One of the most contentious close reasons we have on the site is the one that designates real-world science questions as off-topic. The close reason is worded as follows:

"Questions seeking scientific solutions or explanations are off-topic unless they relate directly to a cited work of fiction."

Unfortunately, that last part seems to seriously muddy the waters: what does it mean for a science question to "directly relate" to a work of fiction? Just about every question asked on here cites some work of fiction. A question like "Could I make dilithium out of a lithium battery?" directly relates to Star Trek but I think it's exactly the kind of question we want to be off-topic.

On the other hand, most fictional works, even pure fantasy ones, operate with an implicit assumption that the laws of physics in the movie work just like the laws of physics in the real world, unless/until the work shows us differently. So many legitimate questions about the fictional universe will end up being answered using real-world science, because it's the same as the fictional science.

Different people, including different moderators, seem to fall at different points along the spectrum of possible interpretations, and it almost always leads to comment and chat "discussions" over which side a given question falls. So, can we try to pin down a community consensus over exactly where we draw the line?

For consideration, here are some previous meta questions that are related, but either don't quite answer this question, or else, there's no clear consensus in the answers:

Also, here are some sample questions that are clearly asking about "real-world science" but with varying degrees of "related to a work of fiction". Note that I've tried to avoid questions from the very early days of the site, since their status may or may not reflect the current consensus (looking at you "Matrix Battery" question).

I think it would also be a good idea to lay out a policy for what good answers to these questions -- assuming they stay open -- ought to look like. That will at least give us something to point users to when trying to help them keep within the scope of the site, or explain why their otherwise-factually-correct answers might be getting downvoted.

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    Mike, can you add a summary heading to the proposals below? Commented Oct 11, 2015 at 14:43
  • You should add What constitutes a “Sol” cycle in the film “The Martian” to the list of questions. Up front: I voted to close this question as it is directly out of NASA's (and other space agencies around the glob) current non-fictional playbook.
    – Lexible
    Commented Oct 13, 2015 at 1:46
  • The question Gun too Large for Helicopter asks about a real world device with a real world solution, but happens to exist in a fictional world. I vtc as there is nothing sci-fi about the question or the object of the question.
    – Firebat
    Commented Oct 26, 2015 at 15:36

5 Answers 5


In-Universe Explanations — Even Based On Real Science — Are On-Topic

Any question that is asking for an answer within the context of a fictional universe, even if that question requires real-world science information, is on-topic.

We should not expect content creators to spell out every detail of the science in their works. We can assume that works of science fiction and fantasy obey all the same natural laws that we are familiar with, until presented with evidence to the contrary in the work itself.

Answers should always be written from an in-universe perspective, and use only scientific information that is either explained, demonstrated, or at least not-contradicted by what can be seen within the work. Answers should also avoid trying to speculate how the science within a work might operate without evidence to support it. (e.g. there are humans breathing unaided, so we can speculate that the atmosphere of fictional Earth is similar to ours.)

Questions which are explicitly asking for an out-of-universe explanation of the science from a work of science fiction or fantasy should be off-topic.

For example:

(Note that, in many cases, merely asking the OP to clarify that they are looking for an in-universe explanation is sufficient to clean up a borderline post.)

