Why would a photon striking an electron "make both recoil"?
If photons have no mass, how can they have momentum?
I have 3 tables and I have to inner join Table A with Table B but a left outer between Table A and Table C.   Can I combine outer and inner join in the same query? I can nest queries and attain the desired result but I am unable to do both the joins in the same query. It appears that in other SQL languages, the order of joining is important. Is this the case in SQL Server as well?    Ok, here's the scenario.  Consider 3 tables. Table A, Table F, Table D.  I will need the recordset to contain all rows in D irrespective of whether it exists in F (after it's inner joined with A). So, a outer join comes to mind. What I would need is:   First do a inner join between A and F to get a set (this may be a null set) Then do a outer join with the recordset in (1) with D Repeating something with (1/n)th chance of success n times Is there anything that can be said about how many attempts it will take to correctly guess a random number out of 1000 numbers? If the number wouldn't change the probability would just increase every guess, giving in the end a probability of 1.  If the number changes every guess tough, you just have a 1/1000th chance everytime. Can it be calculated how many attempts it would probably take, on average?  (I'm sorry, i'm not very skilled in probability maths) Can I clear an area of my prison for everyone BUT max security prisoners? How do I install transition molding between my new hardwood and existing tile floors? I have ripped out some old carpet and am preparing to install a new solid hardwood floor myself.  In several places, the floor transitions to an existing tile floor.  The hardwood floor guys told me the best transition between the two is a T molding.  You simply leave a gap between the two floors, and then place down the T molding between the two floors, so it sits on both surfaces.  Sounds simple enough.  However, the height difference of the two floors is considerable, and the T molding does not sit flush.  What are my options?  Here is a diagram showing the dimensions.      NOTE:  Using the T molding is not a requirement, I could go some other route if there is a better option. Take any three random variables $X_1$, $X_2$, and $X_3$.   Is it possible for $X_1$ and $X_2$ to be dependent, $X_2$ and $X_3$ to be dependent, but $X_1$ and $X_3$ to be independent?  Is it possible for $X_1$ and $X_2$ to be independent, $X_2$ and $X_3$ to be independent, but $X_1$ and $X_3$ to be dependent? When to use \par and when \\, \newline, or blank lines Renaming hundreds of files at once for proper sorting Why did a Dementor try to take Harry's soul in the train? In "Harry Potter and the Prisoner of Azkaban" - when Harry and his friends were travelling to Hogwarts by train, the train stopped in between and Dementors were searching for Sirius Black. Why did one of the Dementors try to take Harry's soul? How do I use a C# keyword as a property name? Using asp.net MVC I'd like to do this inside a view:  &lt;%= Html.TextBox("textbox1", null, new { class="class1" }) %&gt;   This statement does not compile because class is keyword in C#. I'd like to know how I can escape the property names such that this compiles.  It is possible to get this to compile if I change the "class" property to "Class" (uppercase C). But this is not suitable because strict xhtml says that all attributes (and element) names must be lowercase. PHB says 'once per turn,' so, it would seem that a Rogue with Sentinel, for example, could "consistently" deal Sneak attack twice per round (whether the enemy triggers an OA or the melee weapon attack provided by the Feat).  So, can rogues deal sneak attack damage with any weapon attack outside their turn? (obv. one that meets the standard requirements--finesse, adv or adj ally) How to show that the monomials are not a Schauder basis for $C[0,1]$ why the monomials are not a Schauder basis for $C[0,1]$?  $p_n(x)=x^n$ such that $(p_n)$ does not form a Schauder basis for $C[0,1]$  span$\lbrace p_n : n\ge 0\rbrace$ is dense in $C[0,1]$ by Weierstrass approxmation theorem, but I cannot figure out why they are not a Schauder basis.  Could you please explain Hide textfield blinking cursor If votes works differently on meta sites how does that of accepting answers work? In the faq of meta sites you can read something like the following:     Voting here works a bit differently   from other Stack Exchange sites. On   Meta Stack Overflow, voting is used to   express agreement or disagreement, not   to point out a lack of quality or   helpfulness. Please don't be concerned   if you receive downvotes – members of   the community may simply disagree with   your bug, feature request, support   issue, or the nature of the   discussion.   My question is: If votes works differently on meta sites how does that of accepting answers work?  Take for instance a question on a meta site that is meant for the community to discuss some issue. What does it mean if the question is accepted? Accepting an answer is up to the author of the question so it cannot be a sign of what answer the community concludes from the discussion. It could mean that the discussion is over but that should be up to the community and not the author of the question. Is it so that accepting an answer for a discussion question on a meta site does not have a particular function? What happens when you plug two sides of a cable to a single networking device? What is likely to happen when you plug two ends of a network cable to a single switch/router? Will this create problems on the network, or just be ignored? Finding the inverse of the arc length function Is my Ubuntu vulnerable to SambaCry? I read these two threads:         And I got a little bit worried, is my Ubuntu machine safe? Or am I vulnerable to this vulnerability?  The second article mentioned that:     The flaw actually resided in the way Samba handled shared libraries.   The other thing that they say is all versions from versions 3.5.0 onwards since 2010 are vulnerable.     At that time, nearly 485,000 Samba-enabled computers were found to be exposed on the Internet, and researchers predicted that the SambaCry-based attacks also have potential to spread just like WannaCry ransomware widely.   .   I don't have a samba server however I've got samba-libs package installed.  What, if anything, should I do?  I'm running Ubuntu 16.04. When solving this issue (  ), I did a function so that the plugin would auto-hide from all users except one (me:).  The flaw is that it only auto-hides when active.  At first, it was a mu-plugin, but I had to enable/disable it manually. It really doesn't need to run all the time, as it may slow the site (?) or even contain some sensitive manipulation of the site's language (another question mark).  But mainly the motivation is that I don't want the client activating/deactivating/deleting this plugin (is for my own use), and don't want it cluttering her own plugins list.  So, decided to split the functions in two plugins:   One is a Must-Use used to hide the regular one.  The other will be activated/deactivated upon necessity and is the one from the above linked issue.   But now I run into another question: how to hide one plugin from the Must-Use listing? How to simulate slow internet connections on the mac What's a good software solution to slow down internet connections on the mac for testing and simulations?  My primary need is when testing code in the iPhone / iOS simulator, so slowing down the connection for specific applications or processes would be great. How do I save/remember last-used window position and size for applications? How can I retrieve mp3 metadata in Python?