I just read this on youtube and I wanted to pass it on because although it's crazy, it could actually end up being possible. People in this forum are great at coming at the show from all different angles so I can't wait to get a couple of thoughts on this. I'm not claiming this theory as my own; the link where I read this included.
"WHAT IF tate has a twin? in the first epi tate sees a figure looking like tate but with shorter hair behind ben. In a promotional poster you see two boys who aren't bryan and troy in the backround. The tate that shot up the school had scars on his face and the current tate doesn't. And if tate got shot in the chest, why isnt it that when he's topless there are the bullet marks. Good tate and evil tate?"