Guys I just had a thought. It's a weird Undertale theory that even surprised me.

So I was just playing minecraft, building a house when I started thinking. People make a lot of theories on Gaster and Sans. Especially on who they are. Wouldn't it be funny if they were just the same person? That's when it hit me. I mean... it doesn't totally make no sense....

Like sans IS into science and we don't really know his past. We also don't know if that mystery man in that room from the gray door is Gaster. 

Sans and Papyrus just 'showed up one day and inserted themselves' into Snowdin. so...?

In alphys true lab you can tell not all of the entries are hers. The writing has no punctuation, heck it's all lower case! Who talks in lowercase? Sans. It also has the almost professional feel to it. Sans can be like that when he is serious.

Sans has also hinted he knows about the amalgamates. When you call Papyrus outside of Alphys' lab the conversation goes:

Papyrus: HMMM... A MYSTERIOUS SCIENCE HOUSE. 
Sans: the sign outside says "lab."
Papyrus: LAB?
Sans: like... laboratory.
Papyrus: LABRADOR... Y? DOES THAT MEAN THERE ARE DOGS INSIDE?
Sans: i mean. i wouldn't rule it out.  

I really don't know though. Like that conversation could just be Sans remembering a timeline where Alphys admitted everything. Gaster could have also talked in lowercase or Alphys was having a lazy day.... All i know is... it kinda makes sense. It also raises a question...

Maybe Sans is Gaster but not.... and that's why he knows everything.
let me explain....

Just think about it. Maybe not all of  Gaster fell into the void. Maybe he was split to just that weird figure in the room and Sans. That can explain why Sans knows so much. He can see all the timelines because of it. It could explain his eye too....

 Like I said though. This was just a weird thought I had to myself while playing Minecraft. Lol I just thought I should share it. Hope you enjoyed this thought/theory of mine. Like I said, I was just bored.