Homer is composed of slightly underweight electrons imported from a parallel universe, hence the extra size, though I also postulate that for him, Planck's constant (the size constant) is slightly larger than for the rest of the universe.
Standard general relativity is based on Riemannian manifolds.
However, the simplest extension of Riemannian manifolds seems to be Kahler manifolds, which have a complex (hermitian) structure, a symplectic structure, a riemannian structure, all these structures being compatible.
So my question ...
I think it's about time we start thinking about broadening the homework-like close reason. A lot of the questions we close as homework-like these days are not homework, or anything close to homework, and aren't even meant to have educational value.
Instead it seems like we tend to close things that are pure calculation requests, where the asker is trying to get us to do some math for them, rather than asking about some concept so they can do the math themselves.
So it would make sense to introduce a new close reason that talks about calculation requests being off topic. This would replace the current homework-like close reason, and to go along with it we would replace the current homework policy with a new policy prohibiting calculation requests.
@TerryBollinger Yeah, I suspect people mostly agree on that. We need to work out the details of what exactly would be on or off topic under this new policy.
@DavidZ Warning folks that calculation requests are subject to quick downvotes, and encouraging such downvotes, might help even without an official rule.
Items of particular interest: (1) are there a significant number of questions which are off topic under our current homework policy which would be on topic under the new policy? If so, should they be on topic? (2) exactly what sorts of questions would become off topic under the new policy which are not covered by current close reasons?
@TerryBollinger right, but we can do that already. (I certainly favor continuing to do so) The reason I'm proposing this is that I actually see the homework-like close reason being used, in "the wild", for calculation requests that are not, strictly speaking, homework-like by our current policy.
@DavidZ I like the goal. To me, any concept question is OK, even if the understanding behind it is very weak. A good answer to a weak concept question can have high value. Do a calculation, though, and all you did is give away a fish, not teach how to fish.
@JohnRennie One thing I've noticed about some very naive but sincere questions is that they can uncover surprisingly common misconceptions that otherwise can be overlooked.
@TerryBollinger Well, I mostly agree, but that's another story... taking that as a premise, though, I think that sidesteps the issue a bit. Under our current policy, homework-like questions which are asking for a conceptual explanation of something are still supposed to be off topic, but it's not based on whether the asker's understanding is weak.
@JohnRennie indeed, and that happens on all sites. It's kind of part of the design of the system. The idea is that, when people find themselves closing a lot of questions for a particular reason, then you make that reason one of the standard reasons in the list.
@JohnRennie which brings me to my next thought: we could go so far as to define an "insufficient effort" close reason, which would include calculation requests and other questions that are lazy
It'd be a bit different, though. I think there are some questions of the form "I want to calculate [thing]. I tried [X], [Y], and [Z] but I don't know how. Can you just do it for me?" which I think should be off topic, but an insufficient effort close reason wouldn't include those.
@JohnRennie Agree, just making the point. I've seen a few questions, hmm mostly years ago, that were actually good but very hard to read in the English rendition.
@alarge What I have in mind when I say "calculation request" is not so much something like that, but the questions that ask us to do some basic physics. Like no-effort homework questions, for example, but also something like this
Well, actually GR is not really Riemannian geometry. It's Lorentzian, which is in some ways a generalization of Riem. geom. and in some ways a restriction.
Generalization in the sense that we have the distinction timelike/spacelike/null and the consequences of that and a restriction in the sense that there are some Riem. manifolds that are not Lorentzian.
@DavidZ Right, but then I don't see why the current homework-like policy is not enough to cover these cases. Can you give an example of something that you think does not fall under the current policy but is something that should be closed?
@0celo7 That's interesting! So, the Venn diagram has an intersection of Riemannian manifolds and Lorentzian? What is that intersection called? Does it even have a name, other than "GR"?
@David Z : if I were you I'd be wary of making any changes that would make "serious" users unhappy. Instead of downvoting/closevoting a physics-maths question, other users could simply point out that this website isn't for that sort of thing. IMHO you should instead focus your efforts on the naïve/lazy questions from kids.
@alarge I think the issue is less that the current policy doesn't cover it but that "homework" is a bad name and the talk about "questions of primarily educational value" in the faq post does not reflect the kind of questions we mean and close with that reason.
