The Essential Runes for disciples I also accorded a special place for the Yin and Yang notions. Their respective runes were the last runes to be presented. In the explanations at the end, the manual described the 5 elements as an extension or development of Yin Yang. That was why the 5 elements all presented some form of duality. The Yin and Yang didn't just manifest in each element but in their relationships too. There are two types of cyclical interactions between the 5 elements: generating process and overcoming process. Water generates wood, that generates fire, that generates earth, that generates metal, that generates water. As for the overcome cycle, it follows Water, Fire, Metal, Wood, Earth, and back to Water. Those two cycles are another embodiment of yin yang.

Han Lingyun hadn't comprehended the intricacies here yet but he couldn't focus on everything at the same time so he put all those technicalities at the back of his mind for now. There was so much to learn already and he had to prioritize his learning schedule well.

The Second manual, An Introduction to Arrays, was mostly a description of rune interactions with one another.

Array making, like a magic treasure creation, revolves around inscribing runes and arranging them in some specific ways to create a particular effect. There are still some major differences between the two fields.

Treasures are made to be handled by a cultivator, so their use must remain simple and intuitive. Most of the time, forgers work on their choice and combination of materials, and tend to avoid inscribing runes, thereby altering the materials true nature. On a microscopic level, every material is composed of miniaturized runes made by combinations of qi particles, just like with the matter is composed by an arrangement of molecules that are themselves built with atoms. Refining can be seen as "cleaning" all the unwanted or detrimental natural runes so that the material can display the desired properties.

Under that analogy, the qi particles would be the atoms and the runes the molecules. Rune making was thus similar to chemistry: making molecules react with each other to get something different in the end.

Han Lingyun grimaced as he came to that realization.

This analogy wasn't very accurate though, as there wasn't any qi particles and runes were more complicated.

Han Lingyun continued reading. Interestingly enough, at the origin, according to the manual, the arrays and weapons were found mostly with blind guessing. At first, the concept of array and of weapon wasn't defined but that separation rapidly emerged.

Arrays are often defensive, fixed constructs. They don't need a cultivator to be operated and found their energy from qi crystals.

The large area of formations enables their creators to artificially inscribe runes who function like a hidden code for an automation.

Some high-level arrays could also be controlled by a cultivator but as the manual put it: 'that's not a problem a beginner should start with.'

The original approach of experimentation to create arrays rapidly hits a limit when one is trying to build more powerful, complex and diversified creations. Finding new runes isn't enough and increasing the number of runes exponentially lowers the odds of a lucky result, with often the effects of runes canceling each other out.

As the knowledge of runes advanced, the cultivators thus had to search for more methodological approaches, and rune calculation was born. Rune calculation is basically doing math with runes. How to predict the result of two runes being combined in that way? Are there other ways to combine those two same runes and get a different result?

Cultivators managed to build sets of rules and operations that didn't depend on the rune they used. Equivalents to adding or subtracting effects, multiplying and other special operations were found. Once basic principles are found, it becomes way easier to combine a 3rd rune, a 4th, 5th, and so on.

In a sense, rune is a language, just like math or the common tongue. The limitations are mostly the implementations on the material realm and the array master's understanding of a rune.

If you think about it, even the common tongue has its own words for basic operations with the coordinating conjunctions (for, and, no, but, or, yet, so). Punctuations and other word construct fill the other needs.

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The difficulty is to express the right meaning, one can put words next to each other but the resulting sentence wouldn't express anything except some nonsense. To give a simple example "pill mouth put shelf apple" doesn't say anything. But if you rearrange the words, add prepositions, articles, conjunctions, punctuation and you can get:

"Put the pill in your mouth! And the apple on the shelf!" which has a different meaning to

"Put the pill in your mouth and the apple on the shelf." or

"Put the apple in your mouth and the pill on the shelf." or even

"The mouth put the pill and the apple on the shelf."

Rune calculation follows similar principles, only much more complex. Just like words, the nuances of the runes are often restricting the types of operations that could be applied with other runes and their own conceptual meaning shifts depending on the other runes around.

Ever since the discovery and formalization of rune calculations, array creation had shifted from being a profession that progressed with experiments, to a field that theorized new arrays before installing them.

Arrays can be very costly and an array master cannot afford to make a mistake in his deductions.

