Space is big. Really big. You just won't believe how vastly...

@anotherusername said:
once you just assume that FTL travel is possible, you pretty much eliminate the problem of enormous distances and mostly empty space.

Many years ago, I came up with the One Giant Truck Sized Plot Hole rule for good SF.

Good SF has one plot hole you could drive a giant truck through. It's a completely obvious plot hole. There is a gentleman’s agreement between author and audience that it shall be ignored; the payoff is that the author needs to be disciplined about not introducing other, smaller plot holes. An SF plot with two or more holes, even quite small ones, requires juggling too many suspended disbeliefs to be enjoyable.

I don't know, I think most SF has more than one. For example, Universal Translators, or whatever other way of dealing with language problems. A show/movie has FTL travel. Plus it has a magical Universal Translator, where if you contact a totally unknown civilization, your Universal Translator still works. Finding sci fi without at least these two is difficult.

flabdablet

There are Truck Sized Plot Holes, and then there are the usual conventions, like the one about all aliens resembling human beings with prosthetic foreheads on their real heads.
https://www.youtube.com/watch?v=AwqLWGibwDY&t=20m13s

ben_lubar

PJH

@flabdablet said:

wrote

Still writing AFAICT.

flabdablet

Finished March 2015.
[quote=Eliezer Yudkowsky]This is the end of Harry Potter and the Methods of Rationality.

I will write no sequel myself; I have said what I set out to say, and it is done.
You have my enthusiastic consent to write within this universe yourself, if you wish.[/quote]

David_C

@chozang said:

I don't know, I think most SF has more than one. For example, Universal Translators, or whatever other way of dealing with language problems. A show/movie has FTL travel. Plus it has a magical Universal Translator, where if you contact a totally unknown civilization, your Universal Translator still works. Finding sci fi without at least these two is difficult.

Another necessary concession to the need for telling a good story. If you need interaction between different alien races (maybe because their different cultures are critical to the story), then they need some way to communicate with each other.

Universal translators are one way. (And Star Trek has had many very good stories based on what happens when they don't work as expected...)

Another is that the story starts after these civilizations have had contact for some time and can therefore speak each others' languages.

And there are some where they don't understand each other well (or at all), and the process of them learning to communicate is a part of the story.

It's not all that different from non-science fiction that involves people from different countries. If you set a story in the ancient world and someone from (for example) Egypt travels to Scandanavia, there's going to be a massive problem with language. You can ignore the problem and let everyone just talk and be understood, you can create a plot point (maybe a traveling merchant that knows both languages) to allow communication, or you can make this person's language-learning part of the story. The appropriate solution really depends on what kind of story you want to tell.

@flabdablet said:

all aliens resembling human beings with prosthetic foreheads on their real heads.

Yet another concession to the need to tell a story.

If your aliens look too non-human, then the audience will focus on their appearance and not on the rest of the story.

And then there's the fact that you somehow need to make-up a human actor to look like the alien. If you deviate too far from a humanoid face, then make-up becomes very difficult and expensive (and may require expensive CGI work to augment the make-up)

It doesn't even have to be truly alien. Note, for example, the look you see when some show decides to introduce a cat-like race. They create the impression using fur, ears, teeth and contact lenses but rarely go further. The audience doesn't need it for you to make your point, and going further (nose shape, jaw shape, the way eyelids move, etc.) would be difficult and expensive and wouldn't enhance the illusion that much.

You mention foreheads. That's mostly a Star Trek thing, but I assume it's because it's relatively simple and inexpensive (important for a weekly TV show) and still does a good job of telling the audience what world he comes from. Other shows do things differently, but prosthetic appliances are common because they allow the actor a lot of freedom to use facial expressions, which doesn't work nearly as well with rubber masks.

Lorne Kates

@David_C said:

Another necessary concession to the need for telling a good story. If you need interaction between different alien races (maybe because their different cultures are critical to the story), then they need some way to communicate with each other.

Or you could go the route of The Forever War

[spoiler]Interstellar war. Hyperjumps between nodes, but near lightspeed travel to/from nodes means massive time dilation for soldiers. War goes for on for over a thousand years before the two sides manage to actually talk to each other. The conversation goes, almost verbatim:

Man: Why did you start this war?
Alien: Wait, what? No, you started it!
Man: We thought you started it.
Alien: We thought you started it.
Both: Hmm. Peace?[/spoiler]

Edit: Jesus shit fuck, Discourse-- how can you fuck up spoiler tags this bad? Don't know how to fix, apologies for any actual spoilers of this 40+ year old book.

boomzilla

@David_C said:

Physics, as we currently understand it, doesn't say a thing because physics says such speed is impossible to begin with.

