The Departure question

Hey, I read a series awhile ago and never finished it. I was wondering if anyone new what its is. It is about a kid from earth zero(I think). His science teacher is kidnapped to a parallel world that is more technologically advanced. he (I think his nickname is tag, he wears a scarf) is then taken to the headquarters of the multiverse coordinators. He learns about all the different universes and makes friends with a really tall person and a really short person. He also learns about a women who rules her own earth and is experimenting with dark matter. As a side note I believe his name starts with an A. and on another side note, he was the only version of himself that did not die in his universe and could travel to different earths without the machine they use. If you could help me with this you would be a life saver