Stephen Hawking, who once cautioned that both artificial intelligence and invading aliens could wipe out the human race, now has another dire prediction – the Higgs boson, or “God particle,” might destroy the universe. In a preface to a new book, Hawking describes his concern that if the particle became unstable, the “universe could undergo catastrophic vacuum decay,” according to the U.K.’s Sunday Times.

Hawking’s gloomy theory appears in the forward to Starmus: 50 Years of Man in Space, a collection of lectures by noteworthy astronomers and researchers. In the piece, Hawking writes that the particle “has the worrisome feature that it might become metastable at energies above 100bn giga-electron-volts (GEV),” reports CNET.

According to Hawking, the vacuum decay “could expand at the speed of light” and that this could “happen at any time and we couldn’t see it coming.” While that statement might be cause for alarm, Hawking acknowledges in the essay that this threat is highly theoretical. A particle accelerator that could even reach 100bn GEV would need to be larger than the Earth itself, and would “unlikely to be funded in the present economic climate.”

While this cataclysmic scenario is unlikely to happen any time in the near future, Hawking writes that looking into the Higgs boson’s potential instability sheds light on insights into the universe.

Hawking writes that the possible destruction of the Higgs boson “places important constraints on the evolution of the universe,” reports the IB Times.

Fellow scientists have long looked at some of Hawking’s darker predictions with skepticism. Beyond the fears over alien invaders and warnings about the uprising of smart machines, he also stated in 2012 that human life has only about 1,000 years left on Earth before being wiped out by man-made viruses, according to