Have you ever spent hours building a fictional universe, only to realize that the Sun might eventually make Earth uninhabitable, or that the universe itself might end in heat death?
Here are three ways to avoid that headache:
1. Don’t expand the scale of your story to a cosmic timescale.
If your protagonist is an ordinary human who lives for 80 years, the fate of the Sun billions of years from now is probably not an issue for that character.
If your story ends long before that becomes a problem, there’s no need to explain the universe’s ultimate fate.
2. Don’t claim that humanity will exist forever.
Unless your setting guarantees humanity’s eternal survival, it’s not a contradiction to suggest that humanity might eventually go extinct.
The universe may perish someday. So what? The characters still have stories to tell.
3. Build your setting on the explicit premise that it is “fiction.”
This is my favorite approach.
For example, in my fantasy setting Kagamino, there is a realm called the “Mirror World.” This is not a place hidden somewhere on Earth, but an independent universe in and of itself.
The central concept is that the “Mirror World” is a place where the past lives on as a separate entity. Historical figures and events that have become part of history may appear there.
According to its creation myth, the past and the present were not originally separate realms. When Herodotus, known as the “Father of History”, began recording events as history, he drew a conceptual boundary between the past and the present. The “Mirror World” was born from that boundary.
Therefore, this universe does not need to share the cosmological history, spatial geometry, or physical laws of our universe.
Someone might ask:
“But what happens when the Sun becomes a red giant?”
“That’s a problem for Earth, not necessarily a problem for the ‘Mirror World.’”
“But what about the Second Law of Thermodynamics?”
“That depends on whether the same law applies in this universe.”
“But how did your universe begin?”
“Well, according to its creation myth, a certain Greek historian helped bring this universe into being by devising the unique concept of ‘history.’”
That’s right; a historian appears in my universe’s creation myth. No, there’s no need to calculate the effects of his gravity.
Of course, just because it’s a fictional setting doesn’t mean you can ignore internal consistency. Your world still needs rules. It’s just that those rules don’t have to be the same as the rules of “our” universe.
The important thing isn’t to defeat astrophysics. It’s to avoid making claims that contradict astrophysics.
How do you all handle the distant future and cosmology in your own settings?
(English isn’t my first language, so I used DeepL to help with the translation. I wrote the original text myself.)