Hunting pins in a haystack
Our perception of what constitutes fundamental particles has changed continually with the ability to "see" at smaller distances. The microcosm has revealed several layers within itself: starting from molecules and atoms to electrons and nuclei, to protons and neutrons within the nucleus and finally to quarks within the protons and neutrons.
The dimensions of the sub-microscopic domain are so small that ordinary instruments of "sight" are redundant. The human hair is about 100 micrometres in diameter (1 micrometer is one-millionth of a metre). Compared to this, the "size" of an atom is roughly 10-10 m and that of a proton is about 10-15 m. Clearly, ordinary microscopes are useless in exploring these dimensions.
To determine the structure of microscopic matter, physicists use huge machines called particle accelerators or colliders in which electrons, positrons and protons are accelerated to higher energies and made to collide with other particles or fixed targets. It is with the help of these violent collisions that scientists deduce the structure of matter.
The energies of the particles are measured in units called electron volts. This is an extremely small amount of energy by ordinary standards. A person carrying a 100-g weight up a 1 metre staircase expends about 1 Joule of energy. In contrast, 1 electron volt (eV) is about 10-19 Joule. The masses of these particles are also measured in electron volts, since mass and energy equivalence is established through the famous Einstein formula, E=MC2. The mass of a proton is about a billion eV while that of a small twig is a mind-boggling 1,033 eV.
Particles have been accelerated and their properties studied since the advent of the cathode ray tubes (used in television sets). In the early '30s, the cyclotron was invented. In a cyclotron, a combination of electric and magnetic fields is used to speed up and direct the motion of the charged particles along a circular path. The particles are accelerated by repeated, well-timed "kicks", very much like pushing a swing at just the right moment to go higher.
Particle accelerators have come a long way since the original cyclotron, which was housed in a laboratory and could produce particles with energies of a few million eVs. The machines of today are technological marvels, regularly operating at 100 billion eVs or more.
Superconducting magnets, state-of-the-art electronics and high-speed computing have made today's accelerators complex engineering and technological marvels. Consequently, experimental particle physics today is a giant collaborative effort of engineers, software specialists and physicists.
The sheer size of these accelerators is awe-inspiring. The tunnel at CERN is about 27 km long and the SSC would have been more than 3 times longer.