Scientifically, when is the world going to end? How? Is it because of the Sun?
Well, the planet earth could end a number of different ways. These include Gamma ray bursts, Global war, Epidemics, Alien invasion, or getting smashed by a huge asteroid, to name just a few!
click here for a great article on a number of ways Earth could end.
Eventually, the sun will go through the life cycle of all suns (stars) like it, and it will expand into a Red Giant and actually burn up and suck in the relatively tiny Earth!
Click here for a great Physics explanation on the sun and the earths eventual death.
Of course, that raises the question... are we talking about end of the earth itself, the end of all life on earth, or just the human species?