In the preface of an upcoming book, Starmus, Stephen Hawking claims the Higgs Boson particle, a.k.a. the "God particle," could destroy the universe.
As first discovered by the Sunday Times of the United Kingdom, Hawking claims if enough energy is directed at the particle, it could cause space and time to completely collapse. He also claims that we "wouldn't see it coming."
The Higgs Boson particle is said to be the particle that gives matter its mass. "The Higgs potential has the worrisome feature that it might become metastable at energies above 100bn gigaelectronvolts (GeV)," Hawking writes. He claims that under such conditions, it is theoretically possible the particle would cause an unstoppable vacuum to form that would expand at the speed of light.
The likelihood of such an event occurring is apparently very low. According to Hawking, "A particle accelerator that reaches 100bn GeV would be larger than Earth, and is unlikely to be funded in the present economic climate." The end of days scenario is theoretical, but he said he still believes it is possible.