Matter matters

• 'Mind over matter'
• 'Atoms are the building blocks of matter'
• 'Dispose of waste matter carefully'
• 'Matter is never created or destroyed in chemical reactions'

All of these phrases use the term 'matter' - but what do scientists mean by 'matter' - and does it really matter anyway?!

When scientists talk about matter they mean the stuff that everything is made up of - and it has taken literally thousands of years for us to understand just what everything really is made up of - and we may not fully understand it all yet. One of the biggest difficulties in trying to understand matter is that it is made up of particles which are so small that no one has ever seen them.

The story of matter

We take the existence of atoms for granted - yet for centuries no-one believed in them. Around 2500 years ago a Greek philosopher called Leucippus and his pupil Demokritos put forward the idea that the universe is made up of tiny indivisible particles which they called atoms. Unfortunately the great Greek philosopher Aristotle did not agree with them. As Aristotle views were accepted throughout Europe for almost 2000 years the idea of atoms was shelved for centuries to come.

The problem with the idea of atoms is that there is no easily available evidence for their existence. In fact common sense says that solids are solid and liquids are liquids, - not lots of tiny particles which no-one can see. Over the years many great scientists have struggled with different models of the makeup of matter - and some of the stories show how difficult it can be to get new ideas accepted.

In 1808 an English scientist called John Dalton reintroduced the idea of atoms, based on his scientific experiments. His ideas explained the type of results many people were getting in their experiments, and so most people were won over quite quickly. Now scientists wanted to know what atoms were like.

Ludwig Boltzmann (1844-1906) recognised that if he could understand the way the behaviour of particles of matter affected the behaviour of bigger pieces of matter he would understand the inner workings of everything around him. His ideas were ahead of his time and were not proved until shortly after his untimely death. Towards the end of the 19th century Henri Becquerel discovered radioactivity, and this opened the way for experiments which would help to open up the internal structure of the atom :

1897
Joseph John Thompson shows that electrons are found in all matter. He also devises a model for the atom, suggesting that negatively charged electrons are embedded in a sphere of positive charge like dried fruit in a 'plum pudding'.

1911
Ernest Rutherford and his colleagues show that the plum pudding model is wrong. They replace this model with one in which the atom has a positively charged nucleus with electrons moving around it in orbits like the planets orbiting the Sun. Rutherford and his colleagues subsequently identify the positively charged particles in the nucleus as protons.

1915
The Danish physicist Neils Bohr develops Rutherford's work into a model of the atom which contains orbiting electrons in shells. This fits much better with accepted ideas and observations, and explains very elegantly the way in which each element can be made to absorb and emit light with its own characteristic set of frequencies.

1932
British scientist James Chadwick carries out experiments which show the existence of neutrons, the final atomic particle to be discovered.

However, even the discovery of the three basic particles which make up an atom - electrons, protons and neutrons - was not the end of the story. Radioactivity had been discovered at the end of the 19th century. In 1931, Wolfgang Pauli was trying to explain how beta radiation is given off by atoms - but he had a problem. He either needed to rewrite two very important laws of physics - the laws of conservation of energy and momentum - or he had to invent a new particle. He decided that inventing a new particle was much preferable to abandoning two laws of physics that were well-established, and came up with the neutrino, a particle which had to be almost massless and have no charge if it was to explain the existence of beta radiation. This combination of properties meant that neutrinos were very difficult to detect - and it was 25 years later before there was experimental proof of their existence.

By the end of the 20th century, scientists had discovered more and more subatomic particles. Scientists now think that the building blocks of matter are subatomic particles like quarks and leptons, which form families containing particles with weird names like pions, muons and mesons. What will the 21st century bring?

John Dalton

Antoine Henri Bequerel

Ludwig Boltzmann