Science fiction logic

Yes, but the important thing to remember is that, from the point of view of an observer at point A, the event doesn't happen until 100 years after the ship departs, which is when the light reaches them.

Another example - two planets are, let's say, 10 ly apart. A ship leaves planet A and arrives almost immediately at planet B.

Now, from the point of view of an observer on planet B, they won't see the ship leave for another 10 years. In another words, the ship has arrived at planet B 10 years before it left from the observer's frame of reference. And that's time travel. But you might argue, the order of events is still preserved. From the frame of reference of the people on the ship, that's true, but not from the observer's frame of reference.

And frame of reference is important, because that's what relativity is all about. The physics of it is way, way beyond me, but relativity will allow a situation to be created where you meet your past self, if FTL travel were to be true.

 

That's what doesn't make sense to me, I suppose.

It makes no sense to me to say the Event doesn't "happen" if you're at Point A until 100 years later. The people there know the distance, they know about the speed of light, they know it happened 100 years in the past. People at point B watching the ship leave Point A 90 years after it arrives at Point B know they're looking at a past event, not the present.

 

This all sounds more like Relativity than time travel. Einstein began with conjectures about people on trains and how that would affect your percetpion of an event like someone outside of the train firing a gun. If you're on a train moving toward the event you'll hear the shot long before someone on a train moving away from the event. He imagined the trains moving at very fast speeds.

 

It seems like there must be some flaw in our understanding if we truly have to engage in a fiction (pretending something happened 100 years after it did) for it to work. Of course events will be perceived in accordance with the speed of light, and as something accelerates toward relativistic speed you get the dilations that occur. At those speeds frames of reference differ and none are preferred. In my example we are not dealing with relativistic speeds of any kind (by which I mean speeds where the effects make any difference).

 

But there is relativity in the duration of the event depending on where an observer is. To someone on the 'ship' it seems to happen instantaneously, but to someone outside of it it takes much longer. It's very close in spirit to the idea of time travel, like A Wrinkle in Time, which was based on bypassing certain laws of physics (duration).

By taking the wormhole shortcut it's like you literally skipped ahead in time. You don't actually travel at FTL speeds, but the result is the same.

 

But an event doesn't "happen" until its effects reach you - or have the potential to reach you. If the Sun were to blink out, it would take 8.5 minutes for the effects to reach the Earth. For the people of the Earth, for those 8.5 minutes, it hasn't happened yet.

It's confusing. I did read A Brief History of Time and didn't fully understand it, and I'm still confused by it. I occasionally see explanations that shed a tiny bit of light (no pun intended) and go "Aha! NOW I understand it" before realising that I don't.

 

This discussion of FTL is very interesting, but I can't help but feel it sounds a lot like applying a relativistic understanding of physics to FTL motion is equivalent to applying a newtonian understanding of physics to relativistic motion. It is incomplete, and seeing how we have no known way to test how the laws of physics would be different in FTL motion we can't determine the ways those differences would manifest. But I feel like dismissing it as impossible is inaccurate. Unknowable, yes, but not impossible.

The way this article,

described how instantaneous communication creates paradoxes sounds very similar to the twin paradox. The twin paradox is resolved by understanding how non-inertial frames of reference complicate relativistic motion. Which implies to me that FTL inherently complicates relativity in a similar way. Unfortunately it is in a way that science is useless to provide the answer for, since we, as far as we know, are incapable of obtaining FTL motion.

The problem from a writer's perspective then is that most of us aren't Einstein, or as the case would be, smarter than Einstein, because at least he could look at experiments dealing with relativistic motion to get a framework for his equations. We have nothing but thought experiments to guide us.

While this is a fun metaphysical discussion, it is ultimately not something any sci-fi writer should worry over. FTL is as fundamental to sci-fi as AI is. Dropping it, because we don't know how it could be scientifically possible, would only serve to upset a large percentage of sci-fi readers.

 

Well, all he had were thought experiments too, but his 'vessel' was just a lot better than ours.

 

General relativity predicts the behaviour if FTL travel were possible - since general relativity doesn't preclude it.

Depends on your type of sci-fi. Arthur C. Clarke didn't involve FTL travel in his stories.

 

I don't think sci fi, or hard sci fi to be specific, needs its tech to be explainable or justifiable.

The distinction is more about how speculative the fiction is with respect to technology. Star Wars is more regarded as science fantasy by some because its story isn't really coloured by technology. There are warrior monks, empires, honor codes, rebels, all that stuff. Something like Gattaca is much more affected by technology: eugenics drastically change the game.

Thinking about it, it's almost as if science fantasy keeps the societal rules quite similar to the ones we have now, while science fiction tosses a wrench in them to see what would happen to the human condition.

Bookstores still has have the most streamlined solution, which is glorbing the fantasy and sci fi genres together.

 

I have less than a layman's understanding of what you're all talking about. I'm just smart enough to know that I'm missing a big piece of the picture. So, correct me if I'm misinterpreting, but by this logic, are you saying that if you could run FTL, you could conceivably run fast enough to reach out and tap yourself on the shoulder before you take off?

