Do electrons accelerating in the presence of a gravitational field radiate due to this acceleration?
A charged particle undergoing an acceleration radiates photons.  Let's consider a charge in a freely falling frame of reference.  In such a frame, the local gravitational field is necessarily zero, and the particle does not accelerate or experience any force. Thus, this charge is free in such a frame. But, a free charge does not emit any photons. There seems to be a paradox. Does a freely falling charge in a gravitational field radiate?
Calculate the components of a unit vector that lies in the xy-plane and makes equal angles with the positive directions of the x- and y-axes It's just a doubt.  $\vec { A } = A \hat{ x }  + A\hat { y} $  $ A\hat { y} =A\hat{ x} $  $\vec { A } = A \hat { x }  + A\hat { x} $  Now finding the magnitud of the vector,  $A=\frac { 1 }{ \sqrt { 2 }  } $  So the components of the unit vector are:  $\vec { A } = \frac { 1 }{ \sqrt { 2 }  } \hat { x } +\frac { 1 }{ \sqrt { 2 } } \hat { y} $  Is my answer right? In the Futurama episode "" they save the world by rotating the Earth backwards saying it shouldn't matter (which direction Earth rotates). If Earth rotated clockwise and remained in it's current counter-clockwise orbit around the Sun, would it affect anything beyond the direction the constellations move across the sky? What really allows airplanes to fly? How to increase the width and height of the Rich Text area field in Visual force Page? I can't get grub menu to show up during boot How to enable hibernation? In Ubuntu 12.04 and newer, . How can I enable this back? When do I pronounce a non-existent “r” between adjacent vowel sounds? If I say two words consecutively, with the first ending in a vowel sound and the second starting with one, when is it correct to include a non-existent r between those two words?  Examples from phrases I've heard:        I saw (r)a movie   They saw (r)us   Law (r)and order   That's the idea, (r)anyway.      I heard the last one in the movie Edge of Tomorrow yesterday.  Is this grammatically correct? If so, is the omission of the r grammatically incorrect? Are there any rules regarding this? I need to echo a string containing angle brackets (&lt; and >) to a file on a Windows machine.  Basically what I want to do is the following: echo some string &lt; with angle &gt; brackets &gt;&gt;myfile.txt  This doesn't work since the command interpreter gets confused with the angle brackets.  I could quote the whole string like this: echo "some string &lt; with angle &gt; brackets" &gt;&gt;myfile.txt  But then I have double quotes in my file that I don't want.    Escaping the brackets ala unix doesn't work either: echo some string \&lt; with angle \&gt; brackets &gt;&gt;myfile.txt  Ideas? Finding the variable name passed to a function How can I pad an integer with zeros on the left? There has been some recent behavior change on SE (around July 2015).  I have two accounts I use, one Google openId based for one set of sites (call it Account-A) and another SE login based for a different set of sites (Account-B).  Used to be that I could be logged into one set of sites with the first user and a different set with the other users.    But now I am logged in with the Account-A on Site-1.  When I go to one of the sites I use the other account for and click "log in" under the SE menu, I go to a page where I only have an option to confirm creation of an account based on my Google login.  It does not present a way to log in with an SE account.    How can I log in with my other account here?  (and before you flag this as a duplicate, please ensure the other question is recent enough and that the answer is relevant.  This behavior has definitely morphed over the years... and I am having trouble finding something that is relevant.  For instance this question  simply points out how to merge the accounts which is NOT what I want  .  This question  talks about presenting different user info on each site but that's not what I want -- I want totally separate accounts). Is this a plant or a fungus? It was soft and covered in flies. My guess is fungi.  Location: South Florida. Top Bar background does not persist when scrolling horizontally Update  A month Several months later, a new top bar, and the bug still exists. An answer has already been posted that would fix the bug, so is this something that the dev team plans on fixing?  There are also a host of other problems caused by this, especially on the  and . Again, this would be fixed with  html{min-width:1000px;}   There is a slight bug with small windows on both the new meta and main site(s)?, shown here. The problem is that the top bar coloring doesn't stretch across when you resize and scroll left or right.        On Meta, when a horizontal scroll bar is needed, the black background will only be as wide as the width of the viewport, but when you scroll the coloring will not shift.  To reproduce:   Make screen as large as possible, or wait until the menu bar starts expanding Make it smaller and smaller until horizontal scrollbar appears, then scroll left and right. Quick-and-dirty way to ensure only one instance of a shell script is running at a time Korean characters scrambled [XeLaTeX; Noto Sans Korean]? I was trying to find a font which has obsolete jamo and the right combining behaviour. Yesterday I found out about , which seems to have both of these. However, when I use it in XeTeX, I get some seemingly-arbitrary hanja (or blank spaces) instead of the expected characters.  (I’m guessing the composing behaviour will fix itself when the right characters are selected. And yes, I know that Code2000 is working perfectly in this example, but unfortunately it is the ugliest font in the world. :p)  MWE:  \documentclass{article} \usepackage{fontspec}  % 1. precomposed: U+BB47 % 2. separate jamo: U+1106, U+116E, U+11BA % 3. obsolete [separate jamo]: U+113B, U+119F, U+11EB \newcommand\test[1]{#1 &amp; {\fontspec{#1}{뭇; 뭇; ᄻᆟᇫ}} \\}  \begin{document}  \begin{tabular}{rl} \test{Arial Unicode MS} \test{Batang} \test{Code2000} \test{Gulim} \test{GungSeo} \test{HeadLineA} \test{Nanum Brush Script} \test{Nanum Myeongjo} \test{Nanum Pen Script} \test{Noto Sans Korean} \test{PCMyungjo} \test{PilGi} \test{Adobe Gothic Std} \test{Adobe Myungjo Std} \test{Apple SD Gothic Neo} \test{AppleGothic} \test{AppleMyungjo} \end{tabular}  \end{document} When may adjectives precede determiners? (E.g. too difficult a task) The expression too difficult a task sounds a little pompous, but it doesn't sound ungrammatical. According to my folk-beliefs about English grammar, determiners precede adjectives. However, the expression too difficult a task seems to controvert that belief.  Additionally, the expression too difficult of a task seems grammatical too.    Under what conditions may determiners precede adjectives? Are there conditions under which too difficult of a task would be a more grammatical expression than too difficult a task would be?   (This question does not ask what the question “How big of a problem” vs. “how big a problem” asks. That question does not pertain to determiners.) Challenges with Key with Gaps? How to display the final value of a counter at the beginning of a document? Can I start a new Clash of Clans village on my iPhone separate from my account on my iPad? If I download Clash of Clans on my iPhone, can I start a new village despite my account on my iPad? I want to make a village for my younger brother. Idiom/Phrase for "results without work/effort" I'd be greatly appreciative of a cleverly devised idiom/phrase that depicts the following concept:     Results without work/effort.   ...and/or...     My Work/Effort; Your Result.   Any idioms/phrases you can recount or conceive would be of use.    Contextual Edit:  The idiom/phrase should be in the context of service offering/hiring or task delegation, not free-loading as most answers thus far have understandably assumed. E.g.     [You hire me for] My Work/Effort; [My work/effort produces] Your   Result.