Talk:Sans/@comment-76.78.240.209-20151117045618/@comment-25609899-20151117054437

Yes, Sans can time travel, which is why one of the phone calls mentions that he's somehow in multiple sentry stations at once, and why the key to his room is "suddenly" on your keychain.

The best theory (I can come up with) for why he can do this but not circumvent the barrier is because he was assisting Gaster with experiments. Gaster, being the Royal Scientist, is tasked with using science and research to get past the barrier. His research led him to figuring out how time travel works (something already established as possible because it's an innate ability of Determination), sharing the findings with Sans, and then attempting to time travel back to before the barrier. The barrier, being made from 7 of the most Determined humans, exists in no certain point in time, so Gaster, travelling back before the barrier, crashes into it and breaks into pieces across spacetime.

This leaves Sans with the ability to time travel but some serious PTSD revolving around it, developing into depression and a need for companionship, which he covers up with bad jokes and abusing time travel as coping mechanisms.