Personally I think the most useful metric is "would my non-science geek fans like this?". Or to put it another way, is one of the primary appeals of this novel the extrapolation of realistic science. An appreciation that may be lost on someone who isn't as interested in that subject. My fantasy loving friend has been an interesting barometer in this way.

Didn't like The Martian therefore, it's Hard SciFi.

Dune: sci-fantasy

Star Wars Sci-fantasy

Three Body Problem: Hard sci-fi

The Expanse Book 1: Hard sci-fi

The Expanse Season 1: Sci Fantasy

Yes and no. I'm told that if you do the math on the "Epstein Drive" fusion rockets that are in use throughout The Expanse, they are actually _impossibly_ effective regarding reaction mass.

Still, unlike the star gates, they don't take you across light-years in less than actual years, so they're "harder" than the later books. There is indeed no hard boundary.

The response was that "It works very well, thank you!"

Now do it twice.

Maybe I'm completely misunderstanding you or the problem - feel free to correct me, please. I'd really like to understand how causality is broken by FTL but could never grok it.

The phrase "at the same time" means different things in different inertial reference frames. So what is FTL to one observer, is traveling backwards in time to another. If you can warp from any reference frame, you can therefore travel backwards in time.

As for why "at the same time" changes meanings, let's adapt Einstein's example.

I'm in the middle of a moving train. You're on the train station. As we pass, lightning strikes right between us. Will the light from the lightning arrive at both ends of the train at the same time?

According to me, obviously. In my reference frame the train is not moving. Light has a constant speed. It will reach both ends at the same time.

According to you, obviously not. Light travels at constant speed, but the train is moving. Therefore the back of the train is moving towards the light, and the front is moving away. So the light gets to the back of the train before the front.

So when the person on the train says that an event in front and behind happened at the same time, the person not on the train says that the event behind happened before the event in front.

Now consider this. I'm on a spaceship with a warp drive. This is a great warp drive, travels instantly in whatever reference frame I'm in.. I warp forward a long distance - like a light year. I accelerate forward. I warp backwards and arrive back a bit behind where I started at. I decelerate, and I'm in my own past!

That's the causality problem.

You left out the "accelerate forward" bit. That changes your reference frame. Without changing your reference frame, you don't get FTL to turn into time travel.

If you have FTL but on a time scale determined by one reference frame, then as I pointed out in https://news.ycombinator.com/item?id=37012594, no causality issues exist. You need FTL in 2 reference frames to create a closed time-like loop.

So it becomes complicated. But as long as FTL goes forward in time by some unique global definition of time, there is no causality problem.

A warp drive that only works against the fixed reference frame of the distant stars introduces no causality issues.

Physics doesn't have privileged frames of reference.

As for not having privileged frames of reference, that doesn't stop interactions with your environment from mattering.

For a trivial example, "at rest" is a privileged frame of reference for you. If you start moving in a different frame of reference you'll encounter weird things like "wind".

For a non-trivial example, the Standard Model says that there is no privileged ratio of masses between the electron and the proton in the laws of physics. The actual ratio of masses is set by an interaction with the part of the environment known as the Higgs field.

Astronomy shows that the fixed reference frame of the distant stars is environmentally privileged. It is also somewhat privileged physically as well. For example Mach's principle (see https://en.wikipedia.org/wiki/Mach%27s_principle if you don't know it) says that we notice we are rotating when we are rotating relative to that reference frame.

We know of no way to react to this feature of our environment and get from here to there faster than the speed of light. But there is no fundamental principle of physics that we know of which says it is not possible - we just have no clue how it might happen.

And I have no idea why you don't notice that this is moving fast. That's the irony.

https://en.wikipedia.org/wiki/Alcubierre_drive shows that this is, in principle, not a violation of general relativity. But that drive depends on finding something with negative mass. Most physicists don't think that that can be done. (But the phenomena of extracting zero point energy with the Casimir effect holds out a slender ray of hope for cranks who think that they have done it.)

So it isn't that I didn't notice that something was moving fast. It is that I know that the idea is to get from here to there by doing something other than moving.

I think that this is a semantic distinction without any practical difference.

What you think doesn't matter.

General Relativity says that the Alcubierre drive would work if you could find a source of negative mass. It can get a vehicle from here to there, outside of its light cone. And yet that's not game over.

That's not a word game. That's mathematics applied to our best model of how space-time works.

If you want to imagine it, imagine ants crawling on a balloon. Motion is their crawling. But now start blowing up the balloon as it crawls. Distances are changing, and it isn't the ant doing it! Think this is unrealistic? The current model of the Big Bang says that things we see from 13.7 billion year old light are now 47 billion light years away from us. Our naive ideas of motion can't explain that. But general relativity does, and it is exactly parallel to the ants on a balloon image.

