eschatology

Texas-size asteroids make for exciting summer blockbusters, but when it comes to long-term damage, they're not the most menacing threat out there. Lurking at the edge of our galaxy are giant molecular dust clouds -- agglomerations of hydrogen gas, small organic molecules and minerals -- roughly 150 light-years across. If our solar system hit one, it would take 100,000 years to pop out on the other side.

If you put a steamy cup of coffee in the refrigerator, it wouldn’t immediately turn cold. Likewise, if the sun simply “turned off” (which is actually physically impossible), the Earth would stay warm—at least compared with the space surrounding it—for a few million years. But we surface dwellers would feel the chill much sooner than that.