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The Large Hadron Collider will not eat the world Brian Angliss There are a lot of people worried that the world will end soon. This autumn, specifically, when the Large Hadron Collider (LHC) at CERN in Switzerland and France turns on and starts smashing protons together at velocities that are nearly the speed of light. The main concern is that these collisions will create a miniature black hole that will swallow the Earth and us with it. Thankfully for human civilization, black holes just don’t work this way. While the basic level of understanding of science in the United States should be much higher than it is, the science underlying black holes is pretty arcane. While everyone really should remember the basic biology, physics, cosmology, geology, chemistry, ecology, and even genetics that they were taught in high school and maybe college (alas, science is too “nerdy” or “geeky” for most to care, never mind that footballs follow a predictable ballistic trajectory determined by Newton’s Laws of Motion), the science of black holes is strange enough that it’s simply not fair to expect everyone to have much knowledge of them beyond the fact that they exist. Understanding why a LHC-created mini black hole won’t eat the planet requires a basic understanding of how black holes work, some of the weirder things they can do, and why those weird things mean that we don’t need to worry about a mini black hole eating the planet. Our discussion of black holes starts with stars. Stars have a life cycle - they’re born, the live a long, long time, and then they die out. How massive a star is determines how long it lives and the various ways it can die. Stars like our sun, Sol, are pretty average stars, and average stars live 10-30 billion years or so, then blow up to be bigger than the orbit of Venus (some stars can become bigger than Mars’ orbit, some 227 million km, an increase of over 300x larger than the sun is now). Then they go nova, blow off the outer layers of their surface, and gradually shrink down to a dense, cold cinder called a brown dwarf. Big stars, however, live fast and die young, completing their entire life cycle in tens to hundreds of millions of years instead of billions of years. Big stars expand as they’re about to die just like average stars do, but then they go supernova. To understand why a star goes supernova, let’s talk about gravity and fusion reactions. Stars keep their size because the explosive power of the fusion reaction that drives the star is equaled by the force of gravity holding the star together. As a star ages, there’s less and less hydrogen (the main fuel of fusion) to keep the reaction going in the core, so the star starts to collapse under its own weight. When the core of a big star gets too dense, it shrinks until something else stops it, and when that happens the energy released basically blows up the rest of the star - a supernova. The result of a supernova is one of two things, either a neutron star or a black hole. A neutron star is what’s left if the original star wasn’t quite big enough to collapse so far that the force of gravity overwhelmed light - a black hole is what’s left if the original star was so big that it’s core can capture even light. Black holes are named such because the force of their gravity is so great that light, the fastest thing that can exist according to Albert Einstein’s Theory of General Relativity, cannot go fast enough to escape. The reason light can’t escape is essentially the same reason that rockets are huge to get the space shuttle off the Earth - it takes a certain amount of velocity (known as the “escape velocity”) to launch an object out of the Earth’s gravity altogether. When the escape velocity is greater than the speed of light, the body that creates that effect is called a black hole. The mathematical surface around the black hole’s center of mass where the escape velocity equals the speed of light is known as the “event horizon”. Unfortunately, if light can’t escape past the event horizon, then neither can anything else - Einstein also proved mathematically that the speed of light is the universal speed limit, and no object made of matter can ever go any faster than that (in fact, nothing with mass can ever go that fast, but mass inflation and time dilation are topics for a different post). Anything that passes the event horizon is lost to this universe - only it’s gravity remains. So a black hole consumes matter and energy both. There’s other ways to create black holes, though the collapsing star method is the only one that cosmologists are pretty sure they’ve directly observed. But Einstein also proved that energy and mass are equal, with a proportionality constant, using the equation e=mC2, where E is energy, m is mass, and C is the speed of light in a vacuum (i.e. space). Which means that, if you’ve got smaller mass but that is traveling REALLY fast (fast things have more energy than slow things do), it might be able to convert enough of that energy into mass in a collision to create a black hole. And this is where the LHC comes back in again. The LHC is a circular particle accelerator housed underground and straddling the border between Switzerland and France. Its purpose is to test the fundamental laws of physics, specifically the existence of certain types of sub-atomic particles (especially the Higgs boson) and how they interact with each other. To do that, though, it has to accelerate protons to extremely high energy, 7 TeV (tera-electron-Volts, a thoroughly inconvenient unit for anyone not used to working with semiconductor physics and/or particles) per proton. When a collision occurs, the protons will disintegrate into sub-atomic particles that will be indirectly detected and measured by the huge and complex science test equipment around the collision point.
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