 

They’ve clearly never watched Red Dwarf then.

 

I would go even a step farther and point out that George Lucas studied Jopseph Campbell's heroic Monomyth, which is entirely mythology-based. And since fantasy is built from the tropes of mythology (ever since its founding at the hands of Tolkien) that makes it explicitly fantasy. The technology is not a driving factor, it's backgrounded and used as hand-waving to explain things like light-sabers (which really function storywise as something like Samurai swords) and hyperspace (convenient plot device and excuse for cool special effects).

 

"Admiral Ozzel came out of lightspeed too close to the system..."

 

I'm not sure if General Relativity allows this, but Einstein once said, "There are five people in the world who understand General Relativity, and I'm not one of them."

 

I don't get it. The event has happened whether the effects have reached me or not. It doesn't matter that I'm 5 minutes and 27 seconds away from noticing the Sun blinking out, the Sun still blinked out a couple of minutes before. Observation doesn't define reality.

 

Oh, LS is simple.

 

Ever heard of the 'double slit experiment'? It's different than relativity, but it may cause you to question your statement.

 

Well, it really does.

Our reality, for example, is that there are millions and billions of stars in the sky that we can see. Those stars may have blinked out years ago, but from our POV, they are still there.

You've almost certainly heard of the term "observable universe". Beyond the boundaries of the observable universe, there may well be trillions or quadrillions more galaxies and stars, but their light can *never* reach us, and we can never gain any information about them. They are said to be not "causally connected" to us - in other words, nothing that ever happens there can ever affect us. We can't see them, can never see them, so from our POV, it is the same as if they don't exist.

*Note - some of this explanation may be garbled, or garbage. I took ONE university course on astrophysics, and I got lost on the way to the lecture room for the first lesson.

 

How many of us who watched Star Trek when it first hit television knew that FTL travel was impossible -- and how many of us cared?

https://uss-theurgy.com/w/index.php?title=Warp_Factor

The Enterprise had artificial gravity, and nobody seemed to care about how they accomplished that. And how many scenes were there in which Captain Kirk ordered a faster warp factor, and the ship accelerated to a higher multiple of the speed of light instantly -- and nobody on the bridge was even thrown off balance?

 

@Keongxi

It’s great advice, but time is the killer here. Star Trek mentioned as seen the mobile phone over take sci-fi story telling. The internet and even the warp drive by Alcubierre who was inspired by trek to write the paper. Everything becomes awfully dated...

The problem is thinking forward using historical logic. An example is using WW2 thinking in a future environment. First using ground crew to observe a planet up close is ridiculous especially using senior officers. WATCH Aliens, love the movie but strategically its fundamentally flawed. Think how would you right now approach this silent outpost from orbit?

Next question is why? Why would an Alien come to invade? I cannot think of a single reason other than at some point we’ll become really intelligent and be a threat to those aliens. Everything else is rubbish. The reason why we would explore and expand is long term survival. Two systems better than one. But that’s it.

If we developed the ability to build an FTL drive, surely, we’d build a kinetic weapon with it first rather than a means of travel? This makes logical sense. Some one mentioned Atomic Rockets.... what a great resource.

Folding space/time into a 4th dimension makes more sense than FTL.

Even so, sci-fi stories are not driven by tech, but the actual story told. Battlestar Galactica or The Three Body Problem Trilogy by CIXIN LIU or Asimov’s Foundation series are wonderful worlds but believable they feel real. Hard or Soft the sci-fi needs just to under pin the story been told, that is all.

MartinM.

 

I have, but I don't think it's relevant here. It's been known for a while that the rules are different on the atomic scale even if - AFAIK - we have no idea why.

You're talking about subjective experience. Not reality. The fact that we can never gain any information about a star doesn't have any bearing or not on whether the star is there. It'll never affect us either way but the star is not in a superposition; that's applying quantum rules to the non-quantum world.

In Steerpike's earlier example with the astronauts, the fact that they are observing the Planet A astronaut leave now doesn't mean that astronaut is actually leaving now. They left 100 years ago, the observers on Planet B are looking into the past. There's no break in causality, the setup just means that once the Planet A astronaut has arrived, Planet B observers are able to view them at two different points in time simultaneously.

Looking at it another way, the Planet B observers can't travel through the wormhole to Planet A and sabotage the launch, because when they get there, even if the travel time is instant, the launch will have happened a hundred years ago.

 

That's totally illogical. Going back to the example of a European monarch dying during the age of sail, when the news couldn't reach far-flung outposts for several months. Nobody in those times would have posited that the death didn't occur until the news had reached them. Moving up to news traveling at the speed of light doesn't change any of that. If some distant star went super nova 100 years ago, the even happened 100 years ago. It doesn't matter whether or not we know about it, of if we won't know about it for another 50 or 100 years.

You are essentially arguing that when a tree falls in the woods and there's nobody there to gear the sound -- it makes no sound.