Ever since scientists have built massive particle accelerators like the Large Hadron Collider, there have been some dire warnings about what might happen should experiments go wrong. None of those doom and gloom scenarios have come true ... not yet anyway.

According to a thesis by astronomer Martin Rees, however, it's possible that catastrophe could strike, reports The Telegraph. In his new book, "On The Future: Prospects for Humanity," Rees details his concerns.

"Maybe a black hole could form, and then suck in everything around it," writes Rees. "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 meters across."

One hundred meters is roughly the size of an American football field. That's the entire Earth, condensed into that tiny space.

To understand how this might be possible, consider that particle accelerators are large, high-energy structures that use electromagnetic fields to propel charged particles to nearly light speed. Typically, once the particles reach these incredible speeds, they are set to collide with one another. This causes the particles to blow up into their constituent parts so we can learn more about the fundamental particles that make up our universe. The most powerful particle accelerator is the Large Hadron Collider in Switzerland. It's also the largest machine in the world.

Experiments like these, using such powerful machines, can produce unpredictable outcomes by their very design. That's how we learn from the results.

Take a deep breath

Before going into a complete panic, however, it's helpful to remember that Rees' nightmarish concerns are not exactly mainstream, nor is there any indication they are imminent. Cooler heads do tend to prevail on this matter.

For instance, according to CERN (European Organization for Nuclear Research), the organization that runs the Large Hadron Collider: "Could strangelets coalesce with ordinary matter and change it to strange matter? This question was first raised before the start up of the Relativistic Heavy Ion Collider, RHIC, in 2000 in the United States," they write on their website.

"A study at the time showed that there was no cause for concern, and RHIC has now run for eight years, searching for strangelets without detecting any."

Even the late Stephen Hawking has spoken in support of particle accelerator experiments. "The world will not come to an end when the LHC turns on. The LHC is absolutely safe," Hawking has said. "Collisions releasing greater energy occur millions of times a day in the Earth's atmosphere and nothing terrible happens."

This is an important, and comforting, point. Our planet's atmosphere is constantly bombarded by particles that are propelled our way by various powerful events that happen throughout our galaxy and beyond. This causes collisions just as powerful, or more powerful, than anything we produce with man-made particle accelerators on Earth's surface.

While the risk is always there that one of these collisions will produce some rare and catastrophic results, the odds are not likely, and such collisions are happening whether we run our experiments or not.

"Nevertheless, physicists should be circumspect about carrying out experiments that generate conditions with no precedent, even in the cosmos," writes Rees.

Scientist warns that particle accelerator experiments could make Earth implode
Earth could be crushed to the size of a football field if a particle accelerator experiment goes awry, says Martin Rees.