The end of the world will be either:
A) Aliens get really pissed off at us for doing tests on them in the desert and blow the planet up
or
The sun will continue to burn as normal, until it starts expanding into a red giant, happens with most stars as they age. Now, with a red giant, the gravatational field expands as well as the size. Earth will get sucked into the photosphere of the sun and burn up. After frying off all life on earth, of course. By then the earth's magnetisphere will probably be blown away by the intense solar wind, along with our atmosphere. Humans, if still alive, would then be eaten away by gamma and microwave radiation comming from the sun that the magnetesphere and atmosphere protects us from.
or
C) We develop anti-matter power plants that run all power on the planet. Some idiot from the middle east that was pissed off from the invasion in the early part of the century, goes and destroys the reactor, causing the anti-matter to react with matter in a huge display of fireworks that will eat a good chunk of earth and atmosphere also causing us to go off our axis and get closer (or farther away) from the sun, killing off what's left after the explosion because of an unballance..
or... J/k. I'm out of practical Ideas...
Actually, the B is more likely to happen. Do I care? no, cause I will be so far into the ground that my grandchildren ^5 power wouldn't even care. It would take a long time for the sun to even get that far. A few billion years probably.