From Einstein's principle of relativity space-time and mass are relative to the frame from which they are being observed.  Now would that mean a ball moving at the speed of light wrt to earth would become a black hole for an observer on earth but stay normal for an observer moving with the ball at same speed?  If not then how would you justify the observation of infinite relative mass ball not turning into a black hole from the earth frame of reference?
I'm a big fan of the podcast Astronomy Cast and a while back I was listening to a Q&amp;A episode they did. A listener sent in a question that I found fascinating and have been wondering about ever since.   From the show :      Arunus Gidgowdusk from Lithuania asks: "If you took a one kilogram mass and accelerated it close to the speed of light would it form into a black hole? Would it stay a black hole if you then decreased the speed?"   Dr. Gay, an astrophysicist and one of the hosts, explained that she'd asked a number of her colleagues and that none of them could provide a satisfactory answer. I asked her more recently on Facebook if anyone had come forward with one and she said they had not.  So I thought maybe this would be a good place to ask.
Fluent and Query Expression — Is there any benefit(s) of one over other? If I want to draw an overline over some text, not an equation, how can I do it? \overline seems to only work in math mode, and when used outside of math mode, it automatically says "Missing $ inserted". I have seen both usages.    Stay tuned on our Facebook page to know more  Stay tuned to our Facebook page to know more    But don’t know which one is more appropriate. Please help me figure it out. Thanks Can I hire my kid and start a Roth IRA for him? I own an LLC, of which I am currently the sole member. It's my main source of income.  I am wondering if there is a reason why I could not do the following:   Hire my child as a part-time employee of the LLC, for an annual salary of $5500. Start a Roth IRA for the kid and put the $5500 into it. Deduct the $5500 as a payroll expense for my LLC, thereby reducing my amount of taxable income.   To me, this seems attractive because I'd lower my LLC's tax liability. Meanwhile, my kid would not have to pay any taxes on the $5500 because it is lower than the standard deduction. And by putting the money in a Roth IRA, he'd get an investment that would grow tax-free. It would essentially be like getting the pre-tax benefits of a traditional IRA with the post-tax benefits of a Roth.  The way I see it, I'd win, my kid would win and the IRS would lose, for once.  Is there any reason this wouldn't work? There is no minimum age or income for contributing to a Roth IRA. So as long as I could legally hire my kid, I don't see any obstacles. The external Flash is not showing up in the configuration Menu when using Pixel TF-321 hot shoe. Is this the wrong adapter for that camera, as there is no X connection? I want to trigger a studio flash via sync connection. Can you recommend me a working hot shoe? Thanks! How many "Recommend Close" votes is too many? How do I know I have the correct exposure when shooting in manual mode? I have a Canon XTI which I've been using for a few years now. Most of the time I'm been shooting in one of the "semi-manual" modes like aperture priority or shutter priority, but now I'd like to try using full manual mode. I should have a new EF-S 17-55 f/2.8 delivered when I get home today. Before I was using a variable aperture Sigma 17-70 which made manual mode more difficult with the aperture changing arbitrarily.  I understand the effect of changing aperture and shutter speed, but right now I'm accustomed  to only controlling one at a time. The camera is usually setting the other to get the right exposure automatically for me. So if I'm controlling both how do I know I have the correct exposure? I understand I need to use the metering in my camera but I'm not sure exactly how do do that.   First when should I be using each of the metering modes (Evaluative, Partial, Center weighted, or Spot)? These just change the area of the scene which is metered correct?  How do I know what the meter should read off a specific object? Obviously if I just happen to be shooting a 18% gray wall then it should be at zero, but that can't apply to everything? If I'm shooting a black cat and take a spot meter reading off of the cat then the meter should read less then zero right? But how do I know how much less then zero? Are there rules of thumb I can follow? I've ordered a couple gray cards with my new lens. So experimenting with those should help.  How often should I be changing these settings? Say I'm at a party indoors which is consistently lit. I should be able to set the aperture, shutter speed, and ISO and just forget about it unless the lighting changes correct? Does the same apply to outdoor scenes? I've been hesitant to use manual mode in the past because I felt like I was spending a lot of times messing with settings before each shot. But not I'm realizing that this is really only the case when the lighting changes, or I want a different style of photo such as a different depth of field.  Finally, does exposure change with distance to the subject? For example say I want to take a picture of a statue with correct exposure using a gray card. I'd place the card on the statue, and while being careful not the block the light on the card find the correct exposure by spot metering the card. If I were then to step back 20' to get the whole statue in frame would I still have the correct exposure? How to search something on across multiple sites with a single Google query? I tried   (search term site:stackoverflow.com) OR (search term site:superuser.com) OR (search term site:stackexchange.com) search term site:stackoverflow.com,superuser.com,stackexchange.com search term site:stackoverflow.com site:superuser.com site:stackexchange.com   None of them works. What is the correct way to search? Redirect non-www requests to www on Amazon Route 53 I want to redirect all requests from example.com to www.example.com.   