Based on the popular theory that Gaster fell into his “creation” when being a scientist, it must’ve happened in Undertale since in deltarune the game is set in just a normal town (no lab or scientist needed in a small town right?).
So when sans and Papyrus escape to Undertale (theoretically) AFTER gasters disappearance,
How would sans know about all the timeline science, anomalies and overall quantum physics (judging by the fact that they haven’t spent much time in snowdin)?
Wouldn’t he have to have at least some years of experience?
And if he didn’t get his amazing knowledge on quantum physics and other scientific capabilities from Undertale, then he must’ve gotten that knowledge from deltarune.
But there are no scientists in deltarune…
Alphys, a scientist in Undertale, was a teacher when we saw her in deltarune.
So even if an alternate deltarune Gaster was there with sans and Papyrus in hometown, he couldn’t have taught them anything so extremely complicated and vast (being in a small rural town and not having the necessaryresources), since there are no labs, accommodations nor any shifts to scientific studies there (hometown is quaint and small). The only way Gaster was able to continue his experiments and projects (like the core) in Undertale was because King Asgore was aiding him in his research.
Sure deltarune Gaster could've been intrested in quantum physics or science and all that, but he wouldn't get far with it, he'd leave it as a side hobby or interest. Leaving him to focus on other things, such as maybe being a teacher or a professor of sorts (or maybe someone’s therapist, wink, wink).
So sans must've learned about quantum physics during his stay in Undertale, whether it was during his free time or with the help of Alphys, or maybe his knowledge on this topic really did stem from deltarune. Its hard to say with these things.
Oh well, case closed (kinda), let's pack things up and-
Wait..
If Gasters from Undertale, and Papyrus and sans (theoretically) came from deltarune...
Then where the hell are Undertale sans and Papyrus????
Deltarune Papyrus and sans appeared out of nowhere in snowdin, if there was an Undertale sans and Papyrus previously some monsters of the underground were bound to know them for sure.
But they dont.
None of them did. Snowdin, Hotland, Waterfalls, the Ruins, etc., no one in any of these places knew them before.
Its as if Undertale sans and Papyrus.. never existed.
Just like Gaster.
Then they must've been erased from existence during Gasters "creation" swallowing them whole with him. Then they must've turned into goners or Gaster followers. Right?
Right???
Alas, the answer is no. We dont see Goner Papyrus or Goner sans (or Papyrus and sans as Gaster followers)
We don't know or see anything about their past anywhere in the underground.
Undertale sans and Papyrus really did just disappear.
The only thing we see is the replacement. Deltarune sans and Papyrus.
Maybe that is the reason Papyrus and sans have a kind of cheating power over the game.
Because they're not supposed to be there, the game itself knows that, but the code fits, so they are not seen as errors or bugs in the game.
They are seen as the originals by everyone and everything.
Yet their minor mishaps and slip ups show that there is definitely something more to them thats not tied to their powers.
Things like walking on air, altering game mechanics, changing the screen, skiping a turn in battle, knowledge of resets, seeing from our perspective, pranking someone across time and space, copying an entire house to another game, stopping time, shortcuts and etc.
So what was the relationship between Papyrus, sans and Gaster then?
We know from the undertales 10th anniversary stream that the doors from sans’s and Papyrus’s house are the exact same as the one to Gasters room. Which means that Gaster lives (or at least lived) or is somehow connected to the brothers.
Along with other clues such as the gaster blasters, Papyrus’s forgetability and more
Also, during the secret boss fight with Gerson, we get a dialogue scene with him speaking of an author going insane from his creation. Although he is definitely referencing himself, with him being a writer in deltarune and all, he could also be referencing Gaster, since in a way he also went insane from his creation.
Gaster seems to refer to deltarune as “his”
So deltarune is like an experiment for Gaster.
Now you might ask : So.. how could sans and Papyrus come from deltarune if Gaster made it?
Gaster didnt make deltarune, Toby Fox did. Gaster is just simply observing the world, and adding in his own kinds of experiments.
In the game its literally stated : Your choices don't matter.
I believe Gaster is further continuing his experiments in deltarune, adding in diffrent routes, hidden clues, hidden bosses and etc. since he knows that the game will end the same way either way. Our choices dont matter much less do his.
He knows that. Thats why he's taking it to his advantage.