With time traveling wormholes, faster than infinite speed is possible, depending on the frame of reference used.

David_C

@boomzilla said:

... faster than infinite speed ...

That would be, I assume, arriving before you left. Sort of reminds me of [URL=http://www.nbc.com/saturday-night-live/video/einstein-express/n9589]Einstein Express[/URL].

aliceif

I fixed it!

PWolff

@David_C said:

How so? If a star is 4 light years away and I have some means to get there in 3 months, that's faster than light but not infinite.

Not in our frame of reference. But there is a frame of reference where the departure and arrival are at exactly the same time, and there are frames of reference where the arrival takes part before departure. (That's the reason why the possibility of FTL travel is equivalent to the possibility of going back in time.)

The reason is, that for any structure moving faster than light, it is not the 4-dimensional speed vector that behaves like a usual vector in Minkowski space, but the time gradient (its inverse).

@David_C said:

Physics, as we currently understand it, doesn't say a thing because physics says such speed is impossible to begin with.

Physics, as we understand it, states that no kind of energy can be accelerated to a speed greater than that of light, or even up to that point. Either it starts below speed of light and always remains there, or it is transferred to something that always moves at the speed of light (case of light itself, of course), or it always has a speed above the speed of light (and would have some strange properties we didn't observe so far, so it is a sound guess FTL travel is impossible is a safe guess so far).

Structures moving faster than light were known before Einstein came up with his special theory of relativity (or about that time, anyway before it was generally accepted). That group velocity in wave guides is faster than light, follows from the Maxwell equations and has been observed with Hertzian waves.

anotherusername

@PWolff said:

Not in our frame of reference. But there is a frame of reference where the departure and arrival are at exactly the same time, and there are frames of reference where the arrival takes part before departure.-

Well, yeah... I mean, if you lived on planet X, and flew in your FTL spaceship to planet Y, then someone very close to planet Y would see you in 2-3 places at once at times. At the instant you arrive, they'd see you in 2 places, because they haven't seen you leave planet X yet. And immediately thereafter they'd see you there, plus they'd see you coming (assuming your ship interacted with enough light to reflect it... okay probably not, but they'd know you were on your way; call that your ghost), and still see you on planet X because they haven't seen you leave it yet. And finally, when your ghost touches planet X they see you leave planet X and after that they only see you on planet Y.

@PWolff said:

That's the reason why the possibility of FTL travel is equivalent to the possibility of going back in time.

But, you didn't actually travel back in time... it just looks that way to someone on planet Y. It's no different than the old panning cameras where a clever person could appear more than once in the picture by running ahead of the camera's scan. You weren't actually in 2 places at once, you just looked like you were because of the camera's limitations on capturing your precise location. Specifically, that it saw things on one side of the picture sooner than things on the other side.

David_C

@PWolff said:

@David_C said:
Physics, as we currently understand it, doesn't say a thing because physics says such speed is impossible to begin with.

Physics, as we understand it, states that no kind of energy can be accelerated to a speed greater than that of light, or even up to that point. ...

Yes, but you missed my point here. As you wrote, Physics says that a person or spaceship can't accelerate to or beyond light-speed. Therefore it obviously doesn't have anything to say about what would happen to a person or ship that somehow did. Predicting the consequences of the impossible is, by definition, beyond the realm of science.

Of course, many many authors have tried to get around this whole problem by creating various mechanisms whereby a ship can move at normal velocities through an alternate space of some kind, where the distance traveled is shorter, giving the appearance of traveling FTL between two points. And there are as many mechanisms as there are SF authors.

There's no point in discussing the plausibility of these various mechanisms, since each one individually would take more time than I (and I assume you) would want to spend, but it does seem to me that using such a mechanism, you would not experience time dilation effects, because you are never actually approaching light-speed. (Just like how taking a shortcut on the road can get you to a destination faster without increasing your speed.) It would also seem that with such a system, you would arrive at your destination before light originating from your origin, creating the illusion of arriving before you left.

And this problem (ships traveling at apparent velocities far greater than EM-based communication) has also been discussed in many SF universes. Some authors just punt and propose an FTL communication system, to allow direct conversations between people on different worlds. Others establish that ships move faster than broadcasts and develop a system of couriers and drone ships to physically deliver data between worlds, only using EM-based mechanisms over short distances.

PWolff

@anotherusername said:

@PWolff said:
That's the reason why the possibility of FTL travel is equivalent to the possibility of going back in time.

But, you didn't actually travel back in time...

I forgot to add some equally important (but so basic it should be evident) requirements: the principle of relativity and the possibility to change reference frames at will.

