From Jay Pasachoff, Hopkins Observatory, Williams College
Williamstown, Massachusetts
Kate Charlesworth’s delightful “Life, the Universe & (Almost) Everything”
about particle accelerators (26 October, p 52) understates the advantage of
particle colliders by saying that when “magnetic fields steer 2 particle beams
in opposite directions along the same path; this doubles the amount of energy
released”.
First, energy varies with speed squared, so a beam hitting something coming
at it with the same speed is hitting it at twice the speed and so produces four
times the energy. Further, as Richard Wolfson and I explain in Physics:
“From conservation of momentum, much more energy is available in the head-on
collisions…In a fixed-target accelerator, much of the energy goes into the
forward motion of the collision products; in a colliding design, all the energy
is available to create new particles.”
