I read online that wormholes are formed when the fabric of space time is bent, but visualisation was the bending of two dimensional space with a three dimensional object. So what bends three dimensional space to create three dimensional wormholes?
We regularly get questions about wormholes on this site. See for example  and . Various wormhole solutions are known, of which my favourite is  because it's closest to what every schoolboy (including myself many decades ago) thinks of as the archetypal wormhole.  The trouble is that Visser has pulled the same trick as  of starting with the required (local) geometry and working out what stress-energy tensor is required to create it. So Visser can tell us that if we arrange exotic string along the edges of a cube the spacetime geometry will locally look like a wormhole, but we know nothing about what two regions of spacetime are connected.  My question is this: suppose I construct a Visser wormhole by starting in Minkowksi spacetime with arbitrarily low densities of exotic matter and gradually assembling them into the edges of a cube, how would the spacetime curvature evolve as I did so?  I'm guessing that I would end up with something like Wheeler's bag of gold spacetime. So even though I would locally have something that looked like a wormhole it wouldn't lead anywhere interesting - just to the inside of the bag. I'm also guessing that my question has no answer because it's too hard to do any remotely rigorous calculation. Still, if anyone does know of such calculations or can point me to references I would be most interested.
As we know, the tactical downvoting (I'm talking especially about SO, as I don't know about other sites) is more and more becoming a serious problem, as I see, the community can't stop this behavior without some sacrificing.  As a suggestion, I think it makes sense to prevent an answerer from downvoting any answer on the same question, this -sure- has a harm, but IMO, it's less harmful than the tactical downvoting issue, and to make the things a bit more easier, we can prevent an answerer from downvoting a question without posting a comment to that answer before.  And vice versa, if a user downvoted an answer, he shouldn't be able to post another one unless he posted a comment first, to prevent working-around that system, so a user can't downvote other answers before posting his own to avoid posting comments.  EDIT, more clarification: I don't say wrong answers shouldn't be downvoted, BUT if you want to downvote an answer and post your own, you'll have to post a comment, so we make sure you're not just downvoting right answers tactically. Feeling a tingling sensation by touching stuff, Is this safe? I'm putting on my desktop computer on steel rack as usual. A while ago, when I touch the steel rack for seconds, practically I feel a tingling sensation, sort of electrical shock in my finders. After that I measured how voltage the steel rack has, the multi-tester meter indicated almost 50V by AC mode. Is this safe to touch or keep the PC on the position, or I should get away the PC somewhere electricity-safe? I'm not sure this site is suit for asking this kind of question, but I'm very worrying whether this is safe or not since this experience is my very first time. Thank you. Stance on repost question instead of editing to invalidate answers? How do I remap a key in macOS Sierra, e.g., Right Alt to Right Control? I used to use  to remap Right Alt to Right Control (as an Emacs user I use Control MUCH more that Alt) but updating to Sierra broke this.  Downgrading is not an option.  How do I manually remap keys in Sierra?  I specifically would like to remap Right Alt to Right Control. I have built a forecasting model for a company. Since it is dedicated to practical usage, I prefer to use the relative error parameter (like MAPE, SMAPE, &amp; MASE) as a measurement for my model performance and display it on the dashboard (the percentage error is easier to understand by user). I found an interesting reference about the criteria of a good forecast result based on MAPE from Lewis (1982):  ...but in my case, I can't use MAPE for some dataset because there is some zero actual demand so it can't be used as denominator in MAPE. So, I use SMAPE &amp; MASE instead, but I can't find any good references about good forecast result criteria based on SMAPE &amp; MASE, nothing like above. So, I'd really appreciate any help/suggestion about it :), Thank You! Reference: Lewis, C. D., 1982. Industrial and Business Forecasting Methods. London: Butterworths. rtl8723ae unstable on Ubuntu 14.04 I have searched through the internet and in AskUbuntu, but I could not find a working solution for my little problem.  The RTL8723ae WLAN is behaving strangely on Ubuntu 14.04 and drops the WLAN connection constantly. I am using the notebook MSI GE40 and have already seen on the web that there are other people having the same problem but there was no permanent solution. The problem did not exists on the original Windows 8 on the device and the router is a TP-Link, which I can control (channel change and so on, I use WPA2-PSK WLAN security). How can I make things link url references, my index, table of contents, and cross references clickable links in documents produced by LaTeX? I generally use pdflatex to produce my documents. How can you describe someone who gives up too easily? What are some good tutorials on writing custom styles (classes) that clearly explain commands used and some of the features that TeX has to offer in the way of styles? I read this story a long time ago and cannot remember either the title or the author. It was written in the 60s or 70s. The setting is sometime in the 21 century.  