Harry Cliff - The basic building blocks of our universe

Looking at the history of particle physics is a good way to understand what we currently know about the basic building blocks of our universe.

About Harry Cliff

"I am a particle physicist at the University of Cambridge, a populariser of science and a science writer.

I work on an experiment called LHCb, which is a giant particle detector on the Large Hadron Collider at CERN, where we study elementary particles – the basic building blocks of our universe."

The particle pioneers

Looking at the history of particle physics is a good way to understand what we currently know about the basic building blocks of our universe.

The story starts in 1897 at the Cavendish Laboratory in Cambridge, where I’m based. A scientist named Joseph John Thomson discovered the first elementary particle: the electron. His experiment used basic equipment — a glass tube pumped out of all the air through which he just passed an electric current. By manipulating these beams of particles, Thomson figured out that what was flowing through the tube were particles much lighter than the lightest known atom at the time. That’s what we now call the electron – the first elementary particle; a tiny, negatively charged particle. 1897 is really the beginning of a journey of exploration, as other scientists start to gradually unpick and dismantle the atom over the next half-century or so.

The apparatus used by Ernest Rutherford in his atom-splitting experiments, set up on a small table in the centre of his Cambridge University research room – Cavendish Laboratory. Wikimedia Commons. Public Domain.

The next major breakthrough came several decades later, in 1911, when Ernest Rutherford (who had been one of Thomson’s PhD students in the late 1890s) was working at the University of Manchester. Rutherford and his researchers Geiger and Marsden did this very famous experiment where they fired alpha particles, a type of radiation emitted by certain radioactive elements, at a thin gold foil. They discovered something very strange, which is that these alpha particles act like high-velocity bullets. You can imagine them as shells from a cannon being fired at gold atoms. Rutherford was surprised to discover that these alpha particles were occasionally getting knocked backward off the gold foil. This led him to realise that atoms have a tiny, extremely dense centre, which we call the nucleus. The nucleus, which is positively charged, contains almost all the atom’s mass, and the electrons go around it. What was happening in this experiment was that these alpha particles were occasionally coming really close to this tiny nucleus. And when they got really close, this enormous positive charge repelled them backward.

Key Points

• Pioneering scientists like Thomson and Rutherford used basic equipment to make ground-breaking discoveries such as identifying electrons and the nucleus of the atom.
• Since the 1960s, scientists have used huge accelerators to create high-energy collisions between particles, which led to the discovery of quarks.
• The Standard Model explains how these particles interact with one another and is one of the crowning intellectual achievements in human history.
• The framework of quantum field theory allows us to understand the forces of nature, or at least three of the forces of nature.