  • If one were to proceed to ask as a separate question, say repeating "How does combustion work?" for literally every work of science fiction or fantasy in which fire appears—something this answer advocates—that would seem to dilute the worth of SF & Fantasy SE with respect to the actual work of its authors, and to misdirect people away from physics or chemistry SE which are much better situated as a community to answer such questions.
    – Lexible
    Commented Oct 13, 2015 at 1:52
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    it's very easy for someone who is intent on purposefully damaging a site to do so with on-topic questions. You've merely provided one such way to do so.
    – KutuluMike
    Commented Oct 13, 2015 at 10:13
  • But I am not writing of intent to damage the site. I am writing of damage to the site as a consequence of a policy that Sci-Fi SE is now Science Questions SE.
    – Lexible
    Commented Oct 13, 2015 at 14:59
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    it's not. If someone were to try to do what you suggested, they would almost certainly be doing in it bad faith, and the moderators would have justification to intervene for other reasons. If someone genuinely, and in 100% good faith, actually wanted to know how combustion worked in every movie ever, those are legitimate questions. They would also likely get downvoted and ignored as uninteresting.
    – KutuluMike
    Commented Oct 13, 2015 at 15:02
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    Ok. I am with you, but how do we differentiate good faith from bad faith science questions? For example, suppose I say "Gosh, In-Universe Explanations – Even Based On Real Science – Are On-Topic, and start asking my how does combustion work question for every work of sci fi or fantasy I have engaged with, while minding my Ps & Qs regarding asking a good question. What is the criterion that says "that's bad faith?"
    – Lexible
    Commented Oct 13, 2015 at 15:06
  • A second question to try and untangle this thorny issue: when is it appropriate to direct a questioner to another (science-based) stack exchange?
    – Lexible
    Commented Oct 13, 2015 at 15:08
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    On your first question: we assume good faith ; that's a basic principle of the stack network. We let the mods decide when there's enough evidence to demonstrate otherwise :)
    – KutuluMike
    Commented Oct 13, 2015 at 15:15
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    On your second question: we can always recommend someone ask on a different stack, and tell them they'll get a better answer there. That's not the same as decided they can't ask here. The answer to the question here may be as simple as explaining that X movie's physics follows real-world physics rules, and go see this question on Physics:SE for details. (I can also tell you, questions that even mention fictional universes don't tend to fare well on those sites.)
    – KutuluMike
    Commented Oct 13, 2015 at 15:17
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    What about questions that ask about whether some bit of technobabble in a work of fiction has a basis in some bit of real-world science, like this one about Blade Runner? This doesn't clearly fit into either of your two categories.
    – Hypnosifl
    Commented Oct 21, 2015 at 21:38
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    Also, it's not clear why you say the Martian heat ray or machine failure examples are out-of-universe--for example, one could interpret the Martian heat ray question to be asking "What can we conclude about the in-universe power output of the Martian heat ray, given the details of its destructive power in the story, and the assumption that the laws of physics work the same in-universe as in the real world?" (especially since you mention the latter assumption in your own explanation about acceptable questions).
    – Hypnosifl
    Commented Oct 21, 2015 at 21:42
  • @Hypnosifl I agree that the Martian heat ray example is a bad fit for the general intent of the policy, as it could easily be interpreted as asking about the in-universe power output. See the new meta discussion here.
    – Rand al'Thor Mod
    Commented Feb 16, 2017 at 0:47
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    @lexible - If users try to ruin the site by asking thoughtful, well written on-topic questions, we'll probably survive ;-)
    – Valorum
    Commented Apr 24, 2019 at 17:33
  • @KutuluMike I just want to say how much I have come around to the perspectives your have articulated in your responses to me in the intervening years. Good on ye.
    – Lexible
    Commented Apr 25, 2019 at 0:34
  • I asked a question about how an electronic device would survive something done in a specific fantasy series that's not possible in the real world (at least not with some serious equipment) and it was downvoted to hell. Is that question still off-topic? Where should it be asked instead? None of the linked science sites seem to fit because it's not about physics, Math,...
    – Neph
    Commented Feb 5, 2021 at 1:50

I think Mike Edenfield's answer involving the in-universe/out-of-universe one is a good one, but I think there are some ambiguities in the definition and I also disagree with some of the examples given, so I'd like to suggest a slight modification of this idea:

Questions that require taking into account as much relevant canon in-universe information as possible, and then combining it with (or contrasting it to) real-world science to try to give an answer about how things work in-universe, are acceptable; questions that are more focused on how things might work in the real world rather than how we should understand them to work in-universe, particularly questions that require us to selectively ignore bits of canon information because they aren't scientifically plausible, are off-topic.

As an example of the latter, if someone asked "how might we build a Star Trek style faster-than-light warp drive in real life", but they wanted us to ignore all the things that have been said on the show about the warp drive relying on "subspace fields", since there is nothing that seems to resemble "subspace" in real-world physics, that would be too much of an out-of-universe question.*

On the other hand, Mike Edenfield gave the answer How much power does the Martian heat ray output? as an example of an out-of-universe question, but I think according to this standard it could actually be acceptable, provided we are asked to take into account all the scenes that might be relevant to judging its destructive power, and then combining that with "only scientific information that is either explained, demonstrated, or at least not-contradicted by what can be seen within the work" (one of Mike's criteria for acceptable questions). A similar example would be the question What is the wattage of the Death Star's superlaser?, which wasn't closed for being off-topic (though it was closed as a duplicate since the answer was already given incidentally in the answer to another question).