@TerryBollinger basically, to get a Lorentzian manifold you have to get a line element, which is basically a vector field which vanishes nowhere, and this is not possible on all manifolds
How about making the close reason: an lazy, idle and slapdash attempt at a boring question that could be answered by googling in half the time it took to write it
@ACuriousMind yeah, that alludes to something that @DanielSank suggested at some point: the wording of the homework-like close reason no longer reflects the kinds of questions we actually want to close
Given a sperically symmetric problem, I am asked to show that its Cauchy stress tensor, in spherical coordinates will assume the form:
$${\overline{\overline{\sigma}}}=\sigma_{RR}(r)\overline{e_r}\otimes\overline{e_r}+\sigma_{\theta\theta}(r)(\overline{e_\theta}\otimes\overline{e_\theta}+\overli...
Currently, a question which merely shows insufficient effort is supposed to be downvoted, but our policies don't offer any justification for closing it
If I was in a spaceship continually accelerating at $9.81m/s^2 =1g$ in a straight line, I would reach near light speed within a year.
On Earth, we are in a gravitational field of $1g$, which according to the equivalence principle means we are effectively accelerating at $9.81m/s^2$.
What does ...
I've seen that too, and that's one of the big reasons I think it'd be a good idea to replace the HW reason with something that covers insufficient effort questions
@0celo7 Cool... I have questions I don't know how to ask, related to my tendency to view the universe as being "a lot like" a computer simulation, even if it is not. That would put... odd constraints on the manifolds in play?
@ACuriousMind we don't have another slot, but if we really needed one we could ask for the SE team to enable one. The system allows up to 5. (But I don't think we really need an extra one that badly.)
@JohnRennie Hm. I see your point, but I also see the point of the close voters - there's a very obvious and boring reason we're not accelerating, and that's because the force of gravity is counteracted by the normal force. The equivalence principle doesn't say that acceleration is equivalent to standing on a surface in a gravitational field.
@0537 don't worry, it's fine to ask ;-) (i.e. if the community actually thinks a question should be reopened, it's fine to nudge people toward actually voting for it - and similarly for voting to close)
@JohnRennie that to me is a question that would have been worth answering, because I am very sure it bugs a lot of folks who are first told about gravity/acceleration equivalence.
@DavidZ : some people take umbrage at downvoting and closing, and some of them might be the sort of people PSE wants to attract and retain. A polite explanation might serve better.
@JohnRennie I like "lazy not allowed" a lot, with specifics about doing a bit of homework first. But as @JohnDuffield says, polite is always better, especially when a question is first-time.
yeah, that's okay. This is just starting a discussion, at this point. The goal here is not to reach a conclusion, it's to draw attention and generate ideas.
@JohnRennie that's true, but let's also consider the case where someone posts a really interesting homework question that is, nevertheless, directly from a homework assignment. Do we want to provide an answer to that?
My inclination is "no" but I could see it going either way
@JohnRennie again, not saying I necessarily disagree, but if I may play devil's advocate, this position is (apparently) that it's okay for us to help people cheat on their homework if the problem is interesting enough.
@JohnRennie presumably so. But this is what we have to decide.
Later gents, and ladies if any at present? Nice question discussion, and nice thread about manifolds. "It is your destiny... your manifold destiny." (attempt at Star Wars humor...)
@JohnRennie Questions about "advanced" calculations I think can and do stay open - if they make plausible that this is not a straightforward calculation. The question should demonstrate (or state) that the standard methods in the field do not work, and indicate the reason for that. All too often these questions lack that kind of context, and I don't think there is anything worthwhile in a question whose answer is two pages of lengthy, but standard manipulations.
@DavidZ homework is intended to be part of the learning process. If I can answer a homework question in a way thatI think leaves the OP knowing more than they started with then I'm happy with that.
There's a certain class of homework questions which I suppose everyone agrees should be off topic, but the question is why they should be considered off topic. Should it be because they are homework? Because they are educational? (as current) Because they don't show effort? Because they are just asking for a full answer instead of help on the step they're stuck on?
Standard general relativity is based on Riemannian manifolds.
However, the simplest extension of Riemannian manifolds seems to be Kahler manifolds, which have a complex (hermitian) structure, a symplectic structure, a riemannian structure, all these structures being compatible.
So my question ...
If I was in a spaceship continually accelerating at $9.81m/s^2 =1g$ in a straight line, I would reach near light speed within a year.
On Earth, we are in a gravitational field of $1g$, which according to the equivalence principle means we are effectively accelerating at $9.81m/s^2$.
What does ...
