Yay for video game wrapping! 

2D is slightly easier to understand, so I actually understood this blog entry quite well.

As for new entries in the future, I have been quite interested in Diffie-Hellmans lately. It does include wrapping. We are living in a modern world that requires security, and there are ideas like these and they somehow work so well, is very interesting. Also, quantum computing might break these securities, because they have public keys (compared to symmetric keys).

The definition of entropy that I like defines entropy as the number of states available to a system as a function of temperature. For example, gas particles in a vessel have more accessible combinations at higher temperatures. An important fact for this is that each accessible states is for a certain set of macroscopic parameters: temperature, pressure, volume. You won't see a gas spontaneously condense to a liquid and transfer its heat to a surrounding medium.

Imagine a ball on a hill. It has potential gravitational energy. It rolls down and that potential energy is converted to kinetic, and through friction, thermal waste heat. This thermal energy increases the number of states accessible to the atoms, thus increasing entropy. You cannot add heat to a ball and make it move up hill.

This is the entropic arrow of time. But this is not the same as time travel that we see in fiction. Maybe you can make entropy decrease. But this does not mean that you will see a reversal of a macroscopic process. You are as likey to see a totally different macroscopic process. Maybe the ball rolls in a different direction. And this is only for one system. Imagine the super complex interactions of all the macroscopic systems on our planet, or the universe.

So maybe you can make the ball roll back up the hill, but that doesn't mean everything else is going backward in time. If you wanted to go back in time then you would need to reverse every microscopic (statistcal mechanics) process in the universe, and make them all go exactly in the reverse direction (classical mechanics).

@Splashee I don't know much about cryptography, what I know is that there is actually some analogy between it and thermodynamics. I mean that some processes are easy in one direction and hard in the other one. For example factoring a large number into primes consumes a lot of computing power, while multiplying the factors back is very easy. Similar processes are used in cryptography, but I'm not really familiar with the details about the specific methods, like Diffie–Hellman you mentioned. And you're right that the situation can change due to quantum computing, but there is also quantum cryptography, which makes it impossible for a third party to obtain the information and remain undetected.

@Merry Brony 42 You're right that it's unlikely to be able to orchestrate everything in a way that decreases entropy. It's the problem of creating a Maxwell Demon, which is actually impossible due to the energetic cost of erasing information. What I mean here is that a spell can work by transferring the system to the other world, where it naturally evolves in the opposite direction than in ours, and then transferring it back. So it will appear as if it breaks the second law, but actually it's not broken in any of the two universes.

Because going to a different universe is much simpler than breaking the laws of thermodynamics  Ok, fine, but think of these things: Do you really need an explanation if you're just telling a story? And does that explanation raise more questions? Sometimes all you need is the appearance of an explanation. Sort of like technobabble in Star Trek. Make it look like there is a science to the magic, but we don't actually see any explanation.

@Merry Brony 42 Perhaps it's not important for most people, but for me it is. I prefer a story where things that happen have an explanation that make sense. It doesn't have to be perfectly reasonable and consistent with all known laws of physics, but there should be at least some degree of rationality in it. It's better for me than just hand-waving.