I have some confusion about the concept of stationary and static.  A metric $g$ is called stationary if there is a time like Killing vector $K$.  $g$ is called static is further HSO (hyper surface orthogonal), i.e. there exists a foliation of hyper surface orthogonal to the integral curve of $K$.  The Schwarzschild solution requires $g$ to be static, and the Kerr solution only require $g$ to be stationary.  Here comes my question. To my understanding, requiring $K$ to be HSO is to enabling us to slice the spacetime into pieces with fixed time. The Kerr solution is for the metric outside a rotating body. In the note I am reading, it says      Do not require $K$ to be HSO, after all we want a rotating body.   Why a rotating body indicates that the metric cannot be HSO? I think I can also slice the spacetime into piece for every time.
I know that a stationary metric is one which possesses a timelike Killing Vector (so I have time invariance).  I read that a static metric is one which has a timelike Killing vector (so it is stationary) AND this Killing vector is orthogonal to a family of hypersurface (of dimension n-1 is n is the dimension of my manifold). I don't understand the "physical" meaning behind this definition ? Is there a way to explain this in some more intuitive way ? Thanks
So when we view reputation, there is graph view. However, it seems to be off by a day. Here's what I mean:   I'm sure 70 + 20 + 15 is not 15. Its 105, which is what we see below:   And 40 + 10 is NOT 105, unless you did  :)     Anyways 40 + 10 is 50:   So yeah. Did you do what that post on codegolf says? Devs better fix that :) Following on from this question:   It seems all feats carry over to your new form if your new form is capable of using them (so Mounted Combatant and Inspiring leader would usually be ruled as unusable in most circumstances). But what about Tough?     Your hit point maximum increases by an amount equal to twice your   level when you gain this feat. Whenever you gain a level thereafter,   your hit point maximum increases by an additional 2 hit points.   Would this increase your maximum HP by the same amount when in the form of a rat, or brown bear? Meta sites in "Your Communities" display different reputation Prove: If $\gcd(a,b,c)=1$ then there exists $z$ such that $\gcd(az+b,c) = 1$ Why time is considered a dimension? Why is time considered to be a dimension? And the other 7 (except the 3 dimensions of space, and the dimension of time) dimensions that string theory suggests, why can't they be realized? Adding coordinate system to layout in QGIS composer? I would like to know if there is a way to add a dynamic coordinate system field into a QGIS composer layout.  I can use an expression to add many items such as document name, file path, etc but I can;t seem to figure out how to add the coordinate system? Is it possible to test apex that relies on field history tracking? Does a controlled mount share its rider's turn? From "Controlling a Mount" on p.198 of the Player's Handbook:     The initiative of a controlled mount changes to match yours when you mount it. It moves as you direct it, and it has only three action options; Dash, Disengage, and Dodge. A controlled mount can move and act even on the turn that you mount it.   Does this mean that the rider and mount share a single turn? Sometimes I create Material Groups to be used as appendable reusable assets. Unfortunately sometimes parameters I want to control using a Group Node's slider are not available for routing to a Group Node's input socket. Some examples of these are the Color Ramp and the Mapping Node.  So here's what I want to do:    Can this be done? If so, how?  Thanks! Both the Romulans and the Federation have regularly violated the Treaty when it suits them. Starfleet has obviously developed and manufactured cloaking/stealth technology and the Romulans make regular excursions across the Neutral Zone. They obviously aren't declaring all-out war, so what penalties or sanctions have been imposed for violations?  -edit added for clarity-  Has either side ever 'punished' their own people for any violations of the Treaty? What happens if my ESTA expires on the day of arrival? What is the relation between electromagnetic wave and photon? To find tangents to given circle from a point outside it Find the combined equation of two tangents drawn from $P(x_1,y_1)$ to the circle $x^2+y^2 = a^2$. Point $P$ lies outside the circle. The order of words in a clause: "tell me who is the real man" vs. "tell me who the real man is" Closed form for $\sum_{k=0}^{m} {\binom {m}{k}} a^{k} (b+ck)^N$ Is there a closed form for the following?   $$\sum_{k=0}^{m}  {\binom {m}{k}} a^{k} (b+ck)^N$$      how about a pretty limit for large $b$.   I have tried using the binomial expansion for the $(b+ck)^N$ to convert the above expression to double sum and then tried to simplify the double sum which was not successful. Any idea if I have find a closed form for it? Determining ethnicity according to ancestry? Installing ChatJax bookmark on the iPad and iPhone In a world without air, I understand they definitely would. However, with drag taken into account, I think they wouldn't. Since the drag force varies proportional to the square of speed (ignoring the change in coefficient of drag with speed), wouldn't the total impulse due to drag on a bullet fired from a gun from a specific height horizontal to ground be higher than the total impulse on an identical bullet dropped from the same height with no horizontal velocity?  Also, when bullet spin is taken into account, the bullet fired from a gun should resist change in orientation; therefore, it should maintain a small but non-zero angle of attack, and also have a lift force, correct? "going to do" vs. "going to be doing" Note: this post is different to , which just cites part from somewhere else, without any further analysis and thinking. Furthermore, none of the answers to that post answers my question - the situations where &quot;will (going to) be doing&quot; is more appropriate.   I will be participating in IELTS test next Tuesday afternoon.  In an online class, the teacher says the following at the beginning of the lesson.  I will be using NotePod (pointed out by red rectangle) to write relevant points we talk about today.   I guess &quot;will be using&quot; is more appropriate than &quot;will use&quot; there, right?  A  explains  This &quot;tense&quot; is used for reporting a scheduled activity with special focus on its timing— as if one is standing in the future and experiencing the flow of the time. The focus is on the temporary, ongoing, or repetitive nature of the activity.   I understand the grammar rules of those verb tenses and the difference between this group  I am going to drive home tomorrow.   I am going to be driving home tomorrow.  The former is just convey my activity in the near future while the latter probably makes an implication that &quot;don't disturb me as I am driving in that time&quot; However, in the following situations, I don't see the difference between 2 verb tenses.  Welcome back to this class. Today's lesson is for the IELTS students who are going to be taking the IELTS test. it's for everybody to be honest with you. this lesson is useful for anybody who needs to do some writing.   who are going to take the IELTS test ... Can we start cleaning up [table] tag and burninate it ASAP Related questions:     (This led to founding of )   The tag  has become cluttered with all kinds of questions ranging from sql tables (for all DBM systems, HTML tag &lt;table&gt;, outputting content in any language (PHP, C#, LaTeX to name a few) as a table and several plugins of various languages and/or IDEs (like jTable, tablesorters and the kind).  The current count stands at 18,315 questions having this ambiguous tag. A few of possible suggestions for cleaning process:    +  to  |   +  to  |   +  to  |   +  to  |   + other-specific-DBM systems to whatever_DBM_it_is-table  +  to  |    Since I've no idea about other languages and their specific features regarding table, I'd ask the community for their input on this (such as , ,  and ). The other questions are either tagged with arrays or sql and similar tags, and in my opinion, just removing  from such questions would be enough!