What is mass?

Mass is a tricky concept. We all think we know what it is: it’s what you measure when you put something on weighing scales or a digital balance. Alternatively, you could say mass is the property of an object that resists changes to its movement. In other words, an object with lots of mass is one that weighs a lot and also one that is difficult to move (or difficult to turn or stop moving when it is in motion).

But in particle physics, mass is about energy, as expressed in Einstein’s famous equation;

Actually, this is a slightly simplified version but that only matters to particle physicists. For the rest of us, the equation reveals mass to be a form of energy. If you were to obliterate a small amount of mass, a vast amount of energy would be released. This is the principle behind nuclear reactions that are used to generate electricity, via heat, in nuclear power stations. Conversely, if you can pile enough energy into one place, you can create matter out of nothing (other than energy).

Once it exists, the properties of mass are determined by its interaction with an invisible field that pervades the entire Universe: this is known as the Higgs field. Although the field itself is undetectable, any disturbances in the field (think of ripples on the surface of a pond) might be observable in the form of a particle called the Higgs boson, which was theorised in the early 1960s by Peter Higgs and others. It was finally discovered in 2012, not as a visible particle but as a bump in a graph!

The story of the Higgs boson is fascinating and if you want to know more then I highly recommend a series of short videos that explain the discovery of this elusive particle. Don’t be put off when I say the videos are presented by a physicist from CERN: Piotr Traczyk has a very entertaining manner and his explanations really are very accessible. You can find the YouTube playlist here (https://www.youtube.com/watch?v=so2nCu2Jkbc&list=PLAk-9e5KQYEqvdBn_fSMsuVPt-qOBhEEv).

Enjoy the show – and watch out for the analogy about a dice-rolling rabbit in Episode 3.