Festivities began today to commemorate the 125th birthday of the famous physicist Satyendra Nath Bose, who was born this day in 1894. Bose’s name was very much in the news when CERN discovered the Higgs boson a few years back. Many reports pointed out and celebrated the fact that that the word “boson” in “Higgs boson” had been coined from Bose’s surname. The Higgs boson is not the only particle, however, to enjoy this honour, and there is in fact a whole class of elementary particles that share a group name – boson.

Think of the many particles you have heard of, such as electron, proton, neutron, neutrino, and photon. All the particles in this list, except the photon, are so-called matter particles. The photon, on the other hand, is a quantum, or tiny bundle, of the electromagnetic field.

The relation between matter particles and field quanta is simple — Matter particles interact with each other by exchanging the appropriate field quanta.

One fundamental difference between matter particles and field quanta is that while you can squeeze in as many field quanta into a small volume, you cannot do so with matter. To see this, just try sitting close to another person – there is a limit to how close you can get. This is because the electrons, protons etc in our bodies resist being stacked on top of each other. The same is not the case with field quanta, which can be as closely packed as needed.

This essential difference has to be tackled when we look at systems of identical particles, for instance, collections of electrons or photons. The difference manifests in the statistical properties of the many particle system. Matter particles such as electrons, protons etc obey what is known as the Fermi-Dirac statistics and hence are known as ‘Fermions’. Field quanta, for instance, obey what is called Bose-Einstein Statistics and are collectively called ‘Bosons’.

In general we hear less about bosons. There is the Higgs boson which gives mass to particles like protons and neutrons. There are the W and Z bosons associated with the weak force and the nutrinos.

Why call them bosons?

Now, why are these particles known as bosons? It was Bose who actually figured out (in the specific case of photons) how a group of identical photons would behave. He was interested in reproducing, mathematically, Planck’s law of radiation using only quantum mechanical ideas. He employed a technique in this calculation that laid the foundation of quantum statistics. He then sent his paper to Albert Einstein who recognized the value of his calculation and had the paper translated into German and published in the journal Zeitschrift fur Physik. This paper turned out to a seminal one and the technique used by Bose goes under the name of Bose-Einstein Statistics and the particles such as photons that obey these statistics are called bosons.

While Bose himself did not realise the enormous breakthrough he had made, Einstein did, and he took Bose’s work much further. Physicist Paul Dirac was the first to use the term “boson” to describe the particles that obeyed Bose-Einstein statistics, in order to celebrate Bose’s contribution to developing this theory.