Favourite faster than light technology

[Sir_Elderberry]

I wonder if there are any FTL sci-fi stories where the spacecrafts time dilation is the only mitigating factor? You could only ever meet up with travellers via chance, or very accurate and advance predictions otherwise. Especially as everyone not travelling with you will have hundreds or thousands of years pass by.

In the Ender's Game series they travel at very large fractions of c, so interplanetary travel means you're pretty much not going to come back to the people you left.

[AvatarIII]

The Forever War is the same, in that time dilation plays a major factor, the main plot of the book basically revolves around the fact rather than it just being part of the story.
in fact at the end, the character who started off a rookie in the late 1990s (:D) is now 1000 years or so in the future when the war ends, and his girlfriend is basically waiting for him in a ship travelling at relativistic speeds and she leaves intructions for him to find her,

[Idhan]

I wonder if there are any FTL sci-fi stories where the spacecrafts time dilation is the only mitigating factor? You could only ever meet up with travellers via chance, or very accurate and advance predictions otherwise. Especially as everyone not travelling with you will have hundreds or thousands of years pass by.

In the Ender's Game series they travel at very large fractions of c, so interplanetary travel means you're pretty much not going to come back to the people you left.

In terms of material travel, true, but information could be transmitted at much, much faster than c (probably instantly) using ansibles.

[Sir_Elderberry]

Yeah, the ansibles were instant. So they had a unified galactic culture, but they still relied entirely on time dilation effects to make interstellar travel viable.

[MHD]

I like the Culture one where there is hyperspace (infraspace, below the skein of spacetime and ultraspace above) and ships, when accelerating oscillates between the two, tracing sine waves.

It just feels... Elegant.

[Elirra]

My favorite is from a series of novels the first of which is titled The Depths of Time. In this series FTL is achieved through wormholes that travel through time. So for example stars A and B are 40 light years apart. At some point between the 2 stars, say the middle there's a wormhole that allows time travel to the past on the order of 40 years. You arrive at the future end of the wormhole, demonstrate you've been traveling for 20 years, drop through to the past, and get to spend another 20 years to your destination. Meanwhile crews are cryogenically frozen and transportation is largely handled by computer.

My example obviously uses travel at light speed which isn't how the actual novel treats travel, its just useful for demonstrating the concept. What they effectively have is a means of traveling vast distances at effectively speeds far greater than light speed. They also have wormholes that allow people to move through time, the story focuses somewhat heavily on the policing of these wormholes and the conservation of time. The primary fear being that someone traveling through these wormholes freely would have the ability to travel into the past and, among other mischief, mess with the wormholes as they're discovered/created.

I think the biggest handwave is that these wormholes are natural and the gates created simply allow the navigation of them. Everything else seems to build on that without asking the reader to accept any other science fiction elements since travel is taking place at relativistic speeds and not exceeding c.

[BlackHatSupport]

My personal favourite method of FTL is from the Homeworld games, with each ship opening a small "window" into an alternate universe that allows them to bybass C without trouble.



Well, that and the Stellar Fold drives of a book I can't remember now. Folding space is always a good one.

[MHD]

Commonly with Sci-Fi you have to go "FTL, Causality, Relativity; choose two."

I like axing causality in my settings.

[eSOANEM]

Causality is also the one which is arguably on shakiest ground. Relativity is very strongly supported so is the safest, and FTL is, whilst unobserved, not really prohibited by much at all other than our desire for positive energy (which has been slightly eroded through quantum tunnelling)/real mass (arguably a pretty good assumption) whereas casuality has very little going for it at all seeing as there are processes which either have no cause or else are coincidental with that cause (nuclear decay), it's not much of a leap to allow effects to precede there cause.

[tomandlu]

Causality is also the one which is arguably on shakiest ground. Relativity is very strongly supported so is the safest, and FTL is, whilst unobserved, not really prohibited by much at all other than our desire for positive energy (which has been slightly eroded through quantum tunnelling)/real mass (arguably a pretty good assumption) whereas casuality has very little going for it at all seeing as there are processes which either have no cause or else are coincidental with that cause (nuclear decay), it's not much of a leap to allow effects to precede there cause.

Do either have to really break? (at least in sci-fi). Okay, you might travel outside your light-bubble, but you still can't kill your grandfather...

[eSOANEM]

Not being able to kill your grandfather is a necessary consistency requirement in any theory of time travel (and therefore SR+FTL) which is actually true time travel within a universe and not travel to an earlier time co-ordinate in another so I took it (no grandfather-killing for granted). Causality runs a little deeper.

Suppose one day, sitting at my desk, someone walks in and gives me a box and a letter. The letter tells me to wait until a certain date, give the box to a named person. When I give that person the box and walk away, they find a time machine and instructions to go package the box, write the letter to me and give me the box.

This simple loop is completely consistent (there is no grandfather-killing), but causality is still broken, me having the box has been caused by an event in my future light cone. It is impossible (in relatively flat spacetimes, in curved ones you can try to get around this by having the cause lying in both your past and future light cone) to have true time travel without breaking causality. The reason causality is inconsistent with SR+FTL is that SR+FTL=true time travel.

Of course, if it being sci-fi is the reason you think it's allowable then it'll just come down to hard you like your SF. In hard SF though, SR, FTL and causality cannot all live happily together.

[tomandlu]

In hard SF though, SR, FTL and causality cannot all live happily together.

I'm not sure I'd call it 'hard' SF, but in a story wot I rote, I use time-travel for FTL without breaking causality afaict. e.g.

1. Travel at 99% C for one year of travel time
2. 7 years passes on Earth
3. While travelling, gradually travel back in time 6 years
4. Arrive back on Earth one year after you left
5. All parties agree that journey took 1 year

Causality cannot be broken, either by killing grandfathers or delivering boxes, and time travel is just used to recover the difference between the time it takes for the traveller and the observer... basically, take advantage of the fact that FTL travel isn't a problem for the traveller, just for the stay-at-homes and the colonists waiting for the marmite shipment...

[Diadem]

Commonly with Sci-Fi you have to go "FTL, Causality, Relativity; choose two."

I like axing causality in my settings.

It's usually more "FTL, Causality, Relativity, Consistency; Choose three".

Take something like Star Trek. They've obviously heard of relativity. There's no time dilation or anything like that, but the light speed still has a special place. They make a big deal of breaking it, and it requires special 'magical' engines. So relativity is there, in some rudimentary form. It's just that they chose to ignore its consequences. So it's consistency they sacrifice.

Most SF with FTL is similar. They don't abandon causality, because that would make a bad story, and they still pay lip service to relativity (All talk about the light speed as being an important barrier, many have some form of time dilation included, etc). So they include all three of the concepts. They just choose to completely ignore the glaring contradictions this causes. This works very well, because most readers aren't aware of them, and those who are generally don't mind too much as long as it's not made too obvious.

Ender's Game for example has relativistic travel combined with instant communication. Noone uses this to send signals back in time, the possibility is never exploited, never even discussed. It's just entirely ignored. The story still works.

It's really only hard SF authors that worry about consistency. Which is why writing hard SF that includes FTL is so ... hard.