For cosmic jets produced in gamma ray bursts or quasars, I've read that you have to assume a "Force-free magnetosphere" in order to explain these phenomena through electromagnetism. From my understanding, force-free means that the particles from the accretion disk have velocity along the lines of the magnetic field, but my question is how did the particles get velocity in that direction in the first place?
Related:   I have put a bit of commentary enumerating my confusions in parentheses  I read in Black Holes and Time Warps (Kip Thorne), that quasars can generate their jets from four different processes. These all involved the accretion disk, but there was one which doesn't make quite as much sense. It was called the Blandford-Znajek process, and it involved magnetic field lines carrying current.  The process was visualized in two ways. A black hole, with magnetic field lines, is spinning. In the first visualisation (viewpoint actually), the magnetic field lines 'spin' along with the black hole, and nearby plasma is anchored onto the field lines by electrical forces (where did the electrical fields come from?). The plasma can slide along the field lines but not across them (why?).  Since the field lines are spinning, centrifugal forces will fling them up and down the field lines, forming jets.  The other viewpoint is this, and it makes even less sense (to me that is, I haven't had a formal education in GR): The magnetic fields and the swirl of space generate a voltage difference across the field lines (Why? How?). The voltage carries current across the magnetic field lines (why are the field lines behaving like wires?). This current travels across plasma, which accelerates it, creating the jets.  Now the main thing that doesn't make sense, is that magnetic field lines are behaving like wires. Why would they? I suspect the answer lies hidden somewhere in the equivalence of EM waves in different frames, but I can't think up any convincing argument from that side.  If the answer involves GR equations, you don't need to solve it here (wouldn't make sense to me), but if you have to, just refer to the equation and what you did to it, along with the final result. Thanks!
Black hole "no hair" theorem The  (or conjecture), suggests that black holes can be entirely described by their mass, angular momentum and charge. All other details of the BH formation are lost.  Is there a simple way of understanding why you would be able to tell the difference between a BH made from protons and one made from electrons, but not between one made from matter rather than anti-matter?  i.e. What is special about charge, and why aren't lepton number, baryon number, strangeness etc, also black hole properties? Why isn't the 'len' function inherited by dictionaries and lists in Python example:  a_list = [1, 2, 3] a_list.len() # doesn't work len(a_list) # works   Python being (very) object oriented, I don't understand why the 'len' function isn't inherited by the object.  Plus I keep trying the wrong solution since it appears as the logical one to me I'm getting pretty close to the reputation where I can start to edit others' posts, and I'm wondering what the etiquette for when (and when not) to do so. I figure that I should edit in the following circumstances:  Grammatical or spelling errors. Clarification where the meaning is not changed. For instance if the title does not describe the question very well. Where the user has made a very minor mistake that doesn't justify a full post to clarify. To add related resources or links that will help someone answer the post, or provide context  Before the commenting feature was added, I noticed that some moderators edit posts in order to insert a reply or extension to the post. I feel this isn't good etiquette (but I could be wrong) because I don't know what to do with their changes when I come to re-edit or respond. I also feel that I should be very careful not to change the meaning of any question or answer, even if that meaning is misguided. What other rules would be best practice?  Signatures and fluff are discouraged and are fair game to be removed.  See, for example, this post by  and this post by  and also see .  Also see Jeff Atwood's response in the comments to Fix for Hibernate error "Use of the same entity name twice" How you fix the following Hibernate error:  What does "Use of the same entity name twice". How to determine capacitance I’m looking to install a capacitor in a circuit which runs at 12V and &lt;10A, and I want it to discharge in about 3 seconds.   The discharge voltage isn’t too important, but it’s probably best if it is as high as possible (not higher than 12V if that is even possible) for those 3 seconds.  The discharge time can be longer but probably should have an absolute minimum of 1.5 seconds.   Sorry if this sounds like gibberish. If I'm not giving enough info, please let me know what else i need to provide. I’m not an electrical guy; just working on a project and have no clue what I'm doing. What is the ancestral form of language used in the fable that David was studying during the flight? David studies linguistics during the flight to LV-223. We get to listen and read a fable. Is it written in a real language? What is the name of the language? Can the fable be translated?  Approximate quotation:     hjewis jasma hwaelna nahast akwunsez dad'kta, tam ghermha vagam ugenthe How to prove that $z\gcd(a,b)=\gcd(za,zb)$ I need to prove that $z\gcd(a,b)=\gcd(za,zb)$.    I tried a lot, for example, looking at set of common divisors of the two sides, but I can't conclude anything from that. Can you please give me some advice how I can handle this problem? And $a,b,z \in \mathbb{Z}$. Imported CSV data is not displayed in QGIS Why can't my subclass access a protected variable of its superclass, when it's in a different package? Google Chrome doesn't seem to respect my DPI setting in Windows. I run at 150 DPI, but Chrome ignores that, meaning that images and text are teeeeeeny tiny.  I hit:   Ctrl + + Ctrl + +   to zoom in. Unfortunately every new tab, or new window, defaults to the 100% teeny tiny zoom level.  Update: It's also important to note that you cannot click buttons in flash (e.g. YouTube videos), because Chrome mis-handles mouse coordinates. (Fixed 6.0.472.55)  Is it possible for either:   Chrome to respect my Windows dpi setting? Chrome to remember my zoom preference?   Checked version: 4.1.249.1045    Half fixed    While Chome still doesn't honor the Windows DPI setting, it does now remember your zoom level.  