Preferably, this should happen at DNS level. I tried using PTR records, but that simply fails, returning a 404.  wwww.example.com is an ALIAS for an Elastic Load Balancer.  What’s the simplest way to achieve this? How should I install HPLIP binary/proprietary plugin/driver for my HP printer or printer+scanner? No space following macro without argument With a macro such as:  \def\naive{na\"{\i}ve}   I find that the space which I would hope to follow it, is absent. So, with  the \naive approach   I get     the naïveapproach   in the output. How do I bring back the space? Best way to put commas into large numbers I've started a new job and it involves looking at a bunch of big numbers. Is there an easy way to add commas to an int or decimal field to make it readable?  For example, SQL Server outputs the column on the left, but for my own sanity, I need it to look like the one on the right:  2036150 -&gt; 2,036,150     ...or would I have to write some heinous   left(right(vandalized_data),6),3) + ',' + right(left(vandalized_data),6),3)   function?  The perfect thing would be commas in the display grid, then plain integers in the output. Install Win7 theme on Ubuntu 16.04 I'm totally new to Ubuntu. I've installed version 16.04 and I'm having trouble finding my way around. I've tried just about all possible ways to make Ubuntu look like windows 7. Every way I tried was missing something, Is there a way to make version 16.04 be like win7? Addressing a former office-holder by that office's title When is it appropriate to use an "expired" honorific to address or refer to a person?   In the U.S., former state governors are occasionally referred to as "Governor So-and-so", although they have not held that office for several years. I see this happening most often when the former governor is actively campaigning for a new office (usually U.S. President), and my impression is that it's done only by someone with an interest in the campaign (for or against) rather than a (relatively) neutral party like a newspaper.  Certainly this could be used as a jab: in a political campaign for high office, addressing one's opponent by a former title — lower than one's own — could imply that the opponent is not qualified for the new job. It could also be used the other way around, to remind listeners that a candidate one supports used to hold an important title.  I'm curious whether there are formal rules for this in the U.S., or at least style or journalist guidelines, for various offices. Are ambassadors, for example, entitled to some sort of emeritus honorific? Any way to see mail sent by other user through shared address? My wife and I have a "shared" email address, like thesmiths@example.com which we both use from Gmail when we both want to get replies or for signing up for certain websites.  When an email is received at that address, it gets forwarded to both of our personal Gmail accounts.  The problem is that when either one of us "sends as" that address, the other does not see the sent message. So we have to cc or bcc each other (and she usually forgets.)  Is there any automagic way to have those sent emails appear in BOTH of our Gmail accounts?  I've tried filters but I don't think they work on outgoing messages. Basically we want a filter that would automatically forward emails from that address to the other person.  I know this can be done with standalone mail clients, but neither of us uses those. I live in Ethiopia and the government blocks all urls with the word "proxy" in them. I couldn't use that word in the title above because that would make the url contain the word proxy.   When I apt-get upgrade I get errors because some packages like libproxy1, libproxy1-plugin-gsettings, libproxy1-plugin-networkmanager, python-libproxy all contain the p word.  Therefore, it is all blocked. I tried putting the urls into proxy sites, but they all just returned to their home page.   Are there any other solutions? Best VNC / remote desktop software for assistance Poll on best VNC / remote desktop software for assisting others on Windows/Mac machines from Ubuntu?    I've heard good things about TeamViewer and Fog Creek Copilot, but I'm wondering if the included GNOME Vinaigre VNC client is good enough for this.  To specify, I'm looking for best option based on:   SIMPLEST ease-of-use for client to download/use on their end. See #1. Works cross-platform I am able to control client's mouse and/or keyboard from remote machine. Let $a,b,c$ be $3$ distinct integers, and let $P$ be a polynomial with integer coefficients.Show that in this case the conditions $$P(a)=b,P(b)=c,P(c)=a$$ cannot be satisfied simultaneously.  Any hint would be appreciated. Here are two sentences:        Once he got the passport, he went to the Chinese consulate in Toronto and applied for a visa.   Once he got the passport, he went to the Chinese consulate in Toronto to apply for a visa.      Are the two sentences grammatical, and do they sound natural?  If they are both fine, what's the difference? How can I approach implementing the following in Drupal 7?  What I need to do is create a module which defines a new fieldable entity, called 'Company'. I have a list of, let's say, 20 fields that need to be filled out by each Company instance. These questions are predefined and some may contain custom validation.  At the moment, I'm at the point when I can add new fields to the Company entity. This works fine at the moment. My issue is that I need all these fields to be there as soon the module is installed, so adding them via the interface isn't an option.  I was wondering how can I approach this? I'd assume it comes down being able to do what can be done using the 'Manage Fields' UI programmatically.