d j machale

The boy went through a portal type thing in a rundown subway or something similar. He could be transported to these worlds that were on the verge of chaos or being saved depending on a certain decision or action that was about to happen. I dont remember the antagonist(s?) but I think it revolved...

It was a sci fi book where scientists had blown up an atomic bomb in a room surrounded by unexplodable material. It resulted in a portal being created to a parallel universe future. They were separate so anything the past did wouldnt affect the future. The future starts invading the past and...