Now imagine coming along, pinching the balloon, having the ant walk over the fold, then unpinching the balloon. The ant got from here to there faster than it could possibly walk! That's the idea of a warp drive.

Is it possible? Probably not. But we know of nothing that forbids it other than the fact that we can't figure out how to do it.

> It can get a vehicle from here to there, outside of its light cone. And yet that's not game over.

It's time travel, so game over for causality. You're fixated on the details of how you get there, and it is irreverent.

> if you could find a source of negative mass. It

Word games with imaginary numbers.

No, it isn't necessarily time travel.

See https://news.ycombinator.com/item?id=37013305 for my presentation of the standard argument that FTL leads to causality violations. Note that you need it to be FTL in more than one reference frame to do it. That's why, as I pointed out in https://news.ycombinator.com/item?id=37012594, FTL only in the fixed reference frame of the distant stars does NOT lead to causality violations.

Again, we have no reason to believe that this is possible. But if it were possible, the standard objections would not apply.

Word games with imaginary numbers.

No, that's tachyons. This one was just negative numbers.

Of course there are other scenarios where you can get backwards signaling. But some recent papers showed that in these cases, were they possible, then events would arrange themselves to be consistent overall, even though some events have causes from their futures.

The only time when their economy breaks is when they're in an active warzone - and frankly, currency as we know it breaks down in a warzone too, you better have some cigarettes or food if you want to trade.

Then you have the species whose backstory is imperialism or fascism, that control many other species that only have lesser technology. In some episodes, but especially in the books that are considered canon, you can see them influencing (slowing or outright destroying) the development of sufficient technology of their vassals so they remain dependent on the masters.

But the masters themselves (Romulans, Cardassians, Klingons...) have the same post-scarcity economy as the Federation for their "full citizens".

What's interesting is the case of Bajor in DS9, which is developing the post-scarcity utopia after the Cardassians left them in ruins; with Federation help but not too much of it because they want to be independent.

Good guys like the Vulcans seem to have only personal and psychological problems, not material ones.

Starfleet is a totalitarian military dictatorship.

Sisko asked Quark just before he left to remain where he was since the Cardassian occupation so there was some life on the promenade.

> The dirty secret is that Starfleet is actually a totalitarian military dictatorship, on the ground and in the air. That's how they got to take over the Palace of Fine Arts.

Starfleet is a paramilitary organization and Deep Space 9 is a military installation under their control (it has sufficient firepower to defend itself against many of the strongest warships), just like the starships - that's no secret nor is it dirty. There can be civilian elements on military bases. IRL there are civilians living within military areas in some countries - governed/commanded by the military.

But SF doesn't control the Federation, nor Earth or other civilian settlements. There is an episode where Sisko and Odo thwart the attempt of a rogue Starfleet admiral to get Earth under SF/his control.

I always thought it was interesting that the scarce resources you could get at Quark's were non-material (companionship, holodeck experiences, games, etc). The only defining characteristic of the substance the Ferengi use as currency is that it can't be produced by a replicator, which implies that everything else (including all the expensive bottles behind Quark's bar) could be.

Ian M. Banks does a good bit on this in one of the Culture books (Look to Windward, I think) where the Culture "reinvents money" in the form of IOUs over access to a particularly popular live event.

I did have a problem with the retconning where the Federation was never even partially capitalist at all, because The Original Series is full of allusions to the fact that it is: An immortal being (Flynt) who buys his planet outright, miners who make more profits once they start working with the Horta, etc., etc.

Incidentally when Star Wars started inserting technobabble explanations for fantasy elements like the Force (“midi-chlorians”) it was jarring. Nevertheless we can’t really say there is a difference in kind anymore and maybe never really was.

There is a basic difference between Star Trek and Star Wars; but you're right, the level of technobabble deployed before using FTL is not it.

The difference is that whereas Star Wars is basically about a "hero's journey" - a young hero rises from obscurity, travels, learns, trains up and defeats the bad through their courage and skill, and lone derring-do (and inborn hero-quality).

Star Trek is basically about a Team. They might have a strong leader, but (almost always, leaving Michael Burnham plots aside) the victory is not achieved until they pull together as a crew, relying on each other, combining their talents and respecting each other's skills.

Star Wars has a single "evil empire" as the easy-to-spot antagonist.

Star Trek has many political factions, each with their own outlook and self-interests.

The second is IMHO a little more "grown up" than the first.

I should have clarified I was talking about TNG. Not the Netflix mess

I suspect that where Star Trek falls down (in the eyes of fans) is also where it does not adhere to the expected "success as a team" template, notably in ST:Discovery. When Trek tries to be more like Wars, it doesn't work.

