The are many ways the world could end and most of the ways are entirely unavoidable; whether or not prior warning of the end of the Earth is a good thing is truly a subjective matter for discussion, perhaps over drinks and dinner. Armageddon, whether a result of huge asteroids or the demise of the sun, has been a subject of a few major blockbusters and even more made-for-TV, B-grade films.
Common as it may be in films, the idea of a significantly sized asteroid plowing into the planet is without a doubt the least frightening doomsday event. The era of gigantic, rogue hunks of metal and rock patrolling the solar system waiting to cause a catastrophe was millions upon millions of years ago. While astronomers do see some major impacts freckling Jupiter from time to time, for the most part, planet-enders reside beyond the main asteroid belt. Without the large beasts, there are still plenty of smaller baddies out there, but with a little bit of scientific postulation and some precise work, provided there is ample warning, asteroids are by no means a terrifying end. One will eventually hit and it may cause a catastrophe, but not on the level hypothesized in films.
So, without the fear of asteroids, is the Earth, and humanity, invincible? Unfortunately the answer is a succinct, “No.” Asteroids are not the only source of cosmic danger in the universe. The expanding sun, primordial black holes, galactic collision, rogue planets, comet strikes, and the inevitable heat death of the universe are all worth looking forward to too, for one merit or another. Still, all of these can be spotted by one means or another. However, there is a possibility that a lurking surprise with the potential to wipe out at least half of the life on earth exists.
It is a sunny fall day, millions across the United States are tuning in to their favorite major league football game, but even with the reintroduction of professional referees, doom is light-seconds away. On the outer edge of the solar system a gamma ray burst glances through the Jovian system, only hitting a minor moon. The beam continues, barely diminished. A few minutes later, the skies light up as the massive radiation wave pummels the atmosphere. Almost instantaneously all but the deepest life on the exposed side perishes. Within a few days, destruction has spread to the other side, fires along the sides of the exposed earth pollute the skies and irradiated atmospheric contents bring doom to the survivors.
The chances of this happening are minor, but it is a potential event and unfortunately, due to the speed of the wave, there is no way that it could ever be detected. However, despite the danger from the sky, most likely, doom would come from humanity itself. Humanity may be its own biggest downfall; even without the fears of global warming and drought, within the past century, weapons capable of leveling more than just city blocks have been developed. Luckily, the use of such weapons can be avoided. With careful negotiation towards the amiable goal of world understanding, humanity can leave the destruction of the world to the stars.