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Right, so currently for my sci-fi/fantasy multiverse world building project I'm trying to come up with some novel uses for FTL. So far I've come up with one, and I'd like to hear what the tropers here have for ideas.
To start off, Astro-archaeology. Networks of powerful sensors are FTL'ed to a predetermined distance (several hundred or thousand light years from the observation target). From there on, the sensors can observe the target as it was in the distant past and gather data on past civilisations and history. For bonus points, send the network of sensors towards the target at FTL to gather all the data in several months or decades instead of centuries and millennia.
If you have the resolution for it, you could perhaps do the same on a smaller scale for the purposes of investigating crime.
(Or surveilling in general, for that matter...)
Ooh, boy. This gets into some very weird issues with causality. The short answer is: that won't work.
The reason that you're seeing information from something's past when you look at it across very long distances is that the information is taking a long time to get to you. If that information were able to travel faster than light, then you would see something much closer to its "present".
That said, you could allow someone to observe their own past by transmitting your normal, light-speed observations back to them in FTL. Hypothetical: you're on planet A, Bob is on planet B, and the distance between you is 10 light-years. You send an FTL communicator to Bob, by some means.
Note that the maximum time span you can look back in this manner is the light-speed distance between you and the other party. You can't show Bob what his planet looked like 5,000 years ago unless you were observing it 4,990 years ago on your own planet and happened to record it.
On the other hand, if you could travel at FTL speeds yourself, you could go 5,000 light-years away, look at Bob's planet, then send that data back to him instantly. Of course, at that range you wouldn't even be able to see the planet, never mind transmit useful data about it.
There are also some frames of reference in which it might be possible to send that information backwards in time, but I don't understand the math well enough to explain them.
You don't even need FTL to let someone observe their own past. If you transmitted your observation of Bob's planet back to him without FTL, it'd take 10 additional years to get there, at which point he'd be seeing 20 years into his own past.
The point of all this is that, without the weirdness mentioned in my next-to-last paragraph above, you can never transmit information about something that occurred earlier than the fastest light-speed path between you and your correspondent.
Edited by Fighteer on Sep 18th 2019 at 12:30:44 PM
I know about the issues of causality with FTL in general. It's why the worldbuilding project I put this in is soft sci fi and I'm sidestepping the whole headache about it.
Edited by ericshaofangwang on Sep 19th 2019 at 12:37:08 AM
Just remember: if you were able, right now, to instantly traverse the physical distance between you and something far away in the universe, you would arrive at it as it is now, not as it was when you observed it at that original distance.
So, for example, if there's a star ten thousand light-years away, and you FTL to it, it would be ten thousand years older than whatever you were able to observe about it from your starting point. note This would be true if you went there STL as well: you would observe yourself "catching up" to it, or its clock speeding up relative to when you were at home. Correspondingly, you'd see your starting point appear to slow down. This effect would increase the faster you go, at a rate inversely proportional to your travel time.
Ignore causality; this is about the basic rules of relativity.
Soft sci-fi works with FTL generally ignore relativity as well and assume that everything in the universe is happening on a single clock. This is crazy from a physics perspective, but you need it if you aren't going to spend a lot of time explaining relativity to a lay audience. If you're using this sort of ruleset, then the idea of "astro-archaeology" is nonsense.
Edited by Fighteer on Sep 18th 2019 at 2:13:36 PM
But is that not more or less what the original poster was suggesting? Sending probes out to light-year distances via FTL, and then having them look backwards?
(Data-gathering wasn't mentioned, but I imagine that even without an FTL data-transmission system one could just FTL a ship out to the probes, copy their data onto a local device, and then FTL back to wherever you want to work with the data.)
The problem there is you'd see something 5,000 light-years distant. A planet at that range wouldn't even be a pixel in the largest telescope we can build. You'd need to send a telescope the size of a solar system* to get any kind of useful resolution. Even a few light-seconds makes the optical resolution useless for resolving things the size of people or buildings. You can't teleport to Neptune and then look in through your bedroom window to see what you were doing 4 hours ago without using a telescope as big as Neptune.
*Interferometry is a possibility, but a murderously difficult one when you are dealing with visible light. The project would be of comparable scale either way.
Edited by Fighteer on Sep 18th 2019 at 4:57:39 AM
Might be a good use for the Very Dangerous Array.
That's an in universe use for the VDA They teraported in and found that someone had destroyed the Scrapyeard of Insufferable Arrogance so they ported to a point just outside the expanding light cone, deployed the VDA and looked in on the events that from their perspective happened several hours ago.
@Fighteer, yeah, Ars Thaumaturgis has the gist of it. In any case, the scale isn't really a problem. The setting I'm worldbuilding acts something similar in scale to what happens in Xeelee Sequence, for an example.
Edited by ericshaofangwang on Sep 18th 2019 at 7:46:44 PM
Regarding further uses for FTL... Hmm... Other ideas might depend on how the FTL in the setting works. Is it teleportation? An Alcubierre drive? Wormholes? Something else?
... Can FTL be used within the bounds of a planet? If so, you could perhaps use it to create what would, on that scale, essentially be teleportation. Provided a safe means of doing so en masse, you could likely get rid of a huge chunk of road transport. This in turn might have effects like easing commutes, making emergency response far more swift and effective, and so on.
Honestly, I think that I just took it to be something that would have a sci-fi handwave.
It depends. The two most common is by wormhole or by the Void, since it also allows inter-universal travel within the setting. Wormhole networks are maintained both for interstellar transport and communication as well as for dyson spheres and habitats. The other and more dangerous way is to plunge into the chaotic space in between universes and to come back out into physical space. Both can be used in atmosphere, with the latter also being able to be used within the event horizon of a black hole.