If two events are separated by a "space-like" distance - that is, you'd need to travel faster than light to attend both events, which is equivalent to the existence of a reachable inertial system where both events are contemporary (yes, are, not seem).

And due to the relativistic transformation rules of space and time, there are (reachable) reference frames where event A takes place before event B, some reference frames where events A and B take place the same time, and reference frames where event B takes place before event A.

If FTL travel is possible, let's say with a speed v0>c0, to go backwards in time, you choose two events A1, A2, and B so that A1 and A2 take place at the same location in I1 with A1 before A2, A1 occurs before event B in intertial system I1, with a space-like distance, and likewise A2 after B in I1, with a space-like distance too.. The distance from the location of A1 and A2 to the location of B in I1 you can choose as large as necessary, see below.

There is an inertial system I2, where A takes place before B, and you can reach B from A1 with a speed of v0 or less. You transfer yourself into I2, then travel from A1 to B, then back to I1, "staying" as close as possible to B.

There is an inertial system I3, where B takes place before A2, and you can reach A2 from B with a speed of v0 or less. You transfer yourself into I3, then travel from B to A2, then back to I1, staying as close to A as possible.

(Choose the distance of B as large as necessary to cope for durations of changes of inertial systems)

So you effectively

PWolff

@David_C said:

Yes, but you missed my point here.

Yes, you're right in this point. I misread it in the sense of your previous text.

sloosecannon

See MACs from Halo.

Slinging large tungsten slugs at substantial fractions of c

blakeyrat

@David_C said:

It's not all that different from non-science fiction that involves people from different countries. If you set a story in the ancient world and someone from (for example) Egypt travels to Scandanavia, there's going to be a massive problem with language.

The 13th Warrior was a mediocre movie, but the way they portrayed this was amazingly good.

FrostCat

@David_C said:

You mention foreheads. That's mostly a Star Trek thing

One nice thing about Enterprise was that for the Andorians, they used CGI antennae and makeup, rather than fake foreheads. It was a nice change of pace, especially since, unlike in TOS, CGI let the antennae move.

FrostCat

You know, it doesn't actually say "Colonel" on his chest.

Wormholes usually involve being outside our universe, in a "place" where the speed of light is much higher, don't they?

Boner

@PWolff said:

If two events are separated by a "space-like" distance - that is, you'd need to travel faster than light to attend both events, which is equivalent to the existence of a reachable inertial system where both events are contemporary (yes, are, not seem).

And due to the relativistic transformation rules of space and time, there are (reachable) reference frames where event A takes place before event B, some reference frames where events A and B take place the same time, and reference frames where event B takes place before event A.

If FTL travel is possible, let's say with a speed v0>c0, to go backwards in time, you choose two events A1, A2, and B so that A1 and A2 take place at the same location in I1 with A1 before A2, A1 occurs before event B in intertial system I1, with a space-like distance, and likewise A2 after B in I1, with a space-like distance too.. The distance from the location of A1 and A2 to the location of B in I1 you can choose as large as necessary, see below.

There is an inertial system I2, where A takes place before B, and you can reach B from A1 with a speed of v0 or less. You transfer yourself into I2, then travel from A1 to B, then back to I1, "staying" as close as possible to B.

There is an inertial system I3, where B takes place before A2, and you can reach A2 from B with a speed of v0 or less. You transfer yourself into I3, then travel from B to A2, then back to I1, staying as close to A as possible.

(Choose the distance of B as large as necessary to cope for durations of changes of inertial systems)

David_C

@FrostCat said:

One nice thing about Enterprise was that for the Andorians, they used CGI antennae and makeup, rather than fake foreheads. It was a nice change of pace, especially since, unlike in TOS, CGI let the antennae move.

Actually, the antennae were motorized and radio-controlled. ([URL=http://www.trektoday.com/news/041001_05.shtml]source[/URL]) I remember reading (but can't seem to find a source right now) that this was the intention for TOS, but they could never get the mechanism to work right, so they scrapped the idea.

@FrostCat said:

Wormholes usually involve being outside our universe, in a "place" where the speed of light is much higher, don't they?

When I see that definition used in a story, I usually see it applied to "hyperspace" or some similar concept.

Most of the shows I've seen that deal with wormholes describe it as a point-to-point conduit between two parts of space where the distance through the wormhole is much much shorter than the distance you would have to traverse in normal space. Analogous to a tunnel through a sphere to save the time needed to move across the surface.

Of course, I've also seen universes where "hyperspace" refers to a shortcut between points, but instead of point-to-point, it's more like a space that can be navigated through. Analogous to being able to pass through the sphere and go any way you want on the inside before emerging on the surface somewhere else.