> To survive in the really long term, we are going to have do something pretty drastic. Whatever we do (eg interstellar travel, moving the EArth--yes, this is possible)...
I'll bite. :-) Could you elaborate on what it might look like to transport the earth? Where would we move it to? How would life survive in transit without the sun?
There are different froms of this and it depends on your goal.
For the 1-5 billion year range your issue is the Earth overheating because Solar output is increasing by about 10% per billion years. There are three basic ways of doing this:
1. Putting something between the EArth and the Sun to reduce the amount of radiation that hits the Earth. This is by far the easiest;
2. Move the Earth to an orbit further from the Sun; or
3. Removing mass from the Sun to extend its life or reduce its output. This is the hardest.
So how do you move the Earth to a different orbit? Well that's pretty easy actually. I mean "easy" in the sense that it requires no new hypsics, no negative energy or negative mass. It just ruses gravity.
The Earth interacts with any mass. A sufficiently sized mass will attract the Earth. So you just fly large bodies of mass past the Earth to slowly nudge it in the direction you want. The Earth is relatively heavy (~10^24kg) so the energy requiremetns are still immense but it can be done slowly (and probably should be).
One proposal I've seen involves putting asteroids into an orbit such that their gravity pulls the Earth outwards a tiny bit each time they pass. Over an extended period of time (millions of years?) we could move the Earth outwards from the sun before the sun expands and cooks it. Obviously the Earth would pull the asteroid inward as well so we would have to adjust the asteroid's orbit after each pass. One proposal I've seen would be use Venus to keep the asteroid in a stable orbit. Essentially each pass of the Earth would slow the asteroid down a little bit, but each pass by Venus would speed it back up again, essentially pulling the Earth away from the sun while pulling Venus closer to the sun. In theory we could set up a system like this and just let it do its thing over a very long time, the change would be imperceptible over a human lifetime.
I'll bite. :-) Could you elaborate on what it might look like to transport the earth? Where would we move it to? How would life survive in transit without the sun?