Is the person next to you standing too close?
They’re mainly empty space.

We start our story with Rutherford, conducting experiments with his team around 1910.

Ernest Rutherford

Ernest Rutherford was born in New Zealand, although he spent much of his life in the UK.

He is known as the father of nuclear physics and is one of science’s greatest ever experimentalists. He was awarded a Nobel Prize in Chemistry, however, it was after he became a Nobel laureate that he did the work for which he is best remembered. From his gold foil experiment he theorised a revolutionary model of the atom. He is also credited with being the first person to induce an artificial nuclear reaction; he bombarded nitrogen atoms with particles and produced oxygen in the process. In the same experiment he discovered and named the proton.

Under his guidance at Cambridge university, James Chadwick discovered the neutron. And the first splitting of an atomic nucleus was also performed by some of his colleagues. (These colleagues, John Cockcroft and Ernest Walton, an Irish scientist, went on to win the 1951 Nobel Prize in physics for splitting the atom.) Rutherford’s ashes are buried with the finest of British scientists near Newton's tomb at Westminster Abbey.

Before Rutherford, the accepted model of the atom was that they were like a plum pudding: lots of bits baked together into a more-or-less solid blob. Which makes sense; solid things feel, well... solid.

Models of the atom

Scientists use 'models' to represent systems in the world and to understand how these systems work.

When we talk about atomic models, we mean drawings or simulations of what an atom could look like. There have been many different models of atoms over time. From the Dalton model, which is simply a circle illustrating a single ball of matter, through to Thomson’s model (the plum pudding proposition), to Rutherford's and then to Bohr, which is probably the model you’re familiar with from school. Each subsequent model became more complex as experimental data and discoveries accumulated.

Different materials expand...

Rutherford's experiment involved bombarding a very thin sheet of gold with tiny particles. He tracked the path of the particles, expecting them to be slightly deflected by the pieces inside the plum-pudding atom.

This wasn't what happened. Some particles passed straight through without any deflection. Others were deflected at angles of more than 90°. And some were reflected straight back at the source.

Rutherford said:

"It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you."

From this, Rutherford proposed

that atoms weren’t solid blocks. Instead, he described an atom with a tiny core – a core one billionth the volume of the whole – containing nearly all of the atom’s actual mass. This core, or nucleus is surrounded by clouds of negatively charged electrons that have very little mass.

Modern Physics

The Bohr atomic model, which we're probably all familiar with from school, shows electrons in varying orbits around the nucleus.

But our understanding of matter has gone far, far deeper. Scientists have developed the quantum mechanical model, which is a lot more accurate. It describes the probability of an electron being in a certain place around a nucleus. The areas where electrons are most likely to be are called 'orbitals'. It’s a statistical approach that is very different from the electron shell model that Bohr described, or Rutherford’s cloud of electrons.

Combined with subsequent discoveries of new fundamental particles, scientists have arrived at the Standard Model that explains how the basic building blocks of matter interact. Even though the Standard Model is currently the best description there is of the subatomic world, it does not explain the complete picture. The theory incorporates only three out of the four fundamental forces, omitting gravity.

A very different structure in comparison to a plum pudding.

Even though our understanding of the construction of atoms has continued to evolve from Rutherford's results, he was essentially right: atoms are mostly empty space.

Empty space

You could ask, if atoms are mostly empty space, why do things feel 'solid' and take up space?

Good question. The electrons, protons, neutrons and other sub-atomic particles that make-up atoms exert a combination of forces on one another. This means that while an atom is mainly empty space, the balance of forces it maintains prevents its neighbours from getting too close. That’s why 'solid' objects maintain their form.

Every object around you is made from atoms

Every object around you is made from atoms – even you. So just like the person standing next to you on the DART, you're mainly empty space.