I also think it should be acceptable to just ask if a given description of some fictional technology or science could be understood in terms of real scientific ideas or engineering plans, as long as the full description is taken into account rather than being selective about what in-universe information to use. An example would be the question Accelerated decrepitude due to telomere length in Blade Runner, which asks us to consider the whole of a technical discussion about how to stop the accelerated aging of replicants, and asks if it could possibly jibe with real-world scientific ideas about aging being due to shortening telomere length. The focus in such questions should be about how the laws of nature work in-universe, whether certain real-world facts are being referred to by the characters (and thus demonstrating these facts hold in the fictional world as well) or if we have to assume they're talking about scientific findings specific to the fictional world. The focus should not be on asking whether the creators of the fictional world made a scientific error, or asking for detailed information on how things really work as beyond the information necessary to conclude they don't work that way in-universe. As Mike Edenfield suggested in the comments, a question of the type "Does X work in movie Y the same way X works in the real world?" is OK, likewise "Does X work in movie Y the same way X would be theorized to work in the real world, according to modern scientific theories" (for purely theoretical examples like Star Trek warp drive vs. the Alcubierre drive), but a question of the type "Is Thing X from Movie Y really possible?" is not. It can be a subtle distinction, but I would favor erring on the side of a "charitable" interpretation of ambiguous questions, or suggesting edits to make it a more clearly in-universe question.

*There should perhaps be some slight amount of wiggle room on the prohibition on "selectively discarding" in-universe information--the dependence of warp drive on subspace fields was established consistently over and over again in the Trek franchise, but in a question about a Trek technology, it might be acceptable to ignore a single odd statement about the technology made by a character in one episode of Voyager, for example. Likewise, when there seem to be internal inconsistencies in depictions of a given science or technology in the canon of a given fictional universe, it should be acceptable to just pick whichever side of the inconsistency seems to have more weight behind it, seems more favored by fans, or seems more scientifically plausible. Finally, there might be reasonable restrictions the questioner wants on what they want to consider "canon", for example someone might want to ask a question based only on how a technology was presented in the Star Wars films, ignoring books and TV series and other spinoffs.

  • @Mike Edenfield - But what about cases where a person wants a yes-or-no answer to whether it's possible to interpret some bit of fictional science as being the same as a real theory, or whether it requires assuming different scientific truths in the fictional universe than in our world? This might be motivated primarily by curiosity about how we should understand things to work in-universe, whether the fictional universe has different laws of physics or biology for example.
    – Hypnosifl
    Commented Oct 27, 2015 at 20:42
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    @Mike Edenfield - OK, I agree that "Does X work in movie Y the same way X works in the real world?" is an acceptable question while "Is Thing X from Movie Y really possible?" is not, I had edited my own answer to suggest a similar distinction before I saw your last comment, and I just quoted you in the answer for good measure. Let me know what you think of the updated version, whether there's anything there you still definitely disagree with.
    – Hypnosifl
    Commented Oct 27, 2015 at 23:54
  • I don't see the difference between those two questions; the answer would be the same. Commented Jan 19, 2016 at 13:43
  • @Cees Timmerman - I think it would be a difference in emphasis--see the first paragraph under the bolded part in my answer, a question like "is warp drive from Star Trek really possible" might lead to answers that ignore a lot of details about Trek warp and just talk about the general idea, while "Does warp drive in Star Trek work the same way as theoretical proposals by physicists like the Alcubierre drive" would encourage more attention to the details of Trek canon, including things like warp drive depending on "subspace fields".
    – Hypnosifl
    Commented Jan 19, 2016 at 19:26
  • That's a different question, though. Alcubierre drives don't work in the real world, because humanity has been unable to produce them and we haven't found any. Same for Trek's Warp drive. Your new question asks for a comparison of fiction-based and reality-based theory. How detailed should that be? "No, because only the fictional drive needs fictional force x." would suffice. Commented Jan 20, 2016 at 9:35
  • @Cees Timmerman - I was using "possible" in the sense of "theoretically possible according to mainstream physics", the Alcubierre drive is certainly theoretically possible in general relativity. In any case, it was just an example to illustrate the distinction I was making between "is something in the ballpark of a fictional plot element scientifically possible" vs. "can the specifics of the depiction of this fictional plot element be reconciled with real science", I'm sure you could come up with other examples if you don't like warp drive.
    – Hypnosifl
    Commented Jan 20, 2016 at 21:57
  • (cont) And sure, in some cases the answer to the latter type of question will be very short, but not always, particularly if you get creative in your interpretation and allow for the possibility that the fictional depiction might be imagined to be using different terminology for elements of real theories (for example, 'subspace' in Trek could be imagined to be an alternate term for the "bulk" dimension in real theoretical physics theories like the Randall-Sundrum model).
    – Hypnosifl
    Commented Jan 20, 2016 at 22:01
  • "the same way X works in the real world" is a far cry from "scientifically possible". Commented Jan 21, 2016 at 10:52
  • @Cees Timmerman - Are you just objecting to the choice of wording, or do you think the distinction I made doesn't make sense regardless of the exact wording? Maybe "works in the real world" is a bad choice of words for theoretically-possible things that haven't been realized, but one could change that to something like "would work in the real world according to modern science"...I'll add something like that to my answer.
    – Hypnosifl
    Commented Jan 21, 2016 at 16:39
  • That would be the same question as "is it theoretically possible using real science", which belongs on a real science SO. Commented Jan 21, 2016 at 16:48
  • @Cees Timmerman - But the point of my distinction is that it's an OK topic for this stack exchange if they aren't just asking if some general ideal (like some form of spacetime warping to allow faster-than-light travel) is theoretically possible, but instead they are asking if all the nitty-gritty details of what has been presented canonically about the technology (like the fact that Trek warp uses subspace fields, with subspace as another dimension) can be reconciled with real scientific theories, so that the real scientific laws can be imagined to still apply in-universe.
    – Hypnosifl
    Commented Jan 21, 2016 at 16:59
  • If you're not seeking a canon answer, perhaps you should ask here: worldbuilding.stackexchange.com/questions/32007/… Commented Jan 22, 2016 at 11:07
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    @Cees Timmerman - I'm talking about answers that are constrained to be consistent with all existing canon, but which may go beyond what has been established in canon to offer logical speculations about how the canonical facts might mesh with real-world science. I don't think the worldbuilding stack exchange would be the right place for this, and logical speculation seems to be accepted on the science fiction stack exchange.
    – Hypnosifl
    Commented Jan 22, 2016 at 23:10
  • Also, note that Mike Edenfield's accepted answer to this question already seems to allow for a certain amount of logical extrapolation beyond what's explicitly established in the canon, see the line "Answers should always be written from an in-universe perspective, and use only scientific information that is either explained, demonstrated, or at least not-contradicted by what can be seen within the work."
    – Hypnosifl
    Commented Jan 22, 2016 at 23:11
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    Ah, but I see the approved answer to this question from the worldbuilding stack exchange indicates it is OK to have questions about extrapolating existing science-fictional universes there, so perhaps you're right that any extrapolations that aren't fairly simple and straightforward would better go on the worldbuilding stack exchange than the science fiction & fantasy stack exchange.
    – Hypnosifl
    Commented Jan 22, 2016 at 23:47

