Professor Lord Martin Rees has revealed the "worst case scenario" for particle accelerators - and they could mean the end of Earth as we know it.
He warns that if things went wrong, they could result in a black hole being formed, or the Earth being turned into a "hyperdense sphere" measuring just 330 feet (100m) across.
Particle accelerators like the Large Hadron Collider shoot particles at incredibly high speeds, smash them together, and observe the fallout, according to the Daily Mail.
While they have led to massive breakthroughs in our understanding of the universe, they also carry a high risk, Rees says in his new book On The Future: Prospects for Humanity.
"Maybe a black hole could form, and then suck in everything around it," he writes, according to the Telegraph.
"The second scary possibility is that the quarks would reassemble themselves into compressed objects called strangelets."
"That in itself would be harmless.
"However under some hypotheses a strangelet could, by contagion, convert anything else it encounters into a new form of matter, transforming the entire earth in a hyperdense sphere about one hundred metres across."
That's approximately 330 feet, or around the length of a football field.
The third way that particle accelerators could destroy the Earth, according to Reese, is by a "catastrophe that engulfs space itself".
"Empty space - what physicists call the vacuum - is more than just nothingness. It is the arena for everything that happens.
"It has, latent in it, all the forces and particles that govern the physical world. The present vacuum could be fragile and unstable."
"Some have speculated that the concentrated energy created when particles crash together could trigger a 'phase transition' that would rip the fabric of space. This would be a cosmic calamity not just a terrestrial one."
The Atlas sensor at the particle accelerator. Photo / Atlas Experiment
The LHC allowed scientists to discover the once hypothetical particle the Higgs boson, for example.
"Innovation is often hazardous, but if we don't forgo risks we may forgo benefits,' he writes in On The Future.
"Nevertheless, physicists should be circumspect about carrying out experiments that generate conditions with no precedent, even in the cosmos," Rees writes.
"Many of us are inclined to dismiss these risks as science fiction, but give the stakes they could not be ignored, even if deemed highly improbable."
However, many, including Stephen Hawking gave his blessing to the particle accelerator.
"The world will not come to an end when the LHC turns on. The LHC is absolutely safe ... Collisions releasing greater energy occur millions of times a day in the earth's atmosphere and nothing terrible happens," said Hawking.
Cern writes on their website "The LHC Safety Assessment Group (LSAG) reaffirms and extends the conclusions of the 2003 report that LHC collisions present no danger and that there are no reasons for concern."
"Whatever the LHC will do, nature has already done many times over during the lifetime of the Earth and other astronomical bodies."