The mass-energy equivalence is a principle which can not be derived from anything? Not duplication) I couldn't find the answer for the general case, instead of the special case that I already seen in Youtube I hyperlinked.  I will fully satisfy with not only a mathematically rigorous proof, but also just any argument.  For example, I was impressed by the thought experiment(in Youtube :  ) arguing the equivalence principle for the special case that the rest mass of an object actually turned out to be a part of total energy of the object.  Is there any argument like that, but for the general case that the total energy(= rest E's + kinetic E's + potential E) of a system must be the total mass of the system which determines the amount of gravitational attraction and resistance for an acceleration? I think it might require the general relativitistic consideration.
How to derive $E=mc^{2}$? Is there some way to derive ? I can understand that energy in something is proportional to its mass, but the $c^{2}$ part. I have no idea. It seems like the way the units are going it would end up as $kg*(m/s)^{2}$, which I think is the unit for Newtons, not energy. And why is there no constant of proportionality $k$? Did Einstein just set it up perfectly so that there wouldn't be one?
Conditionals (Past Tense) In terms of conditional sentences, is it correct to say:   if you knew why I WAS here, then I wouldn't need to be here.   or   If you knew why I WERE here, then I wouldn't need to be here.   Which type of conditional is this? Type 2? I was thought at school that there are three types of conditionals. Are there more of them? Delta-like symbol in LaTeX I'd like to write a majuscule delta-like symbol in LaTeX but I can't find it's syntax anywhere. You can see the symbol on equation (12) of the following paper:  "". How to declare a variable inside bash -c I can't figure out how to declare a variable inside bash -c command.   bash -c "var=3; echo $var" How can I use Web.debug.config in the built-in visual studio debugger server? How to add a space between a string for every 5th letter? Consider the partial sum of the divergent Harmonic series $H_n = \sum\limits_{k = 1}^{n}\frac{1}{k}$. I recently saw a question which required finding out the asymptotic bounds of $H_n$. Now, I could not find any bound closer than $O(n)$. So I looked up the series and found  Wikipedia article which says that $H_n - \ln n$ approaches a constant (the ). This clearly shows that $H_n = \Theta(\log n)$.  However, considering the question was in an beginners undergraduate algorithms course in CS, I was wondering if there is a simpler proof of this? Is there some clever proof requiring elementary mathematics to show $H_n = \Theta(\log n)$?  PS: This is not homework in the sense that it is not my homework, and the actual question does not ask for a proof, but rather asks a lot of functions to be arranged asymptotically. how to make some border lines of a table thick and colored I'm making a call:  myResult = MakeMyCall(inputParams, out messages);   but I don't actually care about the messages.  If it was an input parameter I didn't care about I'd just pass in a null.  If it was the return I didn't care about I'd just leave it off.    Is there a way to do something similar with an out, or do I need to declare a variable that I will then ignore? bash command for each file in a folder I have a set of files on which I would like to apply the same command and the output should contain the same name as the processed file but with a different extension.  Currently I am doing rename /my/data/Andrew.doc to /my/data/Andrew.txt I would like to do this for all the .doc files from the /my/data/ folder and to preserve the name.  I tried several versions but I guess I have something wrong in the syntax as I an new to linux. How do I get:  $$\cos{\theta} \lt \frac{\sin{\theta}}{\theta} \lt 1$$ It  to disable internet search results in start menu searches before the Windows 10 Creators Update, but I've just clean installed a new Windows 10 Pro image and that setting is gone. Is there some way to disable it through editing the registry/etc? SHA-256 "almost unique"? I have seen numerous references on the internet of people describing SHA-256 as generating an "almost unique" hash.  . there are more.  Is there some mathematical basis to the almost uniqueness? I would have thought that as SHA-256 is an evenly-distibuted (?) hash algorithm which can accept any message (infinitely many) as an input and produces a fixed length (finite) hash - then there will in fact be an infinite number of each possible output - which I would think hardly qualifies as "almost unique".  Is there a basis for this statement? Am I going to have trouble flying without my full name on the ticket? PermGen elimination in JDK 8 We all know you can't do the following because of ConcurrentModificationException:  for (Object i : l) {     if (condition(i)) {         l.remove(i);     } }   But this apparently works sometimes, but not always. Here's some specific code:  public static void main(String[] args) {     Collection&lt;Integer&gt; l = new ArrayList&lt;&gt;();      for (int i = 0; i &lt; 10; ++i) {         l.add(4);         l.add(5);         l.add(6);     }      for (int i : l) {         if (i == 5) {             l.remove(i);         }     }      System.out.println(l); }   This, of course, results in:  Exception in thread "main" java.util.ConcurrentModificationException   Even though multiple threads aren't doing it. Anyway.  What's the best solution to this problem? How can I remove an item from the collection in a loop without throwing this exception?  I'm also using an arbitrary Collection here, not necessarily an ArrayList, so you can't rely on get. Whenever I try to do a fluid simulation, the fluid domain remains visible.  I have tried:ctrl+a-scale, turn on/off visibility for render/viewport  Here's a video demonstrating my problem:   Here's the blend file in case I have messed up some settings:   Thank you for any help! A singularity, by the definition I know, is a point in space with infinite of a property such as density.  Density is Mass/Volume.  Since the volume of a singularity is 0, then the density will thus become infinite because Mass/0 = undefined  However, is it possible to have a singularity with a mass of 0? 0/0 is indeterminate, but would it be possible for a singularity to exist even if its mass and volume were zero? Someone from Mars is called a Martian. Someone from America is called an American. Someone from Europe is a European. Someone from Hyrule is a Hyrulean.  We are not far from colonizing other planets, let alone Earth's only moon. Obviously you wouldn't call someone from the moon a lunatic right? What if you are on Mars? What would I call a foreigner from Earth? Earthean doesn't sound right. What are the different colors on the unity launcher icons? Example:      My question is simple.  What are the different colors representing in the unity launcher background for each icon.  I mean, it seems consistent (firefox is always orange), but it's not jumping out at me what the pattern is.  On my screen, it's:   Firefox: Orange Chrome: Yellow Terminal: Grey RDP App: Blue KeyPassX: Green NetBeans: Blue   I'd like to turn it off if possible, but first I'd like to understand more about it.  Any launcher experts? Real valued analytic function defined on a connected set is constant