlein's juvenile novels (Have Spacesuit, Will Travel?) describes TFA's concept of accelerating at 1g until the halfway mark, then doing a "skew flip maneuver" (I think that was the phrase Heinlein used) to decelerate at 1g. [0]
27,000 light years in just 20 years. This is crazy, I never would have thought these relativistic effects have such impact. I guess we could create a travel into the future this way if the rocket was designed to eventually come back to Earth.
I was wondering, what if there was a spaceship circling outside the solar system at near light speed (not dwelving into whether it is possible ever to design such a ship or what the centigular forces inside would be), if there were people on such ship, that would experience 27,000 years in 20 years, would it be possible to communicate with them given the close proximity? Wouldn't it be weird that they are experiencing time in a much different way?
Heck, even with a rocket that is simply moving away from Earth, the messages that are sent should eventually reach the ship? (because it's not travelling faster than light, and at times it's even slower) How can the ship receive 27,000 years worth of messages in 20 years?
[+] [-] littlestymaar|4 years ago|reply
[1]: https://www.goodreads.com/book/show/89186.Pushing_Ice
[+] [-] rsynnott|4 years ago|reply
[+] [-] mattsoldo|4 years ago|reply
[+] [-] hinkley|4 years ago|reply
The drive is named posthumously after him based on the design notes found on his computer by his widow.
[+] [-] snowwrestler|4 years ago|reply
It was an allegory for the U.S. involvement in the war in Vietnam, in which Haldeman fought.
[+] [-] milansm|4 years ago|reply
[+] [-] jcims|4 years ago|reply
If your rocket starts off 2/3rds fuel by mass, this will result in an average acceleration of 1g as the mass of the fuel is consumed.
The most efficient chemical rockets we have today have a specific impulse in the ~470 second range. The highest specific impulse thrusters of any sort that we have in wide use today are ‘ion thrusters’, which have specific impulses in the 50,000 second range (but can’t generate much thrust at all).
So 10-12 hours at 1g is about as much as we can do with existing hardware.
[+] [-] rbanffy|4 years ago|reply
Remember that when you are travelling to that galaxy 18 billion light years away, you’ll hit every photon it sent our way over 18 billion years in just about 45 years.
[+] [-] jillesvangurp|4 years ago|reply
Scott Manly did a Youtube episode on all sorts of weird propulsion mechanisms that people have come up with over the years a few months ago: https://www.youtube.com/watch?v=QEZv_OXA_NI. There are some interesting concepts in there. Including the anti matter based concept discussed in the article. Particularly fusion looks like it might get us some interesting amounts of delta v.
[+] [-] air7|4 years ago|reply
What happens if I just keep going?
[+] [-] Gunax|4 years ago|reply
But if the expansion of space is accelerating (which we believe currently), this is not true. There really would be destinations that are unreachable.
You would continue to travel further from your origin, but also witness your destination accelerate away.
[+] [-] Lariscus|4 years ago|reply
[1] <https://www.youtube.com/watch?v=uzkD5SeuwzM>
[+] [-] perihelions|4 years ago|reply
I don't know whether you observe this or not.
[+] [-] DarkWiiPlayer|4 years ago|reply
So you're still as far away from your destination as in the beginning (or even further), but now you're the same distance from your starting position as well and are effectively stranded.
[+] [-] gambiting|4 years ago|reply
[+] [-] hoseja|4 years ago|reply
[+] [-] adrianN|4 years ago|reply
[+] [-] neartheplain|4 years ago|reply
The graphic novel version is great too, if you can find a copy:
https://en.wikipedia.org/wiki/The_Forever_War_(comics)
[+] [-] edna314|4 years ago|reply
[+] [-] philiplu|4 years ago|reply
[+] [-] hutzlibu|4 years ago|reply
I just discovered Andymon.
A 1982 sci-fi novel, where a interstellar spaceship reaches the destination star, after travelling a very long, but unknown time (part of the plot).
I do not want to spoiler too much, but it was written by a academic physics/philosopher and his wife a mathematician. Deep shit. Should be standard read in schools.
[+] [-] drittich|4 years ago|reply
[+] [-] vagrantJin|4 years ago|reply
[+] [-] irrational|4 years ago|reply
[+] [-] btbuildem|4 years ago|reply
A fascinating thought. The ship and crew would surely be long forgotten. You may be greeted as an alien visitor, until the people of that time recognize your relatively ancient technology from fragments of historical records. Too bad you speak a language nobody else even remembers.
