## Wednesday, July 4, 2012

### What is god particle?

What is God Particle?Why has it caught our fleeting fancy? Is it more important than proton,photon,electron? Utpal Chattopadhyay explained it in a series of tweets, I am just reproducing these here. Edited after first publish.

One of the not so well understood problem or puzzle in Physics is why the electron or the proton or the photon are as heavy or as light as they are? What are the laws that give rise to these masses? For example, we know that  the (rest) mass of the photon, the particle of light, is ZERO. We may ask why it is zero. Is there a deeper reason? It turns out that the answer is yes,  the zero mass of a photon is directly related to a deep symmetry of the electric and magnetic fields.

Weinberg , Salam and Glashow tried to unify electromagnetism with weak nuclear forces. Weak nuclear force is what causes radioactive elements to decay. One problem they encountered is that  in order to unify through a symmetry principle, most particles needed to be zero mass just like the photon where as we know that the other particles have non zero mass.  This problem was solved by giving one of the fields a "Vacuum Expectation Value". What do we mean by  vacuum expectation value of a field? It means the following: Take elctromagnetic fields for example. In vacuum far away from everything, you would expect the strength of  these fields to be zero. That would be almost right. Almost because thanks to quantum mechanics, electric and magnetic fields will always fluctuate. so their strength is never exactly zero but zero plus minus small amounts. In other words, the AVERAGE value of electric and magnetic field in vacuum is zero, Stated differently, its vacuum expectation value is zero.

What physicists realized in 1960s is that the vacuum expectation value can be NON zero, More importanly, a non zero vacuum expectation value will "spontaneously break" the symmetry of Weinberg, Salam and Glashow,  BUT as a bonus it will generate mass for these too.
Bingo. In one stroke we can begin to understand what part of the physics might be responsible for mass of these particles. Hence the search for this particle. This particle used to be known as "Higgs-Kiggle-Englert-Brout" boson after all the physicists who developed the idea independently but people got tired of the long name. Hence the name Higgs boson survived.. It is called a boson because it follows the statistics of S N Bose (1894-1974) !

The Higgs boson is  no more fundamental than the electron, or the photon. BUT the beauty is that  it allows a unified view of why some particles are massive. This was the last piece of the puzzle of Weinberg-Salam-Glashow theory. BUT it generates another question.. Why does Higgs boson field have non zero vacuum expectation value? NO ONE knows for sure as yet.