Edited by ericshaofangwang on Sep 18th 2019 at 10:32:24 PM
Hmm... In that case, presuming that it's not easy to open a bespoke wormhole, I imagine that wormhole travel within the bounds of a planet might be more likely to cover long-distance travel with set routes than varied short-distance journeys. That is, I imagine wormholes replacing airline traffic, but not commuting and suchlike.
Given the nature of void-travel, I could see some adventurous types dropping into the void, then popping back out at random, to see where they end up. Of course, presuming a random re-entry point and given the vastness of space, they're more likely to end up sitting in intergalactic emptiness than anywhere interesting. But there's always the thrill of thinking that you might appear in the corona of a star, or above an uncharted planet, etc.
On the less-exciting side, I could see FTL of this sort being used to dump trash.
Trash-wormholes might all lead to a central sorting-station (or one of a set thereof), where advanced tech automatically separates out the various types of trash, dropping the results as appropriate into wormholes leading to specialised processing facilities.
Further wormholes then take the processed trash and transport it to various production facilities, which turn it into useful products again.
Or drop it into a black hole to extract energy from the accretion disc. This can result in up to 90% efficiency in mass-to-energy conversion depending on the spin of the black hole. The best part is that you can dispose of anything this way. The most dangerous substances in existence simply turn into fuel for your near-infinite power supply.
Seriously, though, you literally can't see a scene from the past by going a few light-hours away, unless you redefine how optics work as well as relativity. Suspension of disbelief is right out the window.
Edited by Fighteer on Sep 18th 2019 at 11:07:08 AM
It's not supposed to be hard sci fi, though. There's no need to hung up about it. It isn't Orion's Arm where the physics of everything is meticulously dissected before being put into the setting.
Edited by ericshaofangwang on Sep 18th 2019 at 11:41:55 PM
The thing about FTL is that no matter what the method is, if you’re beating light in any way you can break causality by sending information back in time.
Relativity, causality, FTL. You only get to pick two.
Weaponization. If you can fold space, anything caught in that fold gets crushed into a black hole. If you can open a wormhole, you can open it in the space an enemy is standing in. If you can induce a macro scale quantum leap in an object, you can drop it somewhere awful or Tele-Frag it. If Hyperspace Is a Scary Place, find a way to stick them there permanently (see Vortex Weapons on the Lexicanum for a class of weapon that does just that).
True, the setting I'm working on does have an equivalent to the Culture's gridfire as well as 40k's vortex weapons. The quantum leaping in general falls more under a weaponisation of probability manipulation but it's still something to think about, I suppose.
Aside from this being soft sci-fi, rather than hard, it seems very plausible to me that we might in a hundred years discover some way of circumventing that problem. Perhaps some new discovery will enable it—information stored in some as-yet undiscovered way, or some unknown interaction of fundamental aspects. Or maybe some new technique will be discovered—something akin to the discovery that one can reconstruct an image from scatter on a wall. Either way, the fact that it seems impossible now doesn't mean that it will always seem so.
You can use interferometry to combine images from multiple telescopes to form a telescope with an effective diameter equal to the distance between any two components. This means you don't need a solid mirror a light-second (or whatever) across, just a few individual telescopes distributed around that circular diameter. With enormously powerful computing and FTL communication, you could make it work.
I generally try to draw a distinction between soft sci-fi and "space magic". With the former, you bend the rules but try to retain some verisimilitude. With the latter, you don't care. Point a telescope on Neptune at Earth and you can look through someone's window. Why not? But if that's how you want to work, why ask people about plausibility?
Edited by Fighteer on Sep 19th 2019 at 3:09:36 PM
Looking back at the original post, I don't read it as asking after plausibility. My reading is that it just asks for new ways to make use of their FTL ability.
I mean, there’s a line between “we could possibly circumvent this” and “we already know you can’t circumvent this”.
In this case (the FTL telescope), we know exactly how it works (or wouldn't work); there's no new physics waiting under a rock for someone to invent. Optical resolution is something that was figured out centuries ago, even though we didn't know why it was that way until we discovered that light is a wave.
Solar-system scale optical interferometry is completely possible according to modern physics, although we currently lack the technological capability to do it. We already have planet-sized interferometry telescopes, even — the Event Horizon Telescope uses VLBI from radio telescopes located around the planet. That only works in radio frequencies: doing it with visible light requires quite a bit more computer processing power than we can bring to bear at the moment, but it's by no means impossible.
In other words, given FTL as an assumption, it is physically possible to do what you want, but as a mega-scale engineering project, not a casual effort.
Edited by Fighteer on Sep 19th 2019 at 5:12:59 AM
I feel like this argument is derailing the thread a bit, so let me leave my part of it with this post.
When I speak of circumvention, I'm not necessarily talking about discovering new physics (although that is a possibility). I'm thinking of cases like the transistor, or parallel processing to get around the limitations of transistor size, and so on. Tricks, effects, and techniques as-yet undiscovered.
By virtue of the fact that they're undiscovered, we don't know what they might be. But it seems to me that there's a history of finding ways around things that seem to be fundamental obstacles (and indeed of such things being unanticipated, as in the case of the transistor).
(I'm not saying that we will necessarily find a way around any given obstacle. More that, given the possibility, the invention of some new technology that seems beyond what we think is possible doesn't necessarily break my immersion, or make a work non-sci-fi to me.)
Anyway, that's pretty much what I'm trying to say: that we don't know what techniques or pieces of information we haven't yet discovered, or how they might be applied, and thus what technologies they might enable.
@Fighteer I don't believe I asked for plausibility at all. I'm mostly asking for whatever creative uses for differing methods of ftl seem interesting.
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