It’s the perfect doomsday scenario. Thunder and lightning crackle far above a bunker filled with huddled scientists who, hands poised over a big red button, prepare to set particles speeding towards each other, creating an explosion so huge that it replaces the entire Earth with a scorched hole in spacetime. Or a black hole. Or swarming teams of mutant particles made up of differently arranged quarks. Take your pick. 

There have always been concerns about particle accelerators, which is understandable given the imagined stakes (no more Earth, solar system, or universe) if something goes wrong. Luckily, the vast majority of the scientific community has long maintained that these concerns are unfounded. 

Particle accelerators of only a few centimetres in width were first developed in the late 1920’s by physicists in both Germany and America, eventually leading to the advent of current high-speed facilities that span kilometres [1]. Some modern accelerators [2] contain straight or circular particle beams used to shoot X-rays at things we wish to study, like crystals, viruses, or new materials [3], whereas others are colliders designed to fire particles at each other [4] [5]. These facilities help us to unlock the secrets of matter and the universe, as well as to produce technological advances that can be applied in such diverse fields as medicine and transport security [6]. It is these high-energy colliders that tend to cause concern in the press and general public.

When the European Organization for Nuclear Research, otherwise known as CERN [7], switched on the giant and powerful Large Hadron Collider in 2008, there was a frenzy of speculation as to whether we would still be here by tea-time. These discussions tend to resurface periodically [8], often when a new development in accelerator technology is being hailed. The eminent cosmologist Martin Rees speculated in a newspaper interview in 2018 that colliders could create black holes, change the arrangement of sub-atomic particles (altering the matter on Earth), or even unbalance spacetime [9]. His comments, while not new, fed continuing public concerns about using such powerful machines to create unprecedented conditions right here on Earth. 

Let’s start with black holes. We’re on fairly comfortable ground here, as the size of a black hole, a tiny point in space birthed by the gravitational collapse of a massive object, is proportional to just how much matter was compressed to make it. This means that if a black hole were produced in an accelerator (which is unlikely, as the masses involved are far too low), it would be minuscule, and also subject to shrinkage, leading it to decay before it could hit the accelerator walls [10] [11]. This means that any black hole forming in an accelerator would not be in a position to do any damage [12].

Next up, we have strangelets. These are hypothetical lumps of matter (no-one’s yet seen or measured one) that contain a different arrangement of sub-atomic particles than normal matter. It is theoretically possible that a strangelet could be formed in a particle accelerator, and once formed, would grow uncontrollably as it consumed everything around it, quickly engulfing the Earth [13]. However, no strangelets were detected in testing at facilities in America and at CERN, and their creation was concluded to be extremely unlikely [14] [15], not in the least because strange matter favours cold conditions, and accelerators operate at extremely high temperatures [16] [17].

Finally, we have the question of spacetime stability. The idea here is that right now, the universe isn’t as stable as it could be, and one good burst of energy, such as the massive amount of energy released by smashing particles together, could kick us into another state, one in which we couldn’t exist [15]. Ok, this sounds bad, but the most encouraging point in favour of accelerator safety is the fact that billions of collisions are occurring in space all the time, right in our very own atmosphere [13]. High-energy particles known as cosmic rays fly through the universe all the time, entering our solar system and colliding with all kinds of matter at speeds that can far exceed those produced in an Earth-bound accelerator. The fact that our corner of the universe is not currently riddled with little black holes, strangelets, and stability issues is an encouraging sign.

All in all, the use of particle accelerators is widespread across the globe and presents very little risk to life on Earth. Accelerators don’t just expand our knowledge of the universe, they are also used to study anything from new materials and viruses to ancient archaeological finds. In 2020, a group of European facilities including accelerators won a tender by the European Commission to identify molecules against COVID-19 and develop an effective tool to counter future viral epidemics [18]. The advances provided by particle accelerators offer great benefits to society and new insights into the world around us.