Here is a summary of the plot.  One of the great classical composers (maybe it was Schubert, I'm not sure) is revived with some future technology. All the guys in the lab are very happy about it, the world cheers the achievement. The composer is also quite excited to be alive. Naturally, he is asked to perform a concert. He asks for ink and music paper. Nobody knows what that is: in those days everybody writes music directly in "frequency spectrum" and similar stuff.  The composer, excited to create music again, tries to come up with something but he doesn't like anything he writes. The music is well written, but lacks something essential, it doesn't sound like his real music. Finally, the composer realizes that the lab guys recreated his mind from reviews by music critics, and his music just sounds like that. He performs the concert. The audience enjoys it, applauds and bravos. Not only to composer, but also to the lab guys.   At the end, if I remember it right, the composer gloats over the  primitive taste of the audience. The audience who writes music in frequency spectrum and applauds to lab guys at the music concert did not see the failure in the concert and ate it as it is.  Does someone recognize the story?  PS all the recent talk of advent of AI machines with Machine Learning algorithms reminded me of this story. The Start menu no longer shows up when I press the Start button i have a scenario where i want to know in which position number the column name comes   like i have sample data below   ID|NAME|S1|BQ|S2|VN|D1 1|vimal|10.12|12.4|56.2|12.2|11.22 2|vilas|10.12|12.4|56.2|12.2|11.22 3|viky|10.12|12.4|56.2|12.2|11.22   Colum name : S1 S2 D1   output should be :  3 5 7 How do you add more than one material to a mesh?   I have tried adding two materials to the object, and then assigning one of the materials to a vertex-group, but I could not find a place to assign it.  I am making a striped bouncy ball that I want to deform, so adding a different material by separating the mesh into different objects would not be ideal. Half exact functor which is neither right exact nor left exact Synchronizing on String objects in Java Yesterday, I have received two : Revival, and Self-Learner. However I was only notified of the Revival badge, because apparently the Self-Learner badge is not considered "".  What badges have their notification suppressed if the user has a 200-rep account somewhere on the Stack Exchange network, i.e. they won't trigger a new item in our achievements dialog? The question is $$\text{If }\, p, \ q\in \mathbb{N}, \;1-\frac12+\frac13-\frac14-\dotsb-\frac{1}{1318}+\frac{1}{1319}=\frac{p}{q}.\qquad \text{Prove that } 1979\mid p.$$ So my solution went like this:  $$S=1-\frac12+\frac13-\frac14-\dotsb-\frac{1}{1318}+\frac{1}{1319}\Rightarrow S=\sum_{k=1}^{1319}\frac{1}{k}-2\sum_{k=1}^{659}\frac{1}{2k}=\sum_{k=660}^{1319}\frac{1}{k}$$ Now this is equivalent to finding the sum of the roots of the equation $$\left(x-\frac{1}{660}\right)\left(x-\frac{1}{661}\right)\dots \left(x-\frac{1}{1319}\right)=0$$. Rewriting this equation, we get $(660x-1)(661x-1)\dotsc(1319x-1)=0$ (we can discard the $\displaystyle \frac{1319!}{659!}$ since $1979$ is a prime). Calculating the sum of the roots, we get the required value to be equal to $(1320+659)\times 330$ which is obviously divisible by $1979$ (again discarding the coeffecient of $x^{660}$).  Now my question is: Using the same method of converting the problem into finding the sum of roots of a polynomial, we get from the original equation something like this: $$(x-1)\left(x+\frac{1}{2}\right)\dots \left(x-\frac{1}{1319}\right)=0 \Rightarrow (x-1)(2x+1)\dotsc(1319x-1)=0$$ So, the sum of roots would be $-1+2-3+4-\dotsc+1318-1319=-660$ But this is not divisible by $1979$. Why does the former solution work while the latter doesn't? Is there a flaw in my reasoning? Note: I know that the question can be solved by some other methods. Please only explain my given doubts and don't instead give another solution  I realised my mistake after some hours of pondering over it. (In the 1st equation) To get the required sum I would need to take calculate $\displaystyle -\frac{\text{coeffecient of }x^{659}\,}{\text{coeffecient of }x^{660}}$. However what I've done is calculate this:  $\displaystyle -\frac{\text{ coeffecient of }x}{\text{coeffecient of }x^{660}}$ which is actually equal to $\text{sum of roots taken }659 \text{ at a time} $. It was just a coincidence that the value I calculated was divisible by $1979$. The correct way, indeed, would be through the link supplied Why are comments overlapping the sidebar? On , the comments are overlapping the related questions sidebar. Is this something to do with the weird formatting of the first comment?    Browser: Mozilla/5.0 (Windows NT 6.0; rv:16.0) Gecko/20100101 Firefox/16.0 "Failed to create user" due to regular expression error Not sure if there is a cultural difference. In our family it is considered normal to frighten the child so that he behaves the way we want.  Example- Parent: Eat that quickly or the God will punish you! Parent: Don't go on the stairs. The ghost is hiding there and it'll catch you! Parent: Be quiet or the police will grab you!  Does this kind of behavior from the parent's side has any abnormal effects on the baby in the longer run? Can this behavior be accepted as normal?  Has any research been done on this aspect?