The meaning.
I came up with a mini-story to go along with this game. After 9/11, a special team came to investigate in another building. One of the man's jobs was to go back to before 9/11, and try to find a way to prevent it. I think the device freezes time for everyone but the man and the problem. The device also let's him read minds. When he was flying around, he saw a little girl who was not frozen. She was crying, and reaching into the air for a frozen balloon. The man grabbed the balloon, and gave it to the girl. Then, she froze and the device took him back to his time.
So, basically, I say the little girl was the only problem they could prevent.