This question is due to this question on Worldbuilding, but concerns a problem that I think might be encountered often.

I've searched through a few relevant threads, including

but I don't think any of those fully addresses the specific problem I am hoping to consider.

In the specific question linked, the bulk of the first two answers are spent pointing out that there is no plausible way to generate the sustained thrust central to the implementations described in the question. However, the intention of this paragraph

Because burning expensive chemical fuel just so things don’t float away some of the time is extravagant to an appalling degree (and simply isn't sustainable anyway), we might suppose fusion (or some other method of getting a lot of cheap energy from very little mass) is available.

and the wording ('what other obstacles ...') of the question that followed, had been to direct answers towards the other complications (such as those mentioned in Firedrake's answer) that might arise, in which I am more interested.

In this case, the original question is written under the incorrect assumption that having cheap energy would imply having means of generating the required thrust. The answers have been helpful in clarifying that that is not the case. However, this has also caused the question to fail to produce the information that was sought.

(Usually, when problems occur in the context of the question, the comments are used for request for clarification; but here the context is specified in an erroneous or misleading, as opposed to ambiguous, manner, and therefore does not invite comments.)

The quoted paragraph might be edited to better reflect the original intention ('we might suppose a magic space drive is available such that...'), and in retrospect that question might be better posed as 'How could ... be made possible' as opposed to 'Is ... practical' (which is the current form of the question, where the answer is evidently 'no'.) Furthermore, now in the presence of a magic space drive, it might have become necessary for the science-based tag to be lifted.

I fear that these edits would change the meaning of the question to an extent such that it may be considered to be invalidating answers. This is, I gather, usually a sign that one should open a new question for this purpose. However, in this case it seems like doing so would produce what would essentially be a duplicate except with a slightly different constraint imposed. What would be a good course of action in this case?

In general:

When one asks "Is [thing] possible?" and gets the answer "No, unless you had [other thing]", the response might often be "Huh. You're right. Suppose then we had [other thing] ..."

I have found this pattern cropping up frequently in conversation, especially when discussing settings where things are still flexible (so applying some handwavium to the big easy-to-ignore-but-hard-to-solve question is something that one might do for the sake of opening up discussions of arguably more interesting details), or engineering-oriented problems where many obstacles exist to a goal - generally, the scenarios where asking "what's the second biggest problem with this thing?" might be useful.

Is there an equivalent pattern of interaction on this site? Neither editing the question to include modified/additional constraints, nor asking the same question just with a different assumption tacked on, seem satisfactory.


1 Answer 1


A simple approach would be doing something like what I did when I asked What is the smallest change that would allow an Earth-like planet to have atmospheric CO₂ levels of several percent? or perhaps even better in this case What adaptations to a mammal's eyes would allow it to see large contrasts well, and what other effects would those have?

Basically, describe the starting point, state a desired outcome, then ask what is required to get there and possibly what effects on some specific element of the world having the first thing would have. Make sure you aren't asking us to do too much of your work for you, though. Clearly state some limited aspect that you wish to know about, lest your question is likely to be at risk of being too broad.

You can also phrase the question as something like "if adding/removing/changing some specific element of the world allows for this, then what is that element and what would the resulting system look like in the aspects asked about above?" can allow for answers that go like "you can't because X, unless you have Y, at which point Z happens". Such an answer would probably fit when "that's not possible" is an acceptable answer, as long as Y fits within the specific constraints of the question. (For example, you'd probably be hard pressed in proposing adding faster-than-light travel to a hard-science question.)

Asking multiple questions at once is tricky, and I won't pretend that I have always got it right myself despite having been around since the first few days of the site's life; it's very easy to take two questions that are perfectly acceptable each on their own, and turn those into one "too broad" post.

Editing questions in such a way that it invalidates existing answers is something that should indeed be avoided whenever possible. Allowing a question to evolve without invalidating answers is one of the reasons why we have the question sandbox.


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