Milky Way and Andromeda, the two neighbor galaxies are going to collide! Andromeda is coming towards Milkyway at a speed of 110 Km/s. But,even then, it would take about 4 billion years for this to happen .
Scientists estimated that the Sun would turn into a red giant and swallow the Earth and destroy life as we know it ,in over 2 billion years. So we don't have anything to worry about the Milkyway-Andromeda collision....worry about the SUN!
But some scientists said that the Sun won't turn into a red giant,but still the Sun will be too bright that it would be nearly impossible for liquid water to exist on the surface of the Earth,thus ending almost all life except some microorganisms which can adapt to this temperature.