In both settings artificial gravity reduces visual weirdness and special effects costs; ST replicators minimize boring and challenging starship logistics; SW mass cloning allows uniform, socially rootless and irrelevant armies in an absurdly varied universe; ST dilithium crystals are always available as something crucial to repair and acquire whenever a complication is needed or the Enterprise needs to be immobilized; SW hyperspace travel allows hopping between planets rather casually with enough flight time to offer interludes, while the "technically" similar ST warp drive is used more often to meet other ships in deep space and never to land on planets; and so on as the writers find convenient.

In science fiction, on the other hand, the story follows from a coherent and usually simple speculative premise: what if ants went to war with humans? What if someone had a submarine? What if a man became invisible, or extraordinarily fast? What would it be like to fly to the moon? What would it be like to spend generations of subjective time in a generation ship? Given the empirically proven forbidden magical knowledge contained in the Necronomicon, who might be interested enough in it to break into the Miskatonic University library? What kind of trouble would the Three Laws of Robotics prevent or not, and what alternatives to them might be considered?

Soft science fiction mixes rigorous speculation with other priorities but still takes it seriously. For example, long-range balloon travel in Mary Shelley's The Last Man is an atrophic and naive earnest extrapolation of the bleeding edge technology of the time that is clearly meant to establish that the tragic story is a vision of a far future (which, despite this little touch, still looks exactly like the 1820's); the balloon flights in Verne are much harder science fiction because technology is the main subject.

On the other hand fantasy makes the speculative elements arbitrary and therefore magical, hopefully compensating this sin of bullshitting with symbolism and consistency, a good story, etc.

Exactly. The difference starts with plot structure.

The shows plots are optimistic, promoting teamwork and an utopian social structure, IMHO that is far secondary to the "easy FTL" issue.

1 ) https://en.wikipedia.org/wiki/Tachyonic_antitelephone

Not only does FTL ignore physics established since 1910, it is lazy to pretend that it's the same only faster: the truth of relativistic physics is far more complex, interesting and just plain weirder than that. If you're aiming at "sci-fi" not a horse opera in space, why not embrace that?

Like my favorite novel accelerando is about the singularity, a concept many nerds were interested in about 20 years ago. These days we’ve all kind of accepted it’s a silly thing that doesn’t make sense but does that mean we should reclassify all of the fiction written around it as a concept as science fantasy? At one point tech has advanced to the point where they’re cloning humans so cheaply that politicians are cloning multiple versions of themselves to go campaigning. Does this impossible scenario make those books science fantasy, even though they get a lot of the science right elsewhere? Because if the answer is yes then we’d probably need to rename all sci-fi sections in bookstores to science fantasy because that’s the majority of what’s in them: fun shit with a veneer of science behind it.

It makes you feel a sense of wonder through magical abilities, places and creatures - it's fantasy.

It talks about advanced civilizations with unknown/impossible technology - it's sci-fi.

That's the distinction bookstores make, IMHO.

i.e. not actual, not even possible, not even a self-consistent, coherent idea.

If magic dragons were a necessary plot device, they'd still be a fantasy.

It is, but the author didn't base their argument on that entirely. More so, Star Trek has never cared about science except as set-dressing for drama. People say Star Trek's warp drives are based on the Alcubierre drive but they really aren't - they don't behave the way an Alcubierre drive should. Along with all other Trek technology it's basically magic, nothing is bound by realistic physics. You have immortal, godlike beings like the Q, you have people coming back from the dead, psychic phenomena, time travel whose rules change with each episode. In the last episode of SNW, you had a weird space anomaly that made people sing like a musical.

I mean, you could put that in a D&D campaign and call it magic and it would work.

Really, all science fiction is a subset of fantasy. "science fantasy" is just science fiction that isn't actually about the science, which is the bulk of the genre.

All fiction is fantasy. Fantasy is the root of all fiction. As soon as one starts to change reality, by lying about what someone said or thinking about what you could have said, that's fantasy.

All labels are either useful fuzzy groupings or non-useful groupings. "High fantasy" is a label that gets you works closer in some conceptual space to The Lord of the Rings than to The Manchurian Candidate. "Isekai" is a very definite label that applies to The Lion, The Witch And The Wardrobe and does not apply to Space Quest, but it applies more to Space Quest than to most episodes of Star Trek (except The City On The Edge of Forever, which is definitely isekai, and some similar episodes.)

"Science fiction" is a marketing promise that if there are elves, there will be an evolutionary heritage for them and a reason that you don't notice them walking to your local pub (no guarantees about the walk back.) Spock is a kind of half-space-elf. The space elves split into two groups a long time ago -- the ones who subscribed to a rationalist approach, and the ones who had a religion based on passion.

Q, anyone?

A robot with an advanced electromagnetic mind-control device...

One way I thought you could interpret that is that the wormhole aliens in fact only exist when the wormhole is open - their existence is only in those blinks of reality that they perceive, and as a result to handle the universe they have a vast predictive ability that looks like future-knowledge.