Why is the LHC tunnel so big? | Jon Butterworth | Life & Physics

Twin evils: If synchrotron radiation doesn't get you, centripetal force will.I just registered for a meeting of the European Strategy Group on particle physics. This is a year-long talk-fest mapping out plans, aspirations and options for the next few years in the subject1. Amongst the issues being considered is the question of how we might continue to explore the high-energy frontier in the next decades, and what machines we might need to do this.There are multiple constraints to deal with. Budget is one of course. Available, or potentially available, technology is another. But there are some very basic physics constraints too.The main ones are related to the reason the Large Hadron Collider (LHC) is so big in the first place. It is 27km long2. Building a long tunnel is very expensive, so why not make a smaller one? In fact, the length of the tunnel limits the energy of the colliding beams, and in different ways depending what particles are being accelerated. And it's all down to Newton's laws of motion. Particles travel in a straight line at a constant speed, unless acted upon by a force; in which case they accelerate - that is, they change speed or direction. ...