Version: 5.0.375.55    Five-Eighths Fixed    While Chrome still doesn't honor the Windows DPI setting, it does now offer a default "page zoom" option:    Unfortunately there is no zoom level that matches my current DPI setting: 136% (131dpi).  Version: 10.0.648.133  Zoom flag  I tried scoducks' suggestion of the new hidden dpi flag. It's truly awful. It seems to cause Chrome to simply re-scale the final rendered Window; causing text to become blurry (rather than sharper): Implications and Ordinary language I want to express $$\sum_{n=-\infty}^\infty \dfrac{1}{(z+n)^2+a^2}$$ in closed form. What comes to mind is the formula $$\pi\cot\pi z = \dfrac{1}{z}+\sum_{n\ne 0}\left(\dfrac{1}{z-n}+\dfrac1n\right)=\dfrac{1}{z}+\sum_{n=1}^\infty\dfrac{2z}{z^2-n^2}$$  and also $$\dfrac{\pi^2}{\sin^2\pi z}=\sum_{n=-\infty}^\infty \dfrac{1}{(z-n)^2}.$$ But neither of these gives the term $(z+n)^2+a^2$ that we want. Perhaps we can adjust somehow? Marketing Cloud IP Warming - is it critical that we send up to the weekly limits by domain? Word for dismissing someone's opinions as racist, liberal, etc, instead of debating back I'm looking for either a single word or phrase that would describe either someone or the action of dismissing someone's opinions as something "socially unpopular", without giving any reasoning why, either just to spite them, because they have a poor counter-argument, have been backed into a corner, or something similar.  For example, someone who supports something politically incorrect (like, say, stronger gun control or help for male domestic abuse) might have their views dismissed as racist or sexist or liberal without actually acknowledging and debating against them, thus labeling the former as something they might not be.  I was talking to a friend earlier about politics, and she complained about Germany's immigration problem. She said one issue was that many politicians that try to support stronger immigration laws would immediately be shot down as racist or a nazi and forced to resign, instead of being presented with counter-arguments. Regardless of whether you agree with them or not, what would describe that?  EDIT: Forgot to specify -- the word or phrase I'm looking for would be used in an informal context. And to address further questions, to be used when the person's opinion has legitimate worth and isn't just "being racist" etc, i.e. the dismisser is incorrect, and is only making these accusations because they can't argue further. (Added emphasis to the last sentence of the first paragraph) Determining the characteristic of a field mod [= remainder] operation (and relation), name and meaning I am trying to write the Euclidean algorithm in the following way:  $A = \lfloor A \div B \rfloor \times B + (\text{remainder of}) \: A \div B $   Now is there any symbol I can use  to say "remainder of A $\div$ B"? I know that in the C programming language there is the operator % for modulus; is that a valid symbol in maths? Can I write A % B? Or is there some other way? Benefits and Drawbacks of Swapping Associations of Positivity and Negativity of the Proton and Electron For historical reasons, I understand that a proton's charge was assigned the label of "positive", the electron's charge was assigned the label of negative, and, crucially, equations of current in E &amp; M are written with the notion that current is the flow of positive charge despite the rarity of actual flows of protons in real systems (which I understand are mostly biological systems).   If the possibility existed to instantaneously and at no cost, retcon these associations such that protons have a negative charge, electrons have a positive charge, and current remains the flow of positive charge, would there be any beneficial or detrimental outcomes?  For instance, would there be:   new interpretations of physical laws that would provide different or better insights into any relevant subfield of Physics significant simplifications to notation in any field of Physics or Engineering significant increases in understanding in the fields of electricity, electronics, electrical engineering, radiation/radiative transport, etc. a noticeably easier learning curve for any subfield of physics dealing with the concept of charge   Additionally, is there a permutation of positive charge, negative charge, and flow of current definition that would improve upon the one I suggested? Error: You are missing the following 32-bit libraries, and Steam may not run: libXtst.so.6 [...] I'm aware that many people are having problems on launching Steam (downloaded from Steam not the repos) on Ubuntu 16.04 64-bit with this error message:  svetlana@svetlana-desktop:~$ steam Running Steam on ubuntu 16.04 64-bit STEAM_RUNTIME is enabled automatically Error: You are missing the following 32-bit libraries, and Steam may not run: libXtst.so.6 libXrandr.so.2 libgobject-2.0.so.0 libglib-2.0.so.0 libgtk-x11-2.0.so.0 libpulse.so.0 libgdk_pixbuf-2.0.so.0 Installing breakpad exception handler for appid(steam)/version(1463778979) Installing breakpad exception handler for appid(steam)/version(1463778979) Installing breakpad exception handler for appid(steam)/version(1463778979) Installing breakpad exception handler for appid(steam)/version(1463778979) [2016-05-22 16:33:15] Startup - updater built May 20 2016 18:57:58 [2016-05-22 16:33:15] Opted in to client beta 'publicbeta' via beta file You are in the 'publicbeta' client beta. Looks like steam didn't shutdown cleanly, scheduling immediate update check [2016-05-22 16:33:15] Checking for update on startup [2016-05-22 16:33:15] Checking for available updates... [2016-05-22 16:33:15] Download skipped by HTTP 304 Not Modified [2016-05-22 16:33:15] Nothing to do [2016-05-22 16:33:15] Verifying installation... [2016-05-22 16:33:15] Performing checksum verification of executable files [2016-05-22 16:33:15] Verification complete [2016-05-22 16:33:16] Shutdown   My question has anyone found a solution yet? Thick annulus (ring) in 3D How to delete (invalid) files with colon in their name under Windows? I've got a rather large number of files on my Windows drive that have a colon in their name. (These came from unpacking some Unix archives.)   When I try to delete them, Windows (XP) complains that the file does not exist, and refuses to delete it. This happens when trying to delete or rename it from explorer or the command line. Still, chkdsk does not complain about those files nor fix the problem.   Any ideas on how to get rid of them?