This is a way to host a server that actually hide the IP of the server from the client, just like Tor hides the IP of the client from the server. Amazing tecnology!

This is why it enables hosting illegal things like the Silk Road: law enforcement is not able find where the server is hosted, and take it down or identify the owner.

Bibliography:

Considering e.g. Newton's laws of motion, you take a system that is a function of time $f(t)$, e.g. the position of many point particles, and then you reverse the speeds of all particles, then $f(-t)$ is a solution to that.

I guess you also have to change the sign of the gravitational constant?

Light watch transverse to direction of motion. This case is interesting because it separates length contraction from time dilation completely.

Of course, as usual in special relativity, calling something "time dilation" leads us to mind boggling ideas of "symmetry breaking": if both frames have a light watch, how can both possibly observe the other to be time dilated?

And the answer to this, is the usual: in special relativity time and space are interwoven in a fucked up way, everything is just a spacetime event.

In this case, there are three spacetime events of interest: both clocks start at same position, your beam hits up at x=0, moving frame hits up at x>0.

Those two mentioned events are spacelike-separated events, and therefore even though they seem simultaneous to you, they are not going to be simultaneous to the moving observer!

If little clock one meter away from you tells you that at the time of some event (your light beam hit up) the moving light watch was only 50% up, this is just a number given by your one meter away watch!

We looking at the definition the orthogonal group is the group of all matrices that preserve the dot product, we notice that the dot product is one example of positive definite symmetric bilinear form, which in turn can also be represented by a matrix as shown at: Section "Matrix representation of a symmetric bilinear form".

By looking at this more general point of view, we could ask ourselves what happens to the group if instead of the dot product we took a more general bilinear form, e.g.:The answers to those questions are given by the Sylvester's law of inertia at Section "All indefinite orthogonal groups of matrices of equal metric signature are isomorphic".

This game was mind blowing to Ciro Santilli and all kids. It felt so real. The perfect contrast between peaceful town work and saving the world. OMG.

Has the best opening scene of all time.

Top quotes:

There's nothing like seeing the hypocrisy of the "Liberté, Égalité, Fraternité" people destroyed.

Interesting how Algeria now supports China's Xinjiang policy in 2019. But of course, dictatorships tend to work together

Ciro Santilli's father, an avid history reader, and in particular interested in the military dictatorship in Brazil through which he lived, once told Ciro how the French torture doctrine was directly adopted by Brazillian military, e.g. then even invited general Paul Aussaresses who had served in Algeria, to help them out with intelligence operations and give courses. Bro, fuck that.

But of course, the Americans weren't too far behind in Guantanamo.

Respect, big respect to those people.

There aren't any 2020, except in the trivial one-time pad case where the key is as large as the message: crypto.stackexchange.com/questions/10815/how-do-we-prove-that-aes-des-etc-are-secure