Many of the students had read Introduction to Cosmology before and had a basic understanding about the distribution of parallel worlds. They nodded in agreement.
But some of them didn't know much about the universe. Although they were aware of the existence of parallel worlds, they didn't understand why two worlds would collide.
Outside the Heaven's Origin Sector were boundless stars and an endless vacuum. Even the closest galaxy was thousands of light years away. They couldn't imagine how the collision took place.
Seeing the confusion in their faces, Mao Feng further explained, "Yes, from a three-dimensional point of view, all the different worlds are located in the same universe in their respective galaxies.
"The Heaven's Origin Sector is in one of the galaxies, while the Blood Demon Sector is in another.
"Theoretically speaking, there are no barriers between the parallel worlds. We can sail anywhere we want freely. The only thing that stops us is the long distance.
"With the current level of technology in the Heaven's Origin Sector, if we refine a crystal warship that can sail in the universe, it might take us millions of years to reach our neighboring galaxy. Or the parallel world next to us, if you will.
"In the three-dimensional level, the Heaven's Origin Sector and the Blood Demon Sector are at two ends of the universe with a very long distance in between. There's no way that the two of them will ever be related.
"But if you were to jump out of the three-dimension and move on to a higher level, everything would be different.
"In a higher dimension, every parallel world is a sealed egg that is placed next to each other in a way that we can't comprehend. If two eggs are too close, there will be attraction between them which may lead to collision and even fusion of a brand new parallel world.
"The Heaven's Origin Sector and the Blood Demon Sector is exactly such a double-world system.
Noticing that many students were still confused, Mao Feng took out a piece of white paper and drew one circle on either side of the paper.
"See? Let's say this piece of paper is a two-dimensional universe, and the two remote circles stand for the Heaven's Origin Sector and the Blood Demon Sector respectively.
"In the two-dimensional level, the two worlds are far from each other. There is no way for one of the worlds to reach the other one, let alone crushing.
Mao Feng folded the paper. The two circles that had been on opposites sides now overlapped.
"If a strong power can break the two-dimensional rules and understand this fictional universe in the three-dimensional level, it will find that the two worlds are right beside each other.
"This is the relationship between the Heaven's Origin Sector and the Blood Demon Sector, too
"As two galaxies, we are at different areas of the universe with trillions of light years in between.
"But as two parallel worlds in a higher dimension, we're very close to each other like the two circles on the paper. That's why there is attraction between the two worlds that eventually leads to the collision.
"Chances are that, one day, the two circles will merge into one!
"Alright, as battle-type Cultivators, you've learnt enough already.
"The more profound theories will be explored by the research-type Cultivators.
"Anyways, just remember this: The Dark Desolate Domain is the point of impact between the Heaven's Origin Sector and the Blood Demon Sector. Spiritual energies from both worlds intersect here, making this place the most abundant, furious and chaotic in either of the worlds."
This argument was very simple. Everybody understood it immediately.
It was like the intersection of two seas where the resources carried by undercurrents congregated.
Mao Feng continued, "The rich spiritual energy here consolidated into all kinds of Heavenly Materials and Earthly Treasures and mother crystal lodes. They also provide nourishment for the intimidating mutant demon beasts and demonic plants. This is a treasury that boasts inexhaustible resources.
"Despite the ample natural resources, the place is too far away from the federation. Besides, the spiritual fluctuations here are too fierce for large-scale crystal fleets to sail.
"If our main troops were deployed here, they might get caught by the spiritual energy swirls and be torn into pieces by accident!"
The students were reminded of the thunderstorm last night.
It was not a common thunderstorm, but a violent tide caused by the clash of the spiritual energies from two worlds.
The crystal warships that the Heaven's Origin Sector could produce at present were not capable of sailing against such spiritual energy tides.
A war in reality was not a game. It was a money-burning task.
Countless crystals and resources would be consumed for a single quest of a large-scale fleet.
If the fleet were to be scattered by the tides after a long march, the huge military expenditure would be for nothing. And this was not counting the loss of soldiers.
It was also the reason why the Star Glory Federation, after five hundred years of bloody battles, still failed to conquer the Dark Desolate Domain.
Their biggest adversary was not the demon clan but nature itself.
"Listen up, everyone. Strong as the crystal warships may be, they cannot cruise in the Dark Desolate Domain. Here, Cultivators, especially us Exos, are the boss. We are the main forces in the war!"
Mao Feng's words ignited everyone's passion. They all couldn't wait to start hunting demon beasts, plundering Heavenly Materials and Earthly Treasures, and increasing their own ability right now.
Mao Feng pressed his hands down and eased everyone. He continued, "This is about everything related to the Dark Desolate Domain. For the next month, you will be fighting and training here. A fifth of the Heavenly Materials and Earthly Treasures that you collect will go to the training camp, of which half will cover the repair fee of your crystal suits and half will be the instructors' payment. Is that okay with everybody?"
Their crystal suits were all provided by the training camp. It would be costly to fix them if they were damaged. The repair fee seemed reasonable.
The instructors' payment was even fairer.
The five instructors were all above middle-level of the Building Foundation Stage. With the enhancement of the crystal suits of the latest models, they could wield the strength of the Core Formation Stage.
It was under the protection of the five Cultivators that the students dared to fight and train in the Dark Desolate Domain at ease.
Otherwise, they would be committing suicide if they decided to train here, considering that they were all merely in the Refinement Stage.
A tenth of their harvest as payment for the instructors was a deal that couldn't be fairer.
Mao Feng nodded his head, then he brought up something else.
"Alright, since there is no objection, we'll start our training now. But before that, I need to remind you of something very important.
"The Dark Desolate Domain is full of dangers. Thunderstorm zones and dust storm zones are ten times more frequent and stronger than those outside.
"There are also strong mutant demon beasts lurking in darkness waiting for their prey.
"However, none of the above are the most appalling thing.
"The most appalling thing here is the infiltration squad of the demon clan, which is made of the elite soldiers in the demon army. Some of the squads are even made up of silver-blood demons exclusively!"
Everyone gasped at Mao Feng's words.
Li Yao recalled the composition of the demon clan.
Different from mankind, the demon clan was not a unique species, but a collective name for the unification of countless kinds of demon beasts.
Sometimes, the difference between two demon beasts was even bigger than that between a demon beast and a human being.
For example, some mammal demon beasts, especially the primate ones such as demon monkeys or demon apes, looked very similar to human beings, but entirely different from the arthropod demon beasts such as the Gold Armored Saber Mantis.
Why would a monkey consider a mantic to be its own kind, even if the latter had wisdom?
Moreover, many demon beasts were natural enemies and on different parts of the food chain. They had been attacking each other for billions of years. The hatred had melted into their blood.
Therefore, since the Demon Beast Empire 40,000 years ago, strong demons had been oppressing weak demons by ruthless coercion, who then enslaved and shackled the weaker demons.
After 30,000 years of development, four classes had been formed in the Demon Beast Empire.
In the bottom were the black-blood demons, who served as food, peasants and cannon fodder.
Black Armored Saber Mantis was a typical black-blood demon.
They were the main force for the invasion to the Heaven's Origin Sector and also inexhaustible cannon fodder. Even if they were to go extinct, high classes of the Blood Demon Sector wouldn't feel the least bit sorry about it.
Above the black-blood demons were bronze-blood demons, which was a class of warriors.
The Six-Armed Naga that Li Yao came across in the Verdant Tarn City was a bronze-blood demon.
On the top of the bronze-blood demons were silver-blood demons, who were the aristocrats and governors of the world of demon beasts, as well as the main contributors of the demon clan civilization.
One could say that only the demon beasts equal to or higher than silver-blood were the real demons. The black-blood and bronze-blood demon beasts were nothing but slaves or food in their eyes which were no different from human beings, if not worse.
After all, human beings had established a great civilization. Many of their creations were popular among the demon clan, too.
As for the gold-blood demons, also known as sacred-blood demons, were the royals of the world.
During the Demon Beast Empire's 30,000-year reign over the cosmos, more than ten dynasties had replaced one another. Royals of the dynasties all spent boundless resources to improve the quality of their blood, thereby increasing their strength. That's why they were called 'sacred-blood'.
However, during the substitution of dynasties, the sacred-blood demons often turned against each other.
After the Star Ocean Imperium was founded, the Supreme Emperor commanded the annihilation of the sacred-blood demons which almost exterminated them.
Now, the sacred-blood demons only lived among legends. There might not be a single sacred-blood demon in the entire Blood Demon Sector.
The current Blood Demon Sector was made up of hundreds of demon cities created by silver-blood demons. The cities were fighting and merging in conflicts.
An infiltration squad entirely made up by silver-blood demons was like 'the Imperial Guards' of the ancient kingdom. One couldn't think too highly of them.