Hector writes in and asks about someone from Sheffield in the UK who says that the Large Hadron Collider (LHC) will create Dark Matter:
The massive ATLAS detector will measure the debris from collisions occurring in the Large Hadron Collider (LHC) which recreates the conditions found in the early universe during the Big Bang when Dark Matter was first created. If the LHC does indeed create such particles then it will be the first time that the amount of Dark Matter in the universe has increased since the Big Bang – the LHC will effectively be a Dark Matter ‘factory’.
Well, Hector basically wants to know if this is true, or if this is about as likely as your car safely tunneling through a brick wall? Well, the first part is true. The LHC accelerates protons in a big circle. Some go clockwise, some go counterclockwise, and they smash them together at two separate locations, where they have detectors to see what comes out:
The collisions are energetic enough that they can make massive particles from that energy (since E=mc2). They expect to be able to make particles that are up to about 100-500 times heavier than the protons that they started with. This includes the Higgs Boson that particle physicists are looking for, but it also includes other possibilities that might exist at those high energies, including Dark Matter.
And they’re right that if we put enough energy into the accelerator, we can make anything that has a mass! But they’re wrong that that’s the only way to do it in the Universe. Ever hear of a…. black hole? They spin, and they accelerate particles very quickly. Much more quickly than our dinky accelerators on Earth:
In fact, the amount of energy released when particles near a black hole smack into other ones are thousands of times higher than the LHC will ever produce, and so if the LHC can make dark matter, the “natural accelerators” that we see have been making it for billions of years. Also, the LHC, if we’re lucky, will make “thousands” of these dark matter particles, totaling up to a whole 10-20 grams of dark matter! OooOOOooohhh! (That was sarcastic.)
Warning: details ahead! But even if the LHC makes dark matter, I don’t think we’ll be able to know it. Why not? Because dark matter has a mass, but no charge. It also is stable: it doesn’t decay. So if you make dark matter in an accelerator, you don’t see anything! Because we can measure things very well, we will be able to say, “Hey, there’s energy missing from this!” But we produce things very commonly that just show up as missing energy. We call them neutrinos. Will the LHC be precise enough to distinguish between, say, the production of 2 neutrinos (a very common event; it happens 20% of the time whenever you make a Z boson) and the production of a dark matter particle? My sources say no, but it’s possible. In any case, that’s more information than you asked for, but look at me all motivated on a Monday!