PHYSICS STORIES

WHAT IS THE HIGGS PARTICLE ACTUALLY

Here I shall try to present what is the role of Higgs in particle physics in a very non-technical way.

    Before going to the main story, we have to understand the role of symmetry in physics. In 1918, a German mathematician, Emmy Noether, showed that there is an intimate connection between symmetry and conservation laws in physics. Symmetry, in physics, means some operation for which the physical laws remain unchanged. For example, the fact that linear momentum is conserved is the  result of translational symmetry. The translational symmetry, if I state it in the worst possible way, is simply the fact that the outcome of a road accident is independent of whether the accident takes place in Kolkata or in Delhi. Note the crucial point here. The casualties may not be the same. It depends on many parameters, say the population density at that place, vehicle speed etc. But the rule that connects these parameters must be the same at those two places. Since it is a fact that some entities are conserved in physical processes, there must be an underlying symmetry in the equation which describes the process.



   Around 1900, Max Planck put forward his quantum hypothesis which says that 'light' of a particular colour consists of particles. A single particle of a 'particular colour of light'  has a certain amount of energy which depends on the colour of light. These particles are called 'photons'. A 'blue photon' is always more energetic than a 'red photon'. In quantum theory, energy of a system can have some discrete values and photon is emitted or  absorbed whenever the system makes discrete jumps from one energy level to another. This assumption successfully explains the observed pattern of Hydrogen Spectra. There are many other experiments where Quantum Theory   is tested very well.

   Now, we have a feeling how "light quanta" are born. Next, we want to ask a bigger question .... how the other different particles are born. Look, if someone gives you an electron and a proton, you can solve a quantum mechanical  problem to obtain orbital structure, energy spectrum etc. But at this stage you don't know, how those electrons or protons originated. To get the answer you have to look into what physicists call Quantum Field Theory (QFT).


   In simple words, QFT says that, associated with every fundamental particle is a field whose excitation or de-excitation causes the particle to be created or destroyed. For example, in case of electron there is an electron field everywhere in the universe and it is 'discrete'.  This field can jump between different discrete levels causing electrons to appear or disappear. QFT also says why some processes occur in nature and the others do not. It does so using 'symmetry' arguments. For example, all types of interactions of light with ordinary matter can be explained by Quantum Electrodynamics (QED) which is nothing but theory of electron and photon (light) fields. Look, if the electron and the photon have to talk to each other, their corresponding fields have to be combined. But how should the fields be combined? It appears that there are several ways to combine them. Here is the importance of symmetry and it has a special name here : "Gauge Symmetry". If you want your theory of electron to be 'gauge symmetric' you'll find that the electron cannot do it alone; it has to talk with the photon in the "right manner"! Is not it beautiful? Sounds like, "Let there be electron and gauge symmetry" and there was light!

   Now we have to understand what collision means in QFT; I mean how one particle see the other one.



                                                                     TO BE CONTINUED.............