End Of Planets

Lately, my 5-year old has been trying to put her mind around the fact that our planet and to an extent the entire universe will inevitably die or cease to exist. She calls it "the end of all planets."
I asked her where she got the idea and she told me it came from nowhere and that she suddenly got curious about life on planets ending. I didn't buy it. No 5-year old thinks about this stuff. She probably got the idea from a movie or a TV show or something and it just brewed in her little mind Inception-style.
Anyway, for a couple of days now, she has been asking me curious things like: "Daddy when will it happen?" and "How will it happen?" and even questions like "What will we do when the end of planets is here?" (She even asked if the same thing will happen on Pandora and what will Jake and the Na'vi do about it.) You can feel that she's really unsettled by these thoughts. Well the sweet thing about it is that her somewhat fidgety mind came from the fact that she is scared for her family. "I am scared kasi eh, I don't know what will happen to us and what will happen to Sooz." (Sooz or Suzie is her one-year old little sister.)
It is difficult to answer these questions in the way that a five-year old mind will understand. I was tempted to just tell her "Don't worry about it. It won't happen for a long time." But the scientist in me urged me to explain this to her as best as I could. It was like accepting a challenge and I obliged. However, it is particularly difficult to explain all of these with a sense of time on when it will happen. The entire universe has been in existence for around 13.7 billion years. So barring any nuclear holocausts, killer meteors, or zombie infestations, I think human life can exist for at least another 13.7 billion years (it may or may not be on another planet) given that cosmologists still consider our universe to be a young universe. It may take at least that time for the universe to stop expanding and collapse again on itself. That is almost FOURTEEN BILLION YEARS. It's no googleplex, but can a child even grasp that number?
So in the simplest of terms, I told her that, yes, the universe will die of natural causes, and that this will not happen for a very long time. A very long time in fact that everyone you know right now will have gotten old and their children would have children, and their children will have children, and so on. I told her not to be scared because everyone you know would have lived long and fulfilling lives.
After my explanation (she may have understood most of it, she may have not), she just told me "Daddy, I hope it doesn't happen in the night para we're prepared." Yep, this is my daughter. And I am her silly over thinking father.