Fire or Ice

The question was When is the end of the world?

Robert Frost had it right.

In five billion years or so, the Sun will grow into a Red Giant. Its diameter will be about the size of the Earth's orbit. Earth either is engulfed and vaporized, or raises a tide behind itself on the Sun, which removes orbital energy from the Earth, causing it to spiral into the sun, where it is engulfed and vaporized.

However, we're here. We already understand physics enough to know how to move the Earth's orbit out from the Sun. Essentially we steal orbital energy from Jupiter using big asteroid flybys of both planets. At this point, it's an engineering project. A big engineering project that takes millions of years. However, it's feasible, and would be worth doing. After the Sun's Red Giant phase, it shrinks to about the size of the Earth, and though it's really hot, its much smaller size means that it emits less total energy. We reverse the process, and move the Earth into a much smaller orbit for maximum comfort. Eventually the Sun cools. The Earth freezes. But it's ten billion years later, at least.

Robert Frost's Fire and Ice poem says it might happen either way. In his The Road Not Taken poem, he says "Two roads diverged in a yellow wood". The way that the Earth ends is our choice. Fire or Ice. Which do you want?