Relativistic Space Travel Question

[labingi]

A question for you physicsy folks out there (astrogirl?). I'm writing a story that hinges on time dilation in space travel, and to get the sort of time dilation I need for the story to work, I need to reach speeds around 0.9c or higher.

My question is what kind of drive could I posit these people are using? This story is not set in the super distant future: a few to several hundred years. And I can trade on the idea that a lot can happen in 100 years of unexpected innovation (as we've seen in the past), but they're not gods or anything.

These ships are not multi-generational. They are designed to get people from point A to point B in not more than a few years, ship time. (In terms of living space, they are closer to Andy Weir's Project Hail Mary than KS Robinson's Aurora. I'm thinking they rely on acceleration for simulated gravity, not rotation.

This society does have access to lots of raw materials, ranging from bodies to mine to stars, nebulae, etc., and they have big, fast 3D printers.

I want to reasonably appease an audience that is not picky about very hard SF but would like some semblance of scientific plausibility.

Thanks!

Comments

[astrogirl]

Hmm. I mean, the short answer is that the technology for that doesn't remotely exist, and almost certainly won't in the time frame you're talking about. But, of course, that's boring and not very useful, and certainly never stopped anyone from writing it, anyway. :)

I'd recommend doing a bit of research on the topic, if you want to do more than just vaguely wave your hands around about it (which, honestly, is probably fine) in order to find something that might work best for your particular requirements, rather than relying on my very, very out-of-date bachelor's degree.

But off the top of my head, two or three possibilities to explore come to mind.

1) Right now, the only actually reasonable (well, for some variety of "reasonable") proposal we have for getting anything up to relativistic speeds in involves lightsails propelled by lasers. Note that this is about accelerating something the size of a microchip to maybe 0.2% of the speed of light, and even that would take a frankly ludicrous amount of laser power. Scaling it up would require amounts of energy out of the realm of current imagination, so you'd have to posit some kind of truly fantastical breakthrough (which is true of any possibility at all, really). There are also other potential problems with that, too. Like, slowing down can be an issue. And the people back on Earth (or wherever) have to keep running the mega-lasers for as long as you want to keep accelerating.

2) Back in the days when I was reading a lot more hard SF than I am now, the technology of choice for such things was often a ramjet. It seems like that's gotten less plausible with time, rather than more, though. And, again, we're talking frankly incredible levels of technology to build the thing.

Or 3) you could just go full-on Star Trek and have a matter/anti-matter reactor. Even that might not get you close to the speeds you want in reality, but that is the sort of thing people can suspend disbelief for, hopefully.

For an audience that's not super picky about the science, I'd say the less you go into the details of how the thing works, the better, really. But those might provide you some starting places, maybe.

[labingi]

Thanks! That's very helpful. I was also thinking that some vaguely matter-antimatter hand-waving might be the best option. Since a big hindrance with antimatter (theoretically) seems to be lost energy, I was thinking of an Anti-Matter Energy Saver (AMES) drive, and leave it at that. :-)

[astrogirl]

Sounds good to me! :)

[lilacsigil]

I think SF is very good at handwaving this issue and handwaving is a good idea in general unless something about the plot hinges on the technology going wrong.

I read this recently and enjoyed it, maybe it will give you a starting point: https://mashable.com/feature/faster-than-light-space-interstellar-travel

[labingi]

Thanks! I appreciate the link. :)

[vilakins]

What Astro said.

I wouldn't be too specific about the drive; maybe just give it an inventor's name like the Spicer drive. ;)

I've been reading a series which uses hydrogen/oxygen drives along with hyperjumps, and frankly they've given too much information for a nitpicky physicist reader like me to suspend disbelief. The ships don't have artificial gravity, just that provided by acceleration, which means it's limited (when not jumping) to under 6G. It would take months between a system's planets, yet they zip around and easily locate other ships - the author just doesn't grasp the sheer vastness of space, which niggles at me, though the characters and stories are great. If he hadn't specified the slow drives, and just handwaved the propulsion, as he did with the hyperjumps, the books would be so much more fun for a physicist to read.

I like what you're thinking of. It sounds really believable, unlike with that series, and I assume at halfway point, the ship flips and uses the drive to decelerate.

(I loved Hail Mary, and even Greg who doesn't do fiction enjoyed it just as much.)

[labingi]

Yep, the ship flips. I agree less info is better.

I taught Project Hail Mary, somewhat ineptly, to my Science Through SF students last year on the strength of a student's recommendation. He really loved the book. I liked it pretty well but went back to teaching Aurora this year, as a book with more different types of science and related cultural/ethical questions to dig into. Glad I read PHM though.