Real-World Science With Any Relation To a Work Of Fiction Is On-Topic

Any question that relates back to a particular work of science fiction or fantasy, in any way, is on-topic. There is a lot of overlap between fans of science fiction and interest or expertise in real science. There's no reason we shouldn't allow questions that begin with a fictional premise and try to understand how such a premise might be possible.

Ideally answers should be based on as much information as we have about the work, but should feel free to draw on real-world science knowledge to fill in any gaps.

  • 1
    In any way? The well-to-wheel efficiency of any normal car featured in Independence Day sounds off-topic to me. Commented Jan 19, 2016 at 11:08

My viewpoint is that anything unrelated to a work of science fiction or fantasy is off-topic. We don't want people asking "How does a combustion engine work?". The answers are too mundane, and off-topic. Similarly, we don't want questions about fantastical technologies that are not bound to a specific science fiction or fantasy work, so we don't want questions of "How do I build a warp engine?" For one, there is no canonical answer outside of that universe. For two, it's too broad. What sort of warp engine? What laws of physics are we working within?

I would probably add to the first one that, if the question doesn't have a more interesting answer in said work of fiction than in real life, that's pretty off-topic too, but that gets into questions, sometimes, as to whether it's the case. Take, for instance, How did Rick make a silencer out of a flashlight?. It's got a perfectly mundane answer, but it does inform you of something in the show, that such a silencer can be built, and that the parts are likely available in-universe. At least in my opinion it's relevant. Since I answered it and all.

  • It kind of fits in with two of the three, but I can't think of a good way to summarize it other than making multiple comments. :)
    – FuzzyBoots
    Commented Oct 11, 2015 at 21:56

Real-World Science Is Always Off-Topic

Any question that requires answering using real-world science is off-topic. This site is for fans and enthusiasts of Science Fiction and Fantasy. We should not allow questions that require expertise in other areas, such as chemistry, physics, or biology. Those are out of scope for our site.

(See this answer for a longer explanation on this idea.)

  • 2
    A good understanding of chemistry, physics, and biology is integral to good science fiction.
    – Mazura
    Commented Oct 27, 2015 at 19:05
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    Always off topic, ts, ts, ts: "Only a Sith deals in absolutes..."
    – BMWurm
    Commented Oct 29, 2015 at 14:01

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