Or perhaps you emerge as gods on a pillar of fire from the sky, witnessed by the primitive-again survivors of whatever has played out since you left.
I'm strangely tempted. If you offer me a ticket on such a ship, I might just come along.
[+] [-] justsid|4 years ago|reply
[+] [-] Koshkin|4 years ago|reply
[+] [-] Torkel|4 years ago|reply
That is perfectly reasonable! But I hope you can appreciate that the imagined feeling/thought is not shared by everyone.
[+] [-] praptak|4 years ago|reply
[+] [-] scotty79|4 years ago|reply
I ask myself the same question whenever I leave my city.
I guess I'm not really a traveller person.
[+] [-] deepsun|4 years ago|reply
There was a paper considering making a shield against it, either lead, or electric field, or magnetic field, and resources required for it.
[+] [-] api|4 years ago|reply
As you approach 'c' time dilation shrinks time for you. Keep accelerating and eventually a million years outside your reference frame is mere days or hours inside the spacecraft. You could travel to the Andromeda galaxy or beyond as long as you were okay never returning to Earth or returning to a different geological epoch than the one you left. Go far enough and the sun might be in its red giant phase when you get back. You may have aged a few years or decades.
This of course requires stupid amounts of energy and theoretical near maximum specific impulse, what I once heard called a "physicists' nightmare propulsion system." Something like a "photon rocket" or a relativistic velocity ion drive (propellant exit velocity near 'c') plus a very efficient fusion or antimatter reactor might be able to get you there. It was called a physicists' nightmare because if containment fails you become a flash of gamma rays in less than a nanosecond.
One of my favorite wild speculations is that hypervelocity massive particles like the "OMG particle" are the jet wash from someone's engine.
[+] [-] dghf|4 years ago|reply
> If it weren’t for Einstein’s relativity, you might think that, with each second that passes by, you’d simply increase your speed by another 9.8 m/s. If you started off at rest, it would only take you a little less than a year — about 354 days — to reach the speed of light: 299,792,458 m/s. Of course, that’s a physical impossibility, as no massive object can ever reach, much less exceed, the speed of light.
> The way this would play out, in practice, is that your speed would increase by 9.8 m/s with each second that goes by, at least, initially.
From the point of view of an external observer, this seems clear enough: the ship's acceleration would reduce, at first gradually, then ever more sharply as its velocity approached c.
But what about from the point of view of the ship's crew? Would they also measure a drop in acceleration -- e.g., would they weigh less?
Or would it be that they would measure the same acceleration, but the final picosecond (according to their clock), which would without relativity push their velocity to and past c, instead stretches out infinitely, thanks to ever-increasing time dilatation?
[+] [-] sudhirj|4 years ago|reply
There’s all the interesting idea of just accelerating forever, till the end of the universe (which comes faster than you think if you’re going that fast).
[+] [-] simonh|4 years ago|reply
[+] [-] tomxor|4 years ago|reply
What happens if say we double the thrust, presumably halving the timescales and doubling the experienced "gravity"... would a human body be able to adapt and get stronger? or would we experience adverse side effects? (not necessarily mutually exclusive). It could even be a way to acclimatise to a different planet's mass before arriving.
[EDIT]
Looks like 2g is reasonable. The limit is higher but it sounds a bit ridiculous, astronauts would all have to compete in the strongman competitions for 4g. Any higher and we wouldn't be able to walk without breaking our bones.
https://www.discovermagazine.com/the-sciences/whats-the-maxi...
[+] [-] quickthrower2|4 years ago|reply
[+] [-] simiones|4 years ago|reply
[+] [-] CodeGlitch|4 years ago|reply
[+] [-] londons_explore|4 years ago|reply
[+] [-] dctoedt|4 years ago|reply
[0] https://en-academic.com/dic.nsf/enwiki/2241027
[+] [-] journey_16162|4 years ago|reply
I was wondering, what if there was a spaceship circling outside the solar system at near light speed (not dwelving into whether it is possible ever to design such a ship or what the centigular forces inside would be), if there were people on such ship, that would experience 27,000 years in 20 years, would it be possible to communicate with them given the close proximity? Wouldn't it be weird that they are experiencing time in a much different way?
Heck, even with a rocket that is simply moving away from Earth, the messages that are sent should eventually reach the ship? (because it's not travelling faster than light, and at times it's even slower) How can the ship receive 27,000 years worth of messages in 20 years?