In about six billion years, the sun will exit the red-giant stage (which will begin in about 5 billion years). Nothing will be left of the sun except for a dim white dwarf. That white dwarf could not support human life on ANY planet. We have to get out of the solar system before that time and establish a foothold somewhere else in the galaxy. BTC travel is probably necessary, and FTL travel would be practical. However, the star binary star system Alpha Centauri may be a better candidate, as it is possible (though not proven) that planets exist there.