Ideas wanted for a short story, Sci-Fi writing prompt. Got any?

March is Sci-Fi month on this site. That means most (if not all) book reviews will have a sci-fi theme to them. The same goes for the interviews. I'm hoping to put together a sci-fi themed promotion, though I haven't worked out all of the details. Another thing I'd like to try is a community writing prompt.

The purpose of this post is to brainstorm ideas for that prompt. Another post will officially announce the prompt and include details for entering your short story.

The stories will be around a thousand words (a little more or a little less is fine), so a prompt can't be overly complicated. It has to be simple enough to work into a scene or two. But at the same time I don't want a prompt that is too broad. Since short stories often don't answer every question, the prompt doesn't have to lead to a certain resolution.

Perhaps a Sci-Fi What-If scenario that could work in a dozen or more different ways. Got any ideas?

Include your ideas in the comments below. 

If I pick the prompt from your suggestions, I'll feature the commenter some way—haven't decided how yet.