In general, cultivation plays an important role in array masters capabilities. Those at a higher realm would have a better understanding of the runes, calculate faster. Not only would their combinations be more profound but the runes they inscribed would reflect their own cultivation level and thus be applied in more ways. However, the relation also goes the other way: an array master that progresses in his understanding of the formation field would find his cultivation bottlenecks loosen. This process is similar to how sword cultivators that advance in their philosophy and understanding of the sword find less difficult bottlenecks.

These laws attracted Han Lingyun from a profound level as he studied the runes and their operations.

But ever since he had gained an initial comprehension for the true nature of runes and array masters' tasks, he had a thought constantly nagging at him.

Array creation still depends on one's understanding of runes and cultivators often observe nature to get inspired. However, for some reason the cultivators of this world only have a shallow understanding of the physics behind the phenomenon they observe. They seem to attribute most of what they can't comprehend immediately on their lacking cultivation. And indeed, a higher cultivation should let them brute-force comprehension.

Because cultivation seemed like the answer to everything, technology and scientific knowledge seemed to be rather left behind. Or there was just a lack of interest from the cultivator's society.

'But then, doesn't my knowledge of physics give me a huge understanding boost?

The rune notions and material counterpart could be considered as a spiritual idea's projection to the material realm. Then rather than a distant observation of a phenomenon, it would be a huge step forward to be able to model that behavior!'

Han Lingyun thought back to the description of the Water Rune he had worked on previously. It lacked his scientific knowledge!

For all the notions of water associated to its liquid form, Han Lingyun remembered his academic years where he had to engrave an equation to his mind in fluid mechanic's class.

po*(du/dt + (u.V)u) = -VP + mu*V^2u + po*F

V.u=0

Here u represents the speed and this equation describes the movement of a fluid. V.u=0 just expresses the conservation of mass, and the larger equality is the equivalent of Newton's second law for fluids: mass * acceleration=Force, m*a=F.

Mass*acceleration = Internal Forces + External Forces

po * Du/Dt = -VP + mu*V^2u + po*F

F, representing the external forces, is often just gravity.

Han Lingyun took a moment to just admire the beauty of that equation. Modelling the aggregate behavior of millions of water particles in only a couple of symbols. Describing the behavior of so many different phenomena, from the evolution of a fluid in a tube, to how air moves, to that of a river joining the sea and even to giant clouds of gases on galactic scales.

All in a single line.

There was an issue though, solving this equation in a particular case is very hard. Most of the time in Han Lingyun's previous life, solutions could only be found in simplified cases or the calculations were done by computers to find approximate solutions. It wasn't even known if there always exists a solution in 3 dimensions and if a solution is unique!

Basically, the equations work for all practical uses all the time but there are no mathematical proofs that it would always be the case. It is still enough for Han Lingyun to apply the equations and try to get a deeper understanding of their underlying truths hidden behind its simple form.

For Han Lingyun, the equation really had an indescribable beauty and attraction. As he woke up from his reverie, Han Lingyun had another idea of a trail to follow: the molecular construction of water. Two Hydrogens and one Oxygen. The atoms elbowed configuration, give the molecule its polarity, and this property is essential for life.

Its polarization enables water to have amazing dissolving properties. Thus, water became the ideal medium to transmit substances in and out of a cell. Then, because liquid water flows, it can transfer substances from cell to cell. Finally, with some chemical reactions, life can be born from that water.

Han Lingyun's physical knowledge could explain on a deeper level the how of many of water's notions. Again, because the water on the planet could be interpreted as a projection of its concept on the material plane, gaining a better understanding of its behavior would surely translate to getting a better understanding of the concepts it depicted. It would still be an impossible task to try and apply the same method for all the runes he learned.

At least that was Han Lingyun's point of view which reflected the way he perceived the world. This way of thinking was heavily influenced by his previous life and Han Lingyun realized it well but this wasn't a bad thing. Unlike the cultivators around him, he had seen another type of society, a society in which technology was stronger than its creators. Most importantly, he had accumulated enough additional knowledge to make his elders rethink view of the world.

Anyway, Han Lingyun had a lot of work to do on runes, including the exercises elder Wen had provided him, while still maintaining his cultivation speed, and even training his blackbird art. He already felt like he didn't have enough time on his hands!