It has taken human civilization 4.5 billion years to appear after Earth first formed. In one billion years more, give or take, the gradually warming sun will become so hot that Earth's liquid water will evaporate. The extreme heat will destroy all life and Earth will begin to resemble the planet Venus.

So within one billion years, humans must find a new home on a new planet in a new solar system, or perish. When human life disappears, that will be the end of accumulated human knowledge, from quantum scale physics to cosmology to the technology used to create our modern world.

There is just one small problem with finding a new planet, though. Earth is unique. The manner of its formation is so unusual (see Why Are There No Visitors from Outer Space?), that possibly only one in 10,000 solar systems have a planet like Earth.

Given the vast distances within our own Galaxy, the Milky Way, which is 100,000 to 150,000 light-years in diameter, the closest habitable planet is likely to be 30,000 light-years away from us. Since we can probably only travel at half light-speed at most, it would take 60,000 years to reach this solar system in the hope that it would be suitable.

The journey would be perilous too. Cosmic radiation will bombard the spaceships, potentially altering genes, and a space pebble could rupture a hull, All passengers would have to be in suspended animation and well shielded for the duration. A wake-up would be necessary near the destination, to slow the ships down and land them. Those answering the call might be either human or AI robots.

Just to avoid any misconceptions, faster than light speed travel, such as Star Trek's fictional warp speed, is not possible given our current understanding of physics and cosmology. Only objects without mass, such as photons, can reach the speed of light.