"It's very real," Draco answered, happy that they had stopped talking about their love lives for the moment. "We seem to be taken from different points in time. We're not sure if we will be sent back at the same time. It was the original theory based on people we knew."
He had to find a way to explain this to Potter before he got bored. "For example, Sirius and Remus came here. If they had never returned to their life, I wouldn't remember that Remus taught in school, and Sirius escaped from jail. Now, we're not so sure that it's what happens. Remus and I have been looking into this for months. We think that when we're pulled out a new reality branches out, so there's a reality where you're still at home and one where you're here. If we're right, that means that we can't go back."
Draco ate the ice cream as he talked but his mind was now on the explanation. "We also discovered that the bus picks up people who are about to die or that make a wrong choice. Maybe in your reality, you're about to die. Or you're about to do something very stupid. Where we go when we get sent back is still a mystery though."