Board Thread:General Discussion/@comment-26980570-20160320192450/@comment-27907368-20160322205151

You know, I've been thinking about why sans doesn't go back to his time. I think it may have to do with one pesky flower and one pesky human.

He's not from our time, I'm going to assume - going off of his speech in genocide. He gets super mopey about how he can't go back and how the surface has no appeal (because we're going to reset it).

So, we know Gaster lives in the past, before Alphys. I believe that he and sans knew of the multiverse and that the timeline ups and ends at some point... perhaps this is an allusion to the game Undertale ending as Toby didn't make us a game that spans the rest of time. Just one day.

(Side note on this, with the clarified dialogue to 'clam' girl I believe this more to be so. Her dialogue changed from "There is nothing else you can do" to "There is nothing else you can do today." As a player, we are bound to a certain chunk of time because the game ends. If we could keep forward, we would be able to change more or have our main characters live out all of the Surface 'ending'.)

Gaster fell into his machine - whichever that was. Perhaps one dealing with the multiverse. My head canon is that he committed suicide, but that's speculation. sans went in search of the anomaly using a time machine. And boy, he found it. He became stuck in one of the timelines that were shifting left and right - courtesy of Flowey. Such as the Underground, you can enter this period of time but you cannot exit it. (speculation, again. I'm enjoying this. c:)

So, perhaps the machine will never work again because DETERMINATION makes it impossible for sans (and PAPYRUS?) to leave. Space time would chew them up and spit them back out where they were, according to sans' calculations. So, he won't risk leaving his brother alone or his brother's life to fix it.

Thanks for getting me thinking on this stuff, guys!