• Question: what would happen if a particle accelerator explodes

    Asked by anon-217218 to Edoardo on 13 Jun 2019.
    • Photo: Edoardo Vescovi

      Edoardo Vescovi answered on 13 Jun 2019: last edited 13 Jun 2019 9:36 pm

      It doesn’t blow up. I describe what it is before saying why.

      In short, a particle accelerator is a machine that accelerates particles to high speed. The goal is making them hit each other, produce new particles and measure their properties (mass, electric charge, speed, how fast spinning like a toy top, …) as they fly off from the accelerator. Think of coloured billiard balls hitting head-on, turning into other colours in a split second and bouncing back to you.

      Take LHC for example. It is today’s most famous accelerator in CERN in Switzerland. It is a circular tube with nothing — even air — inside. You see pictures here https://cds.cern.ch/record/1211045. Tiny particles fly in circles at 186 000 miles/second. They’re protons, the same particles that made up atoms in anything around us. I’m no expert in precise numbers, but read that there are 100 billion protons travelling together in one direction, the same number in the opposite, and they collide head-on at some special areas along the ring.

      They cannot possibly cause an explosion, despite number and speed. When they collide, all energy goes into new particles, which fall then on the detectors. If protons go off tangent, the tube stops them, because a nail-sized piece of it contains an extremely huge number of atoms.

      Let’s see what else can fail.
      1) Liquid helium cools the tube down. Pipes break (they did in 2008), release a giant amount of gas and helium doesn’t burn.
      2) A fire breaks out in the electric system. I guess a damaged connection may set wires on fire and release toxic smoke, but no explosion.
      3) An electric black-out shuts the tube down. The worst I can think of is 1) and 2).
      4) It’s true that collisions are energetic, but far more energetic collisions happen in the upper atmosphere when particles from outer space hit air. It has going on for billion years and we’re still alive.
      5) You can worry about something dangerous created in particle collisions. Unknown particles may destroy or a mini black hole suck the planet in. Again, I’m no expert, but I know that scientists checked that is impossible to the best of our knowledge.

Comments

  • Photo: Savannah

    Savannah commented on :

    To add to what Eduardo said, the LHC is only allowed to run because scientists are super sure that it is safe – so no big explosions should ever be possible. It is true that some of the magnets failed when the LHC was first turned on in 2008 – this caused a big power outburst and literally blew some of the magnets apart! Here is an article here from the time that shows pictures of what happened to the magnets https://www.theguardian.com/science/blog/2008/dec/14/particlephysics-cern This took a lot of time and money to fix!
    .
    According to some theories of quantum physics, it is also true that smashing particles together at high energies could create mini black holes here on Earth! However, these will be so small that they will evaporate away before they can cause any damage. Here is a really interesting article that explains these quantum black holes in a simple way https://angelsanddemons.web.cern.ch/faq/black-hole 🙂

  • Photo: Harrison

    Harrison commented on :

    Just to add something about black holes and the LHC. Lawsuits were filed against CERN that argued that the risk of creating a black hole, even if small, is not one that should be accepted. Happily, these lawsuits were dismissed. (See, for example, https://phys.org/news/2010-09-lhc-lawsuit-case-dismissed-court.html). When I travel and get into a conversation with a fellow traveler about what I do, occasionally the question of black hole creation at the LHC raises its head. Having a British sense of humour, I usually take the opportunity to both teach some physics and have a bit of cheeky fun. I explain that according to Einstein’s theory of gravity, there is a formula R = 2 GM / c^2, where G is Newton’s constant, M is the mass of an object and c is the speed of light, that allows one to compute the radius R below which you’d have to squeeze something to create a black hole. For the Sun, this radius, which is called the Schwarzschild radius in honor of the scientist who found the first exact solution of Einstein’s equations, literally within months of the November 1915 publication of Einstein’s gravity paper. (Sadly, Karl Schwarzschild, who was also a soldier at the front in World War I died shortly thereafter.) Putting in the numbers for the Sun, G = 6.7 x 10^-11 (in some funny units!), M = 2 x 10^30 kg, and c = 3 x 10^8 m/s, you get about 3000 meters, that is, 3 km! So, you would have to squeeze this ball of radius 700,000 km down to 3km to create a black hole from the Sun. That’s not going to happen! By the way, you’d have to squeeze the Earth so that its radius were just below a centimeter in order to create a black hole from the Earth. That too is not going to happen. Now, back to the LHC. Suppose that all of the 13TeV (trillion electron-volts) of energy could be transformed into mass in accordance with the famous formula m = E / c^2 (you surely know it as E = m c^2!). When you do the sums, you find that you would have to squeeze this energy into a ball of radius less than 100 million trillion times smaller than the smallest size that can be probed by the LHC! So, if Einstein is correct, there is simply, absolutely, no way the LHC can create a black hole. If my fellow traveler has not given up on me by then, I then have some fun at her or his expense! What if Einstein’s theory does not work at those incredibly small distances probed by the LHC, I ask? Indeed, Savannah has pointed you to a nice article at the CERN website that explains an idea of some scientists that the LHC could create quantum black holes. But, if the late Hawking is correct, these black holes would immediately evaporate! So, again, no problem. But, I ask, what if Hawking is wrong and small black holes fail to evaporate? What then? Well, the black hole would slowly sink to the center of the Earth and go back an forth until it settles at the Earth’s core. But, that would not be a problem because it would take this unimaginably small black hole, hundreds of millions of years to find a nucleus, gobble it up, and eventually grow so that the black hole is able to touch a whole bunch of nuclei at the same time, at which point it would indeed be game over as the black grew exponentially gobbling up the entire Earth. But, at least we would have several hundred million years before that happens! So relax, I say, and enjoy the plane ride!