[ He nods and accepts Natasha's help to move the larger pieces into the wheelbarrow, and tosses some of the smaller onto the blanket. At her question he lifts his head and watches her for a moment, then gives a jerky shrug. ]

It's complicated. [ If she couldn't guess by the sprawling math covering the walls. ] I'm trying to do something impossible, but it's proving to be considerably more difficult when time is literally working against you.

[ He knows she's going to ask. He could brush it off and not tell her, but for some reason he feels like giving her context. ]

My brother is dead in my... their timeline. He's alive here, but that timeline also ends with the rest of the universe, a week after I go back. I don't know if I can change that, but I have to give it my best shot.