If two photons were to collide directly, head on, and are of the same energy, what happens? Are new particles created, is energy released? Or do they just pass through one another?
Could someone explain to me what the collision of two photons would look like? Will they behave like,   Electromagnetic waves: they will interfere with each other and keep their wave nature Particles: they will bounce like classical balls   I assume that energy of that system is too small to make creation of pairs possible.
Stored Procedures, MySQL and PHP The question is a fairly open one. I've been using Stored Procs with MS SQLServer for some time with classic ASP and ASP.net and love them, lots.  I have a small hobby project I'm working on and for various reasons have gone the LAMP route. Any hints/tricks/traps or good starting points to get into using stored procedures with MySQL and PHP5? My version of MySQL supports Stored Procedures. Macros for code annotations I am unable to find the link for downloading Ubuntu 16.04 onto my   desktop/laptop. I am able to see the link only for 18.04, but I need 16.04. find command: -or option doesn't work I want to execute a command for an each file that matches a pattern. But the command that seems to be right, doesn't work for me, I have no idea why.  $ find . -type f -name '*.c' -or -name '*.h' -or -name '*.cpp' -exec ls {} \; $ ls script.sh  test.c  test.h found a 1994 uncashed profit sharing retirement plan check If $\gcd(a,b)=1$, how can I find the values that $\gcd(a+b,a^2+b^2)$ can possibly take? I can't find a way to use any of the elemental divisibility and gcd theorems to find them. How to find bases for a subspace defined by an equation If Cooper wanted to stay, why did he send the NASA Coordinates? In Interstellar, after Cooper arrives in the Tesseract, Cooper tries to send the message STAY to his daughter in the past so she won't let him go on the mission. If that was his intention then why did he send the coordinates of NASA afterwards? If he didn't send the coordinates, he wouldn't have found NASA or go into space, he would have stayed. Explain travel times and distances on flight A flight from Los Angeles to ABQ is about 2 hours but is ~670.2 miles  A flight from San Jose to Chicago is 4 hours but is ~1859.0 miles  Can anyone explain why the travel time from San Jose to Chicago is not longer and closer to 5.75 hours?  If the distance increase by 2, shouldn't the time increase by a factor of 2 as well? How to manage users and groups using GUI? Just switched from 10.04 to 11.10. I'm wondering about the limited options in the GUI for managing users and groups. Where is the old GUI to change groups, id's, etc. I know that I can do this from cli, that's no problem. But I want this comfortable GUI back. Extended Rigid Bodies in Special Relativity I was reading Landau &amp; Lifshitz's Classical Theory of Fields and I noticed that they mention that an extended rigid body isn't "relativistically correct".   For example, if you consider a rigid rod and apply a torque at one end, by definition of being rigid, the whole body must start rotating at the same instant. But the information about the force being applied cannot travel faster than the speed of light.   The book hasn't mentioned how to resolve this paradox, and after thinking about it for a while, I'm wondering if one can even define a rigid body in a relativistically correct manner.  To summarize: How does one define a rigid body in special relativity? Prove $\int_0^\infty \frac{\sin^4x}{x^4}dx = \frac{\pi}{3}$ chown -R root.root / So I was working and there was a directory that I was periodically changing to my user in  a root terminal so that I could open the files in text editors, but I accidentally pressed / instead of . and this was the command I put out:  chown -R emil.emil /   Then immediately panicked ^C and put in another command, as I thought I could always change back the files I needed to access:  chown -R root.root /   So now I can't do su from emil to even try to fix this, as I'm getting permission denied error. I'm on Ubuntu could someone tell me if there is a way I could fix this, without absolutely reinstalling the whole thing.  TIP  If you are trying to get root access, and are getting this permission denied error when using su try this command:  gksu gnome-terminal   It will prompt you for the root password and open a new root terminal for some reason this works and gives me root access, when su doesn't. Can anyone explain how one would convert one voltage range to another? I'm going to need to convert a range of -10 to +10 volts into a range of 0 to +5 volts. How would this be accomplished? Thanks!   Let me say  something more. Inside of a torpedo there are gyroscopes. This gyroscope give -10 volts when the torpedo have 180 degrees of deviation to the west and 10 volts when the deviation is to the east. This signal is DC, so i need to change this range a range: 0 to 5 v DC . Thanks I noticed that there is a definition of the pvalue in my textbook is defined says the following:    I have no idea why it is written with a supremum. I've spent hours pondering this, does anyone have enough of a background to help me with this? Thank you! Uniform continuity of $\sin(x\sin x )$ for all $x\in (0,\infty)$ How to map stock ticker symbols to ISIN (International Securities Identification Number)? How can I can convert ticker symbols (which include information on the exchange) to an International Securities Identification Number (ISIN) (which contains no information on the exchange)? Also I am interested in the other way round — given an ISIN and a market identification code (MIC) how can I determine the ticker symbol? Any databases around? Why does an open interval NOT have measure zero? How to make child process die after parent exits? DataGridTextColumn.IsReadOnly seems to be faulty