There is no way fiction in general sees it. Different fiction treats them differently. But as example here the explanation of concepts from Owari no Chronicle.
Spoiler
Ooshiro gave a bitter smile and said, "Unless you jump into the air, what is set as the ground will be constantly updated for you. In other words, the world always exists below your feet in this space. The concept related to gravitational pull has been altered."
"I see," said Sayama as he let go of Shinjou's hand. He looked toward Ooshiro and continued, "What exactly is this power?"
"Let me ask you something instead, Mikoto-kun. How do you think you could explain this power? What if you met with academics and intellectuals from around the world and asked them what power can alter the world so conveniently?"
"They would say it is a trick."
"Exactly. However, this is the truth. Now, another question. …What basis would they use for determining this is a trick?"
"That is obvious. This breaks the laws of physics."
"Yes, yes. Indeed it does. Light is bent by gravity, but with this power, light only bends according to the direction set as the ground for it. Even if the real ground is in a different direction. But Mikoto-kun, when you talk about the laws of physics, what world's physical laws do you speak of?"
"This world's physical laws."
"Then let me ask you something else. If alternate worlds did exist, on what basis would we determine they are different from our own? The terrain? The atmosphere? The life forms? Or perhaps the culture?"
With that question, Sayama realized the answer to it all.
He finally said, "Is this what you want to say? There was a world with physical laws fundamentally different from our own. And this power we are seeing follows that world's laws!"
"Precisely. This world's physical laws cannot be applied to other worlds. A world with different physical laws will naturally overturn the very basics of the physical laws we know."
"But there have to be certain absolutes, right? Like the motion of light."
"No, no. Even that is based on this world's physical laws. When light is emitted, it spreads and continues on. But why does it do that? Why can't there be light that does not do that?"
"That is…"
"That is simply what light is in this world, right? But," Ooshiro took a step forward so their gazes would match perpendicularly, "what if light being that way was actually quite rare?"
"…"
"We only know how things work in this world. We assume the workings of this world are absolute. But what if there were a great number of other worlds and it turned out the rules of this world are great exceptions compared to the other worlds?"
"But we do not know of any other worlds, so we can only assume they would be the same as us."
A bitter smile appeared on Ooshiro's lips when he heard that response.
"True," the old man said. "But another world is another world. They are fundamentally different. What we think is simply 'how things are' and what the other worlds think is simply 'how things are' are fundamentally different."
"Are you saying," Sayama looked down at his feet, "there is a world where this is how gravity works?"
Ooshiro nodded, walked over to the opposite window, and stood on it. He looked straight up toward Sayama.
"The ten other worlds and this world are perceived as individual gears and so we refer to them as such. 1st-Gear through 10th-Gear all had their own unique characteristics. And do you know what we called this power of 'how things are'?" Without waiting for an answer, Ooshiro said, "Concepts. We called them concepts! They are a power that can control even the laws of physics. They are the ultimate reason behind